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.

Bioleaching of sewage sludge for copper extraction using Acidithiobacillus thiooxidans: Optimization and ecological risk assessment

In this study, Acidithiobacillus thiooxidans was used for the bioleaching of copper (Cu) from sewage sludge. In order to find optimization conditions, three factors including solid-to-liquid ratio (S/L) (0.01-0.2 %(w/v)), initial element sulfur (S0) (1-10 g/L), and initial pH (1-3) have been investigated. Based on response surface methodology (RSM) determined a significant reduced quadratic model with a p-value of 0.0022 (<0.05 significant level). The maximum Cu recovery was 85.3% in the optimum condition of S/L = 0.16% (w/v), S0 = 8.2 g/L, and pH = 1.4. Furthermore, a kinetic study based on a shrinking core model was performed and the result showed that chemical reaction was rate limiting in the extraction. Toxicity Characteristic Leaching Procedure (TCLP) results after bioleaching showed the bioleaching process detoxified sludge and the bioleached sludge residue was well within the regulatory limits for disposal. The germination seed with adding bioleached and unbioleached sludge to the soil was determined. Various parameters such as Germination Index (GI), Tolerance Index (TI), Vigor Index (VI), and stem length showed that the sewage sludge indices significantly increased than the sample soil with unbioleached sludge.

A review of toxicity assessment procedures of solar photovoltaic modules

Environmental management of solar photovoltaic (PV) modules is attracting attention as a growing number of field-operated PV modules approach end of life (EoL). PV modules may contain small amounts of toxic metals, and the procedures for assessing and regulating the toxic metal content and release of such materials at EoL differ widely across nations. This paper provides an overview of the metal composition of PV modules and common procedures for toxicity assessment through extensive research and review of technical literature and legislative documents. This review focuses on three primary aspects: first, it explores the distribution of toxic elements within current and emerging PV module designs, with a specific focus on obtaining representative samples for proportional toxicity testing within different module laminate areas. Second, it examines a sampling standard and the diverse toxicity testing methods and regulations employed in various regions, encompassing standards like the Environmental Protection Agency (EPA) Test Method 1311 (Toxicity Characteristic Leaching Procedure, TCLP) in the U.S., Restriction of Hazardous Substances (RoHS) in Europe, and the Waste Extraction Test (WET) in California. Third, the review examines the sources of variability in toxicity testing outcomes, including techniques for securing homogeneous samples from non-uniform PV modules, selecting particle sizes representative of landfill conditions in extracted samples, determining appropriate leachate characteristics such as leaching agents and pH levels, and considering factors like test duration and temperatures. In summary, this review summarizes relevant regulations and offers a comprehensive overview of the strengths and limitations associated with several toxicity assessment procedures currently in practice.

Characterization of textile effluent treatment plant sludge and its industrial application in fired clay bricks with health risk assessment

The textile industry in Bangladesh faces environmental and health challenges due to the disposal of solid waste from Effluent Treatment Plants (ETPs). To address this issue, a study was conducted using soil from a brick industry near Dhaka, amending it with varying amounts of dry sludge to create clay bricks. The original soil had a loam texture and medium plasticity. The research found that adding 9 wt% of sludge resulted in Grade A commercial bricks with a compressive strength of 15.33 MPa and water absorption of 13.33 wt%, meeting BDS 208 standards. However, these sludge-incorporated bricks experienced more shrinkage during the burning process due to organic content, requiring additional soil to maintain conventional dimensions. Also, to assess the health hazards of these sludge-incorporated bricks, a leaching test was performed, revealing that no toxic heavy metals (Pb, Cd, Cr, Cu, Ni, and Zn) in the leachate exceeded the limits set by the United States Environmental Protection Agency (USEPA). The study indicates that textile ETP sludge can serve as a sustainable raw material for bricks, potentially reducing the environmental burden caused by textile sludge disposal by 28.75%. This innovative approach offers a promising solution to both environmental and health concerns associated with textile waste in Bangladesh's industrial sector.

Synergistic utilization of industrial waste red mud and rice husk ash for eco-friendly geopolymer preparation: enhancing strength and mitigating hazardous leaching

The prolonged stacking of substantial volumes of industrial waste red mud (RM) can have significantly hazardous effects on the environment. In order to address this critical problem, this study proposes the synergistic preparation of geopolymers utilizing RM in conjunction with another industrial waste, rice husk ash (RHA). Geopolymers with varying incorporation of RHA were prepared using sodium hydroxide and sodium silicate composite alkaline activator. The mechanical properties, microstructure, and environmental characteristics of geopolymers were investigated. The incorporation of RHA significantly enhanced the strength of RM-based geopolymers, with the highest strength of 25.40 MPa achieved at 40% incorporation. According to XRD patterns and FTIR spectra, C-(A)-S-H and N-(A)-S-H were generated during the geopolymerization, thereby enhancing the strength of geopolymers. From SEM micrographs of geopolymers, it was evident that the geopolymer matrix was constituted by the encapsulation of unreacted inert particles of RM and residual fragments of RHA with C-(A)-S-H and N-(A)-S-H. The leaching levels of trace elements and heavy metals in geopolymers are both below the regulatory thresholds, thereby effectively mitigating the presence of hazardous substances in raw materials. These findings proved that the reuse of RM and RHA for the synergistic preparation of environmentally friendly geopolymers is a promising approach to address the issue of substantial RM stacking.

Self-consumed strategy to reuse cathode residue for Zn stabilization in spent batteries: Structural properties and metal stabilization effect

Due to ecotoxicity, zinc (Zn) as a heavy metal from electronic waste (e-waste) has been a source of pollution to soil and water for several decades. This study proposes a solution to this serious environmental problem via a self-consumed strategy to stabilize Zn in anode residues. This unique method uses cathode residues from spent zinc-manganese oxide (Zn-Mn) batteries as a stabilized matrix via thermal treatment. More specifically, the strategy incorporates zinc metal into a chemically durable matrix comprised of a lattice of AB2O4 compounds. Results demonstrate that 5-20 wt% of anode residue were fully incorporated into the cathode residue to form a Mn3-xZnxO4 solid solution after sintering at 1300 ℃ for 3 h. The lattice parameters of the Mn3-xZnxO4 solid solution reveal an approximately linear decreasing evolution with the addition of anode residue. To determine the occupancy of Zn in the crystal structure of the products, we used Raman and Rietveld refinement processes; the results reveal that Mn2+ in the 4a site was gradually replaced by Zn2+. We then used a prolonged toxicity leaching procedure to evaluate the Zn stabilization effect after phase transformation; this showed that the Zn leachability of sintered anode-doped cathode sample was over 40 folds lower than that of untreated anode residue. Therefore, this study presents an economical and effective strategy for mitigating the presence of heavy metal pollutants derived from e-waste.

Utilization of gasification slag and petrochemical incineration fly ash for glass ceramic production

This study investigated glass ceramics produced using coal gasification slag (CGS) and petrochemical incineration fly ash (PIFA) to immobilize hazardous heavy metals such as Cr and As. However, the crystallization kinetics and stabilization behavior mechanism of different heavy metals in the petrochemical incineration fly ash-derived glass-ceramics remains unclear. And X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and inductively coupled plasma mass spectrometry were used to characterize glass and crystalline products. In this paper, we reported the crystallization kinetics and chemical leaching characteristics of the glass ceramic. A low crystallization activation energy of 121.49 kJ/mol was achieved from crystallization peak of several different heating rates around 850°C, implying that it is easier to produce the glass ceramics at that temperature. The Avrami parameter of the former crystallization was determined to be 1.23 ± .12, which indicated two-dimensional crystal growth with heterogeneous nucleation. The toxicity characteristic leaching procedure results indicated that the heavy metals were well solidified, and that the leaching concentration was significantly lower than the limit specified by governmental agencies. The potentially toxic element index of the parent glass and the two glass ceramics were 11.7, 5.8, and 3.6, respectively. Therefore, the conversion of hazardous petrochemical incineration fly ash and other solid waste into environmentally friendly glass ceramics shows considerable potential and reliability.

