Toxicity Characteristic Leaching Procedure Leachate Research Articles

Remediation of Arsenic and Heavy Metals and Soil Stabilization by Waste Chitosan based Biochar

Remediation of Arsenic and Heavy Metals and Soil Stabilization by Waste Chitosan based Biochar

Reusing ceramic waste in fired brick and as cement additive

AbstractBACKGROUNDAlthough there has been considerable research on the utilization of ceramic and tile waste (CTW) in concrete production, there has been a noticeable lack of studies examining its application in fired brick manufacturing and the use of ceramic glaze powder as an additive in cement. The aim of this study is to assess the potential of reusing CTW as concrete aggregate and as part of fired brick composition. Furthermore, this research investigates the potential application of glaze powder as a novel cement additive, which has not been previously explored.RESULTSThe results indicate that bricks made from waste materials had a moisture absorption of 12.2% and flexural strengths ranging from 15.39 to 24.2 MPa. X‐ray diffraction analysis showed that quartz and kaolinite were the dominant crystalline phases in bricks made from raw glazed ceramic. The concentration of heavy metals in the toxicity characteristic leaching procedure leachate of the waste materials decreased after the firing process during the manufacturing of bricks due to oxidation, immobilization and encapsulation processes, with levels below standard limits. In concrete, the use of 20% ceramic glaze powder as a partial cement replacement resulted in a 55% increase in compressive strength. Additionally, the leaching of barium decreased by 70% and that of strontium decreased by 17%.CONCLUSIONThis study highlights the promising utilization of CTW in fired brick production and the effective incorporation of ceramic glaze powder as a cement additive. The findings suggest enhanced mechanical properties and decreased heavy metal leaching, indicating the viability of CTW reuse in sustainable construction practices. © 2023 Society of Chemical Industry (SCI).

The beneficial reuse of contaminated sediment: Long-term assessment of fly ash and lime-based mixtures

In recent decades, sediment has been recognised as a problematic resource due to its potentially harmful effects and the large quantities present in water bodies. There is a need to properly manage large quantities of dredged sediments so that they can be used as a resource and not necessarily treated as a waste product. This research investigates the effects of ageing and maturation of solidified/stabilized mixtures of contaminated sediment with fly ash and lime. The effects of ageing on the microstructural properties and chemical integrity of mixtures were studied for 7 days, 28 days, and 7 years using scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), X-ray diffraction analysis (XRD), and DIN (German Standard Procedure for Water, Wastewater and Sediment Testing (Group S)) and TCLP (Toxicity Characteristic Leaching Procedure) leaching tests. The results of the microstructure and strength analysis showed that the use of fly ash and lime as binders promoted the permanent structural integrity of the sediment. The treated sediment with 20 wt% fly ash and 10 wt% lime (F20L10) achieved higher overall strength compared to the mixture containing only 30 wt% fly ash (F30). The speciation and redistribution of metals and As in the treated sediment mixtures during the long-term evaluation indicate a strong reduction in their mobility. This material can be considered environmentally friendly and can be used as a fill material in road construction. The investment and operating costs are justified in this solution for sediment management. However, it is important to monitor the produced material over time to ensure that it remains effective and sustainable in the long term.

Long-term stability and toxicity effects of three-dimensional electrokinetic remediation on chromium-contaminated soils

