Standard Toxicity Characteristic Leaching Procedure Research Articles

Use of calcined clay as cementitious addition in mortars to immobilize heavy metals

Abstract The aim of this study was to examine the use of calcined clay (CC), which is a pozzolanic material, as a substitute for 10% by weight of the amount of cement, for the stabilization/solidification (S/S) of hazardous waste using a hydraulic binder. For comparison, an ordinary Portland cement was used. The standard toxicity characteristic leaching procedure (TCLP) test showed that the average concentrations of heavy metals in the raw hazardous waste far exceeded those of the required standards. Leaching of heavy metals from the mortar was evaluated by the monolithic leaching test (MLT) under dynamic leaching conditions for 64 days in sulfated and neutral media. Tests of compressive strength, setting times, and X-ray diffraction were carried out. The addition of CC considerably improved the strength of the mortar specimens containing hazardous waste. Following the MLT test, CC cement-made mortar was more efficient in the S/S of heavy metals than mortar made without CC.

Pb-Based Perovskite Solar Cells and the Underlying Pollution behind Clean Energy: Dynamic Leaching of Toxic Substances from Discarded Perovskite Solar Cells.

Toxicants like Pb in lead-based perovskite solar cells (PSCs) may become available to humans through leaching and transport through water, air, and soil. Here, we summarize the potential toxicity of different substances in PSCs and determine the leaching concentration of typical heavy metals used in PSCs through dynamic leaching tests (DLTs). Extraction fluids for the standard toxicity characteristic leaching procedure, synthetic precipitation leaching procedure, and deionized water were used as the DLT leaching solutions. Results indicated that the leaching concentration of Pb exceeded the hazardous waste limit of 5 mg/L. In addition, Pb was found to continuously leach out in the leaching cycles of water extraction. The findings confirmed that discarded PSCs may release Pb when subjected to water, rain, and landfill leachate. Total organic carbon and chemical oxygen demand analyses indicated that discarded PSCs could increase the oxygen consumption and may release CO2 into the environment.

Speciation analysis and leaching behaviors of selected trace elements in spent SCR catalyst

This study investigated heavy metal chemical speciation and leaching behavior from a board-type spent selective catalytic reduction (SCR) catalyst containing high concentrations of vanadium, chromium, nickel, copper, zinc, and lead. A three-step sequential extraction method, standard toxicity characteristic leaching procedure (TCLP), and leaching characteristic tests have been performed. It was found that the mobility of six heavy metals in the spent SCR catalyst was significantly different. The mobility of the six heavy metals exhibited the following order: Ni > Zn > V > Cr > As > Cu. Meanwhile, TCLP test results revealed relatively high Zn and Cr leaching rate of 83.20% and 10.35%, respectively. It was found that leaching rate was positively correlated with available contents (sum of acid soluble, reducible and oxidizable fractions). Leaching characteristics tests indicated that pH substantially affected the leaching of these heavy metals. In particular, the leaching of Cr, Ni, Cu, and Zn was positively influenced by strong acid, while V and As were easily released in the presence of strong acid and strong alkali (pH < 3 or pH > 11). In terms of kinetics, the leaching of Cr, Ni, Cu, Zn, and As within the spent catalyst was dominated by erosion and dissolution processes, which were rapid reaction processes. V was released in large amounts within 1 h, but its leaching amount sharply decreased with time due to readsorption.

Utilization of graphene oxide for improving the environmental compatibility of cement-based materials containing waste cathode-ray tube glass

Abstract Utilization and processing of waste cathode ray tube (CRT) glass causes serious environmental damage due to its presence of lead and huge growing volume. The use of waste CRT glass in cement-based materials is an effective recycling method, whereas the huge amount of waste CRT glass usually results in severe lead leaching and weakened interfacial bonding. This paper presents an effective method for improving the lead immobilization and microstructure of the interfacial transition zone between cement paste and waste CRT glass (30 and 60 wt% of fine aggregates) using graphene oxide (GO) (up to 0.10 wt%). In order to investigate the environmental compatibility of the GO-waste CRT cement mortars, the standard toxicity characteristic leaching procedure (TCLP) was performed for lead leaching evaluation, and their mechanical properties were examined. Moreover, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) observation with backscattered electron mode were conducted. The results of TCLP indicate that the degrees of lead leaching from the waste CRT cement-based materials with both fine (0.075–0.15 mm) and coarse (8–9.5 mm) size containing 0.1 wt% GO were significantly lower than the regulatory limit specified by the United States Environmental Protection Agency and Chinese standard. The data obtained via mechanical testing revealed that the presence of 60 wt% waste CRT reduced its 28-day compressive and flexural strengths only slightly, whereas 0.1 wt% GO addition significantly increased their values. By analyzing the thermogravimetric and microstructural results, it was found that the increased formation of portlandite (CH) and calcium-silicate-hydrate (C S H) caused by GO addition reduced the number of interconnected cracks and pores and improved the properties of the interface between waste CRT glass and cement paste. This obtained improvement in environmental compatibility of the waste CRT cement mortars not only examines the reduced lead pollution caused by GO addition, but also sustainably promotes the industrial utilization of toxic waste CRT glass.

