New insights into biochar ammoniacal nitrogen adsorption and its correlation to aerobic degradation ammonia emissions

One of the technical barriers to the wider use of biochar in the composting practices is the lack of accurate quantification linking biochar properties to application outcomes. To address this issue, this paper investigates the use of ammonia nitrogen adsorption capacity by biochar as a predictor of ammonia emission during composting in the presence of biochar. With this in mind, this work investigated the use of ammonia nitrogen adsorption capacity of biochar when mixed with solid digestate, and the reduction in ammonia emissions resulting from the addition of biochar during aerobic degradation of solid digestate. A biochar synthesized at 900 °C, another synthesized at 450 °C, and two derivatives of the latter biochar, one chemically modified with nitric acid and the other with potassium hydroxide, were tested. This study concluded that the chemical characteristics of the biochar, including pH and oxygen/carbon atomic ratio, had a greater influence on the adsorption of ammonia nitrogen than physical attributes such as specific surface area. In this regard, nitric acid modification had superior performance compared to hydroxide potassium modification to increase biochar chemical attributes and reduce ammonia emissions when applied to aerobic degradation. Finally, a significant linear correlation (p-value < 0.05, r2 = 0.79) was found between biochar ammonia nitrogen adsorption capacity and ammonia emissions along composting, showing the potential of this variable as a predictive parameter. This study provides insights for future explorations aiming to develop predictive tests for biochar performance.

Fluorine contamination, mobility, and risks in soils at a phosphate-gypsum waste landfill: a new analytical method and comparison with previous methods

This study used a new X-ray fluorescence (XRF)-based analytical method with better precision and sensitivity to evaluate the fluorine concentrations in soil. It was hypothesized that the XRF method with a pellet-synthesizing procedure may effectively analyze the fluorine concentrations in soil with ease and reliability. The total fluorine concentrations determined using XRF were compared with those determined using three different types of analytical protocols-incineration/distillation, alkaline fusion, and aqua regia extraction procedures. Among the three procedures, the incineration/distillation procedure did not show reliable precision and reproducibility. In contrast, the total fluorine concentrations determined using the XRF analysis were linearly correlated with those determined using the alkaline fusion and aqua regia extraction procedures. Based on the results of the Korean waste leaching procedure and toxicity characteristics leaching procedure, the leachability of fluorine from soil and waste was not directly related to total fluorine concentrations in soil. Risk assessment also revealed that the fluorine-rich soils did not show non-carcinogenic toxic effects, despite exceeding the regulation level (800 mg/kg) in South Korea for total fluorine concentrations in soil. Our results suggest that XRF analysis in combination with the newly developed pretreatment method may be a promising alternative procedure for easily and rapidly determining the total fluorine concentration in soil. However, further efforts are needed to evaluate fluorine leachability and its associated risks in fluorine-contaminated soils.

Highly efficient molecular film for inhibiting volatilization of hazardous nitric acid

Nitric acid, an important basic chemical raw material, plays an important role in promoting the development of national economy. However, such liquid hazardous chemicals are easy to cause accidental leakage during production, transportation, storage and use. The high concentration and corrosive toxic gas generated from decomposition shows tremendous harm to the surrounding environment and human life safety. Therefore, how to inhibit the volatilization of nitric acid and effectively control and block the generation of the toxic gas in the first time are the key to deal with the nitric acid leakage accident. Herein, a new method of molecular film obstruction is proposed to inhibit the nitric acid volatilization. The molecular film inhibitor spontaneously spread and form an insoluble molecular film on the gas-liquid interface, changing the state of nitric acid liquid surface and inhibiting the volatilization on the molecular scale. The inhibition rate up to 96% can be achieved below 45 °C within 400 min. Cluster structure simulation and energy barrier calculation is performed to elucidate the inhibition mechanism. Theoretical analysis of energy barrier shows that the specific resistance of the inhibitor significantly increased to 460 s·cm-1 at 45 °C, and the generated energy barrier is about 17,000 kJ·mol-1, which is much higher than the maximum energy required for nitric acid volatilization of 107.97 kJ·mol-1. The molecular film obstruction strategy can effectively inhibit the volatilization of nitric acid. This strategy paves the way for preventing the volatilization of liquid hazardous chemicals in accidental leakage treatment.

An Alternative Procedure for a Win-win African-Swiss Cooperation in Gold Production in Africa

The growth of Africa as a major gold (Au) exporter can not only strengthen economic ties with other parts of the world, but also lead to solutions to global industrial challenges, and the only way to stop gold smuggling out of gold-producing African countries seems to be having multiple refineries in Africa, for which developing gold-producing African countries might need technological assistance provided by a more developed country, especially Switzerland. In this Note, the chemistry of gold mining was discussed, and the idea is conveyed that if aqua regia is used as a main reagent in both gold mining and the electrolytic refinement of gold, then the two systems of gold mining and gold refining can be coupled industrially and geographically, and such a coupling can facilitate the growth of home-grown gold refineries in gold-producing African countries. It is also discussed that with Swiss companies finding it economical to properly use aqua regia in Africa as described, a win-win African-Swiss cooperation will be established that will benefit both the Swiss companies and gold-producing African countries. Further, it is concluded that the addressed cooperation will be accompanied by four of the seventeen goals called 'Sustainable Development Goals' by the United Nations.

Development of a Simultaneous Quantification Method for Multiple Modes of Nitrogen in Leaf Models Using Near-Infrared Spectroscopic Measurement

By focusing our attention on nitrogen components in plants, which are important for cultivation management in data-driven agriculture, we developed a simple, rapid, non-chemical and simultaneous quantification method for proteinic and nitrate nitrogen in a leaf model based on near-infrared (NIR) spectroscopic information obtained using a compact Fourier Transform NIR (FT-NIR) spectrometer. The NIR spectra of wet leaf models impregnated with a protein-nitric acid mixed solution and a dry leaf model obtained by drying filter paper were acquired. For spectral acquisition, a compact MEMS (Micro Electro Mechanical Systems) FT-NIR spectrometer equipped with a diffuse reflectance probe accessory was used. Partial least square regression analysis was performed using the spectral information of the extracted absorption bands based on the determination coefficients between the spectral absorption intensities and the contents of the two-dimensional spectral analysis between NIR and mid-infrared spectral information. Proteinic nitrogen content in the dry leaf model was well predicted using the MEMS FT-NIR spectroscopic method. Additionally, nitrate nitrogen in the dry leaf model was also determined by the provided method, but the necessity of adding the data for a wider range of nitric acid concentrations was experimentally indicated for the prediction of nitrate nitrogen content in the wet leaf model. Consequently, these results experimentally suggest the possibility of the application of the compact MEMS FT-NIR for obtaining the bioinformation of crops at agricultural on-sites.

Making Yellows Last with Nitric Acid: Exploring Colour Permanence in Art and Knowledge, 1600-1850

Nitric acid became commonly available in the seventeenth century. Since then, it held the interest of chemists, especially those interested in the art of dyeing. Due to what is now called the xanthoproteic reaction (from Greek xanthós, describing shades of yellow), nitric acid produces a stable yellow colouration in proteinaceous materials, such as wool, silk, and bones. The chemistry of this reaction is well understood today. Less well-known is that it held the interest of dyers in the past. Dyers considered the ability of nitric acid to give a yellow colour to certain substances a solution to giving materials a durable, that is, a lasting, yellow colour. Yellow, indeed, posed a problem in the art of dyeing. Before the discovery of synthetic dyes in the mid-nineteenth century, there were no organic yellow dyes with long-term colour stability. Using historical dyeing manuals and chemistry treatises, combined with our practical engagement with the processes they describe, this paper traces how, between the seventeenth and nineteenth centuries, dyers explored nitric acid while examining the durability of yellow colourations. Based on these explorations into nitric acid, the chemical arts developed theories about the nature of colour, and about the causes for its relative permanence.

A low-tech, low-cost method to capture point-source ammonia emissions and their potential use as a nitrogen fertiliser

Rising global energy prices have led to increased costs of nitrogen (N) fertilisers for farmers, but N pollution (losses) from agricultural activities can account for over 50% of the nitrogen applied. This study assesses the feasibility of a low-cost and low-tech method of NH3 emission capture from an agricultural point source (chicken manure) using a water column bubbling technique, and its application as a fertiliser to several plant types. Solutions of i) nitric acid (HNO3), ii) calcium nitrate (Ca(NO3)2), iii) a mixture of Ca(NO3)2 and HNO3 and iv) deionised H2O were used to scrub NH3 from air pumped from a storage container containing chicken manure. We conclude that NH3 can be captured from manure using low-tech methods, and that solutions of common fertiliser compounds such as ammonium nitrate and calcium ammonium nitrate can be replicated by binding captured NH3 to solutions of nitrate. Our results suggest that dissolved calcium nitrate is just as effective at scrubbing NH3 from the atmosphere as nitric acid at low concentrations, but could do so at a near neutral pH. For use on common silage grass for livestock feed, all of the captured ammonium solutions significantly increased yields, including the ammonium only solution. However, the aquatic plants (Taxiphyllum Barbieri and Salvinia auriculata) did not respond favourably to a high ratio of NH4+ in solution, and in the case of Salvinia auriculata, the plant was significantly damaged by the ammonium only solution. In conclusion, we highlight that the capture and utilisation of NH3 emissions from point sources is possible using very basic apparatus and that if used correctly, this captured nitrogen can be stored and applied to crops in a variety of forms which could reduce reliance and cost of mineral fertiliser use.

