Metals leachability from medical waste incinerator fly ash: A case study on particle size comparison

This paper presents the results from a study of metals leachability of medical waste incinerator fly ash in Japan on the basis of particle size. Sequential extraction and Toxicity Characteristic Leaching Procedure (TCLP) analysis were carried out in order to quantify the leaching amount of metals in each categorized particle size. Sequential extraction was also subjected to identify the preference of binding matrix of metals. The results of sequential extraction showed an increase both exchangeable and carbonate associated chromium concentrations in the bigger particle size fractions. Likewise, concentrations of carbonate matrix of arsenic and tin tended to increase in the bigger particle size fractions. In contrast, exchangeable associated cadmium as well as both exchangeable and carbonate matrices of barium were found higher in the smaller particle size fractions. However, no correlation was found in Kendal-tau correlation analysis between particle size of the ash and metals leachability of the TCLP.     

Initiatives to reduce lead from electronic devices: evidence of success from the toxicity characteristic leaching procedure

Discarded electronic devices (E-waste) have historically been found to exceed US Toxicity Characteristic hazardous waste thresholds for lead. Research was conducted to assess whether global and national lead reduction initiatives in the past decade translate to reduced toxicity characteristic leaching procedure (TCLP) lead leaching from E-waste. Nine categories of devices were subjected to TCLP and in all devices except one (smoke detectors), mean TCLP lead concentration results decreased by an order of magnitude or more (to levels below regulation thresholds). Mean TCLP lead concentrations decreased from 29.1 mg/L (2000–2005) to 0.224 mg/L (2008+) for cell phones and 1.26 mg/L (2000–2005) to 0.060 mg/L (2008+) for PCs. Most recently manufactured electronic devices (of those types tested here) comply with the definition of non-hazardous waste under US regulations.

Implications: Discarded electronic devices (E-waste) have often been tested as hazardous waste in the US because of lead leaching. Toxicity characteristic leaching procedure (TCLP) testing on more recently manufactured devices reveals that global lead reduction efforts have resulted in newer devices complying with US non-hazardous waste definitions. While these results highlight the success of lead reduction efforts, they raise policy questions regarding how best to incentivize E-waste recycling going forward.     

Evaluation of the stability of arsenic immobilized by microbial sulfate reduction using TCLP extractions and long-term leaching techniques

An investigation was conducted to evaluate the stability or leachability of arsenic immobilized by microbial sulfate reduction. Anoxic solid-phase samples taken from a bioreactor previously used to treat metal and As contaminated water using sulfate reducing bacteria (SRB) were subjected to the toxicity characteristic leaching procedure (TCLP) and long-term column leaching tests. The results from TCLP experiments showed that the concentration of As leached from solid-phase sulfide material (SSM) samples after an 18 h extraction time was <300 microgl(-1), which is below the current maximum Australian TCLP leachate value for As, and thus would not be characterized as a hazardous waste. In terms of percent total As leached, this was equivalent to <8.5% for SSM samples initially containing 61.3 mgkg(-1) As. The levels of As extracted by the TCLP was found to be significantly lowered or underestimated in the presence of dissolved oxygen, with As concentrations increasing with decreasing headspace-to-leachant volume ratios. The concentration of As was also consistently higher in nitrogen purged extractions compared to those performed in air. This was attributed to the dissolution of Fe-sulfide precipitates and subsequent oxidation of Fe(II) ions and precipitation of ferric(hydr)oxides, resulting in the adsorption of soluble As and corresponding decrease in As concentrations. According to the experimental data, it is recommended that TCLP tests for As leachability should be performed at least in zero-headspace vessels or preferably under nitrogen to minimize the oxidation of Fe(II) to ferric(hydr)oxides. In long-term leaching studies (approximately 68 days), it was found that the low solubility of the SSM ensured that rate of release of As was relatively slow, and the resulting leachate concentrations of As were below the current Australian guideline concentration for arsenic in drinking water.     