Leaching Behavior of Heavy Metals from Cement Pastes Using a Modified Toxicity Characteristic Leaching Procedure (TCLP).

As the standard toxicity characteristic leaching procedure (TCLP) can not exhaust the acid neutralizing capacity of the cement rotary kiln co-processing solid wastes products which is particularly important for the assessment of the leaching concentrations of heavy metals. A modified TCLP was proposed. The extent of leaching of heavy metals is low using the TCLP and the leaching performance of the different metals can not be differentiated. Using the modified TCLP, however, Zn leaching was negligible during the first 180h and then sharply increased (2.86±0.18 to 3.54±0.26mg/L) as the acidity increased (pH<6.0). Thus, Zn leaching is enhanced using the modified TCLP. While Pb leached readily during the first 126h and then leachate concentrations decreased to below the analytical detection limit. To conclude, this modified TCLP is a more suitable method for these cement rotary kiln co-processing products.

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.

Potential hazards of brominated carbon sorbents for mercury emission control.

Mercury is a toxic air pollutant, emitted from the combustion of coal. Activated Carbon (AC) or other carbon sorbent (CS) injection into coal combustion flue gases can remove elemental mercury through an adsorption process. Recently, a brominated CS with biomass ash as the carbon source (Br-Ash) was developed as an alternative for costly AC-based sorbent for mercury capture. After mercury capture, these sorbents are disposed in landfill, and the stability of bromine and captured mercury is of paramount importance. The objective of this study is to determine the fate of mercury and bromine from Br-Ash and brominated AC after their service. Mercury and bromine leaching tests were conducted using the standard toxicity characteristic leaching procedure (TCLP). The mercury was found to be stable on both the Br-Ash and commercial brominated AC sorbents, while the bromine leached into the aqueous phase considerably. Mercury pulse injection tests on the sorbent material after leaching indicate that both sorbents retain significant mercury capture capability even after the majority of bromine was removed. Testing of the Br-Ash sorbent over a wider range of pH and liquid:solid ratios resulted in leaching of <5% of mercury adsorbed on the Br-Ash. XPS analysis indicated more organically bound Br and less metal-Br bonds after leaching.

Environmental Release of Mercury from Broken Compact Fluorescent Lamps

This article presents an original study on the releases of mercury (Hg) from broken compact fluorescent lamps (CFLs) under various environmental conditions. Leaching of Hg in liquids was examined using the U.S. Environmental Protection Agency's standard procedures Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure. Emission of Hg in vapor phase from broken CFLs was detected using an emission monitoring system. CFLs of eight different brands and four different wattages were tested. Results show that Hg contents in CFLs varied significantly with brand. Total amount of Hg contained in each CFL ranged from 0.1 to 3.6 mg, and only <4% of the Hg was TCLP-leachable. Hg concentrations in TCLP extracts of all the new CFLs tested were lower than the regulatory level of 0.2 mg/L and thus the discarded CFLs do not fall into the hazardous waste category. Hg concentrations in Synthetic Precipitation Leaching Procedure extracts were lower than those in the TCLP extracts. Hg vapor emission test revealed that the CFLs continuously release Hg vapor once broken and the release can last over 10 weeks. Total amount of Hg vapor released from a broken CFL can exceeds 1.0 mg, which can cause Hg level in a regular room to exceed the safe human exposure limit under poor ventilation conditions. Results provide useful implications in guiding the handling and treatment of CFLs during and after use.