The three-dimensional electrokinetic remediation (3D EKR) achieved efficient removal of chromium (Cr) from the soil through mechanisms including electromigration, electroosmosis, and redox reactions. In this study, the long-term stability, leaching toxicity, bioavailability, and phytotoxicity of Cr in remediated soils were systematically analyzed to comprehensively evaluate the effectiveness of the 3D EKR method. The results showed that the concentration of hexavalent chromium (Cr (VI)) in the leachate of the 3D EKR system with sulfidated nano-scale zerovalent iron (S-nZVI) was more than 40% lower than those of the other 3D electrode groups, and the time required to reach the level III standard of groundwater quality criterion in China (0.05 mg/L, GB/T 14848-2017) was significantly shortened. The stabilization of Cr(VI) in contaminated soil after 3D EKR was maintained for 300 pore volumes (PVs), indicating that the treated Cr(VI) had good long-term stability. The leaching toxicity and bioaccessibility of Cr were assessed by the synthetic precipitation leaching procedure (SPLP), the toxicity characteristic leaching procedure (TCLP), and the physiologically based extraction test (PBET). The concentration of Cr(VI) in the SPLP, TCLP, and PBET leachates of the S-nZVI group decreased by more than 25% compared to the other 3D electrode groups, corresponding to the decrease in leaching toxicity and bioavailability of the treated Cr during the 15-day remediation period. In addition, the germination rate of wheat seeds and the average biomass of wheat seedlings in the S-nZVI group under alkaline conditions (EE) were higher than those in the non-polluting group (Blank-OH), indicating that the remediated soil had no obvious toxicity to wheat. In summary, 3D EKR achieved a satisfactory and stable remediation effect on Cr-contaminated soil, especially when using S-nZVI as the 3D electrode.

Remediation of Cr(VI) contaminated soil by chitosan stabilized FeS composite and the changes in microorganism community

In-suit immobilization is one of the major strategies to remediate heavy metals contaminated soil with the effectiveness largely depends on the characteristics of the added chemical reagents/materials. In this study, chitosan stabilized FeS composite (CS–FeS) was prepared to evaluate the performance of remediating the high and toxic hexavalent chromium contaminated soil from the effectiveness and microbial response aspects. The characterization analysis confirmed the successful preparation of composite, and the introduction of chitosan successfully stabilized FeS to protect it from rapid oxidation as compared to bare FeS particles. With the addition dosage at 0.1%, about 85.6% and 81.3% of Cr(VI) was reduced in 3 d based on toxicity characteristic leaching procedure (TCLP) and CaCl2 extraction, and the reduction efficiency increased to 96.6% and 94.8% in 7 d, respectively. The Cr(VI) was non-detected in the TCLP leachates with increase the CS-FeS composites to 0.5%. The percentages of HOAc-extractable Cr decreased from 25.17% to 6.12% accompanied with the increase in the residual Cr from 4.26% to 13.77% and improvement of soil enzyme activity under CS-FeS composites addition. Cr(VI) contamination reduced the diversity of microbial community in soil. Three dominate prokaryotic microorganisms, namely Proteobacteria, Actinobacteria and Firmicutes, were observed in Cr-contaminated soil. The addition of CS-FeS composites increased the microbial diversity especially for that in relative lower abundance. The relative abundance of Proteobacteria and Firmicute related to Cr-tolerance and reduction increased in CS-FeS composites added soils. Taking together, these results demonstrated the potential and promising of using the CS-FeS composites for Cr(VI) polluted soil remediation.

Dispersive Solid–Liquid Microextraction Based on the Poly(HDDA)/Graphene Sorbent Followed by ICP-MS for the Determination of Rare Earth Elements in Coal Fly Ash Leachate

