Toxicity Characteristic Leaching Procedure Leachate Research Articles

SOLIDIFICATION/STABILIZATION OF NONVALUABLE RESIDUE FROM WASTE PRINTED CIRCUIT BOARD ASSEMBLY

The process of copper recovery from waste printed circuit board assembly (PCBA) hasremained a large fraction of solid waste called “Nonvaluable Residue (NVR)”. This residue is considered tobe a hazardous waste because Pb, Cu, and Sb exceed the regulatory levels. Solidification/Stabilization (S/S)treatment technique is selected to improve waste characteristics before disposal of in hazardous wastelandfills. In this study, a cement-based solidification/stabilization was used to treat NVR. Unconfinedcompression strength test (UCS) and toxicity characteristic leaching procedure (TCLP) were mainly used forphysical and chemical characterization of the solidified/stabilized products. After curing for 28 days, thecompressive strength and heavy metal leachability (Pb, Cu, Sb) were tested. The results showed that thecompressive strength of blank sample was 20.75 MPa while compressive strengths of the solidified/stabilizedNVR products were 7.36, 4.17 and 1.35 MPa for 20%, 30% and 40 wt% of NVR, respectively. Allexperimental mixture ratios satisfied the UCS requirements (0.35 MPa). In addition, the concentrations of Pb,Cu, and Sb in the TCLP leachate of all solidified/stabilized NVR products were lower than the limit valueand the original waste. This study indicated that cement-based S/S treatment process was able to improveheavy metal immobilization and subsequently minimize potential environmental impacts in landfill disposal.

Influence of thermal treatment on fixation rate and leaching behavior of heavy metals in soils from a typical e-waste processing site

A solidification and stabilization method, thermal treatment, was used to investigate the effects of incineration temperature and incineration time on heavy metal fixation rates and leaching behaviors in soils from an e-waste processing site. High concentrations of heavy metals (Ni 153mg/kg, Cu 448mg/kg, Zn 227mg/kg, Cd 0.80mg/kg, Sn 838mg/kg, Sb 658mg/kg and Pb 114mg/kg) were detected in these soils. In addition, the Mn (67.2%), Co (62.7%), Ni (84.8%), Cu (88.3%), Zn (56.5%), Cd (79.9%) and Pb (67.4%) in these soils mainly occurred in the non-residual fractions. Thermal treatment experiments indicated that better (>80%) Be, V, Cr, Mn, Co, Ni, Cu, Zn, Cd, Sn and Sb fixation rates could be obtained in these soils at an incineration temperature of 700°C and at an incineration time of 45min. under these conditions, the concentrations of Be, Cr, Co, Ni, Zn and Cd in the Toxicity Characteristic Leaching Procedure (TCLP) leachates obviously decreased to concentrations that were lower than the corresponding background concentrations of groundwater in Dutch standard, and the Cu concentration in the TCLP leachates decreased from 461μg/L (before incineration) to 66.4μg/L. Therefore, thermal treatment technology could be serve as an appropriate measure for Be, Cr, Co, Ni, Cu, Zn and Cd remediation in the soils from the e-waste processing site.

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.

Treatment of urban river contaminated sediment with ex situ advanced oxidation processes: technical feasibility, environmental discharges and cost-performance analysis

The technical feasibility, environmental discharges and cost-performance of urban river contaminated sediment treatment with ex situ advanced oxidation processes were evaluated for the purpose of achieving an ideal treatment goal (for marine disposal) and a cost-performance treatment goal (for beneficially reusing as a filling material). Sediment samples were collected from a river located in southern China. To achieve the ideal treatment goal, sequential treatments (Fenton's reaction + activated persulphate oxidation) were carried out. One-step Fenton's reaction was applied to achieve the cost-performance treatment goal. The resulting effluent was treated and discharged, and sludge generated in wastewater treatment was characterized. The resources input throughout the treatment processes were recorded for cost estimation. After the treatment designed for achieving the ideal treatment goal, most pollutants fulfilled the treatment goal except Pb, Cd, Hg and Ag, probably because these four metals were present mainly in stable fractions of the sediment. The cost-performance treatment goal was achieved in view of low pollutant contents in the toxicity characteristic leaching procedure leachate of treated sediment. The cost for achieving the cost-performance treatment goal is much less than that for achieving the ideal treatment goal. The major cost difference is attributed to chemical cost. Stringent sediment treatment goals based on existing standards would lead to massive chemical use, complex treatment and hence huge cost. A simpler treatment with fewer chemicals is adequate for sediment beneficially reused as a filling material, and is economically more advantageous than handling sediment for marine disposal.

