Adsorption of Pb(II) from wastewater using a red mud modified rice-straw biochar: Influencing factors and reusability

Mn oxide-modified biochars with high adsorption capacity for Pb(II) in wastewater: Preparation and adsorption mechanisms

The occurrence of excessive levels of bivalent plumbum (Pb(II)) in wastewater poses a notable threat to both human health and ecological safety. In this study, orthogonal experiments were conducted to prepare coprecipitation-modified biochar (C-BC) and impregnation pyrolysis-modified biochar (I-BC) via potassium permanganate (KMnO4) for removing Pb(II) from wastewater. Three types of modified biochars (BCs) (Mn-BCs) namely, C-BC400, I-BC400, and I-BC700, were selected as high-efficiency adsorbents on the basis of their high removal rates (87.2%, 88.0%, and 91.2%, respectively) for 400 mg/L Pb(II) solutions. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM)‒energy-dispersive X-ray spectroscopy (EDS) analysis results indicated that Mn elements were distributed only on the outer surfaces of the C-BC400 particles but occurred on the outer surface and were stably embedded in the I-BC400 and I-BC700 particles. Compared with those of the pristine (BCs), the Pb(II) adsorption rates of C-BC400, I-BC400, and I-BC700 increased by factors of 3.75, 2.09, and 5.70, respectively. The Pb(II) adsorption capacities of C-BC400, I-BC400, and I-BC700 (182.28, 133.16, and 69.25 mg/g, respectively) were significantly greater than those of the pristine BCs produced at 400 °C (45.43 mg/g) and 700 °C (40.71 mg/g). The excellent adsorption ability of Mn-BCs for Pb(II) depends on various adsorption mechanisms, including complexation, electrostatic attraction, surface adsorption, and ion exchange. These results suggest that Mn-BCs exhibit high application potential in the remediation of Pb(II)-contaminated wastewater.

Influence of drought stress on phosphorus dynamics and maize growth in tropical ecosystems

Drought has a significant impact on ecosystem functions, especially on the biogeochemical cycling of phosphorus (P), which is a crucial nutrient for plant growth and productivity. Despite its importance, the effects of different drought scenarios on soil P cycling and availability remain poorly understood in previous studies. This study simulated drought conditions in tropical soils using maize as a test crop under varying field capacity (FC) levels (100%, 80%, 60%, 40%, and 20%) over a 60-day pot experiment. P uptake and plant biomass decreased significantly lower FC level. P uptake was highest at FC100 (5 g kg-¹) and lowest at FC20 (3.5 g kg-¹). Similarly, biomass was greatest at FC100 (70 g plant-¹) and declined to 35 g plant-¹ at FC20, underscoring the adverse effects of drought on P availability and growth. The results showed a substantial increase in calcium-associated P (HClD-Pi), reaching 45% at FC20. Conversely, labile inorganic P fractions (NaHCO₃-Pi and NaOH-Pi) decreased significantly, from 14.73 to 6.2 mg kg-¹ and 29.4 to 17.7 mg kg-¹, respectively, in FC20 compared to FC100. Organic P fractions (NaHCO₃-Po, NaOH-Po) increased by 6 and 2.4 times, respectively, under lower FC treatments, while HClc-Po was also elevated under drier conditions. These transformations were attributed to changes in soil pH and calcium content, favoring the stabilization of P as HClD-Pi. Drought disrupted the replenishment of inorganic P in the soil solution, reducing bioavailability, though phosphatase activity enhanced organic P release. Pearson's correlation analysis revealed positive associations between labile and moderately labile P fractions (NaHCO₃-Pi, NaOH-Pi, HClD-Pi) and soil elements (Ca, Al, Fe). RDA highlighted a positive link between phosphatase activity and reduced labile P, while P uptake and biomass were strongly associated with labile and moderately labile P fractions. These findings demonstrate drought's significant impact on P bioavailability, soil P cycling, and nutrient dynamics.

