Experimental Study On The Remediation Of Simulative Lead Copper And Cadmium Contaminated Soils By Biochars

Biochar is a carbon-rich product obtained when biomass is heated in a closed container with little or no available oxygen.Biochar is a suitable material to remedy the heavy metal pollution of the soil because of its larger specific surface area,higher stability and excellent adsorption performance.In this study,biochars are produced by pine tree and rice straw in a series of diffrtent temperatures.Those biochars are used to adsorb lead ? copper and cadmium in contaminated soil.The relative contribution of different composition to heavy metals adsorption onto biochars was stuied.The main results are as follows:(1) A series of biochars were produced in pine sawdust and rice straw under different temperature conditions, and their physicochemical and structural properties were analyzed.With the pyrolysis temperature increasing, the organic matter in the biomass began to decompose,and the FTIR results showed that aliphatic fraction gradually transformed to the aromatic fraction.Besides, the inorganic mineral components will be gathered on the surface of biochar.The pore structure of biochar also gradually formed, the specific surface area increased, and the p H value increased.Those factors can improve the adsorption properties of biochars.(2) The adsorption capacities of Pb ? Cu and Cd on biochars were studied by orthogonal design experiments and adsorption isotherm experiments and adsorption kinetics experiments. In the process of adsorption and stabilization of heavy metals in the soil, the content of the inorganic mineral component in the high temperature condition is better. Equilibrium adsorption amount of Pb, Cu and Cd in rice starw biochar at 600? is80.77mg/g,70.42mg/g and 38.65mg/g.(3) The main composition for Pb, Cu and Cd adsorption onto biochars were firstly distinguished.Adsorption mechanism and relative contributions were preliminarily elucidated.The organic functional groups,water soluble minerals,HCl soluble minerals,and Si containing compounds were taken into account in adsorption.The relative contribution of HCl soluble minerals is the largest,and the role of Si O2 particles could be ignored.(4) Tessier five step sequential extraction method was used to analyze the forms of heavy metals in polluted soil before and after adding biochars.In the contaminated soil,the cadmium is the most active, the second is the copper, finally is the lead. After adding biochars to the soil,the active exchangeable state, carbonate bound and Fe-Mn oxidation state of Cd are turned into the more stable organic and residual state transition.And the active exchangeable state, carbonate bound of Cu are turned into the more stable Fe-Mn oxidation state and organic state transition.Finally,the lead is the most stable, is not easy to migrate and the harm is low.