Toxicity Characteristic Leaching Procedure Concentrations Research Articles

Removal of heavy metals in water-extracted solution through adsorption by palygorskite and stabilization by comilling.

Removing water-soluble chlorides (WSCs) through water extraction is a common pretreatment technology for recycling municipal solid waste incineration (MSWI) fly ash (FA). However, the extracted solution often contains heavy metals, the concentrations of which exceed standards for effluent. This study aims to investigate the adsorption of heavy metals by palygorskite in water-extracted solution and explore the feasibility of stabilizing heavy metals through comilling palygorskite-adsorbed heavy metals (PAHMs) with water-extracted fly ash (WFA). The experimental parameters include: two-stage water extraction with a liquid-to-solid ratio of 5, adding 0, 0.125, 0.25, 0.5, 1, 2 or 3 g of palygorskite to 100 mL of water-extracted solution, and comilling the mixture of PAHMs and WFA for 0, 0.5, 1, 2, 4, 8, 12, 24 or 96 hours. The experimental results revealed that 3 g of palygorskite in 100 mL of extracted solution could absorb Pb, Cd, Cr, Cu and Zn, meeting the effluent standards. The total amount of Pb, Cd, Cr, Cu and Zn removal rate reached 99.7%. Moreover, 98.44% of the WSCs were not adsorbed, the water extraction process for removing WSCs was not compromised. After the comilling of PAHMs and WFA, the distribution of the heavy metals in the milled blended powder was greater than 99.44%; moreover, toxicity characteristic leaching procedure concentrations were determined to conform to regulatory standards, and the sequential extraction procedure revealed that the heavy metals tended to be in stable fractions. This achieves the goal of preventing secondary pollution from heavy metals during the MSWI FA recycling process.

Characterization, risk assessment, and potential utilization of fly ash from PLTSa Merah Putih at Bantargebang, Bekasi, Indonesia

Municipal solid waste incineration (MSWI) has been adopted in Indonesia to reduce the volume and mass of municipal solid waste. However, as a by-product of waste combustion, fly ash generation cannot be avoided. It can cause an environmental problem if not managed properly. Hence, this study aims to investigate the characteristics of fly ash generated from Indonesia’s first waste-to-energy incineration pilot plant and its potential utilization. Fly ash was characterized using X-Ray fluorescence (XRF), BET surface area measurement, pore size distribution (PSD), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS), and X-ray diffraction (XRD). The characterization results showed that calcium was predominant, around 28%, followed by titanium, silica, iron, and aluminum, with values of 7.10%, 5.70%, 4.40%, and 4.30%, respectively. These results demonstrated that MSW incineration fly ash was classified as a very active high-calcium fly ash. The surface structure of fly ash was flaky and complex, with some irregular material. The particle size distribution of fly ash shows that the diameters of most particles were nearly 12 μm. The specific surface area of fly ash was 3.06 m2/g, the total-pore volume was 0.01 cm3/g, and the average pore size was 11.82 nm. In addition, the environmental risk assessment was evaluated using the toxicity characteristic leaching procedure (TCLP). TCLP concentrations of heavy metals, including arsenic, barium, beryllium, cadmium, chromium hexavalent, copper, lead, mercury, nickel, selenium, and zinc, were lower than the regulatory level, indicating a low environmental risk. Therefore, it has great potential for utilization as a paving block mixture material.

Immobilization of vanadium and nickel in spent fluid catalytic cracking (SFCC) catalysts-based geopolymer