The development of multifunctional biochar with NiFe2O4 for the adsorption of Cd (II) from water systems: The kinetics, thermodynamics, and regeneration

High concentrations of Cd (II) in wastewater have been reported several times which attracted top research attention to mitigate the pollution impacts of the contaminant. Therefore, this study aimed to develop a Zn-doped NiFe2O4- pinecone biochar composite (ZNiF@PB) for the adsorption of Cd (II) from wastewater. FTIR confirmed immobilization of PB on the surface of ZNiF by the presence of C = O at 1638 cm-1, COOH at 1385 cm-1, C-O at 1009 cm-1 and Fe-O at 756 cm-1. Similarly, XRD determined the crystallite structure of the adsorbents where the ZNiF crystallite size of 43 nm was obtained while the particle size of ZNiF@PB was found to be 38 nm. These XRD results agreed with those values obtained from TEM images showing ZNiF and ZNiF@PB had a spherical shape with similar particle sizes. On the other hand, the surface areas of ZNiF, PB, and ZNiF@PB were found to be 78.4 m2/g, 125 m2/g, and 104 m2/g, respectively. These high surface areas have a huge potential to enhance Cd removal. With these adsorbents, the maximum Cd (II) adsorption of 96% was recorded at the optimum experimental condition of adsorbent dosage 0.5g/50 mL, solution pH 6, initial Cd (II) concentration 100 mg/L, and contact time 120 min. Practical adsorption kinetics data were well described by the pseudo-second order model whereas the adsorption isotherm was a perfect fit to the Langmuir isothermal model implying the adsorption process to be a monolayer with mainly a chemically bonded mechanism. In conclusion, this adsorbent is efficient for the adsorption of Cd (II) from wastewater and has also a huge potential to be applied for industrial-scale water purification.

Effects of flotation reagents with aniline aerofloat and ammonium dibutyl dithiophosphate on a constructed rapid infiltration system: Performance and microbial metabolic pathways

Aniline aerofloat (AAF) and ammonium dibutyl dithiophosphate (ADD) are the key flotation reagents in mineral processing. This study investigated the performance of the constructed rapid infiltration systems with coke and red mud as adsorbents for treatment AAF and ADD wastewater. Meanwhile, the effects of AAF and ADD on the microbial metabolic pathways of the systems were unraveled. Results showed that the AAF concentration in influent was 25 mg/L, which promoted chemical oxygen demand (COD) and total phosphorus (TP) removal of the A column (coke) and B column (red mud). While the COD and TP removal of the C column (coke) and D column (red mud) were inhibited with ADD concentration increasing to 50 mg/L and 100 mg/L. The AAF reduced the binding energy of coke C-O bond by 0.9 eV, and down-regulated the C-C bond ratio by 40.72%. The dominant phyla in the columns were Pseudomonadota and Actinomycetota. The pore structure of coke was more conducive to the growth of the Pseudomonadota, while the metal composition of red mud was more conducive to the redox reaction of microorganisms. The presence of phosphofructokinase (2.7.1.11)-related genes was up-regulated in column C compared to other columns. The ADD was beneficial to the expression of norC and nosZ functional genes during nitrogen metabolism process. In contrast, phosphorus metabolism genes were more expressed in the red mud column for treatment AAF wastewater. This study reveals the potential of coke and red mud for the treatment of flotation reagents wastewater, while providing a theoretical basis for the optimal selection of filler types in the constructed rapid infiltration systems.

Wood biochar induced metal tolerance in Maize (Zea mays L.) plants under heavy metal stress

Due to metal toxicity, widespread industrialization has negatively impacted crop yield and soil quality. The current study was aimed to prepare and characterize biochar made from wood shavings of Pinus roxburghii and to determine the plant growth promoting and heavy metal detoxification of cadmium (Cd) and chromium (Cr) contaminated soil. FTIR SEM coupled with EDX characterization of biochar was performed; Cd and Cr were used at a rate of 20 mg/kg. Biochar was used at the rate of 50 mg/kg for various treatments. The completely randomized design (CRD) was used for the experiment and three replicates of each treatment were made. Various agronomic and enzymatic parameters were determined. The results indicated that all growth and enzymatic parameters were enhanced by the prepared biochar treatments. The most prominent results were observed in treatment T5 (in which shoot length, root length, peroxidase dismutase (POD), superoxide dismutase (SOD) catalyzes (CAT), and chlorophyll a and b increased by 28%, 23%, 40%, 41%, 42%, and 27%, respectively, compared to the control). This study demonstrated that biochar is a sustainable and cost-effective approach for the remediation of heavy metals, and plays a role in plant growth promotion. Farmers may benefit from the current findings, as prepared biochar is easier to deliver and more affordable than chemical fertilizers. Future research could clarify how to use biochar optimally, applying the minimum amount necessary while maximizing its benefits and increasing yield.