Study on the mechanism of acid treatment La0.8Sr0.2Mn0.8Cu0.2O3 to improve the catalytic activity of formaldehyde at low temperature

To address the issue of surface enrichment of A-site ions in perovskite and the resulting suppression of catalytic activity, the La0.8Sr0.2Mn0.8Cu0.2O3 was modified by treatment with dilute nitric acid (2 mol/L) and dilute acetic acid (2 mol/L). The results show that the effect of dilute nitric acid treatment on the morphology and catalytic activity of the catalyst is more significant. The specific surface area of the catalyst after dilute nitric acid treatment (268.78 m2/g) is seven times higher than before treatment (37.55 m2/g). The low-temperature catalytic oxidation activity of HCHO of the catalyst after dilute nitric acid treatment is significantly improved, achieving a 50% HCHO oxidation efficiency at 80 °C, while the original sample requires 127 °C to achieve a 50% HCHO conversion. The excellent catalytic activity of the catalyst after dilute nitric acid treatment is related to its large specific surface area, high surface-active site density, and abundant Mn4+ ions. Stability and water resistance experiments show that the catalyst after dilute nitric acid treatment has excellent reaction stability and good water resistance ability. The mechanism of the formaldehyde oxidation reaction is that formaldehyde is first oxidized to a dioxymethylene (DOM) intermediate and DOM dehydrogenation reaction is responsible for the formation of formate species (HCOO-).

The Use of Laser Doppler Imaging in Nitric Acid Burns: A Case Report and Literature Review

Laser Doppler imaging (LDI) technology has been validated to assess thermal burn depth by predicting wound healing potential. However, there is no clear evidence for its use in chemical burns. We present a case of an 8% total burn surface area (TBSA) nitric acid burn following an industrial accident, in an otherwise healthy 36-year-old man. LDI assessment was suggestive of poor healing potential of >21 days, warranting surgical management. However, conservative management was opted for based on clinical assessment as the wound eschar appeared thin and more consistent with epithelial staining. Patient follow-up confirmed a total burn healing time of two months, suggesting that the LDI assessment was accurate. A comprehensive literature review was performed using the MEDLINE (PubMed) database to identify animal or clinical studies evaluating the efficacy of LDI in chemical burns. A qualitative synthesis of our findings is presented. We identified two experimental studies in porcine models with sulfur mustard burns, each confirming the accuracy of LDI assessment when compared to the histopathology findings. Limited experimental animal studies on the use of LDI suggest similar validity in chemical burns, and this correlates with the clinical outcome in this case. However, this alone is insufficient to prove its validity and define its role in the assessment of chemical burns. Clinical trials are required to further assess and define the parameters of LDI use and efficacy in this context.

Investigation of adsorption performance of calcium oxide particles upon various treatments

This study describes the improvements of adsorption capacities for raw calcium oxide (CaO) particles subjected to ultrasonication, activation with nitric acid and thermal treatments. The influence of acids and bases on CaO particle surface was assessed with respect to several variables including treatment methods, adsorption contact times, particle size and specific surface area characteristics, concentration and temperature along with various thermodynamic parameters. Structural analyses and physical characteristics of CaO particles were evaluated using FT-IR and SEM methods. SEM micrographs of samples revealed uniform distributions of CaO particles of average diameter 0.5-2.0 µm. The CaO surfaces showed CH3COOH as having the greatest amounts of adsorbate and modeling of the experimental adsorption isotherm data agreed well with the Freundlich adsorption isotherm. Enhancements in adsorption performance of untreated CaO particles were noted with the ultrasonication, activation with HNO3 and thermal treatment processes. The Langmuir-type adsorption demonstrated that single layer adsorption capacities of adsorbate CH3COOH at 25 oC on sonicated CaO (386.6 mg/g), with nitric acid and thermal activation (354.9 and 320.8 mg/g, respectively) were greater than that of the unsonicated CaO (296.3 mg/g) particles. Adsorption spontaneities of the processes were confirmed by the decreases in adsorption free energy values, ΔGads0, changing from -16.1 to -17.1 kJ mol-1 with temperature range 283-338 K.

Significant parameter for controlling the partition of ambient nitrate species between HNO3(g) and NH4NO3(p)

The equilibrium between nitric acid gas (HNO3(g)) and ammonium nitrate aerosol (NH4NO3(p)) in ambient air was studied based on the monitoring data obtained using a five-stage filter-pack system, in which the fine aerosol and the coarse aerosol were separately collected; this made it possible to evaluate the actual situation of the equilibrium more accurately. The partition between HNO3(g) and coarse particulate nitrate (c-NO3-(p)), as well as that between HNO3(g) and fine particulate nitrate (f-NO3-(p)), could be evaluated individually thanks to the classification separation of the aerosol by size. The c-particle proportion c-NO3-(p)/(c-NO3-(p) + HNO3(g)) between HNO3(g) and c-NO3-(p) had a weak negative correlation (r = -0.46, p<0.001) with air temperature; in contrast, the f-particle proportion f-NO3-(p)/(f-NO3-(p) + HNO3(g)) between HNO3(g) and f-NO3-(p) had a moderate negative correlation (r = -0.80, p<0.001) with air temperature in total; furthermore, the f-particle proportion had an interesting and discriminative dependence on air temperature which could be divided into two regions by an air temperature around 15°C. The condition of high air temperature accompanied by high relative humidity frequently resulted in the deliquescent state of NH4NO3(p), providing the disconnect from the theoretical prediction for the products of [NH3(g)] and [HNO3(g)] ([NH3(g)][HNO3(g)]) by Seinfeld and Pandis (1998).

[Effect of Coconut Fiber Biochar and Its Nitrate Modification on Pb Passivation in Paddy Soils]

The effects of coconut fiber biochar (CFB) and nitrate-modified coconut fiber biochar (NCFB) on the passivation of exogenous lead (Pb) in paddy soils and their underlying mechanisms were investigated using soil incubation experiments combined with spectroscopic techniques such as scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), synchrotron radiation X-ray fluorescence (SRXRF), and Fourier transform infrared absorption spectroscopy (FTIR). The effects of NCFB and CFB on the passivation of exogenous lead (Pb) in paddy soils and its underlying mechanisms were investigated. Compared with that of CFB, the inner wall of NCFB honeycomb pores was rougher, and the amount of alcohol-phenol-ether functional groups containing the C-O structure and the amount of carboxyl groups containing the C[FY=,1]O/O[FY=,1]C-O structure on the surface of CFB was significantly decreased after nitric acid modification. Compared with that in the control (without biochar) paddy soil after 150 d of incubation, the EDTA-extracted Pb content in the paddy soil with CFB and NCFB was reduced by 39.7% and 105.4%, respectively. The carbonate-bound and Fe-Mn oxide-bound Pb contents were significantly lower, and the organic-bound and residue Pb contents were significantly higher in the NCFB-added soil. The SRXRF scans showed that the exogenous Pb was enriched in the microregions of CFB particles rich in Ca and Cu elements and relatively less so in the microregions of soil aggregates rich in the Fe, Mn, and Ti elements. In addition, the characteristic peaks of carboxylates (1384 cm-1) in A-CFBPb and A-NCFBPb were significantly enhanced in the incubation experiment in the presence of exogenous Pb compared to A-CFB and A-NCFB in the absence of exogenous Pb. The addition of CFB or NCFB was more effective in passivating exogenous Pb in paddy soils and promoted the gradual transformation of Pb from unstable to more stable forms in paddy soils to achieve the effect of passivating Pb. The greater amount of carboxyl functional groups in NCFB participated in the passivation of exogenous Pb, which made NCFB more effective than CFB in passivating Pb. NCFB was more effective than CFB in passivating exogenous Pb in paddy soils due to its rougher inner walls of honeycomb pores and abundant carboxyl functional groups. In tropical areas such as Hainan, coconut fiber biochar and its modification can be considered as an environmentally friendly candidate method for the remediation of soil Pb contamination.

Efficient one-pot synthesis of magnetic MIL-100(Fe) using nitric acid without additional Fe ion addition and adsorption behavior of charged organic compounds

Metal organic frameworks (MOFs) are attracting attention as high-performance adsorbents because of their high specific surface area and porosity. In particular, magnetic MIL-100(Fe) has the both characteristics of Fe₃O₄ and MIL-100(Fe), which are magnetic characteristics, high specific surface area and open metal sites. However, multiple synthetic steps are required for synthesis of magnetic MOF, and there is limitation that the residual organic linker and unreacted Fe center ions can be discharged, and they cause water pollution. In this study, magnetic MIL-100(Fe) was synthesized within 4 h without the addition of Fe ions by using nitric acid for the surface modification of Fe₃O₄. Magnetic MIL-100(Fe) was confirmed through XRD, FTIR, and TEM surface analysis, and the optimal conditions for nitric acid addition were selected through magnetization measurements and BET analysis of synthesized magnetic MIL-100(Fe). Thereafter, adsorption evaluation was performed using MB and MO, which are representative cationic and anionic dyes, respectively. The pseudo-second-order Langmuir model showed a relatively high correlation compared to the other models. This shows that the adsorption mechanism depends on both the amount of adsorbent and adsorbate, and Fe₃O₄ modification with nitric acid does not cause any change in the adsorption mechanism. In the case of adsorption selectivity between the MB and MO, removal rates of 93.27% and 58.73% were obtained, respectively. The above results can contribute to the simplification of the manufacturing of magnetic metal organic frameworks for removing ionic organic compounds and the minimization of water pollution in the manufacturing process.