In recent years, the use of spent fluid catalytic cracking (SFCC) catalysts to prepare geopolymers has received attention from academic and industrial circles. However, SFCC catalysts have been classified as hazardous waste in China due to their vanadium and nickel content. In this paper, the immobilization rates of vanadium and nickel in geopolymers prepared with SFCC catalysts were studied through a toxicity characteristic leaching procedure (TCLP). The immobilization mechanism of nickel and vanadium during geopolymerization was investigated by XPS, SEM, XRD, and compressive strength measurements. The nickel and vanadium TCLP concentrations of the SFCC catalyst-based geopolymer are 0.032 mg/L and 10.63 mg/L, respectively. Nickel in the SFCC catalyst is partly dissolved and adsorbed by the negatively charged tetrahedral aluminum in the geopolymer. However, because vanadates formed under alkaline conditions are negatively charged and readily soluble in water, vanadium in the SFCC catalyst is neither immobilized by the charge balance nor effectively immobilized by physical encapsulation. Therefore, the use of SFCC catalysts to prepare geopolymers will lead to vanadium contamination in the environment. In order to clarify the maximum vanadium content in SFCC catalysts for preparing geopolymers without environmental risk, SFCC catalysts with different vanadium levels were prepared by leaching. It was concluded that when the vanadium content in the SFCC catalyst is lower than 1861.4 mg/kg, the vanadium content in the leachate is lower than 2 mg/L and the geopolymer can be considered a non-hazardous material.

Characteristics of MSWI fly ash with acid leaching treatment

The chemical and mineralogical characteristics of fly ash from a municipal solid waste incineration (MSWI) in China and the influence of processing parameters on heavy metals removal during leaching were investigated in this work. The fly ash particles had complex surface structure with limited specific surface area. The alkali chloride and metal salts in MSWI fly ash showed evidently impact on leaching efficiency. Metal leachability was related to their properties and speciation in fly ash. Water-soluble salts such as KCl, NaCl and CaCl2 in fly ash were easily washed out. In this study, removal efficiency by water washing was achieved to 93.1% for Cl, 41.4% for Na, 48.5% for K and 24.8% for Ca, respectively. Mineralogical analysis also revealed change of fly ash mineral phases and specification distribution after water washing. Under liquid to solid ratio of 40:1 L/kg and treatment time of 120 min, the leaching process achieved high dropping yields of toxicity characteristic leaching procedure (TCLP) concentrations for Cu, Zn Cd and Pb (80%–100%), moderate dropping yields for As (30%–80%) and relatively low dropping yields of Ni (< 30%). In addition, heavy metals such as Pb and Zn in fly ash with twice water washing treatment at a low liquid-solid ratio could reach lower TCLP concentrations. The result indicated that the combination process of twice water washing and one acid washing could significantly reduce the environmental risk of MSWI fly ash.

POTENTIAL MOBILITY AND TOXICITY RISK OF METAL POLLUTANTS IN SOILS FROM A TROPICAL AREA AFFECTED BY INDUSTRIAL WASTES

The potential mobility of Cd, Cr, Cu, Ni, Pb and Zn in soils severely impacted by inadequate storage of industrial wastes in Rio de Janeiro State (Brazil) was evaluated by applying the Toxicity Characteristic Leaching Procedure (TCLP). This procedure allowed the estimation of toxicity risks for Cd, Cr and Pb. In a contamination hotspot within the study area, the following order of metal concentrations was observed: Pb > Zn > Cu > Ni > Cd > Cr, with significantly higher values than observed for a control site. Decades of soil exposure to wastes implied TCLP results for Pb above 300 mg/L in this hotspot, which exceed the TCLP regulatory threshold in two orders of magnitude, while Cd (up to 0.8 mg/L) and Cr (up to 0.3 mg/L) results were below the respective TCLP thresholds. Surface soil profile analysis (0-30 cm depth) indicates that Pb vertical migration occurs in the hotspot. TCLP concentrations of Pb were up to four orders of magnitude higher than the groundwater quality threshold preconized by Brazilian regulations for this metal (0.01 mg/L), suggesting that downward dispersion of large loadings of anthropogenic Pb is a major concern.