Lead removal from foundry waste by solvent extraction

Solvent extraction is used to reduce lead concentrations from millpond wastewater solids, a type of foundry process waste. Toluene and toluene mixed with di-(2-ethyl-hexyl) phosphoric acid (HDEHP) have been tried as leaching solvents. Toluene is ineffective as a solvent in extracting lead, but the toluene-HDEHP mixture effectively removes lead from solid foundry waste. The effects of the HDEHP concentration, the contact time, and the amount of solvent used on lead extraction have been investigated. The mass transfer process is rapid: contact time of 1/2 hour has been found to be sufficient to accomplish the leaching process. The concentration of HDEHP significantly impacts lead removal. The optimum concentration of HDEHP is determined to range from 0.05 to 0.1 mol/l. The Toxicity Characteristic Leaching Procedure (TCLP) test of the treated samples gives leachable lead in much lower quantities than those found in the untreated samples. Thus the solvent extraction process appears to be an effective method to significantly reduce the lead content of millpond wastewater solids.     

Thermal Immobilization of Lead Contaminants in Soils Treated in a Fixed- and Fluidized-Bed Incinerator at Moderate Temperatures

Abstract

Artificially lead-contaminated soils with different lead contents (200, 450, 600, and 900 ppm) were thermally immobilized in both fixed-bed and fluidized-bed modes at moderate treating temperatures (less than 500 °C) for various retention times. Cement powder and brick powder were added to the artificially contaminated soils to enhance lead immobilization. Results indicate that increasing treating temperature and time increases the extent of lead immobilization, as determined by the U.S. Environmental Protection Agency's (U.S. EPA) Toxicity Characteristics Leachability Procedure (TCLP). The percentage of lead leached from the soil/ cement mixtures was in the range of less than 0.251%, compared with the range between 13.6% and 40.7% for the corresponding soil/brick mixtures. As the amount of brick dust added to the Pb-doped soil was increased, the specific Pb immobilization effectiveness increased from 0.0675 to 0.149 mg Pb/g brick (for the 20- and 50-gram brick addition, respectively). An increase in air flow rate from 2 to 40 L/min caused a slight decrease in the Pb leaching percentage from 14.96% to 11.59%. Both the Freundlich and Langmuir isotherms give a satisfactory fit (r = 0.945 ~ 0.998) for the data derived from a TCLP test of the thermally-treated soil samples (105 °C and 500 °C) that contained lead contaminants. Sorption of lead contaminants in soil and sorbent matrices was the primary type of chemisorption. The kinetic results indicated that the Pb-doped soil system was too complicated to be described by a simple calculation.     

Fluidized-bed-combustion ash for the solidification and stabilization of a metal-hydroxide sludge

Fluidized-bed-combustion (FBC) ash is a by-product from a developing technology for coal-fired power plants that will economically reduce air emissions to meet requirements of the Clean Air Act. FBC ash has physical and chemical properties similar to Portland cement, but only has moderate success as a pozzolan in concrete applications due to low compressive strengths. However, FBC ash has proven effective for use as a binder for the solidification and stabilization (S/S) of metal-bearing sludges. Physical and chemical characterization procedures were used to analyze FBC ash and a metal-bearing sludge obtained from a hazardous waste treatment facility to develop 12 different S/S mix designs. The mix designs consist of four binder designs to evaluate sludge-to-binder ratios of approximately 0, 0.5, and 1. Portland cement is used as a control binder to compare unconfined compressive strengths and Toxicity Characteristic Leaching Procedure (TCLP) analyses from different ratios of the FBC ash streams: fly ash, char, and spent bed material (SBM). Compressive strengths ranging from 84 lbs per square inch (psi) to 298 psi were obtained from various mix designs containing different sludge-to-ash ratios cured for 28 days. All the mix designs passed the TCLP. Recoveries from leaching for each metal were less than 5% for most mix designs. Results of unconfined compressive strengths, TCLP, and percent recovery calculations indicate that the mix design containing approximately a 1:1 ratio of fly ash to char-and-sludge is the best mix design for the S/S of the metal-bearing sludge.     

