| With the rapid development of China's economy, problem of land shortage is becoming more and more serious. So remediation and secondary development of contaminated soil is the important means to ease the soil pressure and realize the sustainable utilization of land. In this thesis, arsenic-contaminated soils which taking from heavy metal contaminated soil of a tailings were recognized as the research object and feasible materials of arsenic stabilization remediation were be screen out. First,we filtered out the single stabilizer.Then, additives which has the best remediation effect was selected by orthogonal test and the process parameters had been optimized,including the Fe/As, doseage, particle size of the soil, reaction time and the PH value.Finally,we draw up the soil remediation proposals and guide the site rehabilitation.(1)In this thesis, XRF, SEM and Tessier sequential extraction methods for soil physical and chemical properties of the test, morphology and chemical composition and morphology of arsenic were analyzed. The results showed that the polluted soil samples tend to be acidic. There are clear crystal particles in the micro structure and the crystal particles are Irregular, loose and have many debris. Soil structure and composition is very complex. As, Cd, Pb levels are high.The organics bound is 80.09% and residual is 17.96%. The potential hazards to the ecology is terrible and it needs to be handled properly though the effective part is only two percent.The volume of the polluted soil is huge.(2) Stabilization remediation of arsenic contaminated soil:The ability that mineral material make the arsenic in soil stabilized are listed below from strong to weak: High-alkaline red mud>alkalescent red mud> sepiolite> montmorillonite> magnesium series materials. Stabilization efficiency of arsenic are positively correlated with amount of red mud added. Soil's pH which pick at 12.35 increased with amount of calcium oxide added while the leaching concentrations of arsenic in soil decreases at first and then increases with amount of calcium oxide added. This thesis shows that CaO, concentration less than 5%, can reduce the leaching concentration of As.The leaching concentration of arsenic decreases as the Fe/As mole ratio increased.The stabilization rate of arsenic increased at first and then tends to be steady.The results of the orthogonal experiment shows that ferric sulfate is most effective, calcium oxide follow and then the red mud. The best combination is A3B2C1 which the amount of CaO is 2%, ratio of arsenic and iron is 1:2, the amount of red mud is 1%.The stabilization rate of arsenic in the soil reached 60%. After the stabilizing treatment of 8th composite stabilizer, the leaching concentration of cadmium showed a downward trend.When the adding amount was over 6%, part of the lead in the soil was activated. So the amount of 8th composite stabilizer added should be controlled within 6%.(3) Optimization of process parameters in the stabilization process of arsenic:the optimal experimental conditions are listed below,Make the mole ratio of Fe and As is 2 which means the amount of CaO is 2%, ratio of arsenic and iron is 1:2, the amount of red mud is 1%, the amount of stabilizer is 6%. Let the tested soil through a 12 mesh screen to make sure the particle size is less than 1.38 mm.Experimental aging time is 3d.Then the leaching concentration of arsenic was 1.38 mg/L. The stabilization rate of arsenic is 72.6% which is over the required level which is 70%.(4) The proposal of polluted site remediation:After comprehensive screening and comparing, we finally selected PMF composite materials (calcium dihydrogen phosphate, ammonium ferric sulfate dodecahydrate, red mud as main stabilizer and calcium oxide as auxiliary additives) to rehabilitate the soil in the mining area which has polluted by various of heavy metals. When the adding amount of stabilizer reaches 6%, the stabilization rate of arsenic, cadmium and lead are all over 70% which meet the project requirements. |
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