Preparation Of Biochar And Study On Adsorption Characteristics Of Heavy Metals In Soil

Soil contamination by heavy metals (HMs) has been paid widespread attention by researchers of all over the world. Biochar is a stable carbon-rich by-product synthesized through pyrolysis/carbonization of plant-and animal-based biomass. Remediation Technology of soils contaminated with heavy metals is to add biochar into soils and promote HMs in soils from bioavailable form to residual form through adsorption. This technology has unique advantages in carbon sequestration and reduction of pollutions, and is one of the most promising methods for remedying HMs in soils. At present this technology is still in its research and development stage. In this paper, biochars preparation and its adsorption on HMs (Pb and Zn ions) in soils and solution was investigated experimently, and the main work and its conclusions is listed as follows:Three kinds of biomass including poplar branch (PB), water hyacinth (WH), and corn straw (CS) were prepared in a fixed-bed pyrolyzer. The pyrolyzed biochars were characterized by the methpds of N2 adsorption/desorption, SEM-EDS, ICP-AES, XRD and FTIR. The preparation conditions on the physical and chemical characteristics of biochars were obtained. The results indicated that pore structure of biochars are significant change with increasing pyrolysis temperature, and PB biochar prepared at 700 ? shows the best pore structure. The contents of potassium, calcium and magnesium elements in the biochar gradually increase with increasing pyrolysis temperature, and WH biochar has higher cation exchange capacity (CEC). The kind and number of surface oxygen-containing functional groups descrease significantly with increasing pyrolysis temperature. WH biochar could stil retain more surface oxygen-containing functional groups at high pyrolysis temperature.The effects of biochar species, pyrolysis temperature and biochars addition on adsorption characteristics of HMs (Pb and Zn ions) in soil/solution was carried out. The obtained results indicated that WH biochar get the best adsorption ability at the same conditions, whose adsorption efficiency on Zn and Pb ions is 21.83% and 44.57%, respectively, and the relative adsoption capacity of Zn and Pb is 227.65 ?g/g and 363.76 ?g/g. The adsorption efficiency of biochars on soil HMs (Pb and Zn) increase gradually with increasing pyrolysis temperature. The adsorption efficiency of PB char on soil HMs (Pb and Zn) shows the trend of increase first and then decrease with increasing addition amount, however, the adsorption efficiency of WH biochar on HMs in soil increasew and adsorption capacity decreases with increasing addition amount. All biochars have a good performance for adsorption of HMs (Pb and Zn ions) in solution, and the adsorption efficiency of Pb ion is close to 100%.The reduction of greenhouse gas (CO2) in whole life cycle by soil remediation with biochars were assessed using life cycle assessment (LCA) method. The results indicated that all three kinds of biochars have positive effects on CO2 reduction. The CO2 reduction through utilization of biochar of PB, WH and CS is 1196.78,1068.81 and 1272.03 kgCCO2/t, respectively. The greatest contribution on CO2 reduction in whole life cycle is carbon sequestration by biochar. The biggest CO2 emission of greenhouse gas in whole life cycle is the processes of biochar application into field. On the basis of 10% crop yield, biochar utilization in soil could generate profits of 30.21-348.28 (?)/mu, in which, planting vegetable can get the highest profit of 348.28 (?)/mu. On the basis of 20% adsorption efficiency, biochar utilization in soil could reduce the pollution economic loss of HMs (Pb and Zn ions) in vegetable fields of Nanjing, in which, the highest profit up to 2.37 million (?)/a.