Efficient multifunctional PPy-NTs/PEI@alginate@NiFe2O4 magnetic beads for heavy metals removal: Experimental design and optimization interpretations

A highly effective magnetic nanocomposite alginate beads (PPy-NTs/PEI@Alg@NiFe2O4) were synthesized using alginate as the encapsulation reagent and polypyrrole/polyethylene imine with nano NiFe2O4 as a functional filler to remove toxic Zn2+ and Pb2+ from polluted water. A response surface methodology (RSM) was used to statistically assess the influences of pH and the adsorbent dose on the adsorption performance. PPy-NTs/PEI@Alg@NiFe2O4 magnetic microbeads exhibited the optimal adsorption capacity qe (18.6 mg/g) at pH 6 and a 2 mg/L dose for Zn2+ removal. In comparison, the optimal qe (32.6 mg/g) was reached at pH 4.5 with a 1.5 mg/L dose for Pb2+ remediation. From batch experiments, maximal absorption capacities of 53.3 mg/g and 22 mg/g were achieved for Pb2+ and Zn2+, respectively, at 313 K. The pseudo-second-order kinetic model fitted the results well, suggesting that the chemisorption process regulates adsorption. Isotherm models indicate the presence of homogeneous adsorption sites from the well-fitting to Langmuir isotherm. An investigation of the effects of temperature and thermodynamic considerations revealed the endothermic nature of Zn2+ and Pb2+ absorption. The Fourier transform infrared spectra showed that -NH, -NH2, and -COO- are the main groups in PPy-NTs/PEI@Alg@NiFe2O4 composite beads that were responsible for Zn2+ and Pb2+ removal from polluted water.

Unlocking the potential of environmentally friendly adsorbent derived from industrial wastes: A review

With increasing urbanization and industrialization, growing amounts of industrial waste, such as red mud (RM), fly ash (FA), blast furnace slag (BFS), steel slag (SS), and sludge, are being produced, exposing substantial threats to the environment and human health. Given that numerous researchers associate with conventional adsorbents, developing and utilizing industrial wastes derived from adsorption technology still has received limited attention. Utilizing this waste contributes to developing alternative materials with superior performance and significantly reduces the volume of solid waste. The excellent physical and chemical characteristics of these wastes are also investigated in this paper. This review attempts to demonstrate a comprehensive overview of the application of industrial waste-based adsorbent in the adsorption process for removing organic pollutants, dyes, metallic ions, non-metallic ions, and radioactive substances. In addition, industrial waste-based adsorbents are among the most promising and applicable techniques for pollutant removal, offering remarkable adsorption efficiency, rich surface chemistries, reasonable cost, simple operation, and low energy consumption. This review summarizes state-of-the-art advancements in engineered adsorbents (including physical and chemical modifications). It provides a holistic view regarding a comprehensive understanding of the mechanism involved in adsorption for water remediation. The challenges and the prospects for future research in applying these adsorbents are also elucidated, contributing to sustainable waste management and environmental sustainability.

