Assessing arsenic leachability from pulverized cement concrete produced from arsenic-laden solid CalSiCo-sludge (original) (raw)
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Arsenic leachability and speciation in cement immobilized water treatment sludge
Chemosphere, 2005
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 lg l À1 , 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 2 yr. 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.
Arsenic Leachabilty in Water Treatment Sludge
Proceedings of the Water Environment Federation, 2003
The U.S. Environmental Protection Agency (EPA) reduced the maximum contaminant level (MCL) of arsenic for drinking water from 50 to 10 µg/L on October 31, 2001. Since coprecipitation processes with ferric coagulants are commonly used for removing arsenic in source water, large amounts of iron sludge with elevated arsenic content are generated. Accurate determination of the leachability of arsenic in the water treatment sludge is crucial for both economic concerns and the evaluation of environmental impacts. Thermodynamic modeling and batch leaching tests, such as toxicity characteristic leaching procedure (TCLP), California wastes extraction test (WET), availability test (NEN 7341) and sequential extraction test, were performed to investigate arsenic leachability in anaerobic and aerobic sludge from two water treatment plants. The anaerobic sludge samples were obtained from a dewatering pond in surface water treatment plant in Los Angeles (LA) with high arsenite As(III) content and the aerobic sludge samples were obtained from the groundwater remediation treatment plant in Washington State (WA) with elevated arsenate As(V) content. The results showed that arsenic leachability was affected by its oxidation state. Arsenic leachability determined by TCLP was 283 µg/L for anaerobic LA sludge and 21 µg/L for aerobic WA sludge, although total arsenic content was 935 and 8881 mg/kg for LA and WA sludge, respectively. When LA sludge was pretreated by H 2 O 2 , the arsenic leachate concentration was reduced dramatically to 30 µg/L. The presence of dissolved oxygen substantially decreased the WET leachability of arsenic in anaerobic LA sludge, while had little effect on the aerobic WA sludge. The availability of arsenic determined by NEN 7341 was increased when the sludge samples were stabilized with lime and cement, while the arsenic leaching behavior was determined by the final pH of the leachate. Stabilization with cement changed the arsenic association with different phases, that is, exchangeable, bound to carbonate, iron, organic, and residual phase. The molecular structure of As in WA sludge determined by Extended X-ray absorption fine-structure spectroscopy (EXAFS) showed that arsenic formed inner sphere surface complex with iron. The arsenic-iron interatomic distance was 2.89 Å. When the sludge was stabilized with cement, arsenic was associated with calcium and the distance of As-Ca was 3.65 Å.
Disposal Problem of Arsenic Sludge Generated During Arsenic Removal from Drinking Water
Procedia environmental sciences, 2016
Arsenic (As) causes acute and chronic toxicity, it harm the skin and associated with increase risk of cancer in the skin, bladder and kidney. It is very difficult to diagnose the early symptoms of arsenicosis so it depends largely on awareness with improving the quality of drinking water. There are several methods are available for removal of As from water. The most commonly used technologies are oxidation, co-precipitation, adsorption, absorption, coagulation, ion-exchange resin, lime treatment and membrane techniques. Now today the safe disposal of large quantity of As contaminated sludge generated from As removal water treatment plant which contain about 5-7 kg of arsenic per cubic meter due to risk of underground water contamination as arsenic has very high leaching potential. For safe disposal of solid hazardous waste of As requires treatment. A long term solution appears to solidification/stabilization (s/s) of As-sludge and using it for beneficial purposes like bricks and concretes etc. In the field of active research, this paper identifies the gap between the implementation of process as well as new technologies for safe disposal of arsenic sludge.