Effects of nitric acid rain stress on soil nitrogen fractions and fungal communities in a northern subtropical forest, China

Acid rain has severely negatively impacted terrestrial ecosystems and biogeochemical cycles. However, the potential impacts of nitric acid rain (NAR) on soil nitrogen (N) fractions and fungal community diversity in northern subtropical forest soils remain largely unevaluated. In this study, treatments of NAR at pH = 4.5 (AR4.5), pH = 3.5 (AR3.5), and pH = 2.5 (AR2.5) were randomly sprayed in a typical Quercus acutissima Carruth. stand in northern subtropical China. The soil N fractions and soil fungal communities were analyzed after a 12-month experimental period. The results revealed that compared to the control, the soil total N (TN), microbial biomass N (MBN), hydrolysable ammonium N (HAN), amino-sugar N (ASN) and amino-acid N (AAN) contents decreased significantly by 19.61-13.07 %, 20.10-9.04 %, 60.41-28.87 %, 74.10-62.25 %, and 65.69-45.64 % under stronger acidity inputs (i.e., AR2.5 and AR3.5), respectively. Besides, the AR2.5 and AR3.5 treatments increased the α-diversity indices of soil fungal communities and altered the soil fungal community structure. Moreover, the NAR treatments represented an increase in the relative abundance of Ascomycota and Mortierellomycota and a decrease in that of Basidiomycota. Mortierella, Penicillium, and Tomentella can be used as indicator genera for changes in soil fungal community structures under NAR stress. Furthermore, AAN was the main environmental factor affecting soil fungal community at the phylum and genus levels. Cumulatively, findings from this research provide valuable insight into NAR's effects on N cycling and microbial communities in forest soils.

Application Effect of MF-OP on Collection of Trivalent Holmium from Rare Earth Mining Wastewater

Microtube microfilter with organic phosphoric acid (expressed as MF-OP) containing a wastewater portion with buffer fluid and an enriched portion with nitric acid fluid and organic phosphoric extractant dissolved in benzin has been studied for its trivalent holmium (expressed as Ho(III) collection from rare earth wastewater. Common parameters affecting the collection effect have been investigated, including hydrogen ion molar concentration (molar concentration can be expressed as Cm) or pH value, initial concentration (expressed as Co) of Ho(III), ion-force of rare earth wastewater, voluminal proportion of organic phosphoric extractant with benzin and nitric acid fluid (expressed as Vr), nitric acid Cm, extractant Cm, and type of acid fluid in an enriched portion. The virtues of MF-OP compared to the traditional collection was explored. The impacts of hydrodynamic characteristics (steadiness and current speed) and MF parameter factors (inradius of tube, tube-shell thickness, proportion of holes) on the collection performance of MF-OP for Ho(III) collection were also considered. The test results displayed that the greatest collection conditions of Ho(III) were attained as nitric acid Cm was 4.00 mol/L, extractant Cm was 0.220 mol/L, and Vr was 0.8 in the enriched portion, and pH value was 4.60 in the wastewater portion. Ion- force of rare earth wastewater had no noticeable outcome on Ho(III) collection. The collection proportion of Ho(III) was attainable to 93.1% in 280 min, while Co was 1.80 × 10-3 mol/L.

Arsenic pools in soils under native vegetation on a steatite outcrop in Brazil

Pristine soils under native vegetation can present high levels of potentially toxic elements when developed from the weathering of some unusual parent materials, especially ultramafic rocks and some metal ores. Here, we used various selective extractions in order to study the partition and potential availability of As in eight soils developed from steatite (a talc-rich rock) on an ultramafic hill in Brazil. Soils varied from shallow Entisols on the summit to Inceptisols and Oxisols on slopes and footslopes, where total As contents (determined by X-ray fluorescence) reached levels as high as 225 mg kg^-1, which might raise concerns about their potential agricultural use and occupation. Despite these high values for pristine soils, water- and Mehlich-available As were nil or negligible in all soils, whereas oxalate-extractable As reached a maximum 4.2 mg kg^-1, and the highest semi-total (nitric acid digestion) was 9.3 mg kg^-1. However, As relative availability (compared to total As) varied widely among soils, with one Inceptisol (with a total 11-19 mg kg^-1) reaching 100% of its total As extractable by nitric acid, whereas an Oxisol showed <0.1% in nitric acid extract. Generally, we can conclude that, in soils with the highest total As concentrations, most As is contained within resistant, coarse phases such as primary magnetite, chromite and others, and a minor but still considerable part is bound to secondary Fe oxides. Thus, despite the unusually high As contents for soils under pristine savannic and forest native vegetations, the different As pools assessed here apparently do not raise immediate concerns where ultramafic rocks rich in Fe oxides give rise to soils under tropical climate. However, it is theoretically possible that subsoil saturation and Fe oxide reduction release some As in ground- and surface waters, which deserves further investigation.

Immobilization of exopolymeric substances from bacteria for metal removal: A study on characterization, optimization, reusability and toxicity

This study investigated the immobilization of exopolymeric substances (EPS) from Bacillus cereus using sodium alginate to form EPS beads for metal removal. The EPS beads were characterized and their optimum biosorption conditions established (biosorbent dosage, initial metal concentration and pH of metal solutions). The EPS beads were also tested for reusability by using them continuously for five metal removal cycles with desorption process in between cycles. The toxicity of the treated metal solutions was tested by phytotoxicity tests. Results revealed that EPS beads demonstrated significantly higher metal removal efficiency (Pb: 99.26%, Cr: 50.73%, Cu: 48.94%, Zn: 29.81%, Cd: 20.29%) compared to plain alginate beads (without EPS) (Pb: 84.45%, Cu: 31%, Cr: 28.37%, Zn: 11.91%, Cd: 9.37%). SEM-EDX analysis detected Cu, Pb, Zn, Cd and Cr on the surface of EPS beads. Optimum conditions for Pb removal by EPS beads were from the use of 0.1 g of biosorbent at 100 mg/L initial metal concentration and pH 5. By contrast, Cu, Zn, Cd and Cr were optimally removed by 0.3 g of biosorbent at 25 mg/L initial metal concentration and pH 5. EPS beads can be reused up to five times while maintaining a high rate of metal removal efficiency (Pb- 99.52%, Cr- 89.23%, Cu- 89.17%, Zn-52.52%, Cd-39.12%). This was achieved through desorption with nitric acid that consistently recovered 76-93% of the metal adsorbed. FTIR analysis reveals that nitric acid is capable of restoring the functional groups present within EPS beads, allowing it to bind with metal ions in repeated cycles. Metal solutions treated with EPS beads were less toxic as seedling shoots (pre-treated: 0-10 cm, post-treated: 1.2-18.1 cm) and roots (pre-treated: 0-7.8 cm, post-treated: 0.8-15.1 cm) grew well, which suggested that reduced levels of metals led to reduced phytotoxicity. This study provides an insight into the use of EPS beads for metal removal, highlighting the benefits and reusability of the beads for future wastewater treatment.

Development of nitric acid-modified activated carbon electrode for removal of Co2+/Mn2+/Ni2+ by electrosorption

In this paper, nitric acid-modified activated carbon was used as an electrode in the electrosorption process for the removal of Co²⁺, Mn²⁺, and Ni²⁺ from wastewater. The effects of applied voltage, initial pH, and coexisting ions on removal efficiency were investigated. The adsorption process was evaluated by adsorption isotherm models. The results indicated that the electrosorption process was consistent with the Langmuir model, proving that the electrosorption process was a monolayer adsorption process. The maximum adsorption capacities of Co²⁺, Mn²⁺, and Ni²⁺ were 131.58 mg/g, 102.04 mg/g, and 103.09 mg/g. Electrochemical tests revealed that the specific capacitance of AC-HNO₃ was 54.11 F/g when the scanning rate was 5 mV/s, while the specific capacitance of AC was 36.51 F/g. The Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) confirmed that the content of oxygen groups on the surface of activated carbon increased after modification, which provided more adsorption sites for electrosorption. When the selected concentration of HCl was used as the eluent, the elution efficiency of Co²⁺, Mn²⁺, and Ni²⁺ could reach 94.23%, 93.65%, and 90.61%. The removal efficiency could reach more than 95% after three cycles. The results of the study can be used as a reference significance for the removal of cobalt, manganese, and nickel ions from heavy metal wastewater by electrosorption.

A Green Chemical Approach for Iodination of Pyrimidine Derivatives by Mechanical Grinding under Solvent-Free Conditions

The iodination of pyrimidines is usually carried out by using toxic reagents under acidic conditions, such as with sulfuric acid and nitric acid. To avoid toxic reagents, we developed a simple and eco-friendly approach for the iodination of pyrimidine derivatives under solvent-free conditions using solid iodine and AgNO3 as an electrophilic iodinating reagent. The advantages of this method are the relatively short reaction time (20–30 min), simple set-up procedure, high yields (70–98%), and environmentally friendly reaction conditions. Our novel approach for the iodination of pyrimidines, as well as a variety of their derivatives, will contribute to the development of nucleobase-related drug candidates.