Leaching assessments of toxic metals in waste plasma display panel glass

The plasma display panel (PDP) is rapidly becoming obsolete, contributing in large amounts to the electronic waste stream. In order to assess the potential for environmental pollution due to hazardous metals leached from PDP glass, standardized leaching procedures, chemical speciation assessments, and bioavailability tests were conducted. According to the Toxicity Characteristic Leaching Procedure (TCLP), arsenic in back glass was present at 4.46 ± 0.22 mg/L, close to its regulation limit of 5 mg/L. Zn is not available in the TCLP, but its TCLP leaching concentration in back glass is 102.96 ± 5.34 mg/L. This is because more than 90% of Zn is in the soluble and exchangeable and carbonate fraction. We did not detect significant levels of Ag, Ba, or Cu in the TCLP leachate, and the main fraction of Ag and Ba is residual, more than 95%, while the fraction distribution of Cu changes SEP by SEP. Ethylenediamine tetraacetic acid (EDTA)- and diethylenetriamine pentaacetic acid (DTPA)-extractable Ag, As, Ba, Cu, Zn, and Ni indicate a lower biohazards potential. These results show that, according to the EPA regulations, PDP glass may not be classified as hazardous waste because none of the metals exceeded their thresholds in PDP leachate. However, the concentrations of As and Zn should be lowered in the manufacturing process and finished product to avoid potential pollution problems.Implications: The plasma display panel is rapidly becoming obsolete because of the liquid crystal display. In this study, the leachability of heavy metals contained in the waste plasma display panel glass was first examined by standardized leaching tests, typical chemical speciation assessments, and bioavailability tests, providing fundamental data for waste PDP glass recovery, recycling, and reuse.

Effect of ferrous metal presence on lead leaching in municipal waste incineration bottom ashes

The recovery of ferrous and non-ferrous metals from waste to energy (WTE) ash continues to advance as the sale of removed metals improves the economics of waste combustion. Published literature suggests that Fe and Fe oxides play a role in suppressing Pb leaching in the Toxicity Characteristic Leaching Procedure (TCLP); further removal of ferrous metals from WTE ashes may facilitate higher Pb leaching under the TCLP. Eight WTE bottom ash size-fractions, from three facilities, were evaluated to assess the effect of metallic Fe addition and ferrous metal removal on TCLP leaching. Metallic Fe addition was demonstrated to reduce Pb leaching; the removal of ferrous metals by magnet resulted in a decrease in total available Pb (mg/kg) in most ash samples, yet Pb leachability increased in 5 of 6 ash samples. The research points to two chemical mechanisms to explain these results: redox interactions between Pb and Fe and the sorption of soluble Pb onto Fe oxide surfaces, as well as the effect of the leachate pH before and after metals recovery. The findings presented here indicate that generators, processors, and regulators of ash should be aware of the impact ferrous metal removal may have on Pb leaching, as a substantial increase in leaching may have significant implications regarding the management of WTE ashes.

Stabilization of Heavy Metals in Mining Site Soil with Silica Extracted from Corn Cob

Corn cob silica (CCS), produced via a modification of the sol-gel method, can reduce heavy metal availability and stabilize contaminated soil on abandoned mining sites. Adding 5 % (w/w) CCS to mining site soil increased pH from 4.0 to 7.7, and cation exchange capacity increased from 94.5 to 100.3 cmol+/kg. Sequential extraction showed that adding CCS decreased heavy metal availability in the soil. Mobility factor (MF) values indicated that CCS reduced Pb mobility more than that of Zn or Cu in all fractions. Pb concentrations in leachate from all fractions using the toxicity characteristic leaching procedure (TCLP) were greatly decreased by adding 3 % (w/w) CCS. CCS similarly reduced Zn concentrations in TCLP leachate. CCS addition did not impact Cu concentrations in leachate, likely because concentrations were much lower than those of the other metals. As was generally less mobile than the heavy metals; however, As mobility and leachability tended to increase with CCS addition because its oxyanions arsenite and arsenate have low affinity for negatively charged surfaces on the CCS. Shoot and root growth of Spinacia oleracea L. (spinach) was much greater in CCS-treated soil than in unamended soil. Results demonstrate the utility of CCS to stabilize heavy metals in contaminated mining site soil, but this treatment may not be ideal for As-contaminated soils.