A dispersive solid-phase microextraction (DSPME) sorbent consisting of poly(1,6-hexanediol diacrylate)-based polymer microspheres, with embedded graphene microparticles (poly(HDDA)/graphene), was synthesized by microfluidic emulsification/photopolymerization and characterized by optical microscopy and X-ray fluorescence spectrometry. This sorbent was applied for simple, fast, and sensitive vortex-assisted DSPME of rare earth elements (RREs) in coal fly ash (CFA) leachate, prior to their quantification by inductively coupled plasma mass spectrometry (ICP-MS). Among nine DSPME variables, the Plackett–Burman screening design (PBD), followed by the central composite optimization design (CCD) using the Derringer desirability function (D), identified the eluent type as the most influencing DSPME variable. The optimum conditions with maximum D (0.65) for the chelating agent di-(2-ethylhexyl) phosphoric acid (D2EHPA) amount, the sorbent amount, the eluting solvent, the extraction temperature, the centrifuge speed, the vortexing time, the elution time, the centrifugation time, and pH, were set to 60 μL, 30 mg, 2 M HNO3, 25 °C, 6000 rpm, 1 min, 1 min, 5 min, and 4.2, respectively. Analytical validation of the DSPME method for 16 REEs (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in CFA leachate samples estimated the detection limits at the low ppt level, the recovery range 43–112%, and relative standard deviation within ± 22%. This method was applied to a water extraction procedure (EP) and acetic acid toxicity characteristic leaching procedure (TCLP) for leachate of CFA, from five different coal-fired thermoelectric power plants. The most abundant REEs in leachate (20 ÷ 1 solid-to-liquid ratio) are Ce, Y, and La, which were found in the range of 22–194 ng/L, 35–105 ng/L, 48–95 ng/L, and 9.6–51 μg/L, 7.3–22 μg/L, 2.4–17 μg/L, for EP and TCLP leachate, respectively. The least present REE in TCLP leachate was Lu (42–125 ng/L), which was not detected in EP leachate.

Multiple heavy metal immobilization and strength improvement of contaminated soil using bio-mediated calcite precipitation technique.

Bio-mediated calcite precipitation potential for multiple heavy metal immobilization in contaminated soils at industrial, waste dump, abandoned mine, and landfill sites is not explored yet. This study includes investigation of bio-mediated calcite precipitation for strength improvement and immobilization of heavy metals, specifically lead (Pb), zinc (Zn), and hexavalent chromium (Cr(VI)), in contaminated soils. Firstly, the toxicity resistance of bacteria against different concentrations (1000, 2000, 3000, 4000, and 5000 mg/l) of each heavy metals was investigated and observed that Pb and Cr were less toxic to Sporosarcina pasteurii than Zn. The poorly graded sand was spiked with 333-2000 mg/kg concentrations of a selected individual or mixed metal solutions, i.e., 1000 mg/kg and 2000 mg/kg individual concentrations of Pb, Zn, and Cr(VI); 500 mg/kg and 1000 mg/kg concentration of each metal in "Pb and Zn," "Pb and Cr(VI)," and "Zn and Cr(VI)" mixture of heavy metals; and 333 mg/kg and 666 mg/kg concentration of each metal in "Pb, Zn, and Cr(VI)" mixed metal concentration. Contaminated soil was biotreated with Sporosarcina pasteurii and cementation (a solution of urea and calcium chloride dihydrate) solutions for 18 days. Biocemented sand specimens were subjected to testing of hydraulic conductivity, ultrasonic pulse velocity (UPV), unconfined compressive strength (UCS), calcite content, pH, toxicity characteristic leaching procedure (TCLP), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The heavy metal contaminated samples showed decrease in hydraulic conductivity and increase in UPV and UCS after biotreatment; however, the changes in engineering properties were found more moderate than clean biocemented sand. The conversion of Cr(VI) to Cr(III) followed by Cr2O3 precipitation in calcite lattice was observed. Zn was precipitated as smithsonite (ZnCO3), while no Pb precipitate was identified in XRD results. TCLP leaching showed Pb and Cr immobilized proportional to calcite precipitated amount, and higher calcite amounts yielded levels within regulatory limits. Pb and Cr(VI) immobilization up to 92 % and 94 % was achieved, respectively, in contaminated biocemented sand. Zn was found completely leachable as smithsonite is only stable down to pH~5, and strongly acidic TCLP solution reversed all immobilization at natural soil pH~8-9.