Carbonation based leaching assessment of recycled concrete aggregates

The leaching characteristics of seven different recycled concrete aggregates (RCA) samples derived from building demolition waste, concrete pavement, stockpiled, and freshly crushed concrete were evaluated focusing on the effects of carbonation, liquid-to-solid ratio (L/S), and particle sizes. Batch water leach test (WLT), toxicity characteristic leaching procedure (TCLP), and synthetic precipitation leaching procedure (SPLP) were performed to assess the pH, electrical conductivity (EC), alkalinity, and the leached concentrations of Ba, Ca, Cr, Mg, and SO4 in RCA effluent. The leaching efficiency of the test methods at different RCA carbonation levels was also evaluated. Results indicated that the effluent pH, EC, and alkalinity decreased, while the leached fractions of elements increased with an increase in L/S ratio. An increase in calcium carbonate content tended to increase the leaching of Mg, Cr, and SO4. For highly carbonated RCA samples, effluent pH, EC, alkalinity, and Ca concentrations were higher for particle sizes of 1.19 mm–0.149 mm, while fresher RCA samples resulted in higher values from particles finer than 0.149 mm. Carbonated RCA samples leached higher Ca, Mg, and Ba in TCLP, whereas the maximum concentrations of Cr and SO4 were found in WLT effluent. For less carbonated RCA samples, Ca concentrations in WLT and TCLP effluents were comparable, SPLP leached higher amounts of Mg, Ba concentrations were maximum in WLT, and TCLP concentrations of Cr and SO4 were the most critical ones. TCLP alkalinity increased, whereas WLT and SPLP alkalinity decreased with an increase in calcium carbonate content of the RCA.

Critical analysis and valorization potential of battery industry sludge: Speciation, risk assessment and metal recovery

Lime treated battery wastewater sludge (BWS) was collected, characterized to assess the heavy metal fractions, safe disposal potential, and possible valorization through the Community Bureau of Reference (BCR) scheme, Toxicity Characteristic Leaching Procedure (TCLP), diethylenetriaminepentaacetic acid (DTPA) test, risk assessment, and progressive acidification. In the first place, BWS was found to be a potential building material for construction, fortified by spectroscopic studies. Total metal analysis showed that the BWS was highly contaminated with Pb, Fe, Zn, Cu, and Cd with concentration of 8322 ± 11, 15721 ± 21, 310 ± 2, 175 ± 4, and 1215 ± 7 mg/kg, respectively. Physical segregation of BWS particles in <10, 10–45, 45–75, and >75 μm size showed that the heavy metals were more concentrated in the finer fractions and, only 5% were present in coarse fraction. BCR extractions showed that the order of prominence in the exchangeable fraction was as Al > Ca > Cu > Ni > Zn > Mn > Mg > Co > Pb > Cd > Fe, whereas, Fe, Mn, and Zn were abundant in the reducible fraction. Pb (67%) and Cu (55%) showed the highest percentage in the oxidizable fraction and, Mg and Zn were mostly present in the residual form. The TCLP concentrations for Pb and Cd exceeded the prescribed standards and toxicity indices classified BWS as a hazardous waste with very high-risk for land disposal. Valorization of sludge was conducted through progressive acidification using five different acids. Citric acid showed the best metal recovery potential of 47, 77, 60, 19, 58, 59, 67, 41, and 51% for Pb, Fe, Cu, Cd, Ni, Mn, Al, Co, and Zn but the kinetics of metals leaching was slow. H2O2 further improved metal recovery mobilizing organically bound metals mediated through the formation of HO• radicals.

Synthesis of structural binder for red brick production based on red mud and fly ash activated using Ca(OH)2 and Na2CO3

This paper explored the effectiveness of red mud and a mixture powder of Ca(OH)2 (C), Na2CO3 (N), and fly ash (F) (denoted CNF powder) as precursor materials to produce an environment-friendly high strength brick product. Overall, despite the inclusion of up to ∼81% of red mud and fly ash, 7-day strengths were developed ∼17–34MPa; this was high enough to be used as a structural binder for brick production. In particular, the use of NaOH was very effective in increasing flowability, and, more importantly, early strength in the red mud-CNF blended system, despite the red mud inclusion, because NaOH greatly improved the degree of reaction of the system, resulting in more calcium silicate hydrates (C-S-H) formation as well as significant pore size refinement at early days of curing. Trial bricks were also prepared to examine possible toxicity due to the inclusion of red mud and fly ash using the toxicity characteristic leaching procedure (TCLP) test and the TCLP concentrations were very low.

