Toxicity Characteristic Leaching Procedure Test Research Articles

Environmental characterization of Sarcheshmeh Cu-smelting slag, Kerman, Iran: Application of geochemistry, mineralogy and single extraction methods

Annually, more than 370,000tons of slag waste is produced in Sarcheshmeh Copper Complex, the biggest Cu-producer in Iran. Geochemical, mineralogical and single extraction methods were used in order to evaluate the contamination potential of metal(loid)s associated with Sarcheshmeh smelting slags. Results showed that, like the other non-ferrous or base metal slags, Sarcheshmeh slags are considered as one of the metalliferous smelting wastes with the multi-elemental contamination potential of most of the potentially toxic elements. Mineralogical studies revealed that the mineral assemblage of the investigated samples is controlled by at least three main factors, including: (1) primary mineralogy of the ore concentrate (chalcocite, chalcopyrite, covellite±pyrite); (2) smelting process (magnetite, fayalite, pyroxene); and (3) weathering reactions in arid to semiarid climate conditions [thenardite (Na2SO4), bonattite (CuSO4·3H2O) and gypsum (CaSO4·2H2O)]. Results obtained from the U.S. EPA toxicity characteristic leaching procedure (TCLP) and water soluble tests revealed that the order of leachability of target elements from the most to the least in the slag samples is as S≫Cu>>Zn>Fe>Mo>Pb>Ni>Mn>Co>As>Se>Sb>Cd>Cr=Sn=Ag=Bi. The maximum contamination potential, higher than the considered toxicity regulatory levels (one-hundred times the U.S. EPA maximum contamination level in drinking water), of As (9.35mg/L), Mo (186.7mg/L), Sb (3.50mg/L) and Se (6.12mg/L) was observed in the alkaline leached solutions (pH9.67) of the sediments associated with the slag dump drainages, while the maximum concentrations of the other investigated elements such as Cu, Co, Cd, Fe, and Zn were measured in the acidic (pH<5) leached solutions. Annually, about 18.7% of Sarcheshmeh reverberatory slags are used for other purposes such as sandblasting. Wind blowing slag particles, produced from the grinding and sieving facilities, are responsible for the enrichment of elements such as As, Cu, Mo, Pb, Sb, Sn, Zn, Cr, S and Fe in the topsoils around the slag preparation site. Based on the acid acetic (0.43mol/L) and EDTA (0.05mol/L) leaching tests, the solubility and thus the bioavailability of these potentially toxic elements also were increased in the surface contaminated soils, a subject that is very important from environmental point of view. Obtained results also emphasize on the need for the greater caution in the slag waste management.

Water treatment residual (WTR)-coated wood mulch for alleviation of toxic metals and phosphorus from polluted urban stormwater runoff

Aluminum-based water treatment residual (WTR)-coated wood mulches were synthesized and tested for removal of heavy metals and phosphorus (P) in synthetic urban stormwater. WTRs are an industrial waste produced from coagulation in water treatment facilities, primarily composed of amorphous aluminum or iron hydroxides. Batch tests showed that the composite filter media could effectively adsorb 97% lead (Pb), 76% zinc (Zn), 81% copper (Cu) and 97% P from the synthetic stormwater (Pb = 100 μg/L, Zn = 800 μg/L, Cu = 100 μg/L, P = 2.30 mg/L, and pH = 7.0) within 120 min, due to the presence of aluminum hydroxides as an active adsorbent. The adsorption was a 2nd-order reaction with respect toward each pollutant. Column tests demonstrated that the WTR-coated mulches considerably alleviated the select pollutants under a continuous-flow condition over the entire filtration period. The effluent Pb, Zn, Cu, and P varied at 0.5–8.9%, 33.4–46.7%, 45.8–55.8%, and 6.4–51.9% of their respective initial concentrations with the increasing bed volume from 0 to 50. Synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) tests indicated that leached contaminants were all below the U.S. criteria, suggesting that the release of undesired chemicals under rainfall or landfilling conditions is not a concern during application. This study demonstrates that the WTR-coated mulches are a new, low-cost, and effective filter media for urban stormwater treatment. Equally important, this study provides a sustainable approach to beneficially reuse an industrial waste for environmental pollution control.