Waste-treating-waste: Effective heavy metals removal from electroplating wastewater by ladle slag

Ladle slag, a by-product of steelmaking, presents a valuable strategy for waste reduction and valorization in wastewater treatment. This work demonstrates the successful simultaneous removal of Al(III), B(III), Ba(II), Cr(III), Mg(II), Sr(II), Pb(II), and Zn(II), from electroplating wastewater by ladle slag. First, Cr(III) and Pb(II) removals were evaluated in single synthetic systems by analyzing the influence of pH, temperature, and ladle slag dosage. Competitive removal was observed in binary batch experiments of Cr(III) - Pb(II), achieving 88% and 96% removal, respectively, with fast kinetics following a pseudo-second-order model. The findings of XRD, SEM, EDX, and FTIR of the slag after removal helped to elucidate the synergic removal mechanism involving ladle slag dissolution, precipitation, ion exchange, and adsorption in a tight relationship with the solution pH. Lastly, ladle slag was tested in real electroplating wastewater with the aforementioned ions at concentrations ranging from <1 to 1700 mg/L. The removal was performed in two steps, the first attained the following efficiencies: 73% for Al(III), 88% for B(III), 98% for Ba(II), 80% for Cr(III), 82% for Mg(II), 99% for Pb(II), 88% for Sr(II), and 88% for Zn(II). Visual MINTEQ simulation was utilized to identify the different species of ions present during the removal process. Furthermore, the leaching tests indicated a minimal environmental risk of secondary pollution in its application. The results promote an effective and sustainable approach to wastewater treatment within the circular economy.

Bauxite residue (red mud) treatment: Current situation and promising solution

Bauxite residue, an industrial solid waste generated during alumina production, with over 80 % of bauxite residue worldwide being accumulated around alumina plants, which occupying a significant amount of land resources and posing a threat to the natural environment in the surrounding areas. This paper reviews recent advances in extracting valuable resources from bauxite residue, and its applications in building materials, environmental adsorbents, energy storage materials, and soil alkalinization. It also highlighted the main problem existing in these researches, which is the inability of the existing single processes to achieve the comprehensive utilization of various types of bauxite residue or maximize the utilization of bauxite residue components, resulting in a low comprehensive utilization rate and insignificant absorption effects of bauxite residue. To address these issues, we proposed a strategy of classifying and utilizing bauxite residue based on its components and establishing a multi-industry application system, involving sectors such as steel and building materials. This collaborative approach aims to handle various types of bauxite residue more effectively. Additionally, we suggest selecting suitable treatment methods based on the specific characteristics of bauxite residue and implementing measures to promote its comprehensive and large-scale utilization.

Characterization of phosphate modified red mud-based composite materials and study on heavy metal adsorption

In this paper, Bayer red mud (RM) and lotus leaf powder (LL) were used as the main materials, and KH2PO4 was added to modify the material. Under the condition of high-temperature carbonization, RMLL was prepared and phosphate modified red mud matrix composite (PRMLL) was prepared based on KH2PO4 modification, which can effectively remove Pb2+ from water. The optimum preparation and application conditions were determined through orthogonal experiment: dosage 0.1g, ratio 1:1, and temperature 600 °C. The effects of pH, dosage, and initial concentration on the adsorption of Pb2+ were studied. The pseudo-first-order, pseudo-second-order, and Elovich kinetic models were fitted to the experimental data. It was found that RMLL and PRMLL were more consistent with the pseudo-second-order kinetic model and chemisorption. Langmuir, Freundlich, Timkin, and Dubinin-Radushkevich isothermal adsorption models were used to fit the experimental data. It was found that RMLL and PRMLL were more consistent with Langmuir model. In addition, the maximum adsorption capacity of RMLL and PRMLL was 188.1 mg/g and 213.4 mg/g, respectively. It is larger than the adsorption capacity of their monomers. Therefore, the use of RMLL and PRMLL as the removal of Pb2+ from water is a potential application material.

Synthesis, characterization, and phosphorus adsorption of Mg/Fe-modified biochar from cotton stalk pretreated with Coriolus versicolor