Review of the impact of stormwater and leaching from pavements on the environment

The intensive growth of roadway infrastructure worldwide leads to growing concerns over the health impacts of stormwater runoff and leachate from roadway materials. This comprehensive review combines various sources of information from the last 30 years of research on the impact of pavement stormwater runoff and leaching on the environment. Of the 95 papers found in library searches, 42 papers add significantly to the body of literature around this subject after review of content and quality. Normally constructed asphalt and concrete pavements were found to release low levels of contaminants during their life. However, deposition from atmospheric pollutants and materials dispersed by vehicles on pavements do have a measurable impact on the quality of stormwater runoff. These tend to be expressed in initial flush from stormwater events. Reuse of old pavements at end of life tend to have little environmental impact when recycled. However, because of deposition of pollutants over their life these materials can have an impact when used in unbound layers of the pavement or in storage before reuse. Water quality can be improved by porous pavements, which allow infiltration of water and drainage to lower layers, thereby filtering many pollutants in stormwater runoff. The challenge is preventing the high initial pavement porosity from plugging over time. Pavement sealers containing coal tar pitch have high levels of polycyclic aromatic compounds and have been shown to impact aquatic life negatively and produce sediment buildup in ponds and streams. Recent studies have investigated photooxidation of pavements and its influence on leaching, but these remain as laboratory-scale studies. Tables outline materials tested, analytical parameters measured, and methodologies to allow readers to easily identify studies most relevant to their focus on impact of stormwater and leaching from pavements on the environment.

Novel GO/Fe-Mn hybrid for the adsorptive removal of Pb(II) ions from aqueous solution and the spent adsorbent disposability in cement mix: compressive properties and leachability study for circular economy benefits

GO/Fe-Mn hybrids were prepared by a single-pot chemical precipitation method and were characterized using FTIR, XRD, Raman, zeta potential, and FESEM, which confirmed the impregnation of Fe/Mn onto GO sheets. The synthesized hybrids were successively applied in removing the Pb(II) ions from aqueous solution and later utilizing the spent adsorbent to increase the properties of cement. The adsorption capability of the synthesized hybrid was seen in a set of batch studies to find out that about 15 min of contact time was required to remove 99% of the contaminant at a pH of 5 ± 0.2 and a dose of 0.83 g/L. The mechanism of the adsorption process for the synthesized hybrid was well described by Elovich kinetic model with an R² of 0.99 and Langmuir isotherm model, also with an R² of 0.99. The desorption studies conducted using 0.1 M HCl solution showed significant stability of the hybrid with a drop of 12% in the removal efficiency of Pb after up to five adsorption-desorption cycles. This points to an efficient adsorbent having potential for economical use. Later, the spent adsorbent was mixed with cement at ratios of 0.05%, 0.1%, and 0.5%, and compressive strength tests were performed, which showed an increase in the strength by 7.62%, 16.11%, and 26.82% at 28 days of curing time. The TCLP and SPLP tests performed on the hybrid and cement-spent adsorbent mix showed all the leaching parameters were well within the permissible limits. This development shows the potential for the use of spent adsorbent in a circular economy model.

Removal of arsenic in acidic wastewater using Lead-Zinc smelting slag: From waste solid to As-stabilized mineral

High-arsenic wastewater has long been considered a major threat to ecological balance and human health because of its strong toxicity and high mobility. Herein, an environmentally friendly process was proposed for As removal and fixation in the form of As-stabilized mineral, using Lead-Zinc smelting (LZS) slag as the in situ Fe donor, neutralizer, and crystal seed. The slag was dissolved in the wastewater and released Fe and Ca ions, while simultaneously increasing the pH value of the solution to help scorodite synthesis. The dissolved Ca²⁺ ion preferentially reacted with SO₄^2- ion in the form of CaSO₄·2H₂O precipitate as in situ "seeds" for As precipitation. The dissolved Fe(II) and As(III) ions were oxidized to Fe(III) and As(V) ions by H₂O₂, and later reacted with each other to generated amorphous ferric arsenate on the surface of CaSO₄·2H₂O, and then evolved into scorodite crystals with high stability. With a Fe/As molar ratio of 2, a reaction temperature of 90 °C, and a reaction time of 12 h, 98.42% of As was effectively precipitated from the wastewater with an initial As concentration of 7530.00 mg/L. Moreover, the leached As concentration of the As-bearing precipitate in the TCLP test was 3.46 mg/L. The concentration of the residual As and heavy metals ions in the final filtrate was lower than local wastewater discharge standards, successfully realizing the treatment of smelting wastewater. In summary, a prospective process successfully shows a great potential for co-treatment of LZS wastewater and slag, which could advance the large-scale disposal of LZS plants.

Arsenite removal from drinking water by bark-based magnetic iron oxide particle (BMIOP): a column study

The removal of arsenite [As(III)] from drinking water was investigated in a column at flow rates of 2.0 and 5.0 mL/min (up-flow direction) using bark-based magnetic iron oxide particles (BMIOP) prepared by coating (Fe(NO₃)₃.9H₂O) over Tamarindus Indica bark. The BMIOP was compared with regenerated BMIOP, commercial activated carbon, commercial activated alumina (Al₂O₃). At 2.0 mL/min, empty bed contact time (EBCT), breakthrough time (BT), the volume of treated water and breakthrough capacity (BC) on fresh BMIOP were found to be 6.8 min, 33.15 h, 4.380 L and 0.742 mg/g, respectively, and at 5.0 mL/min, were found to be 4.1 min, 13 h, 3.675 L and 0.453 mg/g respectively. EBCT, BT and BC were increased by 65.85%, 155% and 63.79%, respectively, as the flow rate was reduced from 5.0 to 2.0 mL/min. After regeneration of BMIOP, EBCT, BT, saturated time, BC and saturation capacity (SC) were reduced by 21.95%, 15.38%, 55.15%, 16.78% and 29.71%, respectively. The BC of fresh BMIOP was increased by factors 4.15, 3.60 and 1.20 and SC by factors 9.51, 7.88 and 1.42 compared to commercial activated carbon, commercial activated Al₂O₃ and regenerated BMIOP, respectively. Logit model could be used for the design of the adsorption column. Thomas model and artificial neural network (ANN) were applied to predict the characteristic column parameters useful for process design. Quality of treated water meets BIS requirements. Toxicity Characteristic Leaching Procedure (TCLP) and semi-dynamic tests show that the exhausted BMIOP is safe for disposal in a secure landfill; hence, BMIOP has been proved to separate As(III) from water.

A feasibility study on production of concrete blocks using treated municipal solid waste leachate

Increased water demand due to population growth and industrialization has led to increased water consumption. Hence, it is required to find an alternative to water in different industries. Concrete represents a remarkable water-consuming industry. The present study investigates whether the treated leachate of municipal landfills can be employed as a substitute for water in the concrete mixing scheme. For this purpose, concrete samples fabricated at different concentrations of treated leachates were compared to the control sample containing distilled water in terms of unconfined compressive strength (UCS) at the ages of 7 and 28 days. The experimental results revealed treated leachate accelerated the cement setting time by nearly 15 min and increased concrete slumping by 16%. The complete replacement of distilled water with treated leachate decreased UCS by 25% (from 50 to 38 MPa). The scanning electron microscope (SEM) and ultrasonic results showed that a rise in the treated leachate content of concrete increased porosity. Increased porosity would reduce UCS. Leaking of heavy metals existing in the leachate should be also investigated for the solidified matrices. The toxicity characteristic leaching procedure (TCLP) revealed that heavy metals leaching in all the samples are in the acceptable range. Results have shown that the use of leachate up to a concentration of 20% can be used in concrete, and the solidified product can also stabilize the pollutants, successfully. It is a valuable finding because using treated leachate as a practical additive in the concrete can prevent environmental contamination.

The treatment of electroplating wastewater using an integrated approach of interior microelectrolysis and Fenton combined with recycle ferrite

Heavy metal ions in chelated forms have aroused great concerns because of their high solubility, poor biodegradation and extreme stability. In this research, an efficient strategy, interior microelectrolysis-Fenton-recycle ferrite (IM-Fenton-RF), was developed to treat simulated electroplating wastewater containing chelated copper at room temperature. The decomplexation of chelated copper was carried out by both interior microelectrolysis and Fenton reactions. IM process can not only partly degrade the complexes of chelated copper via the microelectrolysis reaction but also it produces Fe²⁺ ions for the Fenton reaction. After decomplexation, the IM-Fenton effluent directly flowed into the RF reactor for copper ions removal. Under optimum reaction conditions (reflux ratio = 0.37, Fe²⁺ concentration = 9.20 g/L at pH 10.18), 99.9% copper was removed by the IM-Fenton-RF system. The produced IM-Fenton-RF sludge is based on ferrite precipitate and has several advantages over metal hydroxides sludge. Ferrite sludge is stable owing to the stability of ferrite's crystal structure, while the toxicity characteristic leaching procedure (TCLP) test meets relevant standards. The sedimentation rate and volume of ferrite sludge were 3.86 times faster and 11.0 times lower than those of metal hydroxides sludge. Furthermore, the yielding sludge of ferrite can be recovered and utilized for the synthesis of Fe-C metallic species, the main compound of IM packing for interior microelectrolysis reaction. All these results show that a combination of IM-Fenton and RF is an effective approach to treat wastewater containing chelated copper, showing great potential for industrial applications.