Arsenic leachability and speciation in cement immobilized water treatment sludge

Arsenic leachability and speciation in cement immobilized water treatment sludge were investigated with leaching tests and X-ray absorption near edge structure (XANES) spectroscopy. The As leachability in the sludge determined with the toxicity characteristic leaching procedure (TCLP) and the waste extraction test (WET) was 283 and 7490 microgl(-1), respectively. Extractions with a lower liquid to solid ratio, under anaerobic conditions, and using citric acid buffer solution dramatically increased the leachate As concentration. XANES results showed that the As(III) composition was reduced from 51.1% of the total As content in the sludge to 16.3% in the cement treated sample with 28 days of cure. When the cement treated sample was cured for two years, the As(III) composition was decreased to 7.4%. The cement treatment reduced the As leachability. The leachate As(III) and total As concentrations were of the same order of magnitude in the samples cured for 28 days as for 2yr. However, consistently lower concentrations were detected in samples with longer cure time. The results of this study improve our understanding of arsenic speciation and leachability in the cement matrix after long cure times.     

A simple and fast screening test to detect soils polluted by lead

Lead pollution is an environmental priority. The evaluation of contaminated soils was often based on the results of the toxicity characteristic leaching procedure (TCLP) or the synthetic precipitation leaching procedure (SPLP). This paper presents a simple and fast screening test to detect soil contaminated by lead. The test is based on the chemistry of the stomach (Cl- concentration, pH 2, T = 37 degrees C) and simulates the incidental oral ingestion of soil by young children. The gastric juice simulation test (GJST) and the TCLP were applied to six size fractions from five soils. The GJST solubilized more Pb (up to 169 mg/l) than the TCLP especially for the smallest size fraction. Particle size had less effect on the TCLP. The percentage of lead released with the GJST, was most significant for the <63 microm size fraction and varied from 18 to 74% of the total lead content. Lead leached during the TCLP as a function of the total lead content showed poor linear regression coefficient (R) values for soils <250 microm. R values were significant for all size fractions with the GJST. The pH of approximately 5 in the TCLP limits the solubilization of lead in the small size fractions. The five soils exceeded the toxicity threshold of 10 microgPb/dl of blood for a significant fraction of children between 0 and 36 months using the EPA's IEUBK model (Integrated Exposure Uptake Biokinetic). But the TCLP did not detect lead contamination in two of these five soils. The GJST proved to be a better estimator of lead bioaccessibility in the gastrointestinal tract.     

A Comparison of Two Techniques for the Collection and Analysis of Polynuclear Aromatic Compounds in Ambient Air

A demonstration of the GHEMFIX solidification/stabilization process was conducted under the United States Environmental Protection Agency’s (EPA) Superfund Innovative Technology Evaluation (SITE) program. The demonstration was conducted in March 1989, at the Portable Equipment Salvage Company (PESC) uncontrolled hazardous waste site in Clackamas, Oregon. Waste containing lead, copper, and polychlorinated biphenyls (PCBs) from four different areas of the site were treated. Results showed substantial reduction of leachable lead and copper between the untreated waste and treated waste utilizing the EPA Toxicity Characteristics Leaching Procedure (TCLP) test. The effectiveness of this process for immobilizing PCBs could not be determined since the raw waste did not leach PCBs at high concentrations, utilizing the TCLP test. Data from other leaching tests for lead and copper would need to be utilized as input into a site specific groundwater model to determine whether solidification/stabilization would be an acceptable remedy for the site. Physical testing results indicated durability in exposed conditions.     

Leaching behavior of Cr(III) in stabilized/solidified soil

The leaching behavior of chromium was studied using batch leaching tests, surface complexation modeling and X-ray absorption near edge structure (XANES) spectroscopy. A contaminated soil sample containing 1330 mg-Cr kg(-1) and 25600 mg-Fe kg(-1) of dry soil was stabilized/solidified (S/S) with 10% cement, 25% cement, 10% lime and a mixture of 20% flyash and 5% lime. The XANES analysis showed that Cr(III) was the only Cr species in untreated soil and S/S-treated samples. The leachate Cr concentration determined using the toxicity characteristic leaching procedure (TCLP) was reduced from 5.18 mg l(-1) for untreated soil to 0.84 mg l(-1) for the sample treated with 25% cement. The Cr leachability in untreated and treated soil samples decreased dramatically as the pH increased from 3 to 5, remained at similar levels in the pH range between 5 and 10.5, and further decreased at pH>10.5. Modeling results indicated that the release of Cr(III) was controlled by adsorption on iron oxides at pH<10.5, and by precipitation of Ca(2)Cr(2)O(5).6H(2)O at pH>10.5.     