Trends in Toxic Metal Levels in Discarded Laptop Printed Circuit Boards

Waste printed circuit boards (PCBs) contain toxic metals at concentrations that could pose human and environmental threats if improperly disposed of. Also, PCBs are known to contain appreciable quantities of precious metals with economic value. This study investigated the levels of Cu, Pb, Ni, Zn and Cd in the PCBs extracted from ten discarded laptops and outlined the trends that can be drawn from the results. The laptops were made by a world-wide leading original equipment manufacturer (OEM). The whole laptops were disassembled to enable the extraction of populated PCBs; components were dismounted and all de-populated PCBs were separately crushed, sieved, and total recoverable metals aforementioned were extracted using EPA 3050B method. Also, PCBs were analysed following the EPA Toxicity Characteristic Leaching Procedure (TCLP) and the EPA Synthetic Precipitation Leaching Procedure (SPLP) tests to study their leachability when exposed to municipal landfill and rain water, respectively. The extracts were analysed for metal levels using atomic absorption spectrophotometric technique. The sequence of total recoverable metals was Cu (3.23±0.41%) > Pb (1.95±0.57%) > Ni (0.88±0.36%) > Zn (0.012±0.003%) > Cd (4.00±2.30 mg/kg). Our study revealed a reduction in average % Cu and Zn by at least 6 and 1.5 times, respectively compared with previous studies. The level of Pb also was noticed to decrease from 2.5% in PCBs produced in 2006 to 1.7% in those produced in 2009. On the one hand, this could be a sign of the efforts conducted by OEMs to shift towards the design of eco-friendly products. On the other hand, average Pb (mg/L) level in TCLP and SPLP leachates was respectively 13 and 11 times higher than EPA limit of 5mg/L. Discarded laptop PCBs should still be handled and disposed of as hazardous waste.

Productive use of steelmaking by-product in environmental applications – II: Leachate geochemistry, ecotoxicity and environmental radioactivity

Detailed laboratory studies have indicated that the HIsmelt steelmaking by-product has the ability to neutralise acidity and hence, may have potential application as an environmental amendment. Prior to widespread environmental use, however, an ecotoxicological characterisation of the by-product leachate and an environmental radioactivity risk assessment are required. Ecotoxicity testing indicated that the HIsmelt steelmaking by-product softwater leachate, adjusted from its natural pH of 10.6–8.0 prior to use, was of low toxicity to Chlorella algae and the marine bacterium Vibrio fischeri, and not toxic to the cladoceran Ceriodaphnia dubia. Leachate metal concentrations in HIsmelt by-product were low. Relative to stringent health-based guidelines for Australian drinking water, the HIsmelt softwater leachate only exceeds the pH guideline of 6.5–8.5. The acidic toxicity characteristic leaching procedure (TCLP) HIsmelt leachate compares favourably with TCLP leachates from international steel-making by-products with low trace element concentrations reflecting low solid-phase concentrations. The HIsmelt steelmaking by-product exhibited low to moderate U and Th decay chain radionuclide activities with an absorbed dose rate of 65nGy/h. Given the low ecotoxicity, low leachate trace elements concentrations and acceptable radioactivity, the HIsmelt steelmaking by-product has potential applications as a construction material or as a soil amendment to ameliorate acidity. However, based on the results of the synthetic softwater leachate tests, it is likely that the HIsmelt steelmaking by-product will require mixing with other materials to reduce leachate pH prior to use as an environmental amendment.

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.

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.

