Experimental Study On Remediation Of Heavy Metal Contaminated Soils In Mining Area By Rice Straw Biochar

At present,with the rapid development of industrial and agricultural production,the pollution of heavy metals in agricultural soils has increased in China.Heavy metals are difficult to degrade in the soil,they will be easy to accumulate in the soil and enter the food chain through plants,which pose a high risk to the agriculture products safety and human health.Therefore,it is particularly important to select appropriate soil passivation materials for remediation of heavy metal contaminated soil.As a new type of biomass resource,biochar can be widely used as a soil amendments in heavy metal contaminated soil to improve soil environment conditions and soil fertility,due to its excellent physical and chemical properties.In this study,the test farmland soils of Huainan mining area was treated as the target of remediation and the biochar derived from rice straw and produced at 550?.The biochar samples were characterized via analysis from Elemental analysis,Specific surface area,Scanning electric microscopy and Fourier transform infrared spectroscopy.The effects of biochar application on the speciation and bioavailability of heavy metals Cd,Cu,Zn and As in contaminated soils of mining areas were investigated by soil-biochar incubation experiments.The effects of biochar application on the adsorption and fixation of Cd,Cu,Zn and As in contaminated soils were studied by simulated rainfall column leaching experiment.Through the above experimental analysis,the main results are as follows:(1)From the test results,it can be seen that the soil in the mining area shows heavy metal pollution to a certain extent.The result showed that the content of Cd in soil was 9.51 times higher than the Huainan soil background values.The contents of Cu,Zn and As were 2.97,1.60 and 1.42 times to the background values,respectively,and the total contents of all study heavy metals were higher than the background values of soil elements in China.Combined with three heavy metal pollution risk assessment methods,it is concluded that the level of heavy metal pollution in farmland soil in Huainan mining area is Cd>Cu>Zn>As.(2)The biochar-soil incubation experiment of simulated natural environment showed that after 60 days incubation,biochar added to the soil significantly increased soil pH value,and the effect increased with the increase of rice straw biochar applied.Speciation analysis of BCR method indicated that Cu and Cd in contaminated soil were mainly associated with the reducible form,while Zn and As were dominated by the residual form.After biochar applied to contaminated soil,the residual form of heavy metals was increased,while the acid soluble form was reduced.According to the results of CaCl2 extraction experimental,the CaCl2-extractable concentration of Cu,Zn,As,and Cd were observed with a biochar dosage rate of 10%,which were 57.26%,51.37%,6.94%and 42.04%lower than those at control soil samples,respectively,but there were no obvious changes of CaC12-extractable As.(3)The biochar-soil column leaching experiment of simulated rainfall showed that the pH value and electric conductivity in leachate increased with the increase of biochar addition amounts,except for the leachate pH value on the first tests.After biochar added,its can effectively fix Cd,Cu and Zn in contaminated soil.Among them,BC-10 treatment had the highest fixation efficiency for Cd,Cu and Zn,followed by BC-6 and BC-2 treatment,and the fixation efficiency of heavy metal for each biochar treatment was Zn>Cd>Cu.From the point of view of fixed efficiency and capacity,the application of biochar could promote the release of As in soil rather than adsorbing As under simulated rainfall conditions.At the same time,compared with the control group(CK),the cumulative leaching amount loss of heavy metals in the soil leachate applied to biochar decreased to some extent.The experiment showed that the addition of biochar could effectively fix the heavy metals Cd,Cu and Zn in the soil,and the fixation effect became more obvious with the increase of the amount of biochar added.However,the amount of As leaching in the soil leachate treated with biochar was much larger than that in the soil control group,and the release amount was higher with the increase of biochar application amount.