Utilization of phosphorus loaded alkaline residue to immobilize lead in a shooting range soil

The alkaline residue generated from the production of soda ash using the ammonia-soda method has been successfully used in removing phosphorus (P) from aqueous solution. But the accumulation of P-containing solid after P removal is an undesirable menace to the environment. To achieve the goal of recycling, this study explored the feasibility of reusing the P loaded alkaline residue as an amendment for immobilization of lead (Pb) in a shooting range soil. The main crystalline phase and micromorphology of amendments were determined using X-ray diffraction (XRD) and scanning electron microscopy-electron dispersion spectroscopy (SEM-EDS) methods. The toxicity characteristic leaching procedure (TCLP), sequential extraction procedure, and physiologically based extraction test (PBET) were employed to evaluate the effectiveness of Pb immobilization in soil after 45 d incubation. Treatment with P loaded alkaline residue was significantly effective in reducing the TCLP and PBET extractable Pb concentrations in contrast to the untreated soil. Moreover, a positive change in the distribution of Pb fractions was observed in the treated soil, i.e., more than 60% of soil-Pb was transformed to the residual fraction compared to the original soil. On the other hand, P loaded amendments also resulted in a drastic reduction in phytoavailable Pb to the winter wheat and a mild release of P as a nutrient in treated soil, which also confirmed the improvement of soil quality.

Evaluation of Leaching Protocols for Testing of High-Carbon Coal Fly Ash–Soil Mixtures

Beneficial reuse of coal combustion byproducts, e.g., in highway construction, requires an evaluation of metal leaching potential. Metal leaching from high-carbon fly ash in soil mixes typical of highway embankment construction was evaluated using different soil-fly ash mixtures and three common leaching tests: the water leach test (WLT), the Toxicity Characteristic Leaching Procedure (TCLP), and the column leach test (CLT). The effect of test methodology and pH on Cu, As, and Cr leaching was examined. TCLP concentrations for Cu and As exceeded those from WLTs in the majority of mixtures due to lower pH conditions, while Cr was higher in the WLT for alkaline fly ash mixtures. Maximum CLT concentrations were higher than TCLP and WLT concentrations for the majority of mixtures, but usually decreased rapidly, suggesting that leachate concentrations might initially exceed regulatory limits, but only for a short time. A comparison of leaching results is discussed as a framework for the development of a flexible, integrated leaching protocol incorporating elements of batch and column leach tests to provide more accurate, site-specific leaching predictions given time and cost constraints. DOI: 10.1061/(ASCE)EE .1943-7870.0000668. © 2013 American Society of Civil Engineers. CE Database subject headings: Fly ash; Chromium; Copper; Arsenic; Coal; Soils; Mixtures; Recycling. Author keywords: Leaching; Fly ash; Batch leach test; Column leach test; Chromium; Arsenic; Copper.

Application of Reutilization Technology to Calcium Fluoride Sludge from Semiconductor Manufacturers

