Study On Leaching Agent Of Chromium-contaminated Soil

Due to the rapid development of chromate production in the past, more than 600 million tons of chromium residue was accumulated historically. The long-term stack of chromium residue resulted in serious soil Cr pollution problems. As the sites distributed widely and the characteristics of contaminated soil differ largely, the remediation measures of contaminated soil in different regions and different pollution degree is not the same. This thesis selects the surface soil of Yima chromium slag contaminated sites and Baotou Hanqing dam chromium slag contaminated sites which possess local South and North soil properties as the research object and uses a variety of agents and washing agent screening experiments.Use the removal effect of Cr?VI? in soil and the total Cr as index, find out the two suitable cleaning agents of the two kind of soil and then perform the cleaning combined agent screening experiments: combined use of the reagent which has good removal effect of Cr?VI? in the soil and the total Cr, adjust the adding order of reagents in order to find out the combined cleaning agent which have good removal effect both of Cr?VI? in soil and total Cr.Research results show that:?1? The status of Cr in Baotou contaminated soil is mainly in extractable acid Cr, accounting for about 70.8% of total chromium, while the percentage of extractable acid Cr in Yima contaminated soil is about 8.7%;?2? If using water as a cleaning agent for cleaning contaminated soil, in the ratio of liquid and solid is 6:1, stirring time is one hour, for Baotou contaminated soil, in times of cleaning for two times, the Cr?VI? removal rate can reach 98.78% and the total chromium removal rate could reach 82.3%; if using sulfuric acid solution of pH=3.2 as cleaning agents, othe Cr?VI? in Baotou contaminated soil removal rate of 99.11% after cleaning twice and total CR removal rate was 67.2%. Therefore, the optimal washing times can be determined as twice.?3? through the stable medicament effect comparison of 7 agents:FeSO₄, Na₂SO₃, Na₂ S and Na₂S₂O₃, glucose, citric acid and humic acid, it is found that for Baotou contaminated soil, FeSO₄, Na₂SO₃ for Cr?VI? removal effect is best, which can reach more than 98% and the glucose, citric acid for the removal effect on the total chromium is remarkable which is about 90%. For Yima contaminated soil, Na₂SO₃, Na₂ S for the removal effect on Cr?VI? in the soil is best which can reach more than 95% and humic acid also has good removal efficiency which can reach 82%;?4? Trough a combination of experimental cleaning agent, it demonstrates that the adding order of cleaning agents have great effect of removal effect of the Cr?VI? and the total Cr.?5? Through the analysis of the combined cleaning agent, we find that the removal effect of combined citric acid / Na₂SO₃ is the best to Baotou contaminated soil. The total chromium removal efficiency can reach 85.52% and the Cr?VI? removal efficiency can reach 99.83%, and soil residual Cr?VI? content is lower than 10 mg / kg. But for Yima contaminated soil, removal effect of N/F combined reagent for Cr?VI? is the best which could reduce the content of Cr?VI? to 15.59mg/kg.