Acid deposition at higher acidity weakens the antagonistic responses during the co-decomposition of two Asteraceae invasive plants

Co-invasion by two invasive plant species (IPS) can occur in the same habitat. Diversified acid deposition may change the co-invasion process by altering litter decomposition and plant-soil feedback signalling. This study examined the co-decomposition of two Asteraceae IPS (Solidago canadensis L. and Bidens pilosa L.) on litter decomposition rate, soil enzyme activities, and soil N-fixing bacterial communities under diversified acid deposition (mixed acid deposition at pH 5.6 and at pH 4.5, sulfuric acid at pH 4.5, and nitric acid at pH 4.5). B. pilosa litter degraded faster than S. canadensis litter. Acid deposition at higher acidity accelerated the decomposition rate of both pure S. canadensis litter and the equally mixed litters from the two Asteraceae IPS. Antagonistic responses may occur during the co-decomposition of the two Asteraceae IPS with mixed acid deposition, regardless of the pH, as well as with nitric acid deposition at pH 4.5; in contrast, there may be neutral responses for the co-decomposition process with sulfuric acid at pH 4.5. The type of acid deposited may be one of the key factors affecting the intensity of the mixing effect affecting the co-decomposition. Acid deposition at higher acidity weakened the antagonistic responses for the co-decomposition of the two Asteraceae IPS compared with the response to weak acids. Together, these results indicate that acid deposition at higher acidity could facilitate the co-invasion of the two Asteraceae IPS mainly through accelerated litter decomposition as well as weakened antagonistic responses for co-decomposition.

Immunomulation effect of alginic acid and chitooligosaccharides in silver carp (Hypophthalmichthys molitrix)

Individual and combined efficacy of chitooligosaccharides (COS) and alginic acid (AA) at 1 g, 2 g, and 3 g per kg diet was assessed on growth and disease resistance in silver carp (Hypophthalmichthys molitrix) against Edwardsiella ictaluri. Growth parameters including specific growth rate (SGR), weight gain (WG), and feed conversion rate (FCR) were significant in fish fed 2 g and 3 g kg^-1 of COS or AA, and fish fed combined COS + AA at 1, 2 and 3 kg^-1 diet. In all groups, the survival rate (SR) was recorded 100%, except in group fed 2 g kg^-1 AA diet. All the hematological and biochemical profiles significantly increased in groups fed 2 g and 3 g kg^-1 of COS, AA, and COS + AA diets. Lipase and amylase enzyme activities and superoxide dismutase (SOD), malondialdehyde (MDA), glutathione peroxidase (GPx) antioxidant enzyme activities were significantly increased in fish fed 2 g and 3 g kg^-1 of COS, AA, and COS + AA diet. Respiratory burst (RB), lysozyme (Lyz), reactive oxygen species (ROS) activities, and immunoglobuline (Ig) level were enhanced significantly in fish fed 2 g kg^-1 of COS or COS + AA and all 3 g kg^-1 diets, whereas nitric acid (NO) production and serum AP activity were improved in 2 g kg^-1 COS + AA and 3 g kg^-1 COS or COS + AA diets. Pro-inflammatory cytokine such as IL-8 mRNA transcriptions was significant in 2 g kg^-1 COS + AA diet and all 3 g kg^-1 diet. The IL-10 anti-inflammatory cytokine mRNA transcriptions were significant in 3 g kg^-1 COS or COS + AA diets. This study was confirmed that H. molitrix fed with 3 g kg^-1 COS or COS + AA diets were better activity when compared to other diet.

Selective recovery of gold from dilute aqua regia leachate of waste printed circuit board by thiol-modified garlic peel

Garlic peel (GP) was chemically modified by using thiourea under hydrothermal treatment, which could selectively adsorb gold ions from the 1/10 dilute aqua regia media directly without needing the dangerous evaporation operation. The synthetic chloroauric solution and practical leach liquor of the waste PCB (printed circuit board) powder in dilute aqua regia were employed to assess the adsorption performance on the thiol-GP and the commercial quaternary ammonia anion resin of D201, respectively. It was experimentally confirmed that the adsorption efficiency of gold onto the thiol-GP and D201 resin both reached 100%, and the maximum adsorption capacity of thiol-GP gel was evaluated as 42.59 mg Au/g that was much larger than that of D201 resin (3.33 mg Au/g). The thiol-GP gel adsorption efficiency of other coexisting base metal ions like Cu²⁺, Ni²⁺, Al³⁺, and Fe³⁺ from dilute aqua regia leach liquor of the waste PCB powder was near zero, and only gold could be enriched by selective adsorption onto the thiol-GP gel. At least 3 cycles of adsorption/elution could be obtained without decreasing the adsorption efficiency drastically. The adsorbed gold on the thiol-GP was able to be eluted effectively by using the mixture solution of 0.1 M thiourea and 0.1 M hydrochloric acid, and finally the solid gold could be recovered by sodium borohydride through a reduction process. This study demonstrated a green, environmentally friendly, low-cost, and efficient method for selective recovery of gold from the dilute leach liquor (aqua regia) of waste circuit boards.

Successful treatment of severe ARDS caused by accidental inhalation of nitric acid fumes with veno-venous ECMO: A case report and literature review

RATIONALE

The treatment of severe acute respiratory distress syndrome caused by accidental inhalation of nitric acid fumes is challenging. Few successful cases have been reported in literature. Owing to the development of extracorporeal life support, extracorporeal membrane oxygenation (ECMO) may play an important role in treatment.

PATIENT CONCERNS

A 40-year-old man was accidentally exposed to nitric acid fumes for 10 minutes in a factory. Mild throat irritation and dyspnea occurred 3.5 hours after exposure. Severe dyspnea recurred approximately two hours later. Chest computed tomography revealed bilateral interstitial edema. Tracheal intubation and mechanical ventilation were provided when the non-invasive ventilator failed to support the patient. However, his vital signs, respiratory function, and circulation were aggravated.

DIAGNOSIS

Aspiration pneumonia (inhalation of nitric acid fumes), acute respiratory distress syndrome, and hypertension.

INTERVENTIONS

Veno-venous ECMO (VV-ECMO) was started 6 hours after exposure at the intensive care unit. During VV-ECMO, hypoxia improved. However, chest radiography revealed aggravated pulmonary edema. Prone positioning under ultrasound monitoring and high-dose methylprednisolone were administered on the first day. Nebulization and fiberoptic bronchoscopy for airway management were performed on the second day after the exposure. Pulmonary secretions were significantly reduced 48 hours later.

OUTCOMES

The patient was weaned off V-V ECMO after 6 days, achieved the standard of extubation after 9 days, and was discharged without serious pulmonary or infectious complications after 12 days of hospitalization. Three weeks after discharge, the patient's lung function showed a slight decline in the diffusion function. Two months after discharge, the patient's lung function returned to normal.

LESSON

Early ECMO combined with prone positioning and visualized management through ultrasonography can better improve the prognoses of patients and promote lung function recovery.

Simulating indoor inorganic aerosols of outdoor origin with the inorganic aerosol thermodynamic equilibrium model ISORROPIA

Outdoor aerosols can transform and have their composition altered upon transport indoors. Herein, IMAGES, a platform that simulates indoor organic aerosol with the 2-dimensional volatility basis set (2D-VBS), was extended to incorporate the inorganic aerosol thermodynamic equilibrium model, ISORROPIA. The model performance was evaluated by comparing aerosol component predictions to indoor measurements from an aerosol mass spectrometer taken during the summer and winter seasons. Since ammonia was not measured in the validation dataset, outdoor ammonia was estimated from aerosol measurements using a novel pH-based algorithm, while nitric acid was held constant. Modeled indoor ammonia sources included temperature-based occupant and surface emissions. Sensitivity to the nitric acid indoor surface deposition rate β g , HNO 3 , g was explored by varying it in model runs, which did not affect modeled sulfate due to its non-volatile nature, though the fitting of a filter efficiency was required for good correlations of modeled sulfate with measurements in both seasons. Modeled summertime nitrate well-matched measured observations when β g , HNO 3 , g = 2.75 h - 1 , but wintertime comparisons were poor, possibly due to missing thermodynamic processes within the heating, ventilating, and air-conditioning (HVAC) system. Ammonium was consistently overpredicted, potentially due to neglecting thirdhand smoke impacts observed in the field campaign, as well as HVAC impacts.

Evaluation of EDTA and nitric acid solutions for decalcification of joints in AG/WT, BALB/c, C57, DBA1/J mice, and in Wistar rats

Decalcification of mineralized samples for microscopic analysis involves competing factors including decalcification time, preservation of tissue integrity and cost. We investigated the utility of different decalcification solutions for studying joints in AG/WT, BALB/c, C57, DBA1/J mice and Wistar rats. The hind paws of the rodents were removed and fixed with 10% buffered formalin. Specimens were divided randomly into three groups for demineralization: 10% nitric acid, 12.5% EDTA at room temperature and 12.5% EDTA at 35 °C with shaking. Sections of joints were stained with hematoxylin and eosin (H & E). We evaluated decalcification time and expense, ease of cutting sections, preservation of nuclear basophilia and intranuclear detail, and intensity of eosin staining. The 10% nitric acid solution produced the most rapid decalcification for the mice, but not the rats. The 12.5% EDTA solution at 35 °C with shaking did not decrease decalcification time. Effects on microtomy were variable as were the effects on H & E staining. The EDTA solution provided the best basophilia and intranuclear detail for the mice. For rats, only 12.5% EDTA at 35 °C with shaking produced good preservation. Preservation of nuclear basophilia and intranuclear detail for rats was best with 10% nitric acid and EDTA 35 °C. For mice, 10% nitric acid failed to preserve nuclear basophilia and intranuclear detail. For intensity of eosin staining, EDTA at room temperature and EDTA 35 °C was best for both mice and rats. Sections also exhibited good H & E staining in most samples decalcified with 10% nitric acid. Although we found considerable variation among groups of animals, we found less variation among the different mouse strains than between mice and Wistar rats.