ABSTRACT Glass ceramics were prepared from mixtures of wastes generated from refining of waste glass and semiconductor industrial wastewater sludge. The aim is then indeed to study the possible use and effects of integrating calcium fluoride (CaF2) as present in semiconductor wastewater sludge in the silica (glass) melts. CaF2 sludge was blended with a conditioner according to characteristics of the target. Calcium oxide-silicon dioxide-aluminum oxide system glass ceramics have relatively high melting points. Addition of CaF2 sludge to fluxes can significantly reduce the melting point and hence improve the kinetics of the reactions. CaF2 sludge and waste glass were co-melted in various ratios to elucidate their interactions at various heating temperatures. The results indicate that the lowest melting temperature was 1163 °C, obtained for the CaF2 sludge-waste glass mixture at a ratio 6:4 (wt:wt), which is significantly lower than that of CaF2 sludge (1378 °C). The benefits of using melting to dispose of sludge are the reduction of waste and the fixation of heavy metals. Heat treatment was used to convert the obtained glass into glass ceramics. Heavy metal leaching tests revealed that melting conditions lowered the heavy metal concentrations in the leachate to an order of magnitude lower than that in the sludge. Consequently, industrial sludge can be safely used as a fine aggregate material for a potentially wide range of construction applications. IMPLICATIONS The semiconductor industrial wastewater sludge presented in this paper contains a large amount of CaF2 and heavy metal, but its toxicity characteristic leaching procedure concentration met the Taiwan Environmental Protection Administration's current regulatory thresholds. Therefore, the reutilization of the waste products of the semiconductor industry as construction materials is feasible.

Performance of Reactive Powder Concrete Containing Arsenic

A mixture of arsenic contaminated soil and reactive powder concrete (RPC) was developed to study the effect of arsenic contaminated soil on RPC mortar and the effectiveness of the mortar in containing the contaminant. The sufficient containment of arsenic contaminated waste products is important to protection of ground and surface water sources. A three phase experiment was designed to study the permeability, absorption coefficients, and Toxicity Characteristic Leaching Procedure (TCLP) leachate concentrations resulting from the application of a range of arsenic concentrations. The results showed that the permeability values for mixes containing different arsenic concentrations did not increase noticeably with adequate curing time. The percentage of absorption slightly increased with increasing arsenic content as did the TCLP leachate concentrations. Statistical analyses, Analysis of Variance (ANOVA) and Paired T-test, were performed to analyze percent absorption, and TCLP results. Based on the results it was concluded that percent absorption decreased significantly with increase in curing time. Although, the TCLP concentrations increased with increased curing time, the increase was not statistically significant.

The fate of Cu, Zn, Pb and Cd during the pyrolysis of sewage sludge at different temperatures

In the present study, a sequential extraction procedure, recommended by the Community Bureau of Reference (BCR), was used for the fractionation of the heavy metals Cu, Zn, Pb and Cd in sewage sludge and its residues produced after pyrolysis at different temperatures from 250 to 700 °C. The results show that, in the sludge sample, the sum of the percentages of the reducible and oxidizable fractions for all metals except Cu was very high (65.4% for Cd, 85.7% for Pb, 78.7% for Zn), whereas the sum of the percentages of the oxidizable and residual fractions for Cu was very high (88.8%). The same result could be attained in the residues. Statistical analysis shows that at low temperatures the variation in pyrolysis temperature did not effectively contribute to the distribution of metal speciation in the residues. Meanwhile a modified Toxicity Characteristic Leaching Procedure (TCLP) was employed to determine the leachability of these four metals. The result indicates that the TCLP concentration of Cu, Zn, Pb and Cd dropped sharply after the temperature reached 350 °C, 550 °C, 500 °C and 400 °C respectively, which means pyrolysis can enhance the stability of these four metals when the temperature is high enough.

Effect of Cu species on leaching behavior of simulated copper sludge after thermal treatment: ESCA analysis

The aim of this study is to evaluate the efficiency of thermal treatment on residual copper sludge after separation treatment. The toxicity characteristic leaching procedure (TCLP) concentration, pattern distribution and possible Cu species of simulated copper sludge were analyzed. Parameters such as different reaction time and temperature are also discussed in this study. The TCLP leaching results showed that the TCLP concentration of Cu in thermally treated simulated copper sludge decreased ( T = 900 °C) as the reaction time increased to 4 h. The sequential extraction results showed that the main fraction of raw simulated copper sludge was carbonate. When temperatures were 500 and 700 °C, the main fraction of thermally treated simulated copper sludge was also carbonate. The percentage of Fe–Mn oxides and residue increased when T = 900 °C. Electron Spectroscopy for Chemical Analysis (ESCA) showed that the possible Cu species of raw simulated copper sludge was Cu(OH) 2. The main possible Cu species of thermally treated simulated copper sludge were CuO and Cu 2O when T was 500 and 700 °C, respectively. CuO, Cu 2O, and Cu 3O 2 were the possible Cu species in thermally treated simulated copper sludge when T = 900 °C.