In recent years, the research potential in utilizing biochars as adsorbents in adsorption processes has grown due to their eco-friendly and economical nature. However, biochar often possesses a negative surface charge that limits its affinity for binding anions. Nitric acid washing and pretreatment with Coriolus versicolor can break down the lignocellulosic structure in cotton stalk waste, facilitating the subsequent impregnation of Mg and Fe metal oxides. These pretreatment steps can lead to the production of diverse and functionalized biochars with higher adsorption capacities. In this study, cotton stalk waste was first washed with diluted nitric acid and then subjected to biological pretreatment by incubation with C. versicolor, followed by impregnation with Mg and Fe to obtain CV-CS/Fe and CV-CS/Mg biochars. The results showed that the applied pretreatments altered the physicochemical properties and significantly increased the phosphorus adsorption capacity. The adsorption capacities of CV-CS/Fe and CV-CS/Mg biochars were found to be 277.88 and 507.01 mg g-1, respectively. The results indicate that the incorporation of multiple metal oxide impregnates enhances P adsorption. Furthermore, in the kinetic study, pseudo-first-order and pseudo-second-order models provided a well fit, determining chemical adsorption as the main adsorption mechanism for phosphorus adsorption. The biochars demonstrated compatibility with Langmuir-Freundlich models. Overall, the findings suggest the possibility of synthesizing biochars with improved adsorptive properties through pretreatment, and these engineered biochars hold promising potential as effective adsorbents in the field. PRACTITIONER POINTS: Eco-friendly, natural, and economical biochar was synthesized. Biochar was produced via Coriolus versicolor pretreatment. High adsorption capacities of CV-PS/Mg biochars were found to be 507.01 mg g-1. Adsorption capacities of biochars can be improved by pretreatment.

Effects of Alkali Activation of the Cotton Straw Biochar on the Adsorption Performance for Cd2

In this study, a single factor exploration method was adopted to optimize the cotton shell-based activated carbon adsorption reaction time, temperature, pH value, initial concentration of cadmium ion, and other conditions. The experimental results showed that under the conditions of Cd2+ solution pH = 8, initial concentration of 100 mg/L, adsorption reaction time of 180 min, adsorption temperature of 45 °C, cotton shell-based activated carbon dosage of about 0.1 g, the removal rate of Cd2+ was 94.03%, the adsorption capacity was 51.95 mg/g, and the error was only 0.05%. The adsorption kinetic analysis of this study conforms to the quasi-second-order kinetic model, the adsorption isotherm analysis conforms to the Langmuir adsorption isothermal model, and the Gibbs free energy of the adsorption process is negative; the above simulation analysis also proves the spontaneity and feasibility of the adsorption process.

Biochar and nano biochar: Enhancing salt resilience in plants and soil while mitigating greenhouse gas emissions: A comprehensive review

Salinity stress poses a significant challenge to agriculture, impacting soil health, plant growth and contributing to greenhouse gas (GHG) emissions. In response to these intertwined challenges, the use of biochar and its nanoscale counterpart, nano-biochar, has gained increasing attention. This comprehensive review explores the heterogeneous role of biochar and nano-biochar in enhancing salt resilience in plants and soil while concurrently mitigating GHG emissions. The review discusses the effects of these amendments on soil physicochemical properties, improved water and nutrient uptake, reduced oxidative damage, enhanced growth and the alternation of soil microbial communities, enhance soil fertility and resilience. Furthermore, it examines their impact on plant growth, ion homeostasis, osmotic adjustment and plant stress tolerance, promoting plant development under salinity stress conditions. Emphasis is placed on the potential of biochar and nano-biochar to influence soil microbial activities, leading to altered emissions of GHG emissions, particularly nitrous oxide(N2O) and methane(CH4), contributing to climate change mitigation. The comprehensive synthesis of current research findings in this review provides insights into the multifunctional applications of biochar and nano-biochar, highlighting their potential to address salinity stress in agriculture and their role in sustainable soil and environmental management. Moreover, it identifies areas for further investigation, aiming to enhance our understanding of the intricate interplay between biochar, nano-biochar, soil, plants, and greenhouse gas emissions.

