Effects Of Different Crop Waste And Its Biochars On Immobilization Of Cadmium In Red Soil

To effectively utilize agricultural wastes for soil cadmium remediation has become hot topic of soil environmental science.This paper focuses on general crop wastes such as rice straw and coffee husk.Firstly,two types of biochar are made from these materials.Then the effects of rice straw or coffee husk on remediation of cadmium in red soil by its biochar has been investigated.Incubation experiment,BCR sequential extraction procedure and the toxicity characteristic leaching procedure(TCLP)are applied to estimate the effects on immobilization of cadmium in soil.The main result are as below:1.Rice straw biochar and coffee husk biochar both have high pH value,are abundant with porous structure and surface-functional groups.After adding 3%of each biochar to soil contaminated with cadmium,soil pH and soil organic matter content increased significantly.The amount of Cadmium in soil is estimated to be decreased by the percentage of 6.2 and 10.3 respectively.Remediation effect of coffee husk biochar is found to be better than rice straw biochar on soil cadmium.2.Each type of biochar at the application rate of 3%,in combination with 1%and 3%its raw material results in effective stabilization of cadmium in soil.As compared with only adding biochar treatment,rice straw were combined with its biochar causes the decline in available cadmium concentration by 2.2%and 8.8%.Mixing decomposed rice straw and rice straw biochar made available cadmium decrease by 6.6%and 12.3%.For coffee husk and decomposed coffee husk combined with coffee husk treatments,the mobile cadmium in soil decreased by 9.2%-25.3%,17.0%-25.2%,respectively.3.Mixing 3%biochar and rice straw in different rate made soil pH increased 0.4-1.0 units,soil organic matter contents rose by 1.5-2.6 folds,available cadmium contents in soil reduced by the percentage of 6.5-25.1.Additional mixing of rice straw to 3%biochar in distinct ratios also promotes remediation effect of biochar on cadmium in soil.The most effective treatment for immobilization of cadmium by biochar of raw rice straw is 3%and 0.6%for decomposed rice straw.4.In treatments of coffee husk combine with its biochar in different rates,soil pH increased by 1.7-2.3 units and soil organic matter increased 1.7-3.4 times,resulting in decreasing the amount of available cadmium in soil by 15.6%-64.2%.Remediation effect of these treatments in different ratios is significantly better than mixing rice straw and its biochar on soil cadmium.This experiment showed that the most effective utilization on immobilization of cadmium by biochar of coffee husk application rate is 1.5%.5.The results for various ratios of decomposed coffee husk,when blended in biochar shows the increase of soil pH by 2.0-2.3 units and soil organic matter by 1.7-3.4 times,which causes the decline in available cadmium concentration by 24.7%-67.5%.However in this case,the residual fraction of cadmium is remarkably higher than the result of non-decomposed coffee husk mixed with biochar treatments.This result indicates that the addition of decomposed coffee husk has more potential of enhancing the ability of biochar in cadmium stabilization.Adding 0.6%of decomposed coffee husk rate was the best choice due to the the most effective utilization on immobilization of cadmium by biochar...