Study on Tailings Covering System Constructed by Geological Polymerization of Mine Waste, Part 1: Material Characterization and Cover Construction

Acid mine drainage (AMD) is a serious and persistent environmental pollution problem. At present, many studies have focused on the tailings pond's cover systems. This paper introduced the research results of using tin tailings from Laili mountain to make the covering layer of tailings pond. The first part included a detailed description of tailings characterization and acid production potential. On this basis, the hard layer (HL) was prepared and its feasibility as oxidation barrier was evaluated. It was found that when the proportion of tailings waste was 70%, the immobilization efficiency of heavy metals can reach more than 99.45%, and the pH of leaching solution was about 10.8. Moreover, the beneficial effect of solid waste addition on the HL was also verified. This suggests that HL as a post-mining restorative strategy has strong positive influence on pollution control.

Conversion of chromium-containing solid wastes into value-added products through a plasma-assisted aluminothermic process

Chromium-containing solid wastes have been generated by chemical and leather/tanning industries, and the management and proper disposal of the same wastes have been challenging tasks. A significant fraction of these wastes contains chromium compounds with chromium present in the hexavalent (Cr⁺⁶) form, which is hazardous to human beings, animals, and ecosystems. Since these wastes are discarded largely without proper treatments, soil and groundwater get contaminated and they can cause several health issues to human beings. Conventional methods developed to convert hazardous Cr⁶⁺ to Cr³⁺/Cr metal either generate secondary toxic wastes and unwanted by-products and/or are time-consuming processes. In this work, a plasma-assisted aluminothermic process is developed to convert the toxic waste into non-toxic products. The waste was mixed with aluminium powder and subjected to transferred arc plasma treatment in a controlled air atmosphere. Chemical analysis and Cr leachability studies of the waste material prior to plasma treatment have shown that it is highly toxic. Analysis of the products obtained from the plasma treatment showed that Cr and Fe present in the waste could be recovered as a metallic mixture as well as oxide slag, which were found to be non-toxic. Easy separation of the metallic fraction and the slag from the treated product is one of the merits of this process. Besides converting chromium-containing toxic waste to non-toxic materials, the process is rapid and recovers the metals from the waste completely.

Urban mining of obsolete computers by manual dismantling and waste printed circuit boards by chemical leaching and toxicity assessment of its waste residues

Waste residues and acidic effluents (post-processing of E-waste) released into the local surroundings cause perilous environmental threats and potential risks to human health. Only limited research and information are available toward the sustainable management of waste residues generated post resource recovery of E-waste components. In the present study, the manual processing of obsolete computer (keyboard, monitor, CPU, and mouse) and chemical leaching of waste printed circuit boards (WPCBs) (motherboard, hard drive, DVD drive, and power supply) were performed for urban mining. The toxicity characteristics of typical pollutants in the residues of the WPCBs (post chemical leaching) were studied by toxicity characteristics leaching procedure (TCLP) test. Manual dismantling techniques resulted in an efficient urban mining concept with an overall average profit estimation of INR 2513.73/US$ 34.59. The chemical leaching of WPCBs showed a high concentration of metal leaching like Cu (229662 ± 575.3 mg/kg) and Pb (36785.67 ± 13.07 mg/kg) in the motherboard after stripping epoxy coating. The toxicity test revealed that the concentration of Cu (245.746 ± 0.016 mg/l) in the treated waste residue and Cu (430.746 ± 0.0015 mg/l) and Pb (182.09 ± 0.0035 mg/l) in the non-treated waste residue exceeded the threshold limit. The concentrations of other elements As, Cd, Co, Cr, Ag, Mn, Zn, Ni, Fe, Se, and In were within the permissible limit. Hence, the waste residue stands non-hazardous except Cu and Pb. Stripping out the epoxy coating of WPCBs enhances the metal leaching concentrations. The study highlighted that efficient and appropriate E-waste urban mining has immense potential in tracing the waste scrap into secondary resources. This study also emphasized that the final processed waste residue (left unattended or discarded due to lack of appropriate skill and technology) can be taken into consideration and exploited for value-added materials.

Evaluation of heavy metal leaching under simulated disposal conditions and formulation of strategies for handling solar panel waste

With the steady growth in the worldwide solar installed capacity, there is an immediate concern about the fate of the solar panels at the end of their life. Solar panel waste is often disposed of indiscriminately, exposing the environment to chemical hazards. The major objective of the current study was to evaluate the leaching potential of the polycrystalline solar panel waste under different simulated disposal conditions through toxicity characteristic leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP) and pH static leaching procedure tests. Moreover, the study evaluates the effects of ageing and the breakage of the Glass Laminate Encapsulation (GLE) of solar panels on their leaching potential. Among the metals studied (silver (Ag), aluminium (Al), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), lead (Pb), and zinc (Zn)), the concentrations of Pb were as high as 9.3 mg/L, 1.4 mg/L, 6.7 mg/L in the TCLP, SPLP, and pH static test respectively. This indicated the hazardous nature of the waste with leaching potential of Pb above the permissible limits stipulated by various regulatory bodies. The presence of GLE reduced the mobility of Pb by a factor of 4.1-8.8 in the TCLP test, thereby rendering the waste as non-hazardous for its disposal in a landfill. However, the indiscriminate disposal of solar panel waste in the natural environment as simulated by the SPLP test indicated its harmful nature irrespective of the physical condition. Ageing of the solar panels before disposal and acidic pH conditions also positively influenced the leaching potential of the selected metals subjected to their reactivity and the accessibility of internal layers of waste to the leaching solution. Strategies such as extended producer responsibilty, advance-recycling fee, and incentivizing the recycling industry will lead to both economic benefit creation and effective waste management of this waste stream.

Biological attenuation of arsenic and nitrate in a suspended growth denitrifying-sulphidogenic bioreactor and stability check of arsenic-laden biosolids

Co-occurrence of arsenic and nitrate in groundwater sources at a wide range of concentrations is reported. In this work, performance of suspended growth semi-batch reactor was assessed for co-removal of arsenic and nitrate from simulated groundwater to meet the drinking water standards in the absence of iron. The bioreactor was inoculated with mixed bacterial culture and operated in the absence of oxygen for more than 450 days under varying influent arsenate (200-800 µg/L), nitrate concentrations (50-250 mg/L), and hydraulic retention time of 3-6 days. Complete nitrate removal was observed at all tested concentrations. Arsenic removal was found to meet drinking water standards from initial concentrations and up to 600 µg/L. The extended toxicity characteristic leaching procedure leaching experiments indicated that arsenic-laden biosolids would not constitute a hazardous waste. The arsenic leaching was found to increase with an increase in dissolved oxygen and the final leachate concentrations of arsenic were below 150 µg/L. The leaching experiments suggested maintaining non-alkaline conditions for minimum arsenic release from arsenic biosolids formed under sulphidogenic conditions. This study is the first to report that nitrate and arsenic can be simultaneously removed to meet drinking standards in a suspended growth bioreactor.

Understanding metal dissolution from solar photovoltaics in MSW leachate under standard waste characterization conditions for informing end-of-life photovoltaic waste management

The upcoming end-of-life solar photovoltaics (PV) waste stream is a huge concern before solid waste professionals due to presence of hazardous metals like lead or cadmium. The objective of present study was to understand the metal dissolution from PVs under four standard waste characterization regulatory tests of U.S., Germany, and Japan and their representativeness with actual landfill leachate. Modules were exposed to real municipal solid waste (MSW) landfill leachate for extended extraction duration, agitation and diluted leachate to investigate the effect of various parameters on metal dissolution. The results indicated that extractions using landfill leachates resulted in lower metal release than standard methods. The leached metal concentrations were found to be within the threshold limits except for cadmium, copper, lead and selenium, with maximum lead release from amorphous-PV of 8.68 mg/L and 6.91 mg/L with respect to TCLP and WET tests, respectively. Arsenic showed negligible release with maximum concentration of 0.046 mg/L from copper indium gallium de-selenide(CIGS) PV. Regardless of small size (1-2 cm pieces) and agitation, Germany and Japan's standard tests resulted in minimal release except of copper from copper indium gallium de-selenide PV. Leaching without agitation, showed negligible release from all photovoltaics whereas when agitation is applied to diluted leachate, significant release was observed with aluminum and copper leached up to 145.32 mg/L (multi-crystalline silicon) and 139.01 mg/L (amorphous-PV), respectively. CIGS was found to be most hazardous with a Metal Hazard Score (calculated on the basis of magnitude of leached metals with respect to their threshold limit and subsequent health effects) of 23.19, when exposed to standard tests. For all scenarios, increased metal release was observed with decrease in sample size and increase in leachate dilution and thus, leaching in highly acidic conditions are by no means representative for modules dumping in realistic conditions.