Static Leaching of Solidified/Stabilized Hazardous Waste from the Soliditech Process

WILT, ANS 16.1 and TCLP leach tests were performed on solidified/stabilized (s/s) wastes treated by Soliditech, Inc. of Houston, Texas as part of a U.S. EPA SITE demonstration project conducted in December 1988 at the Imperial Oil Company/ Champion Chemical Company Superfund site in Morganville, New Jersey. All three leaching tests performed on the s/s wastes indicated that the primary contaminants of concern (lead and PCBs) were not leachable. The ANS 16.1 static leach test for the s/s wastes provided diffusion coefficients (D_e) for Al, Ca, and Na that were comparable to those obtained from the WILT test. However, plots of the ANS 16.1 data indicated that wetting of the samples confounded the static leaching process. The large column WILT D_e was used to estimate that less than 0.8 μg/cm² lead would leach from a one-cubic yard block of s/s waste in contact with groundwater over a 60-month leaching period. This corresponds to concentrations less than 10 μg/L lead in the water contacting the block of s/s waste.     

Limitations of the toxicity characteristic leaching procedure for providing a conservative estimate of landfilled municipal solid waste incineration ash leaching

Limitations of the toxicity characteristic leaching procedure (TCLP) for simulating pollutant leaching from wastes disposed of in full-scale landfills are well understood in the waste management profession; the TCLP solution has a lower pH and greater organic acid content than typical landfill leachate. The TCLP serves its intended regulatory objective, however, as long as a conservative estimate of leaching is provided. Here, we examine TCLP’s ability to represent worst-case leaching conditions for monofilled municipal solid waste incineration (MSWI) ash. A critical examination of TCLP’s applicability to MSWI ash is especially relevant, as ash management at MSWI facilities often centers on passing TCLP, regardless of environmental risk posed by the ash or its recyclability. Multiple batch leaching tests were conducted on different MSWI ash streams: mixed ash, fly ash, and different size fractions of bottom ash. Batch-test results were compared with leachate simulating MSWI ash monofills. The TCLP did not consistently provide the most conservative estimate of leaching, supporting the need to consider alternative methodologies in future regulatory development.

Implications: This paper analyzes the existing hazardous waste regulatory testing requirement for municipal solid waste incinerator (MSWI) ash management to evaluate whether the TCLP serves its intended purpose in providing the most conservative estimate of landfilled MSWI ash. The results will serve as guidance and motivation for policy makers and the regulatory community to reevaluate the TCLP’s application for characterizing MSWI ash leaching in certain disposal scenarios and could promote consideration of alternative testing procedures based upon results of this study. This study serves to promote representative and accurate quantification of leaching risk from MSWI ash.     

Immobilization of antimony waste slag by applying geopolymerization and stabilization/solidification technologies

During the processing of antimony ore by pyrometallurgical methods, a considerable amount of slag is formed. This antimony waste slag is listed by the European Union as absolutely hazardous waste with a European Waste Catalogue code of 10 08 08. Since the levels of antimony and arsenic in the leachate of the antimony waste slag are generally higher than the landfilling limits, it is necessary to treat the slag before landfilling. In this study, stabilization/solidification and geopolymerization technologies were both applied in order to limit the leaching potential of antimony and arsenic. Different combinations of pastes by using Portland cement, fly ash, clay, gypsum, and blast furnace slag were prepared as stabilization/solidification or geopolymer matrixes. Sodium silicate–sodium hydroxide solution and sodium hydroxide solution at 8 M were used as activators for geopolymer samples. Efficiencies of the combinations were evaluated in terms of leaching and unconfined compressive strength. None of the geopolymer samples prepared with the activators yielded arsenic and antimony leaching below the regulatory limit at the same time, although they yielded high unconfined compressive strength levels. On the other hand, the stabilization/solidification samples prepared by using water showed low leaching results meeting the landfilling criteria. Use of gypsum as an additive was found to be successful in immobilizing the arsenic and antimony.

