Study On Adsorption Of Lead By Biochar And Its Modified Materials

Biochar is a group of carbon rich porous material produced by wood,straw,livestock manure through thermal decomposition in a closed system under partial or complete anoxic conditions.Because of the surface oxygen-containing functional groups and developed pore structure of biochar,it has a well adsorption effect on heavy metals and other pollutants.It also has a significant effect on soil improvement.In this word,the branch of kiwifruit was chosen as raw material to prepare the biochar of different pyrolysis temperature,and the biochar is modified by acid-alkali and chitosan.Scanning electron microscopy（sem）,Fourier infrared spectrum and X-ray diffraction（XRD）were employed to characterize the biochar.The Effects of the different pH,different biochar dosage and contact time concentration on adsorption process were investigated and adsorption kinetics and adsorption isotherm of the absorptions of Pb²⁺in the solution by the biochar also were.The effect of biochar on soil pH and available lead content in soil was studied by soil culture experiment.The main conclusions are as follows:（1）The yield of undisturbed biochar is negatively correlated with the pyrolysis temperature.The ash and pH of biochar are obviously positively correlated with the pyrolysis temperature,and there is also a significant positive correlation between the pH and ash content of biochar.With the increase of biochar pyrolysis temperature,the adsorption capacity of biochar to Pb²⁺in solution gradually increased,the pyrolysis temperature rises from 250 to750,the adsorption capacity of biochar to Pb²⁺increased from 88.24mg g^-1 to 150.24mg g^-1,the removal rate of Pb²⁺increased from 44.12%to 75.12%in solution.（2）The biochar modified by acid-alkali has smoother surface,and the biochar modified by chitosan does not show obvious pore structure,and presents a relatively dense mass structure.The number of-OH and-COOH in biochar modified by acid-alkali and chitosan increase.The crystallization degree of the modified biochar was enhanced.After the modification of chitosan,the characteristic diffraction peak of chitosan was observed.（3）The adsorption of Pb²⁺by three biochars were increased with the increase of pH value（pH 2-6）,and the biochar modified by chitosan was not very sensitive to the pH change of the solution.The Pb²⁺removal rate of bichar increased with the biochar dosage,the adsorbed amount of Pb²⁺decreased.（4）The Pb²⁺adsorption of biochar in the solution followed Pseudo-second-order Kinetics more,the R²_adj was 0.9924,0.9968and 0.9942 respectively.The adsorption process of biochar to Pb²⁺can be divided into two stages:membrane diffusion and particle diffusion process.Freudlich adsorption isotherms equation can better describe the isothermal adsorption of Pb²⁺in the solution of biochar,the R²_adj was 0.9980,0.9908 and 0.9904 respectively.（5）Compared with the unmodified biochar,the Pb²⁺adsorption of the biochar modified by acid-alkali and chitosan increase 19.57%and 8.37%respectively.（6）The addition of unmodified biochar and acid-alkali modified biochar according to 3ratios（0.5%,1%and 5%）can improve the pH value of soil.The addition of biochar modified chitosan according to 3 ratios resulted in a decrease in pH value.The addition of three kinds of biochar according to 3 ratios can reduce the content of available lead in soil,and the reduction rate is over 75%.