Recycling Phosphated Residue for Pb2+ Removal from Wastewater

Abstract Phosphated residue (PR), a common solid waste generated from iron and steel plants, was directly reused for removing Pb2+ from wastewater by adsorption. Effectiveness and mechanism of Pb2+ removal by PR were investigated by batch experiments. The toxicity characteristic leaching procedure (TCLP) test confirmed that PR was a nonhazardous material and could be used as an adsorbent for subsequent experiments. Studies of pH impact showed that the optimum pH for Pb2+ adsorption on PR was 5.2 ± 0.2. Kinetic studies illustrated that the sorption behavior of Pb2+ could be described better by pseudo-second order model with high correlation coefficient (0.9999). Sorption equilibrium data could be appropriately fitted by the Langmuir model and the maximum adsorption capacity of Pb2+ obtained from Langmuir equation was 151.2 mg/g. Results of X-ray diffraction (XRD) and scanning electron microscopy–energy dispersive spectrum (SEM-EDS) analysis indicated that dissolution and precipitation mechanism predominate...

Estimation of retorted phosphor powder from spent fluorescent lamps by thermal process

The degree of thermal stabilization of phosphor powder from spent fluorescent lamps (SFLs) manufactured by three companies (A, B, C) was estimated by examining mercury content in phosphor powder with retorting time, retorting temperature and rotational speed of drum. Mercury content of phosphor powders from spent fluorescent lamps manufactured by A, B and C companies as samples in thermal experiments was 4031mg/kg, 3522mg/kg and 3172mg/kg, respectively. In the thermal experiments, the optimal conditions for retorting time, retorting temperature, and rotational speed were determined at 6h, 400°C, and 2.0rpm, respectively. With thermal processing at the optimal conditions, mercury content of all samples for retorted phosphor powder was less than 3.0mg/kg, while efficiency of thermal process to control mercury content was higher than 99.9%. Leaching tests such as Toxicity Characteristic Leaching Procedure (TCLP) and Korea Extraction Test (KET) were subsequently carried out to verify if retorted phosphor powder is hazardous waste. Leaching concentrations of mercury for all samples of retorted phosphor powder were satisfied with regulatory levels in both leaching tests. Hence, retorted phosphor powders at the optimal conditions are considered to be non-hazardous wastes.

Leaching potential of silver from nanosilver-treated textile products.

The use of nanosilver as an antibacterial agent for various products has increased, especially so, in textiles. This study aims to investigate the potential of Ag to leach from commercial products which contain nano-Ag by using the toxicity characteristic leaching procedure (TCLP) test in accordance with USEPA method 1311. Eight nano-Ag products were purchased from the market. Only those products that are likely to be disposed of in a landfill after end use were selected. Nano-Ag fabrics of different concentrations were also prepared at the laboratory scale, and the TCLP test was performed on them as well. The current study assumes that the new products were discarded without use. The Ag content was quantified by inductively coupled plasma-mass spectroscopy (ICP-MS) and ranged from 0.95 to 2.82μg/g of the product in the commercial products and from 1.49 to 350μg/g of the product in the lab-prepared fabrics. In the TCLP test results, Ag concentrations ranged from 4.3 to 64.9μg/L in the commercial products and from 28.9 to 28,381μg/L in the lab-prepared fabrics. The results also indicate that the amount of Ag released depends on the type of the fabrics. Additionally, the size of the nano-Ag released in percentage is different for each prepared fabric. This study can help in understanding the amount of Ag released during the disposal phase of a product in a landfill.

Valorization of Industrial Wastes for the Production of Glass–Ceramics

In the present experimental study, the valorization potential of various industrial wastes, namely fly ash, red mud and ferronickel slag was investigated for the production of CaO–Al2O3–Fe2O3–SiO2 glass–ceramics. Glass was first produced in alumina crucibles at 1300 and 1500 °C and then cast in stainless steel moulds. After cooling, glass was pulverized, uniaxially pressed at 60 MPa and used for the production of glass–ceramics in the form of disks. The chemical composition of glass and the sintering temperature affected the properties, namely microstructure, porosity, compressive strength, Vickers microhardness and linear thermal expansion coefficient of the produced glass–ceramics. The leaching potential of hazardous elements present in glass–ceramics was investigated with the Toxicity Characteristics Leaching Procedure test, their chemical stability was evaluated through immersion of specimens in distilled water, simulated acid rain solution and seawater for a maximum period of 1 month, while their structural integrity was assessed according to ASTM standard C1262-10. Several analytical techniques, namely X-ray Diffraction, Scanning Electron Microscopy, Differential Thermal Analysis and Fourier Transform Infrared Spectroscopy (FTIR) were used to provide insights on the microstructure of the produced glass–ceramics.