Prolonged toxicity characteristic leaching procedure for nickel and copper aluminates

The toxicity characteristic leaching procedure (TCLP) is a regulatory testing method widely employed to evaluate the environmental friendliness of waste materials. TCLP analysis provides a fast, easy and economical way to determine the mobility of waste pollutants under simulated landfill conditions. Recent studies on metal stabilization have reported the potential for nickel and copper aluminates to form in thermal treatment conditions, and suggested a more reliable method of stabilizing hazardous metals, particularly when products are to be reused. There is thus an urgent need for a convenient and effective method of quantifying metal leachability and identifying the metal leaching behavior of sparingly soluble materials. In this study, standard TCLP analysis was modified into a prolonged leaching experiment to investigate the leaching behavior of nickel and copper oxides (NiO and CuO) and their aluminates (NiAl(2)O(4), CuAl(2)O(4) and CuAlO(2)). The results demonstrate the difficulty of differentiating the leachability of highly insoluble phases, such as NiO and NiAl(2)O(4), using the standard TCLP. The prolonged TCLP method, however, confirmed NiAl(2)O(4) to have a lower degree of intrinsic leachability than NiO and that it could be expected to undergo congruent dissolution under landfill conditions. For the more soluble copper system, the aluminates were still found to possess a much lower degree of leachability, and their leaching behavior to follow an incongruent dissolution pattern. The results of this study prove prolonged TCLP analysis to be a convenient and effective way to evaluate the environmental friendliness of metal waste and to identify the leaching behavior of waste materials.

Correlation between the Results of Sequential Extraction and Effectiveness of Immobilization Treatment of Lead- and Cadmium-Contaminated Sediment

The assessment of the quality of sediment from the Great Backi Canal (Serbia), based on the pseudo-total lead (Pb) and cadmium (Cd) content according to the corresponding Dutch standards and Canadian guidelines, showed its severe contamination with these two metals. A microwave-assisted BCR (Community Bureau of Reference of the Commission of the European Union) sequential extraction procedure was employed to assess their potential mobility and risk to the aquatic environment. Comparison of the results of sequential extraction and different criteria for sediment quality assessment has led to somewhat contradictory conclusions. Namely, while the results of sequential extraction showed that Cd comes under the high-risk category, Pb shows low risk to the environment, despite its high pseudo-total content. The contaminated sediment, irrespective of the different speciation of Pb and Cd, was subjected to the same immobilization, stabilization/solidification (S/S) treatments using kaolinite, montmorillonite, kaolinite-quicklime, montmorillonite-quicklime, fly ash, zeolite, or zeolite-fly ash combination. Semi-dynamic leaching tests were conducted for Pb- and Cd-contaminated sediment in order to assess the long-term leaching behavior of these metals. In order to simulate “worst case” leaching conditions, the semi-dynamic leaching test was modified using 0.014 M acetic acid (pH = 3.25) and humic acid solutions (20 mg TOC l-1) as leachants instead of deionized water. The effectiveness of S/S treatment was evaluated by determining diffusion coefficients (De) and leachability indices (LX). The standard toxicity characteristic leaching procedure (TCLP) was applied to evaluate the extraction potential of Pb and Cd. A diffusion-based model was used to elucidate the controlling leaching mechanisms. Generally, the test results indicated that all applied S/S treatments were effective in immobilizing Pb and Cd, and the treated sediments may be considered acceptable for “controlled utilization” based on LX values, irrespective of their different availability in the untreated samples. In the majority of samples, the controlling leaching mechanism appeared to be diffusion, which indicates that a slow leaching of Cd and Pb could be expected when the above S/S agents were applied. The TCLP results showed that all S/S samples were nonhazardous.

Effects of different additives with assistance of microwave heating for heavy metal stabilization in electronic industry sludge

Electronic industrial wastewater sludge in Taiwan is normally passed through an acid-extraction process to reclaim most of the copper ions, the remaining residue may still need to be treated by various stabilization technologies using suitable additives. Cement solidification is used as the common method to stabilize the industrial wastewater sludge in Taiwan. However, this method has the disadvantage of an increase in waste volume. In the present study selective additives such as sodium sulfide, barium manganate and different phase of alumina were tested as a possible alternate additive to stabilize the heavy metal ion in the treated solid waste sludge via microwave heating treatment. The effects of additive amount, power of microwave irradiation and reaction time have been studied. Heavy metal leaching capacity is determined by using standard toxicity characteristic leaching procedure test and elemental content in the leachate is analyzed by inductively coupled plasma analysis. Sodium sulfide is effectively stabilizing the leaching copper ion with high selectivity in the presence of microwave irradiation and finally stabilized in the form of copper sulfide, which is a significant reaction to stabilize the copper ion leaching in the waste sludge. Complete stabilization of heavy metal ion and copper ion content (<5 mg L −1) in industrial sludge is achieved by heating the microwave treated barium manganate and alumina additives by adopting suitable reaction conditions. Hybrid microwave and conventional heating process with minor amount of additive providing the efficient heavy metal stabilization for treated electronic industry waste sludge.