Leaching behavior and immobilization of heavy metals in zinc leach residue before and after thermal treatment

AbstractThe aim of the present study was to investigate the metal leaching behavior of the hazardous waste of zinc industry before and after thermal treatment. Samples were subjected to the TCLP (Toxicity Characteristic Leaching Procedure) and ASTM (American Society of Testing and Materials) methods. The results of TCLP and ASTM leaching methods demonstrate that addition of clinoptilolite, blast furnace slag, and red mud to the zinc leach residue reduces the heavy metal content in the effluent and the red mud performs better than clinoptilolite and blast furnace slag. The leaching tests showed that the content of some elements in the waste before thermal treatment exceeded the regulatory limits and cannot be disposed of in the present form. Metal releases decreased at higher temperatures from 600°C and 800°C and reached to minimum levels at 1200°C because of heat‐induced formation of a glassy matrix. The levels of Zn2+ released for 1200°C was 0.025 mmol/L. Therefore, a stabilization or inertization treatment is necessary prior to disposal. Thermal treatment can be an acceptable method for disposal of zinc leach residue. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Leaching Behavior of Metals Released from Cement-Stabilized/Solidified Refinery Oily Sludge by Means of Sequential Toxicity Characteristic Leaching Procedure

In this study, stabilization/solidification (S/S) of refinery oily sludge was applied using two types of cement (I and II), in cement-to-waste ratio from 0.1 to 0.7. The leaching behavior of heavy metals was investigated, by means of a five-point sequential toxicity characteristic leaching procedure (TCLP) test. Sequential TCLP was used to provide an improved assessment of long-term contaminant potential leachability, because the acidic leachant is renewed, whereas in the single TCLP, contaminant leachability is limited by the pH neutralization of the alkaline binder. Cement-based S/S of real refinery oily sludge resulted in very low leachability of heavy metals. Pb and Cd were not detected in any TCLP leachate. The maximum leachability of Fe, Zn, and Ni occurred in the pH range between 5.5 and 6.5. The leachability of Cu and Cr increased with increasing pH. Maximum cumulative percentage of Fe, Ni, and Zn leaching after five consecutive TCLP extractions (for worst case conditions, i.e., 10% II42.5) were 0.01, 22, and 1.2%, respectively, on the basis of metal content of each solidified sample. Further, the leaching behavior of Zn and Ni was modeled using the chemical equilibrium program Visual MINTEQ. Using several combinations of suspected solid phases of Zn and Ni hydroxides, carbonates and sulfides, and surface complexation onto ferrihydrite the diffuse double layer model did not accurately describe the leaching behavior of Zn and Ni.

Leaching behavior of pollutants in ferrochrome arc furnace dust and its stabilization/solidification using ferrous sulphate and Portland cement

In this study, dissolution properties under different conditions and pollution potential by toxicity characteristic leaching procedure (TCLP) of arc furnace dust generated in the production of ferrochrome were examined and some stabilization/solidification (S/S) techniques were applied to the dust depending on contaminants determined. Dissolution properties and pollution potentials of all the materials stabilized/solidified were also studied under the similar conditions. It was determined that the metallic components concentrations dissolved from the ferrochrome arc furnace dust (FAFD) except for chromium and zinc were below the detection limits. The chromium concentration dissolved from the FAFD by TCLP was found to be 9.8 mg/l. Portland cement (PC), PC–FeSO 4 and PC–sand–FeSO 4 mixtures for S/S of the FAFD were tested. Although metal ions in the cationic form were stabilized when the PC was only used, Cr(VI) in the sample was not changed depending on PC amount and remained in the soluble chromate form. The stabilization efficiency of Cr(VI) increased by the increasing amounts of PC and FeSO 4. The best S/S of the FAFD was accomplished when the 5 stoichiometric amounts of FeSO 4, 30% PC and 16% sand mixture were used. TCLP leaching results of the samples obtained under the optimum conditions were below the EPA landfilling limits.

Evaluating the Applicability of Regulatory Leaching Tests for Assessing Lead Leachability in Contaminated Shooting Range Soils

The toxicity characteristic leaching procedure (TCLP) is the current US-EPA standard protocol to evaluate metal leachability in wastes and contaminated soils. However, application of TCLP to assess lead (Pb) leachability from contaminated shooting range soils may be questionable. This study determined Pb leachability in the range soils using TCLP and another US-EPA regulatory leaching method, synthetic precipitation leaching procedure (SPLP). Possible mechanisms that are responsible for Pb leaching in each leaching protocol were elucidated via X-ray diffraction (XRD). Soil samples were collected from the backstop berms at four shooting ranges, with Pb concentrations ranging from 5,000 to 60,600 mg kg(-1) soil. Lead concentrations in the TCLP leachates were from 3 to 350 mg l(-1), with all but one soil exceeding the USEPA non-hazardous waste disposal limit of 5 mg l(-1). However, continued dissolution of metallic Pb particles from spent Pb bullets and its re-precipitation as cerussite (PbCO(3)) prevented the TCLP extraction from reaching equilibrium at the end of the standard leaching period (18 h). Thus, the standard one-point TCLP test would either over- or under-estimate Pb leachability in shooting range soils. Lead concentration in the SPLP leachates ranged from 0.021 to 2.6 mg l(-1), with all soils above the USEPA regulatory limit of 0.015 mg l(-1). In contrast to TCLP, SPLP leaching had reached equilibrium, with regard to both pH and Pb concentrations, within the standard 18 h leaching period, and the analytical SPLP results were in good agreement with those derived from modeling. Thus, we concluded that SPLP is a more appropriate alternative than TCLP for assessing lead leachability in range soils.