Stabilizing lead bullets in shooting range soil by phosphate-based surface coating

Soil lead (Pb) is well known as a threat to human health and ecosystem. Although relatively insoluble, lead bullets in shooting range soil can be readily released into soluble forms through natural weathering processes and thus pose significant human and environmental risks. In this study, laboratory experiments were conducted to investigate if the Pb bullets in shooting range soil can be stabilized through surface coating of phosphate-based materials. Results indicated that FePO 4 or AlPO 4 coatings, insoluble metal phosphates, have been successfully formed on the surface of the Pb bullets. The EPA Toxicity Characteristic Leaching Procedure (TCLP) test showed that FePO 4 or AlPO 4 surface coating would effectively reduce the Pb solubility or leachability of the bullets. The surface coating under pH of 4 coating and 77–98% by AlPO 4 coating as compared with the non-coating. Leachable Pb concentration in the contaminated shooting range soil was reduced by 85–98% or 77–98% as a result of the FePO 4 or AlPO 4 solution treatment. This study demonstrated that the FePO 4 or AlPO 4 –based surface coating on lead bullets can effectively inhibit the Pb weathering and significantly reduce the Pb release from soil through in situ chemical stabilization, which could be potentially applicable as a cost-effective and environmental-sound technology for the remediation of Pb-contaminated shooting range soil.

Stabilization and solidification of electric arc furnace dust originating from steel industry by using low grade MgO

Abstract In this study, solidification/stabilization (S/S) of electric arc furnace dust (EAFD) which is generated during the production of steel from scrap metals and classified as hazardous waste were investigated by using different ratios of cement and low grade MgO (LG MgO) as binding agents. Type I PC 42.5 R portland cement and LG MgO which contains 70–80% MgO were used. S/S blocks that contain different ratios of binding agents which have 1/0.5 – 1/1 – 1/2 – 1/3 – 1/4 – 1/5 cement/LG MgO ratio and S/S blocks which contain only cement and no LG MgO agents were prepared. These blocks, which contain 3 different waste ratios according to weight, 20%, 30% and 40% respectively, were produced and exposed to 28-day water purification. At the end of the purification process, S/S blocks were extracted using TCLP (Toxicity Characteristic Leaching Procedure) tests in order to determine the leaching behavior of Zn, Pb, and Cd in S/S blocks. By the end of this study, it was concluded that the recovery of EAFD is possible and applicable by immobilization. The findings of the study concluded that environmental performances or structural properties of blocks contain 30% waste by weight are suitable. This method is a proper one for recovering and treatment of EAFD with mixture of cement and LG MgO.

UTILIZATION OF SUGARCANE BAGASSE ASH FOR STABILIZATION / SOLIDIFICATION OF LEAD-CONTAMINATED SOILS

Recently, many researchers are interested in using agricultural waste as an additive to remediate the contaminated soils. In this study, the effectiveness of sugarcane bagasse ash (SCBA) as the substitution binder to Ordinary Portlant Cement (OPC) content in Stabilization/Solidification (S/S) method was investigated through the physical and chemical characteristics namely the Unconfined Compressive Strength (UCS) and Toxicity Characteristic Leaching Procedure (TCLP). Synthetic contaminated soil was prepared in bulk by mixing soil samples with lead nitrate to achieve the concentration of 500 ppm. The OPC and SCBA varying from 5 % to 20 % were added to stabilize and solidify the contaminated soils. The cylindrical specimens (D = 38 mm, H = 76 mm), was compacted in five layers with 50 blows each. A further 3, 7, 14 and 28 days were allowed for curing in the temperature 25±2 ◦C and humidity &gt; 80%. Results indicate that all samples containing OPC and SCBA satisfy the US EPA strength requirement of 0.35 MPa for S/S sample. The TCLP testing shows that sample containing OPC with SCBA has been successful treated which produced the leachability below US EPA limit for lead of 5 mg/L. In conclusion, the use of SCBA as part of replacement of OPC has been successful in increasing the strength and reducing the leachability compared to untreated sample.