ImplicationsDespite the wide use of antimony for industrial purposes, disposal options for an antimony waste such as slag from thermal processing of antimony ore were not reported in the existing literature. This study aimed to develop a disposal strategy for the hazardous antimony waste slag. The findings of this study would contribute to understand the immobilization mechanisms of antimony and arsenic and will also be of interest to the owners of the antimony ore processing plants and to researchers investigating the efficiency of stabilization/solidification and geopolymerization technologies.     

Assessment of the mechanical stability and chemical leachability of immobilized electroplating waste

The effectiveness of cement based treatment technology, in immobilizing chromium laden electroplating sludge was assessed by conducting toxicity characteristic leaching procedure (TCLP). The mechanical stability of the blocks was tested by measuring the compressive strength. Other leaching tests such as NEN 7341 test, ANS 16.1 and multiple TCLP (MTCLP) test conducted on select solidified blocks showed that chromium was immobilized by the binder studied. A linear relationship was obtained between the cumulative fraction of chromium leached (CFL) and square root of time in the solidified samples proving that diffusion is the controlling mechanism for leaching of chromium. The leachability indices (LI) obtained for the solidified materials using cement and cement-fly ash system (EPC6, EPFC6A and EPFC6B) satisfy the guidance value as per US NRC, which clearly indicates that chromium is well retained within the solid matrix. Chromium concentrations in the TCLP leachates of the above mix ratios were well within the regulatory level of United States Environmental Protection Agency (USEPA). Molecular characterization of the solidified material was carried out using Fourier transformation infra red (FTIR) technique.     

Arsenic release from iron rich mineral processing waste: Influence of pH and redox potential

This paper presents the effect of pH and redox potential on the potential mobility of arsenic (As) from a contaminated mineral processing waste. The selected waste contained about 0.47 g kg(-1) of As and 66.2 g kg(-1) of iron (Fe). The characteristic of the waste was identified by acid digestion, X-ray diffraction and sequential extraction procedures. Less than 2% of the total As was acid extractable with the remaining 98% associated with Fe-oxyhydroxides and oxides. Batch leaching tests at different pH conditions showed a strong pH dependence on arsenic and iron leaching. Arsenic leaching followed a "V" shaped profiles with significant leaching in the acidic and alkaline pH region. Acid extractable phases dissolved at acidic pH, while desorption of arsenic due to increase in pH resulted in high arsenic concentration at alkaline pH. Under aerobic conditions and pH 7, As solubility was low, probably due to its precipitation on Fe-oxyhydroxides. Maximum As solubilization occurred at pH 11 (3.59 mg l(-1)). Similarity in the As and Fe leaching profiles suggested that the release of As was related to the dissolution of Fe in the low pH region. In general, redox potential did not play a significant role in arsenic or iron solubilization. It was thus concluded that for this solid waste, desorption was the predominant mechanism in arsenic leaching. A simple thermodynamic model based on arsenic and iron redox reactions was developed to identify the more sensitive redox couple.     

2种浸出方法对水泥熟料的适用性比较

采用2种不同类型的代表性浸出方法:TCLP和NEN7371对不同重金属含量及不同烧制条件下所得水泥熟料进行浸出实验.结果表明,NEN7371方法下各样品中所有受试重金属几乎均有检出,大部分重金属的浸出率均高于10%;重金属的浸出浓度与其在熟料样品中含量的趋势对应性较好;TCLP方法下各样品中的受试重金属均只有部分检出,且浸出率一般在0.5%左右,浸出浓度很低,仪器检测误差较大.说明在考察水泥熟料中重金属的浸出特性时,NEN7371方法的适用性相对更好.     