Oyster Shell Powder, Zeolite and Red Mud as Binders for Immobilising Toxic Metals in Fine Granular Contaminated Soils (from Industrial Zones in South Korea)

Low-cost absorbent materials have elicited the attention of researchers as binders for the stabilisation/solidification technique. As, there is a no comprehensive study, the authors of this paper investigated the performance of Oyster shell powder (OS), zeolite (Z), and red mud (RM) in stabilising heavy metals in three types of heavy metal-contaminated soils by using toxicity characteristic leaching procedure (TCLP). Samples were collected from surroundings of an abandoned metal mine site and from military service zone. Furthermore, a Pb-contaminated soil was artificially prepared to evaluate each binder (100× regulatory level for Pb). OS bound approximately 82% of Pb and 78% of Cu in real cases scenario. While Z was highly effective in stabilizing Pb in highly polluted artificial soil (>50% of Pb) at lower dosages than OS and RM, it was not effective in stabilising those metals in the soils obtained from the contaminated sites. RM did not perform consistently stabilising toxic metals in soils from contaminated sites, but it demonstrated a remarkable Pb-immobilisation under dosages over than 5% in the artificial soil. Further, authors observed that OS removal efficiency reached up to 94% after 10 days. The results suggest that OS is the best low-cost adsorbent material to stabilize soils contaminated with toxic metals considered in the study.

Environmental monitoring of toxic metals in roadside soil and dust in Ulsan, South Korea: pollution evaluation and distribution characteristics

This study investigated toxic metal distribution in roadside soil and dust in the metropolitan city of Ulsan, South Korea, and the factors affecting distribution, using Korean waste-leaching tests, determination of total concentrations, sequential extraction, and statistical analysis. Composite grab samples were collected from high-traffic roads (7 sites), low-traffic roads (2 sites), and an uncontaminated control area (2 sites) in Ulsan. The pH of roadside soil and dust was slightly alkaline. The concentrations of copper, lead, and zinc in soil as determined by Korean waste-leaching tests decreased as soil depth increased, while those of arsenic, nickel, and chromium increased. Leaching concentrations in dust were lower than in soil, with the exception of copper. Total concentrations decreased as soil depth increased, and total concentrations of metals in dust were higher than in soil. The sampling sites that exceeded the regulation levels of soil contamination in South Korea were 7 points in topsoil, 3 points in middle soil, and 9 points in dust. TCLP tests showed that the concentrations of arsenic, cadmium, and lead in topsoil and dust at Duwang and Myeongchon intersections were higher than regulatory levels. The maximum correlation coefficient among two metals in soil and dust was 0.987 (p < 0.01), for cadmium and lead. Concentrations of cadmium, copper, arsenic, lead, nickel, and mercury, mostly from tire and brake-pad abrasion, were highly correlated. The strong positive correlation between traffic volume and metals in dust suggests that vehicle emissions may be responsible for metal contamination of soil and dust. Pollution indices of topsoil at 4 sites and all dust at 7 high-traffic sites were higher than 1.0, which is consistent with an effect of vehicle traffic on metal contamination in soil and dust.

Influence of redox potential on leaching behavior of a solidified chromium contaminated soil

Cement-based solidification/stabilization (S/S) technology is often used to remediate chromium (Cr) contaminated soils. The valence state and mobility of Cr in soils are closely related with redox potential (E_H). However, Cr mobilization from the solidified soils influenced by E_H has received little attention. In this study, semi-dynamic leaching tests and the toxicity characteristic leaching procedure (TCLP) were performed on a S/S treated Cr contaminated soil under various E_H conditions. The effective diffusion coefficient and leachability index were obtained from the leaching data to investigate the leaching behavior of Cr from the S/S treated soil. Speciation of Cr remained in the sample after the leaching process was obtained through the sequential extraction procedures. The results show that an increase in E_H increases the effective diffusion coefficient of Cr and, therefore, the amount of Cr leached. This result is attributed to immobile Cr(III) being oxidized to highly mobile Cr(VI). The leachability index results indicate that the cement solidification of Cr contaminated soil may not be appropriate under oxidizing conditions. For the TCLP and sequential extraction procedures, the leached amount of Cr exhibits a strong dependence on E_H. As E_H increases, the content of Cr remaining in the soil in unstable phases reduced, and more Cr was released to leachant.

Effect of partially replacing ordinary Portland cement with municipal solid waste incinerator ashes and rice husk ashes on pervious concrete quality

Pervious concrete (PC) provides multiple benefits, including reducing stormwater runoff, purifying water, recharging groundwater, and reducing the heat island effect. This study aims to determine an effective way to reuse municipal solid waste incinerator (MSWI) fly ash (FA), MSWI bottom ash (BA), and rice husk ash (RHA) as single or binary partial replacements for ordinary Portland cement (OPC) in PC. The ashes and PC specimens were characterized via X-ray fluorescence spectroscopy, X-ray powder diffraction, field emission-scanning electron microscopy, and Fourier transform infrared spectroscopy. The compressive strength, water permeability, and toxicity characteristic leaching procedure (TCLP)-released metals were investigated to evaluate the PC quality. The main components of the ashes were similar to those of OPC, suggesting that the ashes could be reused as cement materials; however, the cementitious activity of the ashes, especially MSWI FA, was relatively low. All ashes except 1100 °C MSWI FA met the standard requirements and can be applied as pozzolanic materials. The three PC specimens with binary replacements containing RHA (550, 700, and 900 °C) and MSWI BA (1100 °C) showed a synergistic effect and exhibited a higher 90-day compressive strength than the other specimens with single and binary ash replacements containing RHA (550 and 900 °C). The water permeability ranged between 0.106 and 0.391 cm/s, and the TCLP-released metal concentrations from all specimens met the regulatory standards of Taiwan. The results indicated that replacement with MSWI BA and RHA in cement materials provides an acceptable compressive strength and water permeability.

NTA-enhanced Pb remediation efficiency by the phytostabilizer Athyrium wardii (Hook.) and associated Pb leaching risk

Nitrilotriacetic acid (NTA), a biodegradable chelant, has been promoted to effectively assist Pb phytoextraction, while a few researches available on the phytostabilizer of Athyrium wardii (Hook.). In this study, two incubation experiments and a subsequent column experiment were conducted to investigate the effects of application of NTA on Pb availability in soils and Pb accumulation in A. wardii and associated leaching risk. The application of NTA significantly increased the exchangeable Pb and Pb bound to carbonates along with a decreased pH, leading to enhanced Pb availability in soils. It was more effective in enhancing Pb availability in soils by adding 2 mmol kg^-1 NTA into soils at once for 7 d, thus demonstrating potential for enhancing Pb uptake by A. wardii. After the addition of 2 mmol kg^-1 NTA for 7 d, Pb concentrations in roots of A. wardii was enhanced by 23.8%, along with 10.6% of increase for Pb accumulation in roots. No significant changes were observed for the biomass of A. wardii. Meanwhile, the available Pb and TCLP-extractable Pb in 0-20 cm soils increased by 11.1-23.4% and 7.1-31.2%, thus promoting Pb leaching in 0-20 cm soils. However, there were no changes for Pb leaching risk levels of 20-40 cm soils. No Pb was detected in the leachates from all columns. The application of 2 mmol kg^-1 NTA at once for 7 d is therefore proved to show greater potential in enhancing Pb remediation efficiency by the phytostabilizer of A. wardii without increasing Pb leaching risk into groundwater.