Sediment quality of the Ridracoli fresh water reservoir in Italy: Insights from aqua regia digestion and sequential extractions

The inter-element relationships and the forms in which metals exist strongly influence their mobility and, in turn, have a signature on the environment and human health. Located in the northern Apennines within the Emilia-Romagna region, the Ridracoli artificial lake is one of Italy's most important reservoirs that provides drinking water for about one million people. This work characterized the reservoir sediments by ICP-MS after aqua regia digestion (ARD), comparing the limits by law to assess environmental compliance and XRF data from the same sample-set taken as total concentrations. The Degree of Extraction (DE) from pseudo-total concentrations of ARD analysis allows assessing elements mobility and the associated environmental risk. Principal Component Analysis (PCA) on the obtained data helped to investigate inter-element relationships better; for example, we observed carbonate-sourced sediments, many trace elements (e.g., Ni, Zn) linked to FeMn oxyhydroxides, the importance of the grain size in elements distribution, and the central role of the organic matter in element partitioning. In addition, a Sequential Extraction Procedure (SEP) was applied to the sediment samples to understand the partitioning of many analytes, including Potentially Harmful Elements (PHE) such as Fe, Mn, Cu, Cr, Ni, Pb, and Zn. The results indicated that the most easily mobilized forms were predominant in the area near the dam, in correspondence to sediments affected by the formation of a seasonal anoxic layer.

Effects of nitric acid modification on hydrochar's combustion, fuel and thermal properties are dependent on feedstock type

Elevated metal (e.g., alkali metals) and ash contents can negatively impact the use of biomass-derived solid fuels, including hydrochars, in clean energy generation. The effects of nitric acid modification on those and other properties (combustion, fuel and thermal) were studied for hydrochars produced at three temperatures from four feedstocks. Through side-chain oxidation and surface protonation, nitric acid significantly leached metals from pristine hydrochars to a maximum of five order and increased their burnout temperature by 9-41%, but its effect on ash content, gross calorific values and ignition temperature depended on feedstock type and carbonization temperature. Ignition temperature increased by > 2 times for modified manure pellet hydrochar produced at 300 °C. The combustion characteristics index for the hydrochars was above the minimum benchmark (2 × 10^-7 %² min^-2 °C^-3) for a typical solid fuel. Therefore, nitric acid can effectively improve hydrochar's combustion and fuel properties and reduce slagging in industrial boilers.

Recovery of Au from dilute aqua regia solutions via adsorption on the lyophilized cells of a unicellular red alga Galdieria sulphuraria: A mechanism study

The high electrical conductivity, chemical stability, and low toxicity of elemental Au make it a highly valuable resource. However, wastewater produced during the mining, utilization, and disposal of Au inevitably contains small amounts (10-40 mg L^-1) of Au, thus posing environmental risks. It is too acidic to be treated with inexpensive and eco-friendly bioadsorbents previously studied for the remediation of less acidic effluents. Herein, lyophilized Galdieria sulphuraria cells are shown to directly adsorb Au from simulated Au-containing wastewater with a total acid concentration of 4 M, achieving an adsorption capacity of 35 ± 2.5 mg g^-1 Au after 30-min exposure and a selectivity that exceeds that of an ion-exchange resin and is comparable to that of activated carbon. Additionally, Au adsorbed on these cells is more easily eluted than that adsorbed on the ion-exchange resin or activated carbon. Detailed characterizations reveal that Au accumulates on the surface of lyophilized cells, where it is mainly present as AuCl₄^- and not as Au⁰, in contrast to a previously proposed adsorption mechanism. Thus, our work provides valuable insights into the mechanism of Au adsorption on biomaterials and paves the way to the cheap and eco-friendly recovery of Au from acidic wastewater.

Feedstock type drives surface property, demineralization and element leaching of nitric acid-activated biochars more than pyrolysis temperature

Nitric acid activation (NA-A) effects on the surface properties, mineral phases and element compositions of biochars produced from four feedstocks at three temperatures were evaluated. NA-A increased biochar thermal stability, but its effect on ash content and surface area was feedstock-dependent, with ash content in manure pellet biochars less affected due to a high quartz content. Apart from the manure pellet biochars and the sawdust biochar produced at 400 °C, NA-A decreased the surface area of biochars by up to 100% due to reduced pore volume. Nitric acid significantly leached elements such as potassium from biochars due to protonation and their reactions with several mineral phases, such as sylvite, on the biochars (p < 0.05). This study shows that mineral phases and element compositions of nitric acid-activated biochars were driven more by the feedstock type than the pyrolysis temperature and the derived biochars would be poor adsorbents.

Nitric acid-modified hydrochar enhance Cd2+ sorption capacity and reduce the Cd2+ accumulation in rice

Remediating the agricultural soil polluted by cadmium (Cd) is a serious issue in China. Hydrochar showed its potential to purify Cd-contaminated water and improve Cd-contaminated soil due to its vast amounts of macro- and microporous structures. In this study, three concentration gradients of nitric acid (HNO₃, mass fraction: 5%, 10%, 15%) were implemented to age pristine wheat straw hydrochar (N0-HC) aiming to improve surface physiochemical properties. Four HNO₃-aging hydrochars named N0-HC, N5-HC, N10-HC, N15-HC were used to both remove Cd²⁺ from aqueous solution and improve soil properties. Results showed that HNO₃-aging significantly improved the Cd²⁺ adsorption capacity by 1.9-9.9 folds compared to crude hydrochar due to the increased specific surface area (by 1.5-6.5 folds) and oxygen-containing functional group abundance (by 4.5-22.1%). Besides, initial solution pH of 8 or environmental temperature of 318.15 K performed the best Cd²⁺ adsorption capacity. Furthermore, the process of Cd²⁺ adsorption was fitted best to pseudo-second-order (R² = 0.95) and Langmuir models (R² = 0.98), respectively. Nanjing 46 (Oryza sativa L) and HNO₃-aging hydrochars were furtherly applied into Cd-contaminated paddy soil to investigate the mitigation of Cd translation from soil to rice. N15-HC-1% (w/w) performed the best effect on reducing cadmium accumulation in various parts of rice plants. Overall, this research provided an approach to improve hydrochar capacity to remove Cd²⁺ from aqueous solution and mitigate Cd translation from soil to rice.

Nitrogen burden from atmospheric deposition in East Asian oceans in 2010 based on high-resolution regional numerical modeling

East Asian oceans are possibly affected by a high nitrogen (N) burden because of the intense anthropogenic emissions in this region. Based on high-resolution regional chemical transport modeling with horizontal grid scales of 36 and 12 km, we investigated the N burden into East Asian oceans via atmospheric deposition in 2010. We found a high N burden of 2-9 kg N ha^-1 yr^-1 over the Yellow Sea, East China Sea (ECS), and Sea of Japan. Emissions over East Asia were dominated by ammonia (NH₃) over land and nitrogen oxides (NO_x) over oceans, and N deposition was dominated by reduced N over most land and open ocean, whereas it was dominated by oxidized N over marginal seas and desert areas. The verified numerical modeling identified that the following processes were quantitatively important over East Asian oceans: the dry deposition of nitric acid (HNO₃), NH₃, and coarse-mode (aerodynamic diameter greater than 2.5 μm) NO₃^-, and wet deposition of fine-mode (aerodynamic diameter less than 2.5 μm) NO₃^- and NH₄⁺. The relative importance of the dry deposition of coarse-mode NO₃^- was higher over open ocean. The estimated N deposition to the whole ECS was 390 Gg N yr^-1; this is comparable to the discharge from the Yangtze River to the ECS, indicating the significant contribution of atmospheric deposition. Based on the high-resolution modeling over the ECS, a tendency of high deposition in the western ECS and low deposition in the eastern ECS was found, and a variety of deposition processes were estimated. The dry deposition of coarse-mode NO₃^- and wet deposition of fine-mode NH₄⁺ were the main factors, and the wet deposition of fine-mode NO₃^- over the northeastern ECS and wet deposition of coarse-mode NO₃^- over the southeastern ECS were also found to be significant processes determining N deposition over the ECS.