Arsenic mobility in contaminated lake sediments

An arsenic contaminated lake sediment near a landfill in Maine was used to characterize the geochemistry of arsenic and assess the influence of environmental conditions on its mobility. A kinetic model was developed to simulate the leaching ability of arsenic in lake sediments under different environmental conditions. The HM1D chemical transport model was used to model the column experiments and determine the rates of arsenic mobility from the sediment. Laboratory studies provided the information to construct a conceptual model to demonstrate the mobility of arsenic in the lake sediment. The leaching ability of arsenic in lake sediments greatly depends on the flow conditions of ground water and the geochemistry of the sediments. Large amounts of arsenic were tightly bound to the sediments. The amount of arsenic leaching out of the sediment to the water column was substantially decreased due to iron/arsenic co-precipitation at the water-sediment interface. Overall, it was found that arsenic greatly accumulated at the ground water/lake interface and it formed insoluble precipitates.     

水泥回转窑固化处理废弃重金属元素的实验研究

废弃的重金属化学试剂是一类危险的固体废物.通过在水泥回转窑中添加质量小于水泥质量的重金属化学试剂的实验研究表明(本实验添加质量约为水泥的0.1%):掺加化学试剂重金属元素后,各水泥熟料的XRD图谱相似,水泥熟料主要矿物相没有发生大的改变;重金属化学试剂的添加对水泥的7 d、28 d抗压强度的影响较小,符合国家标准;熟料试样在其水化28 d时各重金属的浸出量都很低,已低于工业固体废物浸出毒性鉴别标准规定的指标,由此表明利用水泥回转窑处理废弃化学试剂方法可行.     

Stabilization and Solidification of Metal-Laden Wastes by Compaction and Magnesium Phosphate-Based Binder

ABSTRACT

Bench-scale and full-scale investigations of waste stabilization and volume reduction were conducted using spiked soil and ash wastes containing heavy metals such as Cd, Cr, Pb, Ni, and Hg. The waste streams were stabilized and solidified using chemically bonded phosphate ceramic (CBPC) binder, and then compacted by either uniaxial or harmonic press for volume reduction. The physical properties of the final waste forms were determined by measuring volume reduction, density, porosity, and compressive strength. The leachability of heavy metals in the final waste forms was determined by a toxicity characteristic leaching procedure (TCLP) test and a 90-day immersion test (ANS 16.1). The structural composition and nature of waste forms were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.

CBPC binder and compaction can achieve 80-wt % waste loading and 39-47% reduction in waste volume. Compressive strength of final waste forms ranged from 1500 to 2000 psi. TCLP testing of waste forms showed that all heavy metals except Hg passed the TCLP limits using the phosphate-based binder. When Na₂S was added to the binder, the waste forms also passed TCLP limits for Hg. Long-term leachability resistance of the final waste forms was achieved for all metals in both soil and ash wastes, and the leachability index was ~14. XRD patterns of waste forms indicated vermiculite in the ash waste was chemically incorporated into the CBPC matrix. SEM showed that waste forms are layered when compacted by uniaxial press and are homogeneous when compacted by harmonic press.     

Stabilization and solidification of metal-laden wastes by compaction and magnesium phosphate-based binder

Bench-scale and full-scale investigations of waste stabilization and volume reduction were conducted using spiked soil and ash wastes containing heavy metals such as Cd, Cr, Pb, Ni, and Hg. The waste streams were stabilized and solidified using chemically bonded phosphate ceramic (CBPC) binder, and then compacted by either uniaxial or harmonic press for volume reduction. The physical properties of the final waste forms were determined by measuring volume reduction, density, porosity, and compressive strength. The leachability of heavy metals in the final waste forms was determined by a toxicity characteristic leaching procedure (TCLP) test and a 90-day immersion test (ANS 16.1). The structural composition and nature of waste forms were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. CBPC binder and compaction can achieve 80-wt% waste loading and 39-47% reduction in waste volume. Compressive strength of final waste forms ranged from 1500 to 2000 psi. TCLP testing of waste forms showed that all heavy metals except Hg passed the TCLP limits using the phosphate-based binder. When Na2S was added to the binder, the waste forms also passed TCLP limits for Hg. Long-term leachability resistance of the final waste forms was achieved for all metals in both soil and ash wastes, and the leachability index was approximately 14. XRD patterns of waste forms indicated vermiculite in the ash waste was chemically incorporated into the CBPC matrix. SEM showed that waste forms are layered when compacted by uniaxial press and are homogeneous when compacted by harmonic press.