| Solidification technology has been widely used in the treatment of heavy metal contaminated soil because of its simple operation,low cost,instant effect and high economical efficiency.In the past,the research mainly focused on solidification of the whole soil,but there is a little research on solidification of the classified soil.In the soil used in this experiment,contents of heavy metals in fine soil is relatively high,so this experiment used fine-grained soil as objective.Calcium carbonate and diatomite were selected as curable materials,and the best ratio of curable materials was selected through the leaching toxicity test,the unconfined compressive strength test and the heavy metal speciation analysis to discuss effect of solidification under freeze-thaw condition.The main contents and achievements of the study are as follows:(1)The curing effect of different amount of curable materials(1.2%,2.4%,4.8%,9.6%)and ratio(1:1,1:2,2:1)at different ages(7d,14 d,21d,28d)was investigated.The leaching concentration of Pb in the solidified soil was lowest by 0.06mg/L and the stability efficiency was highest by 91.27%when the amount of curable materials was added by 9.6% of 2:1 ratio at 28d;The leaching concentration of Zn in the solidified soil was lowest by 1.42mg/L and the stability efficiency was highest by 81.47%when the amount of curable materials was added by 9.6% of 2:1 ratio at 28d;The leaching concentration of Cd in the solidified soil was lowest by 0.13mg/L and the stability efficiency was highest by 94.33%when the amount of curable materials was added by 9.6% of 1:2 ratio at 28 d.(2)According to the speciation analysis,the forms of Pb,Zn and Cd in soil changed from the unstable acid extractable state and the reducible state to the stable residue state and the oxidizable state,which reduced the bioavailability.(3)With the increase of curable materials content and curing culture time,the compressive strength of solidified soil increased gradually.The maximum compressive strength of soil was2.18 Mpa when adding 9.6% curable materials of 1:2 of calcium carbonate and diatomite to the soil and it was nearly three times higher than that of soil without curable materials.From these results,it is obvious that the higher the content of diatomite is,the greater the compressive strength is.(4)The freeze-thaw cycle makes the residual and oxidation state of heavy metals transform to the acid extractable and reducible state,which reduces the stabilization efficiency of heavy metals.When the total amount of curable materials was 9.6% and the ratio of calcium carbonate to diatomite was 2:1,the stabilization efficiency of Pb increased from 91.27% to 91.86%after 8 days of the freeze-thaw cycle and decreased to 89.64% after 16 days of the freeze-thaw cycle.When the total amount of curable materials was 9.6% and the ratio of calcium carbonate to diatomite was 2:1,the stabilization efficiency of Zn decreased from 81.47% to 80.91%after 8 days of the freeze-thaw cycle and decreased to 68.67% after 16 days of the freeze-thaw cycle.When the total amount of curable materials was 9.6% and the ratio of calcium carbonate to diatomite was 1:2,the stabilization efficiency of Cd increased from 94.33% to 95.46%after 8 days of the freeze-thaw cycle and decreased to 86.03% after 16 days of the freeze-thaw cycle. |