Dynamic leaching test of personal computer components

A dynamic leaching test (DLT) was developed and used to evaluate the leaching of toxic substances for electronic waste in the environment. The major components in personal computers (PCs) including motherboards, hard disc drives, floppy disc drives, and compact disc drives were tested. The tests lasted for 2 years for motherboards and 1.5 year for the disc drives. The extraction fluids for the standard toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP) were used as the DLT leaching solutions. A total of 18 elements including Ag, Al, As, Au, Ba, Be, Cd, Cr, Cu, Fe, Ga, Ni, Pd, Pb, Sb, Se, Sn, and Zn were analyzed in the DLT leachates. Only Al, Cu, Fe, Ni, Pb, and Zn were commonly found in the DLT leachates of the PC components. Their leaching levels were much higher in TCLP extraction fluid than in SPLP extraction fluid. The toxic heavy metal Pb was found to continuously leach out of the components over the entire test periods. The cumulative amounts of Pb leached out of the motherboards in TCLP extraction fluid reached 2.0 g per motherboard over the 2-year test period, and that in SPLP extraction fluid were 75–90% less. The leaching rates or levels of Pb were largely affected by the content of galvanized steel in the PC components. The higher was the steel content, the lower the Pb leaching rate would be. The findings suggest that the obsolete PCs disposed of in landfills or discarded in the environment continuously release Pb for years when subjected to landfill leachate or rains.

Sorption and stability of mercury on activated carbon for emission control

A leading strategy for control of mercury emissions from combustion processes involves removal of elemental mercury from the flue gas by injection of activated carbon sorbent. After particulate capture and disposal in a landfill, it is critical that the captured mercury remains permanently sequestered in the sorbent. The environmental stability of sorbed mercury was determined on two commercial, activated carbons, one impregnated using gaseous sulfur, and on two activated carbons that were impregnated with sulfur by reaction with SO 2. After loading with mercury vapor using a static technique, the stability of the sorbed mercury was characterized by two leaching methods. The standard toxicity characteristic leaching procedure showed leachate concentrations well below the limit of 0.2 mg/L for all activated carbons. The nature of the sorbed mercury was further characterized by a sequential extraction scheme that was specifically optimized to distinguish clearly among the highly stable phases of mercury. This analysis revealed that there are two forms in which mercury is sequestered. In the sorbent that was impregnated by gaseous sulfur at a relatively low temperature, the mercury is present predominantly as HgS. In the other three sorbents, including two impregnated using SO 2, the mercury is predominantly present in the elemental form, physisorbed and chemisorbed to thiophene groups on the carbon surface. Both forms of binding are sufficiently stable to provide permanent sequestration of mercury in activated carbon sorbents after disposal.

Arsenic stabilization on water treatment residuals by calcium addition

A common method of removing arsenic from contaminated water is the co-precipitation or sorption of arsenic onto oxy-hydroxides formed by the addition of metal salts. Arsenic co-precipitation produces solids containing high concentrations of arsenic. The elevated arsenic content poses leaching problems requiring expensive disposal in certified hazardous impoundments. The objective of this research is to determine the effect of calcium addition as a stabilization agent, on arsenic desorption from ferric water treatment residuals. Due to the treatment residual's buffer capacity, desorption experiments in this study did not follow the standard Toxicity Characteristic Leaching procedure (TCLP) test. Arsenate desorption was induced in two ways: controlling solution pH in de-ionized water, and controlling solution pH in a 1.33 mM phosphate solution where phosphate is a competing anion. Desorption from laboratory treatment residuals did not generate any arsenic when calcium was present in solution, especially when excess calcium that did not join the surface of the treatment residual was present. Similarly, arsenic leaching decreased when field treatment residuals were treated with lime as stabilizing agent. Ordinary Portland cement (OPC) was also tested as a stabilizing agent in conjunction with lime since long term lime stabilization can be slowly consumed when directly exposed to atmospheric CO 2. The solidification and stabilization (S/S) technique with lime and OPC was shown to be successfully applied to the immobilization of arsenic tainted water treatment residuals.

