Effects of Different Biomass and Pyrolysis Technique on Biochar Characterization and Immobilization of Heavy Metal in Contaminated Soil

Using reed and corn straw as raw materials, different biochars were prepared by orthogonal experimental design and applied to the remediation of Cd- and Pb-contaminated soils to find out the best preparation technique of biochar. The results show that carbonization temperature was the most important factor for the preparation of biochar. The yield of biochar decreased with the increase of temperature, while the pH and ash content of biochar increased. The specific surface area of biochar increased as temperature rising in a certain range. Other factors such as the moisture content, heating rate, and carbonization time of raw materials had less effect on the preparation of biochar compared with carbonization temperature. The yield of reed straw biochar (LWC) and corn straw biochar (YMC) was similar, the pH value and ash content of YMC was higher than that of LWC, and the specific surface area of LWC was higher than that of YMC. Considering the optimum level of factors and efficiency, the optimum pyrolysis condition for the preparation of LWC and YMC was found to be the same with moisture content of 25%, heating rate of 20℃·min^-1, carbonization temperature of 600℃, and carbonization time of 0.5 h. Compared with the control, the application of LWC and YMC increased the soil pH. Additionally, the immobilization efficiency of Cd and Pb increased with the incubation time. At 35 days, the contents of available Cd and Pb in soils maximally decreased by 51.7% and 44.9% with the addition of biochar. The inactivating effect of LWC to Cd and Pb in soils is better than that of YMC. The present research provides a technical support for the engineering preparation of biochar and a theoretical basis for the remediation of heavy metals in soils.