| With the rapid development of China's economy,the deepening of industrial restructuring,and the implementation of the"two-in-three"policy,the number of industrial enterprises relocated or demolished increased,resulting in a large number of polluted sites?also known as"brown fields"?.In recent years,heavy metal pollution incidents occur frequently,which poses a threat to human health and the ecological environment.Soil heavy metal pollution needs to be solved urgently.Solidification/stabilization technology has attracted much attention due to its low consumption and high efficiency.Previous studies on single heavy metal contaminated soils are rich,but few on complex heavy metal contaminated soils.It is especially urgent to study high-intensity and multi-heavy metal contaminated soils caused by non-ferrous smelting enterprises.In this study,cement was selected as curing agent,sodium sulfide,calcium dihydrogen phosphate and lime as stabilizers.Through experiments,the relationship between various factors and treatment effect was determined,the optimum ratio of curing agent and stabilizer was screened,and the solidification/stabilization repair conditions were optimized.The main research results were as follows:?1?Sodium sulfide,calcium dihydrogen phosphate and lime were used as stabilizers respectively.When the curing time was 28 days,14 days and 28 days,and the adding amount was 20%,6%and 8%,the leaching concentration of lead in stabilized soil was the lowest,which was 3.7 mg·L-1,0.0 mg·L-1 and 44.7 mg·L-1,respectively,the highest stabilization efficiency was 98.34%,100%and 79.96%,respectively.When the curing time was 7 days,7 days and 28 days,and the addition amount was 15%,4%and 8%,the leaching concentration of cadmium in stabilized soil was 0.0 mg·L-1,20.6 mg mg·L-1 and 6.9 mg·L-1,and the stabilization efficiency was 100.00%,32.01%and 77.23%,respectively.The lead and cadmium contaminated soil up to the hazardous waste level can be treated to the general soilid waste level.?2?When the curing time is 28 days and the proportion of cement is 40%,the leaching concentration of lead is 82.4 mg·L-1,and the stability efficiency is 94.08%.When the curing time is 28 days and the proportion of cement is 40%,the leaching concentration of cadmium is the lowest and the stability efficiency is the highest,which is 8.8 mg·L-1 and 70.96%.?3?After 28 days of solidification/stabilization with compound reagent,there are two kinds of compound reagents that lead and cadmium in soil are lower than the standard limit in Standard Leaching Toxicity Identification of Hazardous Waste?GB5058.3-2007?:15%sodium sulfide+3%calcium dihydrogen phosphate+35%cement and 15%sodium sulfide+6%calcium dihydrogen phosphate+25%cement.?4?After solidification/stabilization with compound reagents,the acid extractable state of lead and cadmium in soil decreased from 8.62%,81.56%to 0.12%and 0.75%,the reducible state decreased from 27.09%,12.80%to 0.82%and 1.93%,the oxidizable state increased from 2.20%,2.51%to 4.58%and 20.11%respectively,and the residual state increased from 62.09%,3.14%to 96.05%and 77.37%,respectively.With the addition of compound agents,lead and cadmium can be transformed into stable forms and their bioavailability is reduced. |
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