Simultaneous reduction and immobilization of Cr(VI) in seasonally frozen areas: Remediation mechanisms and the role of ageing

Among the toxic metals, hexavalent chromium [Cr(VI)] has attracted much attention due to its high mobility and toxicity, rendering considerable challenges for long-term remediation. In this study, the soil was collected from a dichromate contaminated industrial site in Liaoning Province, a seasonally frozen area in northern China, and subjected to frequent freeze-thaw cycles. Three additives, including (i) ferrous sulfate; (ii) calcium polysulfide; and (iii) combined biochar and calcium polysulfide were applied to reduce and immobilize Cr(VI) in the soils. The samples underwent 28 days of incubation followed by 16 freeze-thaw cycles. The toxicity characteristic leaching procedure (TCLP) and simulated acid rain leaching were adopted to test the remediation performances. It was observed that all three treatments can significantly reduce and immobilize Cr(VI) after short-term incubation, while biochar with abundant functional groups could adsorb and reduce Cr(VI) effectively. Notably, the concentration of Cr(VI) in TCLP leachates after incubation in combined treatment decreased by 67.87% and 37.27%, respectively, compared with the application of ferrous sulfate or calcium polysulfide alone. Freeze-thaw cycles induced the disintegration of soil particles and increased the risk of contaminant mobilization. Conversely, biochar particles has become finer and even produced nanoparticles with ageing, accompanied by the increase in oxygen-containing surface functional groups. Additionally, the specific surface area increased with the pyrolysis of biochar, which further enhanced the retention of soil colloidal particles and suppressed the migration of contaminants. Therefore, the cumulative release of Cr(VI) in the combined treatment (i.e., 10.97 ~ 32.97 mg/kg) was much lower than that of the other two treatments after freeze-thaw ageing. Overall, the combination of biochar and calcium polysulfide displayed advantages in the reduction and immobilization of Cr(VI), and offered a long-term, effective strategy for the remediation of Cr(VI) contaminated soils in cold regions.

Leaching Performance and Zinc Ions Removal from Industrial Slag Leachate Using Natural and Biochar Walnut Shell.

This study aims to investigate leaching characteristics of zinc slag according to leaching tests, including; TCLP (Toxicity Characteristic Leaching Procedure), SPLP (Synthetic Precipitation Leaching Procedure), ASTM-D3987 (American Society for Testing and Materials), and TS EN-12457-4 (Turkish Standards Institute) tests methods. The present study describes the adsorption potential of natural and biochar walnut shells for removing ions from the zinc leachate. TCLP leachate, with a value of 38.575 mg/L, has a high zinc (Zn+2) concentration compared to other methods. Therefore, TCLP leachate was used in the adsorption experiments. Adsorption experiments were carried out at different adsorbent dosages, pH values, and contact time conditions. In the dosage study, the highest removal efficiency was obtained as 84% and 92% in natural and biochar walnut shell adsorbents, respectively. As a result of pH study, it was observed that adsorption under alkaline conditions had a much higher removal efficiency. Moreover, adsorption studies performed against contact time were applied to four different kinetic models and both adsorbents were found to be fit with the pseudo-second-order model. This kinetic model showed that the Zn+2 adsorption mechanism of natural and biochar walnut shells is chemical adsorption. With this study, it was shown that a very high 96% zinc removal can be achieved under optimum adsorption conditions. This may be the first study of zinc removal after leaching from industrial slag in the literature. This study has shown that high removal efficiencies can be obtained by an economical adsorbent.

Material composition and associated toxicological impact assessment of mobile phones