Utilizing different types of biomass materials to modify steel slag for the preparation of composite materials used in the adsorption and solidification of Pb in solutions and soil

This study utilized discarded steel slag (SS) as raw material and prepared modified steel slag materials (SS-SBC, SS-NBC, SS-BHA) through modification with biomass materials such as straw biochar (SBC), nutshell biochar (NBC), and biochemical humic acid (BHA). These materials were then applied for the removal of Pb from both solution and soil. The physical and chemical properties of the materials were analyzed using characterization techniques such as SEM, EDS, XRD, and BET. The specific surface area of the modified materials increased from the original 3.8584 m2/g to 34.7133 m2/g, 181.7329 m2/g, and 7.7384 m2/g, respectively. The study then explored the influence of different adsorption conditions on the adsorption capacity of Pb in solution, determining the optimal conditions as follows: initial concentration of 200 mg/L, adsorbent mass of 0.04 g, temperature of 15 °C, and pH = 2. To further investigate the adsorption process, kinetic and isotherm models were established. The results indicated that the adsorption process for all three materials followed a pseudo-second-order kinetic model and Freundlich isotherm model, suggesting a multi-layer chemical adsorption. Thermodynamic analysis revealed that the adsorption process was an exothermic spontaneous reaction. Soil cultivation experiments were conducted to explore the effects of different material addition amounts and cultivation times on the passivation of Pb-polluted soil. Analysis of heavy metal forms in the soil revealed that the addition of modified materials reduced the acid-extractable form of Pb in the soil and increased the residual form, which is beneficial for reducing the migration of Pb in the soil. FT-IR and XPS analyses were employed to study the functional groups, element composition, and valence states before and after adsorption passivation of Pb by the three materials. The results confirmed that the adsorption mechanisms of SS-SBC, SS-NBC, and SS-BHA mainly involved electrostatic adsorption, ion and ligand exchange, and surface precipitation. This study not only provides a new material for adsorbing and immobilizing heavy metals in soil and water but also offers a new approach for the resource utilization of steel slag waste.

Chemical and mechanical coating of sulfur on baby corn biochar and their role in soil Pb availability, uptake, and growth of tomato under Pb contamination

In recent ages, industrial revolution and natural weathering processes have been increasing lead (Pb) contamination in agricultural soils, therefore, green remediation technologies are becoming attractive and cost-effective. In the current pot study, 1% and 2% (w/w) application rates of sulfur (S) alone and novel chemo-mechanically S-modified baby corn biochars (CSB and MSB) were applied in a Pb-contaminated (500 mg/kg) soil to evaluate tomato (Lycopersicon esculentum L.) growth, Pb uptake and its soil availability. The results from SEM-EDS and XRD patterns confirmed the S enrichment on the surface of baby-corn biochar. Further, Pb treatment alone imposed a significant reduction in biomass accumulation, photosynthetic pigments, antioxidative mechanism, root traits, and Pb-tolerance index because of increased soil Pb availability and its uptake, translocation and biological accumulation in various tissues of tomato. However, incorporation of lower rate of elemental S (1%) and higher rates of biochars, especially chemically S-modified biochar, CSB (2%) significantly improved dry biomass production, Pb-tolerance index, physiological attributes and antioxidative defense system of tomato plants. These results might be due to a prominent decrease in soil Pb availability by 37.5%, Pb concentration in shoot by 66.7% and root by 58.3%, soil to root transfer by 33.8%, and root to shoot transfer by 20.2% in tomato plants under 2% application rate of CSB, as compared with the Pb treatment without any amendment. Moreover, sulfur treatment induced a significant impact in reduction of soil pH (from 8.97-7.47) as compared to the biochar treatments under Pb-toxicity. The current findings provided an insight that 2% chemically S-modified biochar (CSB) has significant potential to improve the tomato growth by reducing Pb bioavailability in the Pb-contaminated soil, compared to the S alone and MSB amendments.

Phytosphere purification of urban domestic wastewater

Industrialization and overpopulation have polluted aquatic environments with significant impacts on human health and wildlife. The main pollutants in urban sewage are nitrogen, phosphorus, heavy metals and organic pollutants, which need to be treated with sewage, and the use of aquatic plants to purify wastewater has high efficiency and low cost. However, the effectiveness and efficiency of phytoremediation are also affected by temperature, pH, microorganisms and other factors. The use of biochar can reduce the cost of wastewater purification, and the combination of biochar and nanotechnology can improve the efficiency of wastewater purification. Some aquatic plants can enrich pollutants in wastewater, so it can be considered to plant these aquatic plants in constructed wetlands to achieve the effect of purifying wastewater. Biochar treatment technology can purify wastewater with high efficiency and low cost, and can be further applied to constructed wetlands. In this paper, the latest research progress of various pollutants in wastewater purification by aquatic plants is reviewed, and the efficient treatment technology of wastewater by biochar is discussed. It provides theoretical basis for phytoremediation of urban sewage pollution in the future.