Subcritical water treatment of explosive and heavy metals co-contaminated soil: Removal of the explosive, and immobilization and risk assessment of heavy metals

Co-contamination of explosives and heavy metals (HMs) in soil, particularly army shooting range soil, has received increasing environmental concern due to toxicity and risks to ecological systems. In this study, a subcritical water (SCW) extraction process was used to remediate the explosives-plus-HMs-co-contaminated soil. A quantitative evaluation of explosives in the treated soil, compared with untreated soil, was applied to assess explosive removal. The immobilization of HMs was assessed by toxicity characteristic leaching procedure tests, and by investigating the migration of HMs fractions. The environmental risk of HMs in the soil residue was assessed according to the risk assessment code (RAC) and ecological risk indices (Er and RI). The results indicated that SCW treatment could eliminate the explosives, >99%, during the remediation, while the HM was effectively immobilized. The effect of water temperature on reducing the explosives and the risk of HMs in soil was observed. A marked increase in the non-bioavailable concentration of each HM was observed, and the leaching rate of HMs was decreased by 70–97% after SCW treatment at 250 °C, showing the effective immobilization of HMs. According to the RAC or RI, each tested HM showed no or low risk to the environment after treatment.

Cadmium telluride leaching behavior: Discussion of

Zeng et al. (2015) evaluate the leaching behavior and surface chemistry of II–VI semiconductor materials, CdTe and CdSe, in response to pH and O2. Under agitation in acidic and aerobic conditions, the authors found approximately 3.6%–6.4% (w/w) solubility of Cd content in CdTe in the Toxicity Characteristic Leaching Procedure (TCLP), Waste Extraction Test (WET), and dissolution test, with lower solubility (0.56–0.58%) under agitation in acidic and anoxic conditions. This range is comparable with prior long-term transformation and dissolution testing and bio-elution testing of CdTe (2.3%–4.1% w/w solubility of Cd content in CdTe). The implications for potential leaching behavior of CdTe-containing devices require further data. Since CdTe PV modules contain approximately 0.05% Cd content by mass, the starting Cd content in the evaluation of CdTe-containing devices would be lower by three orders of magnitude than the starting Cd content in the authors’ study, and leaching potential would be further limited by the monolithic glass-adhesive laminate-glass structure of the device that encapsulates the semiconductor material. Experimental evaluation of leaching potential of CdTe PV modules crushed by landfill compactor has been conducted, with results of TCLP and WET tests on the crushed material below regulatory limits for Cd. CdTe PV recycling technology has been in commercial operation since 2005 with high yields for semiconductor (95%) and glass (90%) recovery.

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 96h 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 18h 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.

Evaluating the cement stabilization of arsenic-bearing iron wastes from drinking water treatment

Cement stabilization of arsenic-bearing wastes is recommended to limit arsenic release from wastes following disposal. Such stabilization has been demonstrated to reduce the arsenic concentration in the Toxicity Characteristic Leaching Procedure (TCLP), which regulates landfill disposal of arsenic waste. However, few studies have evaluated leaching from actual wastes under conditions similar to ultimate disposal environments. In this study, land disposal in areas where flooding is likely was simulated to test arsenic release from cement stabilized arsenic-bearing iron oxide wastes. After 406 days submersed in chemically simulated rainwater, <0.4% of total arsenic was leached, which was comparable to the amount leached during the TCLP (<0.3%). Short-term (18h) modified TCLP tests (pH 3–12) found that cement stabilization lowered arsenic leaching at high pH, but increased leaching at pH<4.2 compared to non-stabilized wastes. Presenting the first characterization of cement stabilized waste using μXRF, these results revealed the majority of arsenic in cement stabilized waste remained associated with iron. This distribution of arsenic differed from previous observations of calcium–arsenic solid phases when arsenic salts were stabilized with cement, illustrating that the initial waste form influences the stabilized form. Overall, cement stabilization is effective for arsenic-bearing wastes when acidic conditions can be avoided.