Stability of metal-rich residues from laboratory multi-step treatment system for ferriferous acid mine drainage

Passive systems are often used for the treatment of acid mine drainage (AMD) on closed and abandoned mine sites. Metal-rich residues (solid precipitates) with variable chemical composition and physical properties can be generated. Their characterization is required to better anticipate the potential fate, including stability for disposal, potential recovery, or reuse. The present study evaluated the leaching potential of solids from a laboratory passive multi-step treatment for Fe-rich AMD (2350 ± 330 mg/L Fe_tot, 0.7 ± 0.4 mg/L Ni, 0.2 ± 3.0 mg/L Zn, and 5073 ± 407 mg/L SO₄^2-, at pH 3.04 ± 0.45). To do so, post-treatment solids from three units (Fe-pretreatment reactor (50% wood chips and 50% wood ash, WA50), passive biochemical reactor, PBR for SO₄^2- treatment (30% inorganic materials, 70% organic substrate), and polishing reactor (50% calcite and 50% wood chips, C50)) of a pilot laboratory treatment system were sampled. Physicochemical and mineralogical characterization, as well as static leaching tests were then performed. Results showed that all solids had high neutralizing potential, while high inorganic carbon was found in C50. Moreover, high metal concentrations were found in WA50. Metals and sulfates in all solids precipitated in the form of oxyhydroxides, oxy-hydroxy-sulfates, carbonates, sulfides, sulfate, and native sulfur. The Fe was not found as problematic contaminant in solids, but it was in AMD. However, a probable generation of contaminated neutral drainage by Ni and Zn could occur from WA50. The C50 had the highest acid neutralizing capacity and could better resist to acid aggression relative to solids from PBR and WA50. The PBR and C50 solids were considered as non-hazardous towards regulation's limits and a potential co-disposal with municipal wastes could be a storage option. Further studies should be undertaken by testing other leaching and kinetic tests to assess long-term metal stability.

The Preparation of Biochar Particles from Sludge and Corncobs and Its Pb2+ Adsorption Properties

In the present study, biochar particles (BPs) produced by the co-pyrolysis of sewage sludge and corncobs at temperatures of 300, 500, and 700°C were characterized. The Pb²⁺ adsorption properties and the heavy metal leaching toxicity rates of the BPs were investigated. It was found that the adsorption kinetics of the Pb²⁺ can be accurately described by a pseudo-second-order model, and the equilibrium adsorption data were well represented by both the Langmuir and the Freundilich Equations. The toxicity characteristic leaching procedure (TCLP) results indicated that the leaching concentrations of all the heavy metals were below the set limit of China's national standard (Identification Standard for Hazardous Waste Extraction Toxicity Identification, China National Standard, GB 5085.3-2007). The results of this study can successfully provide scientific support for future corncob treatment and sludge pollution control.

Leachability of heavy metals in loess-amended dredged sediment from Northwest of China

Considerable studies have been done on heavy metal removing from aqueous solutions using loess. However, application of loess to heavy metal contaminated sediment is limited. The present study was to determine the effectiveness of loess to immobilize Cu, Zn, Cd and Pb in sediment. The loess was incubated with 10 kg wet sediment in doses of 0, 0.5, 1, 2, 5, 10 and 20 kg for 70 d and then subjected to the toxicity characteristic leaching procedure (TCLP). The possible mechanisms for heavy metal immobilization were illustrated using X-ray diffraction and scanning electron microscope. Results from TCLP confirmed loess reduced leaching rate of Cu and Zn achieving up to 42.4% and 17.6% reductions, respectively, when compared with untreated sediment. The loess could significantly immobilize Cu and Zn in sediment, and the optimum dose of loess in 10 kg wet sediment was 5 kg. However, loess was inefficient for Cd and Pb immobilization. Correlation analysis showed that TCLP extraction method could be used to predict the toxicity of Cu, Zn, Cd and Pb in the loess-amended sediment. The pH, EC, OM and CaCO₃ of the loess-amended sediment played predominant roles in the TCLP leaching test.

Evaluation of heavy metal leachability of incinerating recycled aggregate and solidification/stabilization products for construction reuse using TCLP, multi-final pH and EDTA-mediated TCLP leaching tests

Incinerating recycled aggregate (IRA) produced using bottom ash generated from the incineration of municipal solid wastes can be reused as construction materials and cement-based solidification/stabilization (S/S) can be employed to improve their environmental compatibility. Toxicity characteristic leaching procedure (TCLP) is commonly used to evaluate heavy metal leachability before reuse. However, the applicability of TCLP to IRA and their S/S products can be limited because of their alkaline nature which may cause underestimation of metal release. In this study, the leaching of heavy metals from an IRA and two S/S products, low-strength material (CLSM) and multi-functional regenerated concrete (MRC), were evaluated using TCLP, multi-final pH leaching test and EDTA-mediated TCLP. The results showed that TCLP results generally met the reuse standards. However, the results obtained from multi-final pH leaching test and EDTA-mediated TCLP showed exceedances of reuse standards for Pb and Cu when the final pH was < 5 or in the presence of> 7 mM EDTA. The results suggested that the reuse of IRA or S/S products requires further evaluation of their metal leachability in more harsh environmental conditions. Considering its simplicity, it is suggested that EDTA-mediated TCLP could be used for this purpose.

Limitations of the TCLP fluid determination step for hazardous waste characterization of US municipal waste incineration ash

The Toxicity Characteristic Leaching Procedure (TCLP) requires the use of one of two acid-based extraction fluids: fluid #1 or fluid #2, determined by the fluid determination step (FDS). Fluid #1 is a buffered solution of acetic acid and sodium hydroxide while fluid #2 is an unbuffered acetic acid solution. Motivated by divergent fluid determination results among different laboratories, the limitations of the FDS in the TCLP used for characterizing municipal solid waste incineration (MSWI) ash were investigated by varying three test parameters: solution cooling rate, degree of particle size reduction, and sub-sample selection. A faster cooling rate decreases the needed cooling time and has the potential to alter the fluid outcome to fluid #1. Excessive size reduction of particles forces all the fluid outcomes to fluid #2, possibly due to increased surface area and reaction rate of MSWI particles with the FDS media. Selecting larger particles increases the likelihood of obtaining fluid #1 while selecting smaller particles increases the possibility of requiring fluid #2, possibly due to the lower alkalinity of larger particles and higher alkalinity of smaller particles. These findings suggest that FDS can be conducted using different allowable approaches, based on the interpretation of the users who have the potential to alter the fluid outcomes to achieve a favorable extraction fluid. These limitations may allow MSWI ash to consistently "pass" the TCLP. These phenomena highlight a major flaw in the existing hazardous waste testing protocols for MSWI ash.

Environmental assessment of utilizing date palm ash as partial replacement of cement in mortar

Saudi Arabia's date palm industry generates date palm ash (DPA) from the thermal processing of palm oil fibers and shells. This waste material has potential to be used as partial replacement of cement in structural mortar. However, no studies to date have examined its pollution potential. DPA was used as a cement replacement in Portland cement mortar (PCM) using a 10% and 100% replacement rate and then compared to an ordinary PCM control sample. Total elemental analysis, the toxicity characteristic leaching procedure (TCLP) and monolith leaching tests were conducted. Elemental analysis revealed a standard elemental profile similar to data for the comparably used wood ash. Aluminum (Al) and iron (Fe) were elements with the greatest abundance in DPA but no element exceeded regulatory thresholds. Leachability testing revealed that while concentrations of Al and Fe may appear high in DPA, they experience relatively low mobility when encapsulated in PCM matrices as indicated by their calculated leachability index. The results presented in this paper indicate that DPA poses no environmental risk to human health when used as cement replacement in PCM.

Assessment of the Remediation Effect of Nano-hydroxyapatite in Exogenous Pb-contaminated Soil Using Toxicity Characteristic Leaching Procedure and Soil Enzyme Activities

Lead (Pb) is one of the most abundant metal soil pollutants. In this research, effects of nano-hydroxyapatite (NHAP) on remediation of Pb-contaminated soil were evaluated by the measure of extractable Pb using toxicity characteristic leaching procedure (TCLP) and soil enzyme activities. Results suggested NHAP significantly decreased the concentrations of extractable Pb, achieving the maximum decrement rate of 75.71%. Activity of urease decreased with increasing Pb concentrations. Moreover, activities of alkaline phosphatase, dehydrogenase, and catalase increased at the lower Pb levels and decreased at the higher Pb levels. NHAP had a positive effect on regulating soil enzymes. Thus, soil enzyme activities, especially dehydrogenase, could be used as biological indicators of Pb pollution and NHAP remediation. Moreover, NHAP could reduce the mobility and bioavailability of Pb, while increasing enzyme activities, thereby lowering the leaching risk and biotoxicity of Pb.