Highly efficient catalytic ozonation degradation of levofloxacin by facile hydrogenation-modified red mud wastes

Iron-rich red mud (RM) is a potential catalyst. However, as industrial waste, is strongly alkaline, low effectiveness, and safety concerns are problems that cannot be ignored, it is urgent to mine out a reasonable disposal and utilization technology for the waste. In this study, an effective catalyst (H-RM) was obtained by facile hydrogenation heating modification of red mud. Then above-prepared H-RM was applied in the catalytic ozonation degradation of levofloxacin (LEV). The H-RM exhibited more remarkable catalytic activities than the RM in terms of LEV degradation, and the optimal efficiency can reach over 90% within 50 min. The mechanism experiment proved that the concentration of dissolved ozone and hydroxyl radical (•OH) significantly increased, which enhanced the oxidation effect. Hydroxyl radical played a dominant role in the degradation of LEV. In the safety test, it is concluded that the concentration of total hexavalent chromium (total Cr(Ⅵ)) in the H-RM catalyst decreases and the leaching concentration of water-soluble Cr(Ⅵ) in aqueous solution is low. The results indicated that the hydrogenation technique is an available Cr (Ⅵ) detoxification method for RM. Moreover, the H-RM has excellent catalytic stability, which is beneficial to recycling and maintains high activity. This research provides an effective means to fulfill the reuse of industrial waste as an alternative to standard raw materials, and comprehensive utilization of the waste to attain the purpose of treating pollution with wastes.

Exploring biochar and fishpond sediments potential to change soil phosphorus fractions and availability

Phosphorus (P) availability in soil is paradoxical, with a significant portion of applied P accumulating in the soil, potentially affecting plant production. The impact of biochar (BR) and fishpond sediments (FPS) as fertilizers on P fixation remains unclear. This study aimed to determine the optimal ratio of BR, modified biochar (MBR), and FPS as fertilizer replacements. A pot experiment with maize evaluated the transformation of P into inorganic (Pi) and organic (Po) fractions and their contribution to P uptake. Different percentages of FPS, BR, and MBR were applied as treatments (T1-T7), T1 [(0.0)], T2 [FPS (25.0%)], T3 [FPS (25.0%) + BR (1%)], T [FPS (25%) +MBR (3%)], T5 [FPS (35%)], T6 [FPS (35%) +BR (1%)], and T7 [FPS (35%) + MBR (1%)]. Using the modified Hedley method and the Tiessen and Moir fractionation scheme, P fractions were determined. Results showed that various rates of MBR, BR, and FPS significantly increased labile and moderately labile P fractions (NaHCO3-Pi, NaHCO3-Po, HClD-Pi, and HClC-Pi) and residual P fractions compared with the control (T1). Positive correlations were observed between P uptake, phosphatase enzyme activity, and NaHCO3-Pi. Maximum P uptake and phosphatase activity were observed in T6 and T7 treatments. The addition of BR, MBR, and FPS increased Po fractions. Unlike the decline in NaOH-Po fraction, NaHCO3-Po and HClc-Po fractions increased. All Pi fractions, particularly apatite (HClD-Pi), increased across the T1-T7 treatments. HClD-Pi was the largest contributor to total P (40.7%) and can convert into accessible P over time. The T5 treatment showed a 0.88% rise in residual P. HClD-Pi and residual P fractions positively correlated with P uptake, phosphatase activity, NaOH-Pi, and NaOH-Po moderately available fractions. Regression analysis revealed that higher concentrations of metals such as Ca, Zn, and Cr significantly decreased labile organic and inorganic P fractions (NaHCO3-Pi, R 2 = 0.13, 0.36, 0.09) and their availability (NaHCO3-Po, R 2 = 0.01, 0.03, 0.25). Excessive solo BR amendments did not consistently increase P availability, but optimal simple and MBR increased residual P contents in moderately labile and labile forms (including NaOH-Pi, NaHCO3-Pi, and HClD-Pi). Overall, our findings suggest that the co-addition of BR and FPS can enhance soil P availability via increasing the activity of phosphatase enzyme, thereby enhancing plant P uptake and use efficiency, which eventually maintains the provision of ecosystem functions and services.