[Determination of manganese in urine by direct dilution-inductively coupled plasma mass spectrometry]

Objective: To establish a direct dilution-inductively coupled plasma mass spectrometry method for the determination of manganese in urine. Methods: Using 1% nitric acid solution as diluent, the urine dilution factor and internal standard elements were determined by single factor rotation experiment. The linear range, correlation coefficient, precision, accuracy and detection limit of the direct dilution-inductively coupled plasma mass spectrometry for the determination of manganese in urine were evaluated. Results: The linear range of this method was 0.0-20 μg/L, the correlation coefficient was 0.999 9, the detection limit was 0.02 μg/L, the recoveries were 84.65%-103.40%, the relative standard deviations were 0.26%-8.17%. Conclusion: This method has the advantages of simple operation, high sensitivity and low detection limit. It can be used for the determination of urine manganese at the same time with other elements. It is suitable for the determination of urine manganese in workers and ordinary people.

Enhanced electrokinetic remediation for Cd-contaminated clay soil by addition of nitric acid, acetic acid, and EDTA: Effects on soil micro-ecology

Enhanced electrokinetic remediation (EKR) allows the rapid remediation of heavy metal-contaminated clay, but the impacts of this process on soil micro-ecology have rarely been evaluated. In this study, nitric acid, acetic acid, and EDTA were applied for enhancement of EKR and the effects on Cd removal, soil enzyme activity, and soil bacterial communities (SBCs) were determined. Nitric acid and acetic acid allowed 93.2% and 91.8% Cd removal, respectively, and EDTA treatment resulted in 40.4% removal due to the formation of negatively charged EDTA-Cd complexes, resulting in opposing directions of Cd electromigration and electroosmosis flow and slow electromigration rate caused by low voltage drop. Activities of soil beta-glucosidase, acid phosphatase, and urease, were all reduced by enhanced EKR treatment, especially nitric acid treatment, by 46.2%, 58.8% and 57.7%, respectively. The SBCs were analyzed by high-throughput sequencing and revealed significantly increased diversity for acetic acid treatment, no effect for EDTA treatment, and reduced diversity for nitric acid treatment. Compared with nitric acid and EDTA, acetic acid treatment enhanced EKR for higher Cd removal and improved biodiversity.

Laboratory Investigation of Renoxification from the Photolysis of Inorganic Particulate Nitrate

Nitrogen oxides (NO_x) play a key role in regulating the oxidizing capacity of the atmosphere through controlling the abundance of O₃, OH, and other important gas and particle species. Some recent studies have suggested that particulate nitrate, which is conventionally considered as the ultimate oxidation product of NO_x, can undergo "renoxification" via photolysis, recycling NO_x and HONO back to the gas phase. However, there are large discrepancies in estimates of the importance of this channel, with reported renoxification rate constants spanning three orders of magnitude. In addition, previous laboratory studies derived the rate constant using bulk particle samples collected on substrates instead of suspended particles. In this work, we study renoxification of suspended submicron particulate sodium and ammonium nitrate through controlled laboratory photolysis experiments using an environmental chamber. We find that, under atmospherically relevant wavelengths and relative humidities, particulate inorganic nitrate releases NO_x and HONO less than 10 times as rapidly as gaseous nitric acid, putting our measurements on the low end of recently reported renoxification rate constants. To the extent that our laboratory conditions are representative of the real atmosphere, renoxification from the photolysis of inorganic particulate nitrate appears to play a limited role in contributing to the NO_x and OH budgets in remote environments. These results are based on simplified model systems; future studies should investigate renoxification of more complex aerosol mixtures that represent a broader spectrum of aerosol properties to better constrain the photolysis of ambient aerosols.

Response of soil chemical properties and enzyme activity of four species in the Three Gorges Reservoir area to simulated acid rain

The chemical composition in the precipitation is constantly changing, thus acid rain type is gradually changing from sulfuric type to mixed type and then nitric type. The influence of the changing acid rain type on the rhizosphere soil of tree species remains unclear. A pot experiment was performed with two-year-old Pinus massoniana, Cunninghamia lanceolate, Cyclobalanpsis glauca and Phyllostachys edulis seedlings with similar growth condition. Simulated acid rain consists of sulfuric(S/N = 5), mixed(S/N = 1) and nitric(S/N = 0.2) acid rain, and each type acid rain diluted to three acid rain intensity: pH = 2.5, 3.5, 4.5. Soil pH, soil organic matter, cation exchange capacity, the exchangeable Na⁺, K⁺, Ca²⁺, Mg²⁺ and enzyme activity were inhibited by acid rain intensity, while exchangeable Al³⁺ and H⁺ were promoted. Mg²⁺ was most relevant index to the tolerance to acid rain and the correlation degree of soil chemical index was higher than that of enzyme activity. Response of soil chemical properties differed in tree species under different acid rain types. Soil enzyme activity of Pinus massoniana, Cunninghamia lanceolate, and Phyllostachys edulis reached lowest under nitric acid rain, and that of Cyclobalanpsis glauca reached highest. Rhizosphere soil of Cunninghamia lanceolate is tolerant to sulfuric and nitric acid rain, and that of Cyclobalanpsis glauca is tolerant to mixed acid rain.

Efficient cesium encapsulation from contaminated water by cellulosic biomass based activated wood charcoal

In this study, cost-effective cellulosic biomass based activated wood charcoal was developed from Japanese Sugi tree (Cryptomeria japonica) by concentrated nitric acid modification for adsorption of Cs from contaminated water. The physicochemical properties of specimens were investigated using N₂ adsorption-desorption isotherms (BET method), FESEM, FTIR, and XPS spectra analysis. The experimental results revealed that the surface area of the raw wood charcoal was significantly decreased after boiling nitric acid modification. However, several oxygen-containing acidic function groups (-COOH, -CO) were introduced on the surface. The adsorption study confirmed that the equilibrium contact time was 1 h, the optimum adsorption pH was neutral to alkaline and the suitable adsorbent dose was 1:100 (solid: liquid). The maximum Cs was removed when the concentration of Na and K were lower (5.0 mM) with Cs in solution. The Cs adsorption processes well approved by the Langmuir isotherm and pseudo-second-order kinetic models and the maximum adsorption capacity was 35.46 mgg^-1. The Cs adsorption mechanism was clearly described and it was assumed that the adsorption was strongly followed by chemisorptions mechanism based on the adsorbent surface properties, kinetic model and Langmuir isotherm model. Most importantly, about 98% of volume reduction was obtained by burning (500 °C) the Cs adsorbed charcoal, which ensured safe storage and disposal of radioactive waste. Therefore, this study can offer a guideline to produce a functional adsorbent for effective Cs removal and safe radioactive waste disposal.

Determination of microplastic content in seafood: An integrated approach combined with the determination of elemental contaminants

A method for the determination of microplastic (MP) content in seafood is proposed based on the selective digestion of seafood without the degradation of MP. A simple approach was developed using diluted acid with microwave-assisted wet digestion. The following parameters were evaluated: nitric acid concentration (0.5 to 14.4 mol L^-1), digestion temperature (180 to 220 °C), irradiation program holding time (10 to 30 min), MP particle size (0.3 to 5 mm), and the seafood mass (0.5 to 2 g). To develop a reliable method for the determination of MP amount, up to 2 g of an in natura seafood sample were spiked with a known amount of MP (100 mg of mixed MP). Suitable conditions were obtained using 1 mol L^-1 HNO₃ at 200 °C (10 min holding time). Digests were filtered and the plastic content was gravimetrically determined. The heating program was 20 min, which represents a significant reduction in the time normally reported in the literature for MP analysis (from few hours up to 3 days). The proposed method allowed gravimetric determination of eight plastic types (polyethylene terephthalate, polystyrene, expanded polystyrene, polypropylene, high and low density polyethylene, polycarbonate and polyvinyl chloride) with particle size ≥0.3 mm. Up to 2 g of an in natura seafood sample (shark species, acoupa weakfish, tuna fish, trahira, and pink shrimp) were efficiently digested, which opened the possibility of using the proposed digestion method for determining elemental contaminants (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, La, Mg, Mn, Mo, Ni, Pb, and Zn). Thus, as the main feature of the proposed digestion method is the possibility of determining MP and elemental contaminants using the same digestion protocol, saves time and reagents and provides accurate and precise information about different classes of marine pollutants (MP and elemental contaminants).

Cesium removal from a water system using a polysulfone carrier containing nitric acid-treated bamboo charcoal

Laboratory scale sorption and desorption experiments were performed to investigate the cesium (Cs) removal efficiency of a bead-shaped polysulfone carrier containing HNO₃-treated bamboo charcoal (BC). The average Cs removal efficiency of BC only and of polysulfone carrier without BC after 1 h sorption reaction was 53 and 18%, respectively. However, the Cs removal efficiency for the polysulfone carrier with 5% HNO₃-treated BC (P-5N-BC) after 1 h and 24 h reaction was 66 and 98%, respectively. The Cs removal efficiency after 24 h reaction remained >85% over a wide range of pH and temperature conditions, suggesting that using P-5N-BC as the Cs adsorbent is feasible in a variety of aquatic environments. The maximum Cs sorption capacity (q_m) of P-5N-BC, as calculated from a Langmuir isotherm model, was 60.9 mg/g, which is much higher than those of other adsorbents from previous studies for 1 h of sorption time. The Cs desorption rate of P-5N-BC for 24 h desorption time was <17%, showing that the Cs was stably enough attached to the HNO₃-treated BC for long-term use. The results of continuous column experiments showed that the total amount of treated water from the column packed with P-5N-BC increased more than nine times when compared with that from the only BC-granule-packed column. The P-5N-BC maintained more than 68% Cs removal efficiency after 90 pore volumes of flushing, suggesting that only 15 g of P-5N-BC (with only 0.75 g of HNO₃-treated BC) could clean 5 L of Cs-contaminated water (initial Cs concentration: 1.0 mg/L; effluent concentration: < 0.09 mg/L). The present results demonstrate that P-5N-BC has remarkable potential for removal of Cs from diverse water systems.