Evaluation of the encapsulation of nickel, chromium and lead-rich wastes in cement matrices by TCLP test

This study focuses on the characterisation of industrial waste coming from an Algerian factory of cutlery and the feasibility of its solidification/stabilisation (S/S) using hydraulic binders. Toxicity characteristic leaching procedure (TCLP) test, XRD and SEM–EDX analyses performed on the raw waste show that the latter has a high potential pollutant due to the presence of heavy metals such as “nickel, trivalent chromium, hexavalent chromium and lead” in high concentrations. Therefore, its S/S by cement seems to be a solution of its storage. For the study of its feasibility, two types of mix design were used with different waste/cement ratios. The initial and final setting times were evaluated for cement pastes. The mechanical strengths were evaluated at 7 and 28 days. Solidified/stabilised materials were submitted to TCLP test after 7 and 28 days. The leachates were analysed by flame atomic absorption spectrophotometry. XRD and SEM–EDX analyses were used to characterise the solidified/stabilised materials compounds. TCLP results highlight the efficiency of S/S treatment by reducing the pollutant potential of the waste. TCLP results show that mortars have a better efficiency in encapsulation pollutants compared to cement pastes, due to the difference in microstructure network between the two materials and the particle size of the waste.

Hydrometallurgical recovery of heavy metals from low grade automobile shredder residue (ASR): An application of advanced Fenton process (AFP)

To investigate the leaching and recovery of heavy metals from low-grade automobile shredder residue (ASR), the effects of nitric acid (HNO3) and hydrogen peroxide (H2O2) concentrations, liquid/solid (L/S) ratio, leaching temperature and ASR particle size fractions on the heavy metal leaching rate were determined. The heavy metals were recovered by fractional precipitation and advanced Fenton process (AFP) at different pHs. The toxicity characteristic leaching procedure (TCLP) test was also performed in the residue remaining after heavy metal leaching to evaluate the potential toxicity of ASR. The heavy metal leaching efficiency was increased with increasing HNO3 and H2O2 concentrations, L/S ratio and temperature. The heavy metal leaching efficiencies were maximized in the lowest ASR size fraction at 303 K and L/S ratio of 100 mL/g. The kinetic study showed that the metal leaching was best represented by a second-order reaction model, with a value of R2 > 0.99 for all selected heavy metals. The determined activation energy (kJ/mol) was 21.61, 17.10, 12.15, 34.50, 13.07 and 11.45 for Zn, Fe, Ni, Pb, Cd and Cr, respectively. In the final residue, the concentrations of Cd, Cr and Pb were under their threshold limits in all ASR size fractions. Hydrometallurgical metal recovery was greatly increased by AFP up to 99.96% for Zn, 99.97% for Fe, 95.62% for Ni, 99.62% for Pb, 94.11% for Cd and 96.79% for Cr. AFP is highly recommended for the recovery of leached metals from solution even at low concentrations.

Iron oxide-modified nanoporous geopolymers for arsenic removal from ground water

Abstract Composite materials of hierarchically porous geopolymer and amorphous hydrous ferric oxide were produced and characterized as a new potentially cost-effective arsenic adsorbent. The arsenic removal capabilities of the iron (hydr)oxide (HFO) media were carried out using batch reactor experiments and laboratory scale continuous flow experiments. The Rapid Small-Scale Column Tests (RSSCT) were employed to mimic a scaled up packed bed reactor and the toxicity characteristic leaching procedure (TCLP) test of arsenic adsorbed solid material was carried out to investigate the mechanical robustness of the adsorbent. The best performing media which contained ~20 wt% Fe could remove over 95 µg of arsenic per gram of dry media from arsenic only water matric. The role of the high porosity in arsenic adsorption characteristics was further quantified in conjunction with accessibility of the adsorption sites. The new hierarchically porous geopolymer-based composites were shown to be a good candidate for cost-effective removal of arsenic from contaminated water under realistic conditions owing to their favorable adsorption capacity and very low leachability.

Recycling flue gas desulphurization (FGD) gypsum for removal of Pb(II) and Cd(II) from wastewater

The present study aims to verify the feasibility of directly reusing the flue gas desulphurization (FGD) gypsum generated from coal-fired power plants to adsorptively remove Pb(II) and Cd(II) from wastewater. The Toxicity Characteristic Leaching Procedure (TCLP) test was conducted to evaluate the leachability of toxic heavy metals from FGD gypsum. The adsorption behaviors of FGD gypsum for Pb(II) and Cd(II) such as pH impact, sorption kinetics, sorption isotherms and sorption thermodynamics were studied in a series of batch experiments. The pH studies indicated that the adsorption of Pb(II) and Cd(II) had their best adsorption amounts both at the pH values from 5.0 to 7.0. The kinetic analysis displayed that the adsorption processes both followed the pseudo-second order model well, and the FGD gypsum provided a higher sorption rate for Pb(II). Equilibrium studies showed that the adsorption of Pb(II) and Cd(II) could be properly described by Langmuir isotherms model, and the predicted maximum adsorption capacities were even greater than some specially prepared adsorbents. The thermodynamic investigation confirmed that the removal of Pb(II) and Cd(II) from aqueous medium could carry out spontaneously, and the higher temperature favored the processes. The instrument analysis techniques were also employed to deeply understand the mechanism involved in Pb(II) and Cd(II) removal by FGD gypsum. Overall, good sorption performance together with cost-effective characteristic makes FGD gypsum potentially attractive material for the Pb(II) and Cd(II) removal in industrial wastewater.