Stabilization of arsenic-bearing solid residuals in polymeric matrices

This research investigates the use of polymeric matrices to encapsulate solid sorbents used to remove arsenic from drinking water. Arsenic-containing granular ferric oxy/hydroxide and ferric hydroxide amended alumina residuals were encapsulated in a polymeric matrix using a novel aqueous-based manufacturing process. The polymer was a blend of poly(styrene butadiene) and an epoxy resin. The polymeric waste forms produced were capable of containing more than 60 wt% of sorbent (dry basis), while keeping good mechanical properties. Arsenic leaching from encapsulated and unencapsulated residuals was evaluated using the standard toxicity characteristic leaching procedure (TCLP) and the California Waste Extraction Test (CA-WET). The results show that waste forms of the polymer-encapsulated residuals crushed for testing retain good leaching resistance when evaluated with the more aggressive CA-WET test, yielding leachate arsenic concentrations below the toxicity characteristic (TC) standard of 5 mg/L. When residuals were preprocessed and encapsulated in a polymer form that avoided the size reduction required by leaching protocols, arsenic leached up to 700 times less than that from the unencapsulated residuals. Comparison of the waste form developed here with conventional cement matrices containing the same residuals show that the polymeric matrices were capable of encapsulating appreciably more material and leached arsenic at concentration levels that were more than an order of magnitude lower than cement.

Removal of Perchlorate from Contaminated Waters Using Surfactant‐Modified Zeolite

We investigated the potential of using surfactant (hexadecyltrimethylammonium)-modified zeolite (SMZ) as an inexpensive sorbent for removing perchlorate (ClO(4)(-)) from contaminated waters in the presence of competing anions. In batch systems, the presence of 10 mM OH(-) (i.e., pH 12), CO(3)(2-), Cl(-), or SO(4)(2-) had little effect on the sorption of ClO(4)(-) by SMZ, indicating that the sorption of ClO(4)(-) by SMZ was very selective. The presence of 10 mM NO(3)(-), however, reduced the sorption of ClO(4)(-) at low initial concentrations. The maximum sorption capacity for ClO(4)(-) by the SMZ remained relatively constant (40-47 mmol kg(-1)), in the absence or presence of the competing ions. In flow-through systems, ClO(4)(-) broke through the SMZ columns much later than other anions present in an artificial ground water. The affinity of the anions for SMZ followed the sequence of ClO(4)(-) > > NO(3)(-) > SO(4)(2-) > Cl(-). Perchlorate loading under dynamic flow-through conditions was 34 mmol kg(-1), somewhat less than the maximum loading of 40 to 47 mmol kg(-1) determined by the batch method. Less than 1% of previously sorbed ClO(4)(-) was leached out by ultra-pure water, by extraction fluid #1 of the standard toxicity characteristic leaching procedure (TCLP), or by a solution of 0.28 M Na(2)CO(3)/0.5 M NaOH. About 40% of the previously sorbed ClO(4)(-) was leached out from SMZ by a 0.5 M NO(3)(-) solution. The exchange of ClO(4)(-) with NO(3)(-) corroborated results of the batch tests where NO(3)(-) was shown to compete with ClO(4)(-) sorption.

RCRA Toxicity Characterization of Discarded Electronic Devices

The potential for discarded electronic devices to be classified as toxicity characteristic (TC) hazardous waste under provisions of the Resource Conservation and Recovery Act (RCRA) using the toxicity characteristic leaching procedure (TCLP) was examined. The regulatory TCLP method and two modified TCLP methods (in which devices were disassembled and leached in or near entirety) were utilized. Lead was the only element found to leach at concentrations greater than its TC limit (5 mg/L). Thirteen different types of electronic devices were tested using either the standard TCLP or modified versions. Every device type leached lead above 5 mg/L in at least one test and most devices leached lead above the TC limit in a majority of cases. Smaller devices that contained larger amounts of plastic and smaller amounts of ferrous metal (e.g., cellular phones, remote controls) tended to leach lead above the TC limit at a greater frequency than devices with more ferrous metal (e.g., computer CPUs, printers).