Journal of Environmental Management, 2019
In this study, concrete stabilization is adopted to sustainably manage hazardous arsenic-iron sludge near the vicinity of a community-based arsenic water treatment plant for potential use as material for local construction. The strength and workability of the sludge mixed with fresh concrete were investigated to determine the suitability of the concrete mixture for building materials. We found that over 25% sludge (with respect to cement weight) can be incorporated safely into different grades of concrete (M15 and M20). Structural characterization of the concrete mixtures by Fe and As K-edge X-ray absorption spectroscopy indicated a structural transformation of Fe in the sludge from a hydrous ferric oxide to a less ordered phase consistent with Fe siliceous hydrogarnet. Differences in the As K-edge XAS data of samples before and after stabilization in concrete were interpreted as a decrease in As-Fe coordination after concrete stabilization in favor of As-Ca coordination. The leaching of arsenic in the stabilized concrete was examined by the Toxicity Characteristics Leaching Procedure (TCLP) and found to produce < 15 μg/L As, even at the highest sludge mixture fraction (40% sludge with respect to cement weight). The formation of calcite in concrete stabilized arsenic sludge, which was detected by X-ray diffraction (XRD), contributes to the low leachability of arsenic in the sludge for a variety of reasons, including decreasing pore size. In addition, the formation of poorly soluble calcium arsenates can also be responsible for the low mobility of arsenic. Overall concrete stabilization of arsenic-iron sludge can be an effective pre-treatment to safe landfill disposal and, when the arsenic-iron sludge is mixed in specific proportions to achieve desired strength, we propose this concrete can be used locally in nearby construction.
Arsenic waste from water treatment systems: characteristics, treatments and its disposal
Water Supply, 2014
As with other water treatment systems, arsenic treatment creates not only quality water but arsenic waste as well. Management of arsenic waste is now becoming a major public concern due to its harmful effects on the surrounding environment, including serious health problems such as skin cancers and various internal carcinomas. The main aim of this paper is to review: (i) the characteristics of arsenic waste produced by arsenic treatment systems; and (ii) the treatment and disposal methods of this waste. Arsenic waste type or its characteristics play an important role in choosing the best method of treatment and disposal. Currently, encapsulation of arsenic waste through solidification/stabilization (S/S) techniques is considered to be the most attractive solution and this method is the focus of this review. A number of studies have used cement by itself and in combination with additives such as lime, iron, silicates, or fly ash in the S/S process. Although there is a lack of systema...
A SEM and X-ray study for investigation of solidified/stabilized arsenic–iron hydroxide sludge
Journal of Hazardous Materials, 2005
Despite the fact that the solidification/stabilization of arsenic containing wastes with Portland cement and lime has an extensively documented history of use, the physical and chemical phenomena as a result of the interaction between arsenic and cement components have not been fully characterized. The study investigates the behavior of synthesized arsenic-iron hydroxide sludge, the by-product of arsenic removal by coagulation with ferric chloride, in solidified/stabilized matrices as well as its binding mechanisms by exploring the cementitious matrices in the micro-scale by scanning electron microscopy equipped with energy dispersive X-ray spectrometer (SEM-EDS). It was revealed that arsenic can be chemically fixed into cementitious environment of the solidified/stabilized matrices by three important immobilization mechanisms; sorption onto C S H surface, replacing SO 4 2− of ettringite, and reaction with cement components to form calcium-arsenic compounds, the solubility limiting phases.
Arsenic stabilization on water treatment residuals by calcium addition
Journal of Hazardous Materials, 2009
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&amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;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.
Immobilization Mechanism of Arsenic in Waste Solidified Using Cement and Lime
Environmental Science & Technology, 1998
The material studied, a waste fly ash from the metallurgical industry, contains the toxic element As in high concentrations, ranging from 23% to 47% (wt %). Besides As, Sb and Pb are present in the waste material. The waste was solidified with inorganic materials such as cement and pozzolanic materials in order to reduce the leachability of the contaminants from
2006
Stabilization/solidification (S/S) is used as a pre-landfill waste treatment technology that aims to make hazardous industrial wastes safe for disposal. Cement-based solidification/stabilization technology is widely used because it offer assurance of chemical stabilization of many contaminants and produce a stable form of waste. The leaching behavior of arsenic from a solidified/stabilized waste was studied to obtain information about their potential environmental risk. Activated alumina (AA) contaminated with arsenic was used as a waste, which was stabilized/solidified (S/S) using ordinary portland cement (C), fly ash (FA), calcium hydroxide (CH) and various polymeric materials such as polystyrene and polymethyl methacrylate (PMMA). Toxicity characteristics leaching procedure (TCLP) and semi-dynamic leach tests were conducted to evaluate the leaching behavior of arsenic. Formations of calcite along with precipitate formation of calcium arsenite were found to be responsible for low leaching of arsenic from the stabilized/solidified samples. Effective diffusivity of arsenic ion from the matrix and leachablity index was also estimated. Minimum leaching of the contaminant was observed in matrix having AA + C + FA + CH due to the formation of calcite.