Leachability of printed wire boards containing leaded and lead-free solder

Due to environmental concerns and regulatory initiatives, electronics manufacturers are replacing the tin/lead solder commonly used on printed wire boards (PWBs) with alternative solders. To determine the potential waste management impacts of the alternative solders versus the tin/lead solder, two leaching tests on PWBs manufactured with five alternative types of solder were performed: the toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP). These tests are commonly used in the US regulatory community to assess pollutant leachability in different disposal scenarios. The article discusses the application and limitations of these tests. The five types of solders investigated were 63Sn/37Pb, 99.3Sn/0.7Cu, 95.5Sn/4Ag/0.5 Cu, 96Sn/2.5Ag/1Bi/0.5Cu, and 42Sn/1Ag/57Bi. The leaching tests were conducted on four PWB sections, each with a unique configuration and solder density. The largest lead concentrations were observed from the PWBs containing Sn/Pb solder, with concentrations exceeding the hazardous waste toxicity characteristic (TC) in TCLP leachates. Silver, the other regulated element used in the solders, was rarely detected, with none of the samples exceeding the TC limit for silver. High copper concentrations were observed and were determined to result from the PWB itself, not from the copper-containing solders.

Aquatic Toxicity of Leachates Generated from Electronic Devices

Heavy metal leaching of electronic waste has been documented in recent literature. Heavy metal aquatic toxicity in the toxicity characteristic (TC) leachates produced from 56 electronic devices were tested using the aquatic toxicity assays such as Ceriodaphnia dubia 48-hr acute toxicity assay, the Selenatastrum capricornutum chronic algal growth inhibition assay (test used only for circuit-board leachates), and the MetPLATE acute heavy metal toxicity tests. The electronic devices tested, include 9 circuit boards (printed wire boards), 2 videocassette recorders, 4 remote controls, 1 cathode ray tube, 15 cellular phones, 1 calculator, 5 smoke detectors and their PC board components, 3 printers, 4 laptop computers, and 7 personal computer central processing units (CPUs). The toxicity tests showed toxicity in 51 of the 56 Toxicity Characteristic Leaching Procedure leachates of electronic devices assayed.

Immobilization of lead in shooting range soils by means of cement, quicklime, and phosphate amendments

Lead (Pb) contamination at shooting range sites is increasingly under environmental concern. Controlling Pb leachability from shooting range soil media is an important step to minimize Pb exposure to the surrounding environment. This study investigated stabilization of Pb in shooting range soils treated with cement, quicklime, and phosphate. Two soils were used and collected from two shooting ranges, referred to as SR1 and SR2. The treatment additives were applied to the soils at rates from 2.5% to 10% (w/w). The effectiveness of each treatment was evaluated by Pb (w/w). The effectiveness of each treatment was evaluated by Pb leachability, measured by the Toxicity Characteristic Leaching Procedure (TCLP). The possible mechanisms for Pb immobilization were elucidated using X-ray powder diffraction (XRPD). Cement and quicklime treatments were effective in immobilizing Pb in SR1 soil, with reduction of Pb concentration in TCLP leachate (TCLP-Pb) to be below the U.S. EPA non-hazardous regulatory limit of 5 mg L(-1) at application rates of > or =5% and 28-d incubation. By contrast, cement and quicklime amendments were less effective for Pb stabilization in SR2 soil because the TCLP-Pb levels in the treated soil were still higher than the limit of 5 mg L(-1) at all application rates, although they were significantly reduced in comparison with the untreated soil. Phosphate application was most effective in reducing Pb leach ing in both soils. Even at an application rate as low as 5% and 1-d incubation, phosphate could reduce TCLP-Pb to be below the limit of 5 mg L(-1) in both soils. Immobilization of Pb in the SR1 soil amended with cement and quicklime was attributed to the formation of pozzolanic minerals (e.g., calcium silicate hydrate C-S-H and ettringite) that could encapsulate soil Pb. The pozzolanic reaction was limited in the SR2 soil upon the application of cement and quicklime. Reduction of the TCLP-Pb might result from complexation of Pb on the surface of the formed calcite. Phosphate-induced Pb immobilization was mainly attributed to formation of less soluble PbHPO4. The results indicate that effectiveness of cementitious treatments (cement and quicklime) in immobilizing Pb varies in two soils, being effective in SR1 soil but less in SR2 soil. For one given soil, no difference was observed of the effeciveness between cement and quicklime treatments, whereas phosphate amendment emerges as a most effective treatment means for stabilizing Pb in both two soils, and it also shows a faster immobilization process and little effect on the soil acid buffering capacity. Recommendations and Perspectives. Overall, our study reveals that immobilizing Pb can be one of the best management practices for Pb contamination at shooting range sites. Phosphate amendment is most effective in immobilizing Pb in any kind of the soil ranges to minimize negative Pb impacts on the shooting range sites.