Dynamic progress in technology coupled with various restrictions has brought about extensive changes in the material composition in various components of a mobile phone as a product. This research focuses on assessing whether the mobile phone industry has taken into account the environmental impacts of their products while making rapid technological progress. Three components each, namely liquid crystal display (LCD), plastic housing (PH), and printed circuit board (PCB) of twenty-six end-of-life mobile phones (EoL-MPs) comprising six basic phones manufactured during 2000–2004 and twenty smartphones manufactured during 2005–2016 were characterized for twenty-six elements including heavy and precious metals. Leaching potential and toxicological impact were also assessed using the toxicity characteristic leaching procedure (TCLP) and the USEtox® model, respectively. Results revealed that technological advancement rather than the regulations showed a significant influence on the total metal content in the EoL-MPs and associated toxicological impacts. Metal content in the LCDs was found to be almost tripled from an average of 4270 mg/kg in the basic phones (2000–2004) to 12,803 mg/kg in the smartphones (2011–2016). Few EoL-MPs were also found to possess hazard potential due to the high concentration of Pb (range: 7.21–84.38 mg/l) in the TCLP leachates. Cr, Pb, and Cu were found to pose the most significant human carcinogenic (highest: 1.83 × 10−5 cases/kg), human non-carcinogenic (highest: 8.34 × 10−5 cases/kg), and ecotoxicity (highest: 171275 PAF. m3.day/kg) risk, respectively. Results from the study could be useful for the eco-design of mobile phones and the development of effective e-waste management strategies.

Removal of heavy metals in medical waste incineration fly ash by Na2EDTA combined with zero-valent iron and recycle of Na2EDTA: Acolumnar experiment study

ABSTRACT In this study, an effective circulating system was developed to remove heavy metals in medical waste incineration (MWI) fly ash. MWI fly ash (MWIFA)-column experiments were performed to remove Cu, Pb, Zn, Cd, and Ni from MWIFA using EDTA disodium (Na2EDTA). Iron-column experiments were conducted to study the removal effect of zero-valent iron on the five heavy metals from washing wastewater. Toxicity Characteristic Leaching Procedure (TCLP) test method was employed to evaluate heavy metals toxicity of MWIFA residues generated after 0–0.2 mol/L Na2EDTA solution treated. After being washed by 0.2 mol/L Na2EDTA solution, TCLP leaching values of Cu, Pb, Zn, Cd, and Ni were the lowest and satisfied the standard (GB 5085.3–2007), and the leaching values were 58.4 ± 2.0 mg/L, 2.81 ± 0.14 mg/L, 64.3 ± 4.0 mg/L, 0.156 ± 0.005 mg/L, 0.381 ± 0.006 mg/L. Concentrations of Cu, Pb, Zn, Cd, and Ni in iron-column effluent were reduced by 99.7%, 91.6%, 91.6%, 75.4%, and 75.7%, respectively. Na2EDTA was recovered and recycled to the removal of heavy metals from MWIFA. Comparing new Na2EDTA solution with recycled Na2EDTA solution, recycled Na2EDTA and water could be reutilized to dispose MWIFA. The removal efficiencies of Cu, Pb, Zn, Cd, and Ni by recycled 0.2 mol/L Na2EDTA solution were 67.1%, 68.8%, 63.2%, 73.9%, 50.7%, respectively, the removal efficiencies using recovered Na2EDTA decreased by 2.6%, 3.9%, 3.3%, 4.2%, and 1.6%, respectively. Successive batch experiments were also conducted to evaluate industrialization potential and reusable times for recycled Na2EDTA. After four recirculation cycles, extraction efficiencies of Pb and Cd (removal efficiency at different cycles divided by removal efficiency of new Na2EDTA) declined toward 80%. Results from this research indicated that this circulating system possessed industrialization potential. Implications: An effective circulating system was developed to remove heavy metals in MWI fly ash (MWIFA). Integration of Na2EDTA with Fe0 promoted the removal of heavy metals from MWIFA. Na2EDTA, NaCl and water were stepwise extracted from iron-column effluent, respectively. Recovered Na2EDTA can still effectively remove heavy metals from MWIFA. Results from this research indicated that this circulating system possessed industrialization potential.