Investigation on stability and leaching characteristics of mixtures of biogenic arsenosulphides and iron sulphides formed under reduced conditions

Arsenic is removed from aqueous phase through precipitation as arsenosulphides and/or co-precipitation and adsorption on iron sulphides. Studies were carried out to ascertain the stability of reduced biogenic arsenic and iron sulphide precipitates formed in an attached growth reactor (AGR) through a series of experiments based on Toxicity Characteristic Leaching Procedure (TCLP), aging and long term leaching tests. About half of the AGR was initially added with waste activated carbon (WAC) to support the growth of mixed microbial consortia and used for treatment of arsenic and iron contaminated simulated groundwater. The X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy results indicated that the biosolids were mainly composed of arsenosulphides and iron sulphides. While TCLP and aging tests were conducted in anoxic as well as oxic conditions with the aim to evaluate stability of biomass containing biogenic sulphides, long term leaching test was conducted through supply of aerated distilled water to evaluate the stability of spent WAC as well. Results generated from the research indicate that the concentration of leached arsenic never exceeded 123 μg/L under all conditions tested, thus biosolids not imposing an environmental hazard.

Stabilization of lead (Pb) and zinc (Zn) in contaminated rice paddy soil using starfish: A preliminary study

Lead (Pb) and zinc (Zn) contaminated rice paddy soil was stabilized using natural (NSF) and calcined starfish (CSF). Contaminated soil was treated with NSF in the range of 0-10 wt% and CSF in the range of 0-5 wt% and cured for 28 days. Toxicity characteristic leaching procedure (TCLP) test was used to evaluate effectiveness of starfish treatment. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analyses were conducted to investigate the mechanism responsible for effective immobilization of Pb and Zn. Experimental results suggest that NSF and CSF treatments effectively immobilize Pb and Zn in treated rice paddy soil. TCLP levels for Pb and Zn were reduced with increasing NSF and CSF dosage. Comparison of the two treatment methods reveals that CSF treatment is more effective than NSF treatment. Leachability of the two metals is reduced approximately 58% for Pb and 51% for Zn, upon 10 wt% NSF treatment. More pronounced leachability reductions, 93% for Pb and 76% for Zn, are achieved upon treatment with 5 wt% CSF. Sequential extraction results reveal that NSF and CSF treatments of contaminated soil generated decrease in exchangeable/weak acid Pb and Zn soluble fractions, and increase of residual Pb and Zn fractions. Results for the SEM-EDX sample treated with 5 wt% CSF indicate that effective Pb and Zn immobilization is most probably associated with calcium silicate hydrates (CSHs) and calcium aluminum hydrates (CAHs).

H2S adsorption by municipal solid waste incineration (MSWI) fly ash with heavy metals immobilization

As a byproduct of municipal solid waste incineration (MSWI) plant, fly ash is becoming a challenge for waste management in recent years. In this study, MSWI fly ash (FA) was evaluated for the potential capacity of odorous gas H₂S removal. Results showed that fly ash demonstrated longer breakthrough time and higher H₂S capacities than coal fly ash and sandy soil, due to its high content of alkali oxides of metals including heavy metals. H₂S adsorption capacities of FA1 and FA2 were 15.89 and 12.59 mg H₂S/g, respectively for 750 ppm H₂S. The adsorption of H₂S on fly ash led to formation of elemental sulfur and metal sulfide. More importantly, the formation of metal sulfide significantly reduced the leachability of heavy metals, such as Cr, Cu, Cd and Pb as shown by TCLP tests. The adsorption isotherms fit well with Langmuir model with the correlation coefficient over 0.99. The adsorption of H₂S on fly ash features simultaneous H₂S removal and stabilization and heavy metals found in most MSWI fly ash, making fly ash the potential low cost recycled sorbent material.

Effect of nanoparticle hydroxyapatite on the immobilization of Cu and Zn in polluted soil

Phosphate compounds and related materials are effective amendments for immobilization of heavy metals in contaminated soils. A greenhouse pot experiment with ryegrass (Lolium perenne) as the test plant was conducted to explore the impact of nanoparticle hydroxyapatite (HAP) on the immobilization and bioavailability of Cu and Zn in a heavy metal-polluted soil. The addition of nanoparticle HAP significantly decreased the uptake of Cu and Zn by ryegrass. As a result, the biomass of ryegrass increased as the rate of nanoparticle HAP increased. The toxicity characteristic leaching procedure (TCLP) and physiologically based extraction test (PBET) results of the treatments showed that the leachable and bioaccessible concentrations of Cu and Zn were significantly reduced after the soil stabilized with nanoparticle HAP. The XRD pattern of nanoparticle HAP was not changed by the presence of Cu and Zn, which suggests that Cu and Zn were immobilized by the formation of solid amorphous phosphate. Nanoparticle HAP was an effective material to immobilize heavy metals in contaminated soils.

Cadmium solubility and bioavailability in soils amended with acidic and neutral biochar

This study was designed to investigate the effects of acidic and neutral biochars on solubility and bioavailability of cadmium (Cd) in soils with contrasting properties. Four Cd contaminated (50mg/kg) soils (EN: Entisol, AL: Andisol, VE: Vertisol, IN: Inceptisol) were amended with 5% acidic wood shaving biochar (WS, pH=3.25) and neutral chicken litter biochar (CL, pH=7.00). Following a 140-day incubation, the solubility and bioavailability/bioaccessibility of cadmium (Cd) were assessed. Results showed that both biochars had no effect on reducing soluble (pore water) and bioavailable (CaCl₂ extractable) Cd for higher sorption capacity soils (AL, IN) while CL biochar reduced those in lower sorption capacity soils (EN, VE) by around 50%. Bioaccessibility of Cd to the human gastric phase (physiologically based extraction test (PBET) extractable) was not altered by the acidic WS biochar but reduced by neutral CL biochar by 18.8%, 29.7%, 18.0% and 8.82% for soil AL, EN, IN and VE, respectively. Both biochars reduced soluble Cd under acidic conditions (toxicity characteristic leaching procedure (TCLP) extractable) significantly in all soils. Pore water pH was the governing factor of Cd solubility among soils. The reduction of Cd solubility and bioavailability/bioaccessibility by CL biochar may be due to surface complexation while the reduced mobility of Cd under acidic conditions (TCLP) by both biochars may result from the redistribution of Cd to less bioavailable soil solid fractions. Hence, if only leaching mitigation of Cd under acidic conditions is required, application of low pH biochars (e.g., WS biochar) may be valuable.

Utilization of Zn-containing electric arc furnace dust for multi-metal doped ferrite with enhanced magnetic property: From hazardous solid waste to green product

One-step solid state reaction method was proposed for the first time to realize the transformation of the Zn-containing EAFD from hazardous solid waste to multi-metal doped ferrite with enhanced magnetic property. The effect of Zn-containing EAFD to NiCl₂·6H₂O mass ratio (R_ZE/N, g·g^-1) on the phases transformation was investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy. The as-synthesized samples were treated by toxicity characteristic leaching procedure (TCLP). It is shown that the TCPL played a key role in determining both the purity and toxicity of the obtained ferrites. The pure metal doped Ni-Zn ferrite with higher saturation magnetization (Ms, 56.8 emu·g^-1) and lower coercivity (Hc, 58.5Oe) was gained under the optimum conditions. And the pure ferrite was a green product according to the TCLP and EN12457 standards. Moreover, the evaluation of environmental impact and the recovery ratio of the dust were also discussed.

A simultaneous stabilization and solidification of the top five most toxic heavy metals (Hg, Pb, As, Cr, and Cd)

A novel chemically bonded phosphate ceramic (CBPC) binder was developed for the simultaneous treatment of the top five most toxic heavy metals (Hg, Pb, As, Cr, and Cd). Various CBPC binders were synthesized and tested, and their toxicity characteristic leaching procedure (TCLP) values were obtained. A magnesium/calcium-potassium phosphate ceramic binder with FeCl₂ (M/C-KP-FeCl₂) simultaneously stabilized multiple heavy metals. The TCLP value of the final product for industrial waste (IW) treatment using the M/C-KP-FeCl₂ technology was well below the Universal Treatment Standard (UTS). Additionally, the compressive strength of the final product was below the US Nuclear Regulatory Commission Standard.

