The Effect Of Biochar And Its Complex On The Passivation Of Cd In The Contaminated Soil

Biochar is a new material, which has an effective passivation of Cd. Moreover,the use of inorganic and organic conditioners together with the biochar can realize mutual compensation of advantages. Hence, it is a promising approach to apply inorganic and organic conditioners with the biochar by following some proportional relations. In this study, the capability of peanut shell-derived biochar（PSDB） to absorb Cadmium（Cd） were investigated in the lab. By making use of soil incubation experiments, pot experiments and field tests, the beneficial effects of PSDB and the use of PSDB in combination with conditioners on soil p H, stable effect of DTPA-Cd, Cd accumulation of vegetables, soil enzyme activity and nutrient content of vegetables were also studied. The main results were as follows:（1）PSDB had a large number of different sizes of holes and neatly arranged on its surface. Most of pores were large and they had a large surface area and pore volume. It provided the space for the adsorption of Cd²⁺. PSDB also contained large amounts of nutrients such as N, P, K, etc. They also had a lot of functional group like-OH,-C=O,which could offer potential spots for the Cd²⁺ adsorption. The results of adsorption test showed that the adsorption kinetics of Cd²⁺ by PSDB were in line with the Elovich model,while its complex were secondary dynamic model. Both characteristics of the Cd²⁺ adsorption could be used by the Langmuir equation.（2）PSDB and its complex could increase the soil p H value, reduce the availability of Cd. In the soil incubation experiments, both conditioners can reduce the availability of Cd up to 31.2% and 29.1%. While pot experiments showed that PSDB and its complex could reduce up to 31.8% and 37.1% effectively increase the soil p H value and reduce the DTPA-Cd content in the soil, the maximum by 31.8%. The results of field experiment showed that 2 t/667m2 of PSDB was the best to reduce the biological availability of Cd.（3）PSDB and its complex could reduce the Cd content of vegetable.The application amount of 6% and 8% biochar were the best to reducing the Cd content of Ipomoea aquatic Forsk, by 43.4 %, 51.1%, 49.3% in the 3 crops respectively. While the application amount of 6% PSDB-conditioner complex reduced the Cd content of Chinese cabbage by85.7%（drop to 0.10 mg/kg, satisfied with the food safety standards）. However, a higher amount of biochar or its complex went against to the growth of vegetable, resulted in decreasing its biomass. This varied in the field trials of two crops, the amount of 2 t/667m2 in the first crop while 6 t/667m2 in the second crop. The Cd acquisition by roots was negatively related with the application amount of PSDB.（4）PSDB-conditioner complex could ameliorat the Cd-polluted soil. The resistance index such as malondialdehyde accumulation（MDA）, superoxide dismutase（SOD）,peroxidase（POD）, catalase（CAT） activity significantly decreased by 20.4%, 41.6%, 29.7%and 18.5%, respectively. Furthermore, PSDB-conditioner complex had an impact on soil enzyme activity and soil microbial activity. The treatment can significantly increase the urease activity by 40%⁴70% and increase microbial nitrogen by 16.4%²83.9%, and both were positively related with the amount of the biochar; while reduce microbial carbon by36.6%⁷6.7% and reduce phosphatase activity by 36.6%⁷6.7%, and both were negatively related.