Green remediation of Cd and Hg contaminated soil using humic acid modified montmorillonite: Immobilization performance under accelerated ageing conditions

Solidification/Stabilization (S/S) is an effective way to immobilize toxic metals in contaminated soil. However, utilization of ordinary Portland cement (PC) in this process has raised environmental concerns owing to the high carbon footprint from PC manufacturing and the risk of toxic element leaching in the long term. Hence there is an urgent need to seek for “green” immobilization approaches with long-term stability. In this study, a clay-based material, humic acid modified montmorillonite (HA-Mont) was applied to a Cd and Hg contaminated soil. Field emission scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (FESEM/EDS), N2 adsorption-desorption, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses were performed to investigate the characteristics of this material. Compared to the soil without any treatment, dosage of 5 % HA-Mont could effectively reduce Cd and Hg concentrations by 94.1 % and 93.0 %, respectively and to below the regulatory limits in the TCLP (Toxicity Characteristic Leaching Procedure) leachates. Compared to the soil treated with virgin montmorillonite, HA modification resulted in the reduction of leachate concentrations of Cd and Hg by 69.5 % and 65.9 %, respectively. Long-term immobilization performance of the HA-Mont treatment was examined using a quantitative accelerated ageing method. In order to examine the ageing features, a novel method based on conditional probability was developed, and the reliability of HA-Mont immobilization was found to fit the Weibull model well, as the ageing rate of immobilization effect increased with time. After 120 years of ageing, reliability of both metals could still remain above 0.95. Cd concentration in TCLP leachates at 120th year could still remain below the regulatory limit (294 μg/L vs 1000 μg/L), while Hg concentration reached the regulatory limit of 200 μg/L in 96th year. This is the first attempt developing a green S/S method of Cd and Hg contaminated soil using HA-Mont and examining the long-term ageing characteristics of the stabilized soil using a probability-based approach.

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.

Pb–Zn mine tailings reprocessing using centrifugal dense media separation

The management of mine tailings has become a worldwide environmental concern. In fact, with the more restrictive environmental regulations, there is a pressing need to develop efficient and clean techniques to properly manage these industrial wastes. This work investigates the use of centrifugal Dense Medium Separation (DMS) as a depollution process of Pb-Zn tailings in order to reduce their residual metal content. The obtained results showed that DMS technique allowed high recovery of cerussite (PbCO3) and smithsonite (ZnCO3) present in the studied tailings. Consequently, it has successfully depolluted the studied mine tailings. The effectiveness of DMS was accessed both by the Separation Efficiency (SE) factor and the Toxicity Characteristic Leaching Procedure (TCLP) environmental test. The recoveries of Zn and Pb to the heavy fraction are 88.83% and 91.66% respectively. The observed concentrations of contaminants in TCLP leachates from the light fraction, consisted mainly of dolomite and silicates (quartz, orthoclase, albite and chlorite), are below the limits authorized by the US-EPA regulation for non-hazardous wastes. The DMS allowed a reduction of the concentration of leached Pb by more than 95% in both tailings, and a reduction of the concentration of leached Zn by more than 78% in the case of Bb tailings.

Using an integrated method for the determination of environmental TCLP arsenic for sulphide-rich mine tailing remediation in Ghana, West Africa

Toxicity characteristic leaching procedure (TCLP) is a versatile short-term leaching protocol used to estimate the release of toxic metals from waste prior to disposal to a repository. This paper uses the integrated TCLP leachate data from tailings, tailings dam monitoring borehole data, and acidity ratio (AR) range of sulphide-rich ores to simulate the environmental TCLP As in tailings at the AngloGold Ashanti Obuasi mine in Ghana. The aim was to incorporate long-term leaching characteristics of tailings to minimise the risk of TCLP As test failure. The mean As concentration and pH value are 2.26 mg/l and 5.7 in TCLP leachate, 0.35 mg/l and 6.7 in monitoring boreholes, and < 0.01 mg/l and 5.7 in control boreholes, respectively. The evaluation of the TCLP As data using a one-sample t test performed at 80% confidence interval has the upper confidence limit (UCL) of 2.41 mg/l; this value which constitutes the short-term characterised environmental TCLP As is below the USEPA criterion of 5 mg/l and, therefore, qualifies the waste as safe for disposal. Alternatively, TCLP leachate, borehole and AR data were integrated to simulate the long-term environmental TCLP As of 2.40 mg/l and pH value of 5.7, and As concentration and pH value of 0.01 mg/l and 6.7 in monitoring boreholes, respectively. Such laboratory simulations of TCLP As leaching aimed at achieving 0.01 mg/l in field monitoring data would provide a more robust predictive value for environmental management decision making due to long-term considerations.

