The Technical Optimization Of The Removal Of Heavy Metals In Contaminated Farmland Soils

Seiral experiments were conducted aiming at the most common heavy metal pollution in farmland soil which are Zn,Cu,Cd and Hg.Experiments simulated the common concentration of heavy metals in farmland soil.In the experiments,Pteris vittata,Brassica juncea,Solanum nigrum and Thlaspi caerulescens four hyperaccumulators have been used to study their remediation effect of mild to moderate concentration heavy metal contaminated soil and the optimization of remediation techniques.The biomass,enrichment efficiency and coefficient were compared so as to provid theoretical basis and data support for the remideation.A pot experiment with these four hyperaccumulators was conducted to filter out the suitable hyperaccumulator of specific heavy metals by the comparison of Zn,Cu,Cd and Hg content in different plants.The reults showed that,in mild to moderate heavy metal contaminated soils,Thlaspi caerulescens had the best extraction effect of Zn,Brassica juncea had the best extraction effect of Cu,Solanum nigrum had the best extraction effect of Cd,and Brassica juncea has the best extraction effect of Hg.By adding different types of chelating agent into the four heavy metal polluted farmland soils with hyperaccumulators,comparing heavy metal content in the body of plants,biomass and available content of heavy metals in soil,filter out the chelating agents that can improve the redemiation effect on mild to moderate contaminated soil.The results showed that adding wood vinegar in the soil decrease the available content of Zn,Cu,Cd,in which Cd reduced mostly by a quarter,and promotedplant growth.Adding chitosan activated four heavy metals in soil,increased available content.Adding EDTA activated heavy metal ions in the soil,but it has some influence on plant growth,use carefully according to the situation.Different planting densities are used for different hyperaccumulators,compared each hyperaccumulator biomass and heavy metal extraction efficiency under different planting densities in order to get the relationship between planting density and remediation effect.Results showed that the higher planting density,the higher extraction of heavy metal content per unit area,but the lower biomass of single plant and extracting effect.By conducting cutting process at different points of time to Solanum nigrum,compared the biomass,Cd content in plants and total Cd extracting content.Results showed: cutting process performed when planting 10 d and 20 d compared with the control increased its biomass,Cd content per plant and total extraction content,increasing more evident when perform at 20 d;cutting process performed between 30 d and 40 d,its biomass,Cd content per plant and total extraction content are all reduced.To increase the remediation effect of Solanum nigrum to Cd,20 d after planting is the best time of cutting process.