Stabilization Treatment Of Availablearsenic In Contaminatedsoils And Assessment Studies

In recent years,environmental pollution and health hazards caused by heavy metals has caused widespread concern. As one of the "Five Toxic Elements"(mercury,cadmium,lead,chromium,arsenic),the environmental hazards and health and safety of Arsenic (As) is particularlyof consideration. In the pollution sites of U.S. Superfund remediation, arsenic has been ranked as second inorganic contaminants.In this paper, arsenic-contaminated soils were recognized as theresearch object,using orthogonal test method,Limeand Ferrous salt were used as the auxiliary agent and stabilizing agentto treat two arsenic contaminated soils(heavy metal contamination and organic compound contamination), resultsshowed that, when the ratio of exogenousFe and soil As (mol/mol)was6:1～8:1and the dosing ratio of CaO was0.05%～0.1%(w/w), the curing period was7-14days, the best PH of soil was7.1～7.5,the stabilizing efficiency of availablearsenicin the two soilswere all over85%.Following chemical leaching test, In vitro bioexperiment, the stabilizing effectiveness and mechanism of available arsenic on treated soil were shown using morphology and structure analysis.1) Different leaching evaluation methods, leaching concentration of availablearsenic was different.The concentration of available arsenic in Sequential Extraction Procedure(SEP) was the highest after extraction, followed by Toxicity Characteristic Leaching Procedure (TCLP), and then the Sulfo-nitric process and Synthetic Precipitation Leaching Procedure(SPLP).2) When the pHof extracting agent was2.88～6, total leaching concentration of available arsenicwas decreased with the increase of pH; pH in7～9, leaching concentration of available arsenic increased with the increase of pH.3) The results of SEP also showed that the availablearsenic in soil mainly transforms into the weak state of Fe-Al or crystalline hydrated iron and manganese oxides, crystalline iron and manganese or iron hydrated oxides of aluminum.The results of In vitro test SBET indicated that, the bioavailability of arsenic in both soils significantly decreased after the stabilization treatment, rrespectively22.2%and13.2%,it showed that the consistency of the results of available arsenic between the biological effectiveness and chemical leaching.The analysis associated with physical structure characterization (XRD/SEM/EDS)showed that the main phasesof the two types of original soils contain quartz, albite, muscovite, nickel-aluminum serpentine, etc., and the new phase of hydroxyl arsenic copper mineral (AS2Cu5H4O12) generates after the stability treatment of heavy metal contaminated soil, and the hydroxyl arsenic copper mineralis present before and after the of the organic compound contaminated soils, but its content increase after stability, the two types of soilsdo not have iron-arsenic minerals generation. SEM imaging showed no significant reorganization of the internal structure of the crystal phenomenon, the appearance of the morphology of the major mineral component is almost unchanged, but the particle size decreases slightly with the extraction.