Influence of organic and inorganic passivators on Cd and Pb stabilization and microbial biomass in a contaminated paddy soil

Soil contamination with heavy metals, such as Cd and Pb, has caused severe health and environmental risks all over the world. Possible eco-friendly solutions for Cd and Pb immobilization were required to reduce its mobility through various cost-effective amendments. A laboratory incubation study was conducted to assess the efficiency of biochar (BC), zeolite (ZE), and rock phosphate (RP) as passivators for the stabilization of Cd and Pb in paddy soil as well as soil microbial biomass. Various extraction techniques were carried out: a sequential extraction procedure, the European Community Bureau of Reference (BCR), toxicity characteristic leaching procedure (TCLP) test, and single extraction with CaCl2. The impact of passivators on soil pH, dissolved organic carbon (DOC), and microbial biomass (carbon, nitrogen, and phosphorus) was examined in the metal contaminated soil. The results showed that the exchangeable portion of Cd in soil was significantly reduced by 34.8, 21.6, and 18.8% with ZE, RP, and BC at a 3% application rate, respectively. A similar tendency of reduction in Pb soluble portion was observed by ZE (9.6%), RP (20%), and BC (21.4%) at a 3% application rate. Moreover, the TCLP leachate of Cd and Pb was apparently reduced by 17 and 30.3% with BC at a 3% application dose, respectively, when compared to the control. Soil pH, nutrients, and microbial biomass C, N, and P were significantly increased with the addition of BC, RP, and ZE passivators. The results showed that the incorporation of BC, ZE, and RP significantly reduced the Cd and Pb mobility in paddy soil as well as enhanced soil nutrients and microbial biomass. Overall, among all the amendments, rice straw derived-BC performed better for Cd and Pb immobilization in paddy soil.

Contaminated dredged soil stabilization using cement and bottom ash for use as highway subgrade fill

Large amount of sediments are dredged from connecting drains of River Yamuna as a part of its regular maintenance in Delhi. These dredged soils generally considered as waste due to its poor engineering properties. In this study attempt has been made to improve strength, durability and immobilize contaminants of the contaminated dredged soil collected from Najafgarh drain by mixing it with different proportion of cement–bottom ash mix so that it can suitably fulfill the requirements of highway subgrade materials. Compaction test, California bearing ratio test, wetting and drying test, toxicity characteristic leaching procedure leachate test and scanning electron microscope test were performed on the contaminated dredged soil specimens and the results indicated that cement–bottom ash mix was effective in improving the engineering properties of the contaminated dredged soils. Also, the test results of the contaminated dredged soil stabilized with cement–bottom ash mix were better in comparison to cement alone. From the study it reveals that the optimum proportion of additive to be used to improve properties of the contaminated dredged soils was 10% cement + 10% bottom ash mix for use it as a highway subgrade fill materials.

Effects of carbon nanotube and biochar on bioavailability of Pb, Cu and Sb in multi-metal contaminated soil.