Investigation of permeability and leaching of hot mix asphalt concrete containing oil-contaminated soils

Oil-contaminated soil (OCS) results from leaking underground storage tanks, oil spills on clean soils, or soils surrounding petroleum refineries and crude oil wells. In Oman, Petroleum Development Oman (PDO) generates more than 50,000ton/year of oil-contaminated soil. Recycling of OCS can be considered a viable solution to the disposal problem. This paper presents the results of investigating the permeability and leaching of asphalt concrete mixes containing OCS. Two types of soil were obtained from an asset area in northern Oman. Physical and chemical characterizations were performed on the OCS. The two soils were used as a replacement of fine aggregate in the asphalt concrete mix with percentages up to 40%, by total aggregate weight. Mixes were designed using the Marshall mix design method. Optimum asphalt contents were determined and samples were prepared at these asphalt contents and tested for permeability using a flexible-wall permeameter. Environmental assessment was performed by subjecting the mixes to the Toxicity Characteristic Leaching Procedure (TCLP) and analyzing the extract for heavy metals. The permeability was found to decrease with the addition of OCS. A significant decrease resulted when the percentage of OCS was increased to 30%. The leaching tests from the mix indicated that TCLP concentrations of the selected heavy metals were well below the TCLP regulatory limits for all OCS mixes.

Investigation of Barium Treatment of Chromite Ore Processing Residue (COPR) 031

Abstract Barium addition to chromite ore processing residue (COPR) was investigated in order to address (a) the pronounced heaving phenomena that are associated with mainly the presence of ettringite and (b) hexavalent chromium leaching. Sulfate was added to representative samples of grey-black (GB) and hard-brown (HB) COPR to simulate worst-case conditions of sulfate influx and ettringite formation. Both the X-ray powder diffraction (XRPD) and the modeling results showed that ettringite is a thermodynamically favored reaction in COPR. The subsequent addition of barium lead to the formation of both barite and barium chromate, observed as solid solution between the two phases. Modeling results confirmed that barium sulfate is the more stable species that will dissolve ettringite and that barium chromate will also dissolve COPR chromate phases when sulfate is depleted. The Toxicity Characteristic Leaching Procedure (TCLP) test on GB samples showed that the optimal stoichiometry to maintain Cr and Ba TCLP concentrations below the U.S. Environmental Protection Agency regulatory limit of 5 and 100 ppm, respectively, lies between 1:1 (Ba to sulfate plus chromate ratio) and 1.5:1. The respective optimal stoichiometry for the HB COPR was found to be higher, between 2:1 and 5:1. Considering that COPR is actually a Cr-contaminated cement form, a further area of research is the identification of barium-containing wastes (i.e., heavy-metal sludges, contaminated soils, etc.) that would be suitable for combination with COPR; in this way, an environmentally sustainable yet cost-effective treatment application can be realized.