Assessment of alternative management techniques of tank bottom petroleum sludge in Oman

This paper investigated several options for environmentally acceptable management techniques of tank bottom oily sludge. In particular, we tested the applicability of managing the sludge by three options: (1) as a fuel supplement; (2) in solidification; (3) as a road material. Environmental testing included determination of heavy metals concentration; toxic organics concentration and radiological properties. The assessment of tank bottom sludge as a fuel supplement included various properties such as proximate analysis, ultimate analysis and energy content. Solidified sludge mixtures and road application sludge mixtures were subjected to leaching using the toxicity characteristic leaching procedure (TCLP). Tank bottom sludge was characterized as having higher concentrations of lead, zinc, and mercury, but lower concentrations of nickel, copper and chromium in comparison with values reported in the literature. Natural occurring radioactive minerals (NORM) activity values obtained on different sludge samples were very low or negligible compared to a NORM standard value of 100 Bq/g. The fuel assessment results indicate that the heating values, the carbon content and the ash content of the sludge samples are comparable with bituminous coal, sewage sludge, meat and bone meal and petroleum coke/coal mixture, but lower than those in car tyres and petroleum coke. The nitrogen content is lower than those fuels mentioned above, while the sulfur content seems comparable with bituminous coal, petroleum coke and a petroleum coke/coal mixture. The apparent lack of leachability of metals from solidification and road material sludge applications suggests that toxic metals and organics introduced to these applications are not readily attacked by weak acid solutions and would not be expected to migrate or dissolved into the water. Thus, in-terms of trace metals and organics, the suggested sludge applications would not be considered hazardous as defined by the TCLP leaching procedure.

Application of leaching tests for toxicity evaluation of coal fly ash

The toxic properties of coal fly ash samples obtained from various coal combustion power plants were evaluated in this work using physicochemical analyses and bioassays. Physicochemical analyses showed that heavy metals present in solid samples included Cr, Cu, Mn, Ni, Pb, and Zn. The results of the chemical analysis of eluates deduced by the application of standard leaching tests according to EN 12457-2 and Toxicity Characteristic Leaching Procedure (TCLP) methods indicated that the compounds contained in fly ashes could potentially be transferred to the liquid phase depending upon the leaching method used. Heavy metal concentrations were higher in TCLP eluates, indicating that the initial pH value of the leaching medium significantly affected the transfer of these elements to the liquid phase. Tests conducted with the photobacterium Vibrio fischeri (Microtox test), the crustacean Daphnia magna, and the rotifer Brachionus calyciflorus were used to assess toxicity of eluates obtained by both leaching tests. Daphnia magna was the most sensitive test organism. The EN 12457-2 method proved to be more reliable for toxicity evaluation of eluates. In contrast, the TCLP method showed some interference owing to acetic acid toxicity, and precipitation occurred after pH adjustment of eluates from acid to neutral range. The toxicity of both fly ashes and the corresponding solid leaching residues of EN 12457-2 and TCLP leaching tests was also measured using the Microtox Basic Solid phase Test. The results generated with this bioassay indicated that toxicity was greatly influenced by the pH status of the solid samples.