[Correlations Between Different Extractable Cadmium Levels in Typical Soils and Cadmium Accumulation in Rice]

Pot experiments were used to study the correlations between different extractable cadmium levels in typical soil and cadmium accumulation in rice. To analyze the pH, Cd in soil solution(SSE-Cd), TCLP extractable Cd level(TCLP-Cd), and Cd accumulation in rice at different growth stages of rice, we conducted pot experiments which selected the reddish clayey soil(developed from quaternary red clay parent materials) and purple paddy field(developed from purple sandy shale parent materials), meanwhile added with exogenous Cd with the gradients of 0, 0.5, 1, 2, 5, 10 mg·kg^-1. The results showed that, during the rice growth period, the content of SSE-Cd in reddish clayey soil was in the range of 0 and 2.5 μg·L^-1, and the average content was 0.57 μg·L^-1; TCLP-Cd was in the range of 0 and 0.25 μg·L^-1 with the average content of 0.10 mg·kg^-1;The content of SSE-Cd in purple paddy field was in the range of 0 and 1.6 μg·L^-1 with the average content of 0.48 μg·L^-1; TCLP-Cd was in the range of 0 and 0.2 mg·kg^-1, and the average content was 0.07 mg·kg^-1. It showed that the cadmium concentrations in soil solution and the TCLP extractable Cd levels were both significantly reduced in two types of soil with the extension of rice growth period, and the content in reddish clayey soil was higher than that in purple paddy. The TCLP extractable Cd level was significantly positively correlated with Cd concentration in soil solution. The total Cd accumulation in rice plants gradually increased with increasing exogenous Cd concentration. There were significant positive correlations between Cd concentration in soil solution and Cd concentration in rice, Cd concentration in soil extracted by TCLP method and Cd concentration in rice and total Cd accumulation in rice plant. The soil environmental capacities of the two different parent materials varied greatly,and the safety threshold of Cd in purple paddy field was 2.06 times of that of reddish clayey soil. There were significant differences in Cd uptake and accumulation in different soils, so different measures may be needed to control Cd pollution in different parent materials. TCLP extractable Cd was more relevant with total Cd accumulation in rice, and had more extraction amount. Therefore, the TCLP method can more accurately evaluate the biological availability of soil Cd.

Sustainable use of tannery sludge in brick manufacturing in Bangladesh

Chromium-rich tannery sludge generated from tanneries has the potential to become a serious environmental burden in Bangladesh and a promising avenue for disposal of this sludge is by stabilizing it in clay brick products. But for sustainable industrial application of such technique it needs to be ensured first that the engineering properties of bricks as a building material are not diminished by addition of sludge, the process becomes energy efficient compared to alternatives and the use of such bricks do not pose any harmful environmental effects in the long run. In this study, clay bricks were prepared with different proportions of sludge (10%, 20%, 30% and 40% by dry weight) in both laboratory-controlled and field conditions and their suitability as a construction material was assessed based on their strength, water absorption, shrinkage, weight-loss on ignition and bulk density. For the sludge incorporated bricks, the compressive strength ranged from 10.98MPa to 29.61MPa and water absorption ranged from 7.2% to 20.9%, which in most cases met both the Bangladesh and ASTM criteria for bricks as a construction material. Volumetric shrinkage, weight loss and efflorescence properties of sludge-amended bricks were found to be favorable and it was estimated that an energy saving of 15-47% could potentially be achieved during firing with 10-40% tannery sludge-amended bricks. The quality of sludge-amended bricks made in the brick kiln was relatively inferior compared to bricks produced in the laboratory due to operating in a less-controlled environment with respect to maintaining adequate compaction and optimum moisture content. The leaching behavior of several heavy metals (Cr, As, Cu, Ni, Cd, Pb and Zn) from sludge-amended bricks has been found to be insignificant and far below the Dutch regulations and USEPA regulatory limits. Results from this study indicate that tannery sludge can be sustainably stabilized in clay bricks and large-scale application of this technique can be envisaged in the context of Bangladesh where brick remains a dominant building material.

Removal of arsenic(III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column

Magnetic binary oxide particles (MBOP) were prepared by template method using chitosan in the laboratory for the removal of As(III) from water. The prepared MBOP has super paramagnetic property which is sufficient for magnetic separation. Column study was performed at two different flow rates of 2.0ml/min and 5.0ml/min and comparison was made with regenerated MBOP, commercial activated carbon and commercial activated alumina. It is observed that fresh MBOP has higher breakthrough time and capacity than regenerated MBOP by a factor of 1.25 and 1.37 respectively. In Logit method, the values of K (adsorption rate constant) and N (adsorption capacity coefficient) were obtained as 0.2066 (L/mgh) and 1014(mg/L) for 5.0ml/min flow rate. All the drinking water parameters are within the limit of BIS 10500-2012. Toxicity characteristic leaching procedure (TCLP) and semi dynamic tests were performed for the mix ratios of 01:02:01, 01:02:05 and 01:02:10 and were found safe for the disposal.

Recovering lead from cupel waste generated in gold analysis by Pb-Fire assay

Because of its precision and accuracy, Pb-Fire assay is the most employed method for gold analysis in geological materials. At the second stage of the method, namely cupellation, lead is oxidized to PbO which is absorbed by the cupel, leading to metallic gold as a tiny bend at the bottom of the recipient. After cupellation, cupel becomes highly contaminated with lead, making its disposal a serious risk of environmental contamination. In the present work, a leaching process for removing lead from cupel waste is proposed, which allowed for removing 96% of PbO by weight. After a precipitation step, 92.0% of lead was recovered from leachates in the form of PbSO₄. Lead in the solid wastes left by the extraction was above the limit established by Brazilian legislation and these were classified as non-hazardous. Finally, secondary effluents generated after the precipitation step presented lead content more than twenty times lower than that of leachates from cupel waste. Tons of cupel waste are annually generated from gold analysis by Pb-Fire assay. Thus, the proposed method can contribute to prevent the discharge of high amounts of lead into the environment. Also, recovery of lead can help to partially meet the industrial demand for lead compounds.

Influence of pyrolytic and non-pyrolytic rice and castor straws on the immobilization of Pb and Cu in contaminated soil

Soil contamination with heavy metals has become a global environmental health concern. In the present study, European Community Bureau of Reference (BCR) sequential extraction and toxicity characteristic leaching procedure (TCLP) techniques were used to evaluate the Pb and Cu subsequent transformations, immobilizing impact of pyrolytic and non-pyrolytic rice and castor straws and their efficiency to reduce the metals mobility and leachability in the polluted soil. Obtained results highlight the potential of biochar over non-pyrolytic residues to enhance the immobilization of Pb and Cu in the soil. Castor leaves-derived biochar (CLB), castor stem-derived biochar (CSB), and rice straw-derived biochar (RSB) prominently decreased the mobility (acid-soluble fraction) of Pb 49.8%, 31.1%, and 31.9%, respectively, while Cu decreased 15.8%, 11.5%, and 12%, respectively, as compare to control. Sequential extraction showed that biochar treatments prominently modified the proportioning of Pb and Cu from acid soluble to a less bioavailable fraction and increased the geochemical stability in the polluted soil as compared to relative feedstocks as well as the controlled soil. Additionally, the soil pH increased markedly after the addition of biochar. Compared with control, the TCLP-extractable Pb and Cu were reduced to 29.2-41.4% and 5.7-22.8% from the soil respectively by the application of CLB. The immobilization and reduction in leachability of Pb and Cu were correlated with the soil pH. The biochar effect on the Pb immobilization was much better as compared to Cu in co-contaminated soil. Overall addition of CLB offered the best results and could be effective in both Pb and Cu immobilization thereby reducing their mobility and bioavailability in the co-contaminated soil.

Leaching Behavior of Selected Trace and Toxic Metals in Coal Fly Ash Samples Collected from Two Thermal Power Plants, India

Studies on leaching behavior of metals associated with coal fly ash (FA) are of great concern because of possible contamination of the aquatic environment. In the present study, leaching behavior of metals (As, Se, Cr, Pb, V, Zn, etc.) in two different FA samples (FA1 and FA2) was investigated at various pH (2-12), temperatures of leachate solution and using TCLP. At pH 2, the highest leaching was observed for Fe (21.6 and 32.8 µg/g), whereas at pH 12, Arsenic was found to have the highest leaching (1.5 and 2.4 µg/g) in FA1 and FA2. Leachate solution temperature showed a positive effect on the metal's leachability. In TCLP, most of the metal's leachability was observed to be higher than that of batch leaching tests. The present study suggests that, leaching of As and Se from FA samples can moderately affect ground/surface water quality at the study locations.

