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.