Effects And Mechanism Of Remediation Of Amendments In Cd-Zn Contaminated Soils

Red soil from Qiyang County, Hunan province, and paddy soil from Jiaxing City, Zhejiang province, were collected and cultured into cadmium and zinc contanminated soils, then three amendments (lime, munare and sepiolite) were added into soils. Through soil culture experiment in laboratory and rape pot experiment in solarium, the effects of amendments on rape biomass and uptake of cadmium and zinc, and on the value of pH, exchangeable amount and other species of heavy metals between rhizosphere and non-rhizosphere soils were studied systemically. In order to disclosure the mechanism of amendments in remediation of soils contaminated by heavy metals, and to guide the selection of suitable amendment in practical remediation of heavy metal-contaminated soils, it aimed at researching on the remediation difference of amendments in soils contaminated by single heavy metal and combined heavy metals, studying on the difference of amendments with single application and combined application in remediating heavy metal-contaminated soils. The results in this experiment showed as follows:1. Rape growed in cadmium and zinc contaminated soils was greatly inhibited or hurted by toxicity of heavy metals. However, amendments could effectively release the toxicity due to decreasing the uptake of cadmium and zinc by rape and increasing rape biomass, and their effect order was lime>manure>sepiolite. Though there was insignificant difference in amendmemts with single application and mixed application, due to the shorter residual action for lime than for manure and sepiolite, mixed application of lime and manure should be the best measure with marked and long-term effect on remeditation of soils contaminated by heavy metals.2. The effects of amendments on soils contaminated by single and combined cadmium and zinc were conform, that is, amendments could significantly decrease the available form (exchangeable speciation) of heavy metals and increase their unavailable forms (iron and manganes oxides bound and carbonate bound fractions), so they effectively decreased the bioavailability of heavy metals. Their effect order was also lime>manure>sepiolite, which was consistent with their effects on rape growth and uptake of cadmium and zinc. Thus, it could be considered that the decrease in available form of heavy metals due to application of amendments was main mechanism of amemdmetns in remediation of heavy metal-contamintated soils.3. The pH of soils contaminated by heavy metals markedly rised after application of amendments, but the effect order of amendments was lime>sepiolite>manure, which was not completely consistent with those mentioned above. So probably the increase in soil pH was mainly intrinsic factor but not only cause to explain the remediation effect of amendments in soils contaminated by heavy metals.