This study examined the effects of carbon nanotube and biochar on the bioavailability of Pb, Cu and Sb in the shooting range soils for developing low-cost remediation technology. Commercially available multi-walled carbon nanotube (MWCNT) and biochar pyrolyzed from soybean stover at 300°C (BC) at 0.5, 1 and 2.5% (w w-1) were used to remediate the contaminated soil in an incubation experiment. Both DTPA (bioavailable) and TCLP (leaching) extraction procedures were used to compare the metal/loid availability and leaching by the amendments in soil. The addition of BC was more effective in immobilizing mobile Pb and Cu in the soil than that in MWCNT. The BC reduced the concentrations of Pb and Cu in the soil by 17.6 and 16.2%, respectively. However, both MWCNTs and BC increased Sb bioavailability by 1.4-fold and 1.6-fold, respectively, in DTPA extraction, compared to the control. The toxicity characteristic leaching procedure (TCLP) test showed that the leachability of Pb in the soil amended with 2.5% MWCNT was 1.3-fold higher than that the unamended soil, whereas the BC at 2.5% decreased the TCLP-extractable Pb by 19.2%. Precipitation and adsorption via electrostatic and π-π electron donor-acceptor interactions were postulated to be involved in the interactions of Pb and Cu with surfaces of the BC in the amended soils, whereas ion exchange mechanisms might be involved in the immobilization of Cu in the MWCNT-amended soils. The application of BC derived from soybean stover can be a low-cost technology for simultaneously immobilizing bioavailable Pb and Cu in the shooting range soils; however, neither of amendments was effective in Sb immobilization.

Solidification optimisation of electroplating sludge

A systematic study was conducted for the treatment of electroplating sludge by solidification and stabilisation (S/S) with ordinary Portland cement, lime and magnesium oxide (MgO). Response surface methodology (RSM) and artificial neural networks (ANNs) in combination with central composite design were employed to develop the predictive models for simulation and optimisation of the S/S process. The independent variables were magnesium oxide, electroplating dried sludge, lime and distilled water, while the compressive strength and the concentrations of zinc and chromium in the toxicity characteristic leaching procedure leachate of the solidified waste were the response variables. Both the RSM and ANN models were developed based on the experimental designs. The generalisation and predictive capabilities of RSM and ANN were compared by unseen data (the data set that is not used for model training or validation). Both the RSM and ANN models determined the optimum S/S process. The results show that all independent variables had significant effects on the properties of the S/S products. The optimised method as determined by ANN or RSM can be used with confidence for determining response variables. However, the data predicted by the ANN model are more similar to the experimental results than that of RSM predicted results.

Immobilization of Heavy Metals by Solidification/Stabilization of Co-Disposed Flue Gas Desulfurization Brine and Coal Fly Ash

The coal-fired power industry in the United States faces growing needs to improve wastewater treatment and disposal practices, especially for wet flue gas desulfurization (FGD) systems. Zero liquid discharge (ZLD) treatment systems may be implemented, and one ZLD option is the coupling of brine concentration with solidification/stabilization (S/S). This S/S process could be achieved by co-disposing the concentrated FGD brines with coal fly ash (CFA) and Portland cement. S/S using bituminous CFA (BCFA) achieved good retainment (average 68–90%) of AsV, CdII, HgII, and SeIV in the toxicity characteristic leaching procedure (TCLP); however, poor retainment was observed for CrVI and SeVI. Separate experiments showed good sorption of AsV, CdII, HgII, and SeIV (average 56–100%) but poor sorption of CrVI and SeVI to S/S solids. Meanwhile, CrVI and SeVI retainment could be enhanced by addition of FeSO4 to the S/S mixture, likely due to reduction of these metals to lower oxidation states. Compared to BCFA, S/S using sub-bituminous CFA (SCFA) resulted in higher pH S/S solids and final TCLP leachate, which increased retainment of AsV, CdII, and SeVI. Apart from the pH impact on the process, AsV retainment was likely improved by the high Ca content of SCFA and SeVI retainment was improved by the incorporation of SeO42– in Friedel’s salt (AFm-Cl) by exchange with Cl–. Friedel’s salt was positively identified by X-ray diffraction in the SCFA S/S solids but not for the BCFA S/S solids. Even so, reduction of SeVI plus S/S is likely a better immobilization strategy than SeO42– substitution in the AFm phase because of higher stability under long-term landfill conditions.