Preservative leaching from weathered CCA-treated wood

Disposal of discarded chromated copper arsenate (CCA)-treated wood in landfills raises concerns with respect to leaching of preservative compounds. When unweathered CCA-treated wood is leached using the toxicity characteristic leaching procedure (TCLP), arsenic concentrations exceed the toxicity characteristic (TC) limit of 5 mg/L in most cases. The majority of discarded CCA-treated wood, however, results from demolition activities, where the wood has typically been subjected to weathering. Since preservatives do migrate from the wood during its normal use, leaching characteristics of weathered and aged CCA-treated wood may differ from unweathered wood. To evaluate this, CCA-treated wood removed from service after various degrees of weathering was collected from multiple sources and leached with the TCLP, the synthetic precipitation leaching procedure (SPLP) and California's waste extraction test (WET). Five to seven individual pieces of wood were analyzed from each source. The average TCLP arsenic concentration for the 14 sources ranged from 3.2 to 13 mg/L. The average TCLP concentrations of the 100 wood pieces tested were 6.4, 5.9 and 3.2 mg/L for arsenic, copper and chromium, respectively. Overall, in 60 out of 100 samples tested by the TCLP, arsenic concentrations exceeded 5 mg/L (the TC regulatory value). SPLP leachate concentrations were similar to TCLP concentrations, although copper leached somewhat more with the TCLP. WET leachate concentrations were approximately a factor of 10 higher than TCLP concentrations. Discarded CCA-treated wood, even after exposure to years of weathering, often exceeds the TC limit for arsenic and without the current regulatory exemption would possibly require management as a TC hazardous waste in the US.

Investigations of ash topography/morphology and their relationship with heavy metals leachability

The leachability of heavy metals such as chromium (Cr), lead (Pb) and cadmium (Cd) from the ash material obtained from waste combustion was studied. The effects of ash surface topography and morphology on the leachability of these elements were examined using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM (scan size 10×10 μm) and SEM images of the simulated ash pellet obtained at various operating temperatures (1000, 1400 and 1500°C) showed significant microstructural and topographical changes. Ash pellets treated at 1000°C contain porous and non-continuous surface. On the other hand, the ash pellet obtained at higher temperature (1500°C) was found to contain a smooth, continuous and non-porous surface. The AFM height profile studies indicated that the top surface variation of the ash pellet at 1000, 1400 and 1500°C were found to be −40.0 to 25.5, −3.7 to 4.7 and −0.10 to 0.66 nm respectively. The SEM analyses also confirmed the presence of smooth, non-porous outer surface of ash formed at 1500°C. In addition, it also showed the presence of compact and rigid interior for the same ash pellet. The leachability of the heavy metals was determined using standard toxicity characteristic leaching procedure (TCLP) test and the samples were analysed using atomic absorption spectroscopy. The results showed that the TCLP leaching ratios of the heavy metals were Cr=0.30, Pb=0.05 and Cd=0.09 at 1000°C. However, the ash obtained at 1400°C showed negligible heavy metals leaching ratio while at 1500°C no leachability was detected (TCLP concentration dropped to nondetectable levels). The use of high temperature treatment enabled the immobilization of heavy metals in the ash preventing their leaching. Such ash can be considered as a non-hazardous material for reuse or safe disposal.

Heavy metals in cement and cement kiln dust from kilns co-fired with hazardous waste-derived fuel: application of EPA leaching and acid-digestion procedures

Substantial leaching from cement and cement kiln dust (CKD) of specific metals, especially Cr and Ba, resulted from application of the standard Toxicity Characteristic Leaching Procedure (TCLP). However, all TCLP concentrations are below limits for hazardous waste defined in the Resource Conservation and Recovery Act (RCRA). Four variations on the TCLP were assessed. The primary discernible enhancement of Tier-III metals release, relative to the standard TCLP, is increased leaching of Cr by chlorinated-water solutions. This likely results from enhancement of metal dissolution by chloride complexation. The final pH of each extract remained high. Thus, the capacities of these cement and CKD samples to buffer the acidity of the leaching solutions were not exceeded, even after two sequential exposures. This factor calls into question whether these high-pH solutions could represent any `real-world' condition and implies that the TCLP is not suitable for assessing the leaching behavior of alkaline systems such as cement and CKD. The EPA SW-846 microwave-assisted, acid-soluble procedure produces only partial recovery of any metal relative to dissolution-independent concentrations obtained by X-ray fluorescence spectrometry. Our results contradict previously published statements that TCLP and acid-soluble metal concentrations showed no consistent relationship. Both current results and re-evaluation of previously published data indicate correlations between TCLP and SW-846 acid-soluble concentrations, for several metals, that are significantly >0 at high levels of confidence.