Adsorption of Pb 2+ in Waste-Water by Biochars Derived From Different Crop Residues

Nine types of biochar (WH500/600/700、CO500/600/700、SO500/600/700) were prepared by pyrolyzing crop straw(like wheat(WH), corn(CO) and soybean(SO)) at different temperatures ( 500，600 and 700°C)under the limited oxygen condition. The absorbability of various biochars to Pb²⁺ in waster-water and its influential factors were investigated. The results indicated that the biochars pyrolyzed at 600°C showed the highest adsorption rate to Pb²⁺ in waster water, and the adsorption percentage decreased in the order of CO600 (81.9%) > SO600 (64.9%) > WH600 (52.9%). The sorption capacity of Pb²⁺ was enhanced with the input amount of biochar increased. It should be noted that the adsorbability increased slowly when the adsorbent was fewer, the removal rates of Pb²⁺ from waster-water increased significantly when the input amount was over 3.3 g· l^-1, and equilibrium could be achieved at 10 g· l^-1. Biosorption of Pb²⁺ was a rapid reaction, and the biosorption of Pb²⁺ on the studied biochars can be segmented into two phases: the first speedy process and the next slow process; Only the pseudo-first-order model presented the best appropriate for all of the tested data and equilibrium could be achieved within 30 to 60 min. pH had great influence on biosorption of the metals, the adsorption of Pb²⁺ was enhanced with the raise of pH, and adsorption percentage of Pb²⁺ increased rapidly when the initial pH increased from 4 to 6. Under the same conditions, the maximum sorption capacity of Pb²⁺ by WH, CO and SO decreased in the order of corn>soybean>wheat. These observations provided useful information in precisely predicting the adsorption behavior of biochar to Pb²⁺ in waster water.