Aqua regia digestion cannot completely extract Hg from biochar: A synchrotron-based study

Mercury (Hg) is commonly extracted from solid phase samples using aqua regia for total Hg (tHg) analysis. However, uncertainties exist regarding the complete extraction of Hg by aqua regia, especially from carbonaceous materials. To investigate whether aqua regia can completely extract Hg from biochars, batch-style experiments were carried out to evaluate extraction efficiency of aqua regia with respect to Hg-loaded biochar and to characterize the residual Hg speciation and spatial distribution. Different types of biochars (raw, FeCl₃-modified, and FeSO₄-modified, prepared at different temperatures) were reacted with Hg-spiked solution before the digestion experiments. Adsorption analyses indicate the biochars were successfully loaded with Hg and that the Hg content was higher in biochars pyrolyzed at higher temperature (900 versus 300 or 600 °C). The results of digestion experiments indicate Hg could not be completely extracted from the biochars tested, with a greater percentage of residual Hg in biochars pyrolyzed at 600 (60 ± 15%) and 900 (75 ± 22%) than 300 °C (7 ± 2%). Furthermore, the fraction of residual Hg in FeSO₄-modified biochars after aqua regia digestion was significantly lower than in FeCl₃-modified and unmodified biochars. Confocal micro-X-ray fluorescence imaging (CMXRFI) showed residual Hg in biochars is concentrated on surfaces prior to digestion, but more homogeneously distributed after digestion, which indicates Hg on biochar surface is more easily digested. Hg extended X-ray absorption fine structure (EXAFS) spectra modelling showed residual Hg in biochars mainly exists as Hg(II)-Cl. These results indicate extra caution should be paid for tHg determinations using aqua regia digestion method in soil (especially in forest), sediment, and peat samples containing black carbon, activated carbon, or biochar.

Does dilute nitric acid improve the removal of exogenous heavy metals from feathers? A comparative study towards the optimization of the cleaning procedure of feather samples prior to metal analysis

Feather analysis has been widely used as a biomonitoring tool to assess metal contamination in birds, as their sampling is a non-destructive and ethically preferable technique. However, for feathers to be useful as a biomonitor of heavy metals, exogenous contamination has to be efficiently removed. Although much effort has been put into this, no washing procedure has yet proven able to ensure the total removal of the surface-associated metals. The purpose of this study was to propose an efficient washing procedure of feather samples prior to metal analysis, on the basis of comparison of various washing schemes designed according to previous analytical trials, and of the verification of the efficacy of the optimal scheme in cleaning intentionally contaminated feathers. Our investigation showed that dilute nitric acid alone or in combination with a detergent (Extran) or acetone under mild agitation of the samples performed better that any other cleaning scheme applied. Thus, a multi-step procedure including the sequential use of all three reagents was tested against feather samples contaminated by adsorbed or particulate metal species. The procedure was able to completely eliminate the external metal loads in all cases except for the partial removal of severe contamination with adsorbed Cd.

The classic aqua regia and EPA 3051A methods can mislead environmental assessments and certifications: Potentially harmful elements resorption in short-range order materials

EPA 3051A and Aqua Regia (AR) are widely adopted by global environmental agencies to assess soil quality in relation to potentially harmful elements (PHE). However, previous study has shown the formation of large amounts of short-range order materials (SRO) in the residues of these extractions. Residues obtained from the 3051A and AR were recovered from filter papers. To characterize the SRO in these residues, sequential extractions were performed with 0.2 mol L^-1 ammonium oxalate (AO) and 0.5 mol L^-1 NaOH. On average (n = 15), the 3051A and AR residues contained 37% and 60% of SRO, respectively. The largest amounts of SRO formed in the AR residue was in sample 5 (99% of SRO). The main component of the SRO was Al₂O₃-AO, Fe₂O₃-AO and SiO₂-NaOH. The formation of SRO and PHE resorption levels were random and highly dependent on the mineralogy of the soil clay fraction. Soils rich in smectites, which are more common in temperate regions, formed larger amounts of SRO. The association of Pb with the SRO was more pronounced in the 3051A residue than in the AR residue. If SRO was not extracted after 3051A, in sample 7, for example, 595 mg kg^-1 of Pb (10.2%) would have not been accounted. The maximum PHE resorptions in SRO were (%): Pb - 10; Cu - 470; Ba - 280; As - 21. The underestimation of PHE contents due to resorption mechanisms may lead an environmental agency to certify the use of an area contaminated with PHE.

A microbial fuel cell system with manganese dioxide/titanium dioxide/graphitic carbon nitride coated granular activated carbon cathode successfully treated organic acids industrial wastewater with residual nitric acid

To meet the urgent demands for sustainable and efficient, environmental-friendly wastewater treatment, a Microbial fuel cell reactor system with MnO₂/TiO₂/g-C₃N₄ (manganese dioxide/ titanium dioxide/graphitic carbon nitride) @GAC (granular activated carbon) electrode was developed. It was both efficient and energy-saving in treating organic acid wastewater generated in Nylon production, with high-concentration COD and residual nitric acid. The MnO₂/TiO₂/g-C₃N₄ catalyst was deposited on GAC via in-situ growth and sol-gel method. The COD, NH₄⁺-N and NO₃^--N was efficiently removed (respectively 98%, 99% and 99%). The COD removal capacity (17.77 kg COD m^-3d^-1) and the maximum power density (1176.47 mW m^-3) was respectively 36.83% and 65.29% higher than the GAC cathode system. The anodic and cathodic microbial consortiums in MFC were analyzed and compared. The MnO₂/TiO₂/g-C₃N₄@GAC MFC system is technically feasible and cost-effective in treating industrial wastewater.

Comparative effects of the recovery from sulfuric and nitric acid rain on the soil enzyme activities and metabolic functions of soil microbial communities

Acid rain (AR) is a serious issue in China, particularly in the Yangtze River Delta region where the economy has undergone rapid development. Over the last few years, the composition of acid rain in the Yangtze River Delta region has gradually changed from sulfuric acid rain (SAR) to nitric acid rain (NAR) due to controls on SO₂ emissions, but increased NO_x emissions. These changes have made ecosystems more complex. For this study, we halted AR treatments in Quercus acutissima forest plots that had received simulated AR for one year and monitored them from the following February to November. We investigated their soil resident enzyme and microbial metabolic activities, as well as community functional diversity. The results revealed that AR treatments negatively affected both the soil microbial activity and soil microbial community functional diversity; however, both managed to recover over time, once the AR treatments were stopped. During the AR treatment and recovery periods, four main categories (carbohydrates, carboxylic acids, amino acids, and polymers) were dominantly utilized. The utilization of pyruvic acid, which was affected by the AR treatments, as well as d-mannitol and tween 80, accounted for changes in the peak values of the C substrate groups during the AR treatment recovery period. Finally, changes in the activities of soil enzymes recorded following AR recovery, were closely related to the utilization of six C substrate groups. Our results suggested that the recovery of soils following the cessation of NAR stress was more rapid than from SAR. Further, that short-term NAR could be easily treated during the transformation from SAR to NAR in the Yangtze River Delta region. These results might also enrich the basic data relating to post-AR treatments on the soil environment, while having significance toward guiding further studies on the recovery of ecosystems from AR.

Optimizing carbon fibre supports for bioreactors by nitric acid oxidation and calcium ion coverage according to extended DLVO theory

Optimizing supports for microorganisms is required for bioreactors. Carbon fibres (CF) were employed as supports for microorganisms. To optimize CF supports for immobilizing bacterial cells, we used methods of nitric acid oxidation and calcium ion coverage. We evaluated the capacity of these CF supports (untreated CF, nitric acid oxidation CF and Ca²⁺-covered CF) via bacterial cell adhesion tests, based on extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The results implied that because of the high hamaker constants, oxidized CF supports had higher capacity in this regard than untreated CF supports. However, the growing oxygen groups increased the negative zeta potential of CF supports, thus likely to reduce their capacity, in accordance with XDLVO theory. Since the Ca²⁺ coverage could decrease the negative zeta potentials of CF without reducing the hamaker constants, it could enhance the capacity of oxidized CF supports. We concluded that a combination of nitric acid oxidation and Ca²⁺ coverage could increase the capacity of CF supports to immobilize bacterial cells.