Evaluating Solidification Characteristics of Textile Dyeing Sludge with Addition of Portland Cement and Attapulgite

Cement-based solidification/stabilization (S/S) has been considered as an effective method to deal with hazardous wastes such as textile dyeing sludge. In this study, sludge from textile wastewater treatment plant was solidified by Portland cement and attapulgite at different mass ratios (sludge 0.1~0.8, cement 0.1~0.8, attapulgite 0.1~0.8), and the characteristics of the solidified blocks were evaluated. The maximum unconfined compressive strength (UCS) of 15.8 MPa was obtained at 28 d when the mass ratio of attapulgite, sludge and cement was 0.1:0.1:0.8, while in toxicity characteristic leaching procedure (TCLP) test, relatively low concentrations of COD (100~150mg/L) in the leachate were found when the mass ratio was set to 0.3:0.1:0.6. Results of XRD and SEM/EDS indicated the existence of calcium silicate hydrate (CSH) in the solidified blocks. ANOVA results proved that the quadratic model could be utilized to characterize the relationship between COD of the leachate and the components in the mixture.

Clay stabilization using coal waste and lime — Technical and environmental impacts

This study evaluates the technical and environmental effects of coal waste materials on the stabilization of a medium plastic clay. The coal waste was used in its natural state and after igniting at 750°C to produce the coal waste ash. In addition, hydrated lime powder was applied as a traditional stabilizer. Atterberg limits, California bearing ratio (CBR) in dry and saturated condition along with swelling and unconfined compressive strength tests were carried out. Soil structural changes during the curing period were analyzed using the X-ray diffraction and scanning electron microscope (SEM) tests. About the environmental issue, toxicity characteristic leaching procedure (TCLP) test was carried out to analyze the leachate obtained from different studied samples for heavy metal concentrations. Based on the CBR and compressive strength tests, the addition of coal waste powder and its ash to some extent enhanced the soil bearing capacity. However, the combination of these additives with lime resulted in considerably higher compressive strength and CBR especially in saturated condition. The results of X-ray diffraction and SEM analyses indicated substantial changes in the soil structure after adding the additives. The initial structure of the soil was porous and flaky which transformed to a solid and coherent structure after treating with the combination of coal waste and lime. Concentration of heavy metals in stabilized samples containing the coal waste and its ash was less than the regulatory levels determined for hazardous materials and properly satisfied the minimum requirements.

Diffusion and leachability index studies on stabilization of chromium contaminated soil using fly ash

Experiments were performed to establish a feasible treatment process for the solidification and stabilization (S/S) of soil contaminated by leaching of Cr(VI) from Chromite ore processing residue (COPR). Reduction of the highly mobile Cr(VI) was performed using calcium polysulfide (CaS5) with a dosage of 3 times the molar stoichiometric ratio for the initial concentration of Cr(VI) present in the chromium contaminated soil (CCS). The CCS was solidified and stabilized (S/S) using fly ash (FA) in various proportions i.e., 1:1, 1:2, 1:3 (FA: CCS) with and without using reducing agent i.e., CaS5. Leachability tests such as Toxicity Characteristic Leaching Procedure (TCLP) and semi-dynamic long term leachability tests indicated that the CaS5 was effective in reduction of Cr(VI) followed by the S/S process. Leachability Index was derived from the results of the semi-dynamic long term leachability tests and was between 8 and 9, indicating that FA is an effective treatment for disposal into secured landfills for CCS. The characteristic compressive strength of the CaS5 treated CCS with FA mortar blocks were between 24.47 and 40.49kg/cm2. Considering the cost of CaS5 and FA, a total expenditure of Rs. 7826 i.e., US $ 130.4 would be required for remediation of one tonne of CCS.