Effective adsorption of Pb(ii) from wastewater using MnO2 loaded MgFe-LD(H)O composites: adsorption behavior and mechanism

Pb(ii) adsorption by MnO₂/MgFe-layered double hydroxide (MnO₂/MgFe-LDH) and MnO₂/MgFe-layered metal oxide (MnO₂/MgFe-LDO) materials was experimentally studied in lab-scale batches for remediation property and mechanism analysis. Based on our results, the optimum adsorption capacity for Pb(ii) was achieved at the calcination temperature of 400 °C for MnO₂/MgFe-LDH. Langmuir and Freundlich adsorption isotherm models, pseudo-first-order and pseudo-second-order kinetics, Elovich model, and thermodynamic studies were used for exploring the Pb(ii) adsorption mechanism of the two composites. In contrast to MnO₂/MgFe-LDH, MnO₂/MgFe-LDO_{400 °C} has a stronger adsorption capacity and the Freundlich adsorption isotherm model (R² > 0.948), the pseudo-second-order kinetic model (R² > 0.998), and the Elovich model (R² > 0.950) provide great fits to the experimental data, indicating that the adsorption occurs predominantly via chemisorption. The thermodynamic model suggests that MnO₂/MgFe-LDO_{400 °C} is spontaneously heat-absorbing during the adsorption process. The maximum adsorption capacity of MnO₂/MgFe-LDO_{400 °C} for Pb(ii) was 531.86 mg g^-1 at a dosage of 1.0 g L^-1, pH of 5.0, and temperature of 25 °C. Through characterization analysis, the main mechanisms involved in the adsorption process were precipitation action, complexation with functional groups, electrostatic attraction, cation exchange and isomorphic replacement, and memory effect. Besides, MnO₂/MgFe-LDO_{400 °C} has excellent regeneration ability in five adsorption/desorption experiments. The above results highlight the powerful adsorption capacity of MnO₂/MgFe-LDO_{400 °C} and may inspire the development of new types of nanostructured adsorbents for wastewater remediation.

Facile one-step synthesis of a versatile nitrogen-doped hydrochar from olive oil production waste, "alperujo", for removing pharmaceuticals from wastewater

In line with the principles of zero waste and recycling, alperujo (AL) was used in this study to produce a value-added product: hydrochar (HC) with high adsorption capacity. An optimization of the hydrothermal carbonization (HTC) conditions, such as temperature, residence time, and water/solid ratio, was carried out to maximize the adsorption capacity. Eight HCs were obtained, and an in-depth comparative characterization, as well as adsorption tests of two pharmaceuticals with very different physicochemical properties (fluoxetine (FLX) and cefazolin (CFZ)), were performed. This first step allowed for elucidation of the best candidates to carry out nitrogen grafting on their surface, resulting in the HC obtained at a higher water/solid ratio and temperature, and longer residence time: 3-220ºC-2.5 h with a maximum uptake of 4.6 and 0.4 mg/g for FLX and CFZ, respectively. After that, a facile one-step, one-pot synthesis of nitrogen-doped hydrochars (N-HC) was developed to prepare a versatile bio-adsorbent with enhanced adsorption capacity. Two N-HCs were prepared using urea (U-HC) and polyethyleneimine (PEI-HC) and were intensively characterized to shed light on the adsorption mechanism. In both cases, amide groups were formed, which favored the adsorption process. PEI-HC acquired an outstanding maximum adsorption capacity of 983.84 mg/g for CFZ, and 29.31 mg/g for FLX, and the process was well described by the Freundlich isotherm and pseudo-second-order kinetic model. A co-adsorption test was performed using PEI-HC for both pharmaceuticals, finding that the adsorption process occurs in different active sites because there was no interference between the pollutants. This fact corroborates the versatility of the new bio-adsorbent synthesized.