LEACHING OF LEAD FROM DISCARDED NOTEBOOK COMPUTERS USING THE SCALE-UP TCLP AND OTHER STANDARD LEACHING TESTS

The proper management of discarded electronic devices (often called electronic-waste) is an emerging issue for solid waste professionals throughout the world because of the large growth of the waste stream, and the content of toxic metals in them, most notably heavy metals such as lead. Notebook computers are becoming one of the major components of discarded computer devices and will continue to increase in the waste stream in the future. While the computers hold great promise for recycling, a substantial amount of this waste is often disposed in municipal solid waste (MSW) landfills. The toxicity characteristic leaching procedure (TCLP) is commonly used to simulate worse case leaching conditions where a potentially hazardous waste is assumed to be disposed along with municipal solid waste in a landfill with actively decomposing materials overlying an aquifer. The objective of this study was to examine leaching potential of lead from discarded notebook computers using the scale-up TCLP, other standard leaching tests such as California waste extraction test (Cal WET), and the synthetic precipitation leaching procedure (SPLP) and actual landfill leachates as leaching solution. The scale-up TCLP is a modified TCLP (where the device was disassembled and leached in or near entirety) to meet the intent of the TCLP. The results showed that the scale-up TCLP resulted in relatively high lead found in the leachate with an average of 23.3 mg/L. The average level was less than those by the standard TCLP and WET (37.0 mg/L and 86.0 mg/L, respectively), but much greater than those by the SPLP and the extractions with the landfill leachates (0.55 mg/L and 1.47 mg/L, respectively). The pH of the leaching solution and the ability of the organic acids in the TCLP and WET to complex with the lead were identified as major factors that controlled the amount of lead leached from notebook computers. Based on the results obtained by a number of leaching tests in this study, notebook computers may present a potential leaching risk to the environment and human health upon land disposal. However, further investigation is still needed to assess the true risk posed by the land disposal of discarded notebook computers.

Evaluation of a modified TCLP methodology for RCRA toxicity characterization of computer CPUs

A leaching method similar to the toxicity characteristic leaching procedure (TCLP) was designed and evaluated for testing of bulky wastes, such as discarded electronic devices. The objective was to meet the intent of the TCLP (same leaching solution, liquid-to-solid ratio and same leaching time) but to allow more representative and rapid testing. The procedure was evaluated by examining lead leaching from computer CPUs as a test case; disassembled CPUs were leached in their entirety (or close to entirety) in a large vessel using a drum rotator. The difference in rotation speed between the large-scale test and the TCLP was found to have no statistical impact on lead leaching. The lack of size reduction resulted in less reducing conditions than the standard TCLP (because of increased iron and zinc leaching), and this resulted in greater lead leaching. For electronic wastes with large amounts of steel, the large-scale procedure provides a more conservative estimate of TCLP lead leaching. The large-scale procedure greatly reduces sample processing effort but does increase the cost of analysis. Evaluation of this approach by the regulatory community is important as the CPUs tested here tended to leach lead at greater than the toxicity characteristic (TC) limit (5 mg/L) using the large-scale test, but less than the TC limit using the standard TCLP.

Application of ferric sludge to immobilize leachable mercury in soils and concrete

A Hg‐contaminated site in B.C. Province, Canada was caused by the previous operation of Hg‐cell in chlor‐alkali process for over 25 years. The soils and groundwater at the site are highly contaminated with mercury. An analysis of groundwater at the site has shown that most of the mercury is bonded with humic and fulvic acids (HFA) in colloidal form. The Hg‐HFA colloids can be completely removed from the groundwater with ferric chloride treatment under optimized process conditions to form ferric sludge (FS), which is rendered non‐leachable by standard TCLP (Toxicity Characteristic Leaching Procedure) test. The effluent discharged from a clarifier has achieved mercury levels of < 0.5 μg 1−1. The studies of mercury adsorption characteristics of FS show it has low mercury leachability by TCLP, and great mercury adsorption capability. This feature is the basis for the application of FS to immobilization of leachable Hg‐contaminants in solid wastes. Full‐scale stabilization tests of Hg‐contaminated soil have been carried out, and the time‐based stability of the treated soil has been monitored by TCLP over a period of 60 days. All the results have shown a small variation in TCLP mercury levels within a range of 10–40 μg l−1. Based on these results and with the approval of the B.C. Ministry of the Environment, 1850 tons of Hg‐contaminated soils and 260 tons of Hg‐contaminated concrete fines have been treated, stabilized with FS, and disposed in a non‐hazardous waste disposal site.