Chemical immobilization of Pb, Cu, and Cd by phosphate materials and calcium carbonate in contaminated soils

Soil contamination with toxic metals has increasingly become a global concern over the past few decades. Phosphate and carbonate compounds are good passivation materials for Pb immobilization, while the effect of phosphate and carbonate on the immobilization of multiple heavy metals (Pb, Cu, and Cd) in contaminated soils was seldom investigated. In this study, bone meal (BM), phosphate rock (PR), oxalic acid-activated phosphate rock (APR), super phosphate (SP), and calcium carbonate (CC) were added to the contaminated soils to evaluate the effect of phosphate materials and calcium carbonate on the immobilization of Pb, Cu, and Cd. The results showed that the pH of the treated soils increased 1.3-2.7, except SP which decreased 0.5 at most. Compared to the control treatment, all phosphates and calcium carbonate added to the polluted soils increased the fraction of residual metals, and the application of APR, PR, BM, and CC significantly reduced exchangeable and carbonate-bound fraction metals. PR and APR were the most effective for the immobilization of Pb, Cu, and Cd in the soils among these materials. Moreover, the concentrations of all metals in the toxicity characteristic leaching procedure (TCLP) leachate decreased with increasing amounts of amendments, and the concentrations of Pb in the TCLP leachate for soils treated with PR and APR were below the nonhazardous regulatory limit of 5 mg L(-1) (US Environmental Protection Agency). Based on our results, phosphate rock and oxalic acid-activated phosphate rock are effective in the immobilization of multiple metals by reducing their mobility in the co-contaminated soils.

A nanoremediation strategy for the recovery of an As-polluted soil

The present study investigates the impact of the nanoremediation treatment on soil recovery as evaluated by the development of barley plants. Highly As-polluted brownfield soil was treated with nanoscale zero-valent iron (nZVI) commercial suspension at two doses (1% and 10%). Barley plants were cultivated in treated and untreated soils in a growth chamber, and the As, Fe, and nutrients uptake were determined. The efficacy of As immobilization was evaluated according to the toxicity characteristics leaching procedure (TCLP) as well as using a sequential extraction procedure. The application of nZVI reduced the amount of As in the more available fractions and increased the amount of As in the residual fraction. The best immobilization results were obtained for the highest dose of nZVI (10%). In turn, the lower availability of As in nZVI-treated soils, particularly at the dose of 10%, stimulated the development of the barley plants and decreased the As uptake. Neither an important increase of available Fe nor negative impact on soil physico-chemical and biological properties were observed. Thus, our results show that the use of nZVI could be an adequate strategy to recover the land use in As polluted soils.

Fractionation and leachability of heavy metals from aged and recent Zn metallurgical leach residues from the Três Marias zinc plant (Minas Gerais, Brazil)

Various mineral processing operations to produce pure metals from mineral ores generate sludges, residues, and other unwanted by-products/wastes. As a general practice, these wastes are either stored in a reservoir or disposed in the surrounding of mining/smelting areas, which might cause adverse environmental impacts. Therefore, it is important to understand the various characteristics like heavy metal leaching features and potential toxicity of these metallurgical wastes. In this study, zinc plant leach residues (ZLRs) were collected from a currently operating Zn metallurgical industry located in Minas Gerais (Brazil) and investigated for their potential toxicity, fractionation, and leachability. Three different ZLR samples (ZLR1, ZLR2, and ZLR3) were collected, based on their age of production and deposition. They mainly consisted of Fe (6-11.5 %), Zn (2.5 to 5.0 %), and Pb (1.5 to 2.5 %) and minor concentrations of Al, Cd, Cu, and Mn, depending on the sample age. Toxicity Characteristic Leaching Procedure (TCLP) results revealed that these wastes are hazardous for the environment. Accelerated Community Bureau of Reference (BCR) sequential extraction clearly showed that potentially toxic heavy metals such as Cd, Cu, Pb, and Zn can be released into the environment in high quantities under mild acidic conditions. The results of the liquid-solid partitioning as a function of pH showed that pH plays an important role in the leachability of metals from these residues. At low pH (pH 2.5), high concentrations of metals can be leached: 67, 25, and 7 % of Zn can be leached from leach residues ZLR1, ZLR2, and ZLR3, respectively. The release of metals decreased with increasing pH. Geochemical modeling of the pH-dependent leaching was also performed to determine which geochemical process controls the leachability/solubility of the heavy metals. This study showed that the studied ZLRs contain significant concentrations of non-residual extractable fractions of Zn and can be seen as a potential secondary resource for Zn.

Toxicity characteristic leaching procedure over- or under-estimates leachability of lead in phosphate-amended contaminated soils

In this study, Pb(NO3)2-, PbSO4-, or PbCO3-contaminated soils were treated with triple super phosphate (TSP) or phosphate rock (PR) and then subjected to the toxicity characteristic leaching procedure (TCLP) to assess Pb leachability. Soluble TSP resulted in the transformation of Pb into insoluble Pb phosphate precipitates in all contaminated soils, and the transformation increased with extended leaching times. Consequently, Pb concentrations in the TCLP leachates treated with TSP were reduced by 97.3-99.7% compared with the untreated soils, and Pb leaching decreased over the extraction time and did not reach equilibrium even after 96 h of extraction. Precipitation of Pb phosphate minerals in the less soluble PR-treated soil was limited, and Pb leaching was controlled by the dissolution of the Pb compounds, resulting in elevation of Pb in the TCLP leachate. Pb leaching continued to increase with time due to continuous dissolution of PbSO4 and PbCO3. The results indicated that Pb leaching is kinetically controlled by either Pb compound dissolution or phosphate mineral formation. The standard TCLP test using a designated 18 h incubation time can overestimate the leachability of Pb in soils contaminated with lead and amended with soluble TSP and underestimate the leachability of Pb in soils contaminated with Pb and amended with less soluble PR. Therefore, wide use of TCLP for assessing Pb leachability in all contaminated soils is insufficient, and development of a site-specific evaluation method is urgently needed.

Detoxification of ashes from a fluidized bed waste incinerator

This paper was to test and control the toxicity of bottom and fly ashes from a circulated fluidized bed (CFB) incinerator. Bottom and fly ashes were firstly subject to TCLP test. Even though leachates of most particle size of bottom ash were below regulatory limit, the leachates of finer bottom ash may exceed the regulatory limit. Therefore, finer bottom ash should be separated and treated before landfilled directly or used as cement replacement. Due to high amounts of leached heavy metals, thermal treatment of fly ash was carried out to remove heavy metals. The influence of temperature, residence time, metal chloride and gas velocity were studied. In all conditions, Cd can be well removed. Pb can be almost completely removed with MgCl2 addition at 1000°C in 1h. The removal of Zn and Cu was accelerated significantly by MgCl2 and higher temperature separately. At optimum conditions, more than 90% of Cu and 95% of Zn could be removed, while a maximum 20% of Cr was removed due to the existence or formation of CaCr2O4, MgCr2O4 and K2Cr2O4 in raw or treated fly ashes.

Evaluating the mutagenicity of leachates obtained from the bottom ash of a municipal solid waste incinerator by using a Salmonella reverse mutation assay

The mutagenic potential of leachates derived from the bottom ash of a municipal solid waste incinerator in Taiwan were evaluated using an Ames Salmonella mutagenicity assay with three standard tester strains, TA98, TA100, and TA1535. Three types of leachants, leachant A (pH 4.93), leachant B (pH 2.88), and leachant C (deionized water, pH 6.0), were carried out according to toxicity characteristic leaching procedure (TCLP). Moreover, two types of bottom ash, nonsieved and sieved bottom ash (particle size <4.75 mm), were analyzed with the TCLP and the Ames assay. The concentrations of five heavy metals (Cd, Cr, Cu, Pb, and Zn) in the leachates were also estimated with an ICP-OES. The results indicated that the metal concentrations in the TCLP leachates of bottom ash were all below the limits set by Taiwanese regulations. However, leachate A from nonsieved and <4.75-mm-sieved bottom ash showed mutagenicity. Moreover, leachate A from <4.75 mm-sieved bottom ash displayed stronger mutagenicity than that from nonsieved ash. The leachate A from <4.75-mm-sieved bottom ash, that were diluted by 100-fold showed no mutagenicity. In conclusion, our results suggested that the chemical composition and mutagenic potential of leachates should be monitored to evaluate the safety of bottom ash.