Genomic marker assisted identification of genetic loci and genes associated with variation of grain zinc concentration in rice

A study was conducted to examine the genetic divergence and to determine the genetic loci and genes associated with natural variation of grain zinc (Zn) concentration among 28 landraces, improved varieties and advanced breeding lines of rice using candidate gene specific primers. Field evaluation of the experimental material was conducted in randomized block design with three replications and Zn content in unpolished grains of the entries was determined by addition of nitric acid and perchloric acid (1:3) following the procedure of diacid digestion method. Statistical analysis revealed the exploitable extent of variability with respect to grain Zn concentration among the entries. Eighteen entries were selected from the two extremes of grain Zn distribution range and subjected to molecular profiling using a panel of 14 candidate genes specific 12 reported and 14 designed primer pairs. Only eight (OsZIP1-1, OsZIP3a, OsZIP4a, OsZIP5-3, OsZIP7-2, OsZIP8b, OsNRAMP7 and OsNAAT1) reported and eight (OsZIP3K, OsZIP4K, OsZIP5K, OsZIP7K, OsNRAMP7K, OsNAAT1K, OsNACK and OsYSL14K) designed primers generated polymorphic amplified products showing sequence length variation due to targeted amplification of candidate genes specific genomic regions. Ample genetic differentiation and divergence were revealed among the entries, which were accommodated into similarity coefficient-based six clusters, remarkably consistent with grain Zn concentration of the entries. Hierarchical classification pattern of entries was almost completely corroborated by principal co-ordinate analysis based spatial distribution pattern of their genetic profiles. Molecular analysis based on candidate genes specific primers appeared to be an efficient approach for the elucidation of genetic differentiation and divergence in relation to variation of grain Zn concentration among entries. Hence, these markers can be effectively and efficiently utilized for grain Zn concentration related discrimination of rice genotypes and selection of parental genotypes for grain Zn biofortification. Microsatellites were detected within the candidate genes and amplicons, thereby providing a basis to deduce that the repeat sequence length variation in candidate genes may be a role player in the differential grain Zn accumulation in rice varieties. Single marker analysis established the association of OsNACK, OsZIP1-1, OsNRAMP7 and OsNRAMP7K with grain Zn concentration. Thus, these four markers can be effectively used in marker-assisted selection programme for grain Zn biofortification in rice.

Waste-to-resources: Exploratory surface modification of sludge-based activated carbon by nitric acid for heavy metal adsorption

Sewage sludge has the potential to be utilised as a sorbent for dissolved pollutant removal. This study investigated metal removal efficiency of carbonised sewage sludges obtained via pyrolysis at 500 °C: biochar/carbonised sludge (CS), ZnCl₂-activated sludge-based active carbon (SBAC), and three SBACs modified by nitric acid at different concentration and temperature (MSBACs). Batch adsorption kinetic tests indicated that the Pb²⁺ adsorption equilibrated in <5 min. Efficiencies of these sludge-based sorbents for Pb²⁺ adsorption followed the order MSBAC > SBAC > CS. Metal leachabilities were low or negligible for the SBAC and MSBACs. A comparison of 5-min adsorption of the best-performing MSBAC with different sorbents indicates that performance followed the trend MSBAC > grundite (illite) > zeolite (clinoptilolite) > commercial activated carbon (CAC) > kaolinite > perlite. Furthermore, MSBAC achieved 98.9%, 42.6%, and 34.6% removal of Cu, Zn, and Al, respectively, from spiked natural acid rock drainage in <5 min. The modified sludge-based activated carbon is an effective and sustainable sorbent for removing metals from aqueous environments.

Development of a novel recycling system for waste cathode ray tube funnel glass based on the integration of nanoscale Fe0 with ball milling

A novel and effective system was developed for recycling cathode ray tube (CRT) funnel glass wastes. Initially, the combination of nanoscale Fe⁰ with ball milling promoted lead transfer that was strongly encapsulated in the glass inner structure to the surface of funnel glass and/or adhere to iron substance due to the collapse of SiO bonds. This condition enhanced the dissolution of lead in the acid solution. A high lead extraction rate of 97.8% from funnel glass was achieved through nitric acid leaching by optimizing the operational parameters (Fe⁰/funnel glass mass ratio, 0.5:1; ball milling time; 72 h). Subsequently, lead sulfate, iron hydroxides, and sodium nitrate were gradually recovered from the acid leachate by using three simple operations, namely, sulfation, alkali neutralization, and salt evaporation. Meanwhile, the leaching results of short-term toxicity characteristic leaching (TCLP) and long-term multiple extraction procedures (MEP) clearly demonstrated that the residual high silica products (after acid leaching) had no impact on the environment and could be used to synthesize high value-added zeolites as raw materials. With the addition of Al sources, the complete conversion of high silica residues into high crystalline zeolites with high cation exchange capacity value was realized by applying an alkaline fusion method during the hydrothermal treatment. Furthermore, lead, NO^-₃, and SO^2-₄ concentrations of the resulting drainage were considerably lower than the relevant standard for surface water quality. Therefore, the proposed recycling system provided an eco-friendly and feasible technique for complete reutilization of obsolete CRT funnel glass.

Adsorption mechanism of 2,4-dichlorophenoxyacetic acid onto nitric-acid-modified activated carbon fiber

Adsorption by carbon materials is one of the relatively fast methods in present research, which is widely used in emergency events. Activated carbon fiber (ACF) modified by nitric acid (N-ACF) was studied in this research to determine the adsorption performance for 2,4-dichlorophenoxyacetic acid (2,4-D). Subsequently, influence factors, adsorption isotherm models, kinetics and thermodynamic were investigated in a batch system to realize this adsorption. Experimental results showed that ACF modified by 0.1M nitric acid had a better removal ability than 2,4-D. Removal rate of 2,4-D by N-ACF was greatly influenced by pH with the optimum pH at 2. The superiority of the Langmuir isotherm model in describing the adsorption equilibrium was revealed by correlation coefficients R2 (R₂ ≥ 0.997). Furthermore, adsorption kinetics was well described by pseudo-second-order model. The results of thermodynamic showed that adsorption was a spontaneous, endothermic process with randomness increasing. Additionally, surface structure properties of adsorbent were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy, Specific surface area analysis of Brunauer, Emmett and Teller and Boehm's titration. It turned out that the micropore structure and functional groups on N-ACF all can contribute to the removal of 2,4-D.

Extracorporeal membrane oxygenation combined with continuous renal replacement therapy in cutaneous burn and inhalation injury caused by hydrofluoric acid and nitric acid

RATIONALE

Hydrofluoric acid (HF) is a highly corrosive agent and can cause corrosive burns. HF can penetrate deeply into tissues through intact skin and the lipid barrier, leading to painful liquefactive necrosis, and inducing hypocalcemia and hypomagnesemia. In this study, we hypothesize that continuous renal replacement therapy (CRRT) may be beneficial in addressing hemodynamic instability in cases of HF poisoning.

PATIENT CONCERNS

A 25-year-old man fell into an electroplating pool containing 10% HF and 50% nitric acid.

DIAGNOSES

He had severe cutaneous injuries involving approximately 60% of his total body surface area including the head, face, neck, right upper arm, right hand, trunk, perineum, and both lower limbs and feet. Examination at admission showed the following electrolyte concentrations: ionic calcium 0.192 mmol/L, total calcium 0.72 mmol/L, magnesium 0.4 mmol/L, potassium 5.49 mmol/L, and sodium 136.8 mmol/L.

INTERVENTIONS

An initial 20 mL intravenous bolus of 10% calcium gluconate was followed by a continuous infusion at 6 g/h plus continuous intravenous drip 25% magnesium sulfate at 1.5 g/h. Continuous cardiac monitoring was performed in the intensive care unit. Extracorporeal membrane oxygenation (ECMO) was used to improve oxygenation function at 38 hours post exposure. Antibiotic therapy using imipenem/cilastin plus vancomycin was required.

OUTCOMES

After treatment for 12 hours, electrolyte concentrations returned to normal. On day 11, the hemodynamic parameters were stable and oxygenation function had improved. On day 26, the patient was weaned off CRRT. One month later, the patient twice received skin grafting, then was discharged from the hospital without pulmonary, cardiac, or neurological complications 3 months later.

LESSONS

The present case study demonstrates that CRRT may be an effective and potentially lifesaving therapy after severe exposure to HF. Prolonged hemodialysis is recommended to remove delayed release fluoride ions to avoid delayed systemic injury. When conventional therapy can not improve oxygenation and/or carbon dioxide retention, ECMO should be performed as soon as possible.

Extraction of rare earth elements from a contaminated cropland soil using nitric acid, citric acid, and EDTA

Rare earth elements (REEs) contamination to the surrounding soil has increased the concerns of health risk to the local residents. Soil washing was first attempted in our study to remediate REEs-contaminated cropland soil using nitric acid, citric acid, and ethylene diamine tetraacetic acid (EDTA) for soil decontamination and possible recovery of REEs. The extraction time, washing agent concentration, and pH value of the washing solution were optimized. The sequential extraction analysis proposed by Tessier was adopted to study the speciation changes of the REEs before and after soil washing. The extract containing citric acid was dried to obtain solid for the X-ray fluorescence (XRF) analysis. The results revealed that the optimal extraction time was 72 h, and the REEs extraction efficiency increased as the agent concentration increased from 0.01 to 0.1 mol/L. EDTA was efficient to extract REEs over a wide range of pH values, while citric acid was around pH 6.0. Under optimized conditions, the average extraction efficiencies of the major REEs in the contaminated soil were 70.96%, 64.38%, and 62.12% by EDTA, nitric acid, and citric acid, respectively. The sequential extraction analyses revealed that most soil-bounded REEs were mobilized or extracted except for those in the residual fraction. Under a comprehensive consideration of the extraction efficiency and the environmental impact, citric acid was recommended as the most suitable agent for extraction of the REEs from the contaminated cropland soils. The XRF analysis revealed that Mn, Al, Si, Pb, Fe, and REEs were the major elements in the extract indicating a possibile recovery of the REEs.