Competitive Adsorption And Sequestration To Cd²⁺,Cu²⁺,Zn²⁺ By Biochar

Heavy metal pollution has always been one of the severe environmental challenges in China due to their widely distribution,higher toxicity and hard to control.As a biomass-rich,low-cost and simple-produced adsorbent,biochar can be used to control the soil and water heavy metal contamination effectively.In the field,the contaminated soil is typically found in combination with various inorganic contaminants.Thus,the competitive sorption performance of biochar for coexisting heavy metal may be different from that for single heavy metal,and the revelent mechanisms need to be further investigated.Therefore,the remediation of biochar for coexisting heavy metal adsorption need to be further investigated.In this research,biochar was made at two pyrolysis temperatures for wheat straw biomass（350°C and 650°C）.The following studies were carried out in this paper:（1）the physio-chemical properties of biochars;（2）biochar sorption performance for Cd²⁺、Cu²⁺、Zn²in single and coexisting heavy metal aqueous solution;（3）the immobilization of heavy metal Cd²⁺、Cu²⁺、Zn²⁺on biochar-amended soil and the combination of the effect of p H and acid rain leaching on by conducting soil column experiments.The results showed that biochar pyrolyzed at high temperature（650°C）owned developed pore structure and high aromaticity,whereas biochar pyrolyzed at low temperature（350°C）owned more surface functional groups.The main sorption mechanism of heavy metals on biochar included surface complexation,ion exchange,co-precipitation and physical adsorption.The adsorption capacity was gradually enhanced with environmental p H increasing.Biochar could efficiently adsorb and immobilize Cd²⁺、Cu²⁺、Zn²⁺in water and soil.Meanwhile,biochar could increase the p H and water hold capacity of soil,and increased the soil’s buffer ability acid rain environment.Biochar pyrolyzed at high temperature exhibited better performance than that pyrolyzed at low temperature.The sorption performance of biochar for coexisting heavy metal was significant different from that for single heavy metal.In the Cd²⁺--Zn²⁺system,the antagonism effect could be found,which the adsorption performance and immobilization ability for Cd²⁺and Zn²⁺on biochar are both decreased.In the Cd²⁺--Cu²⁺and Cu²⁺--Zn²⁺systems,the adsorption and immobilization ability for Cd²⁺or Zn²⁺on biochar was greatly inhibited by Cu²⁺,which showed preferentially adsorbed advantages and maintained a highest adsorption capacity.In Cd²⁺--Cu²⁺--Zn²⁺ternary systems,Cu²⁺also present higher affinity that other two heavy metals,where biochar could adsorbed and immobilized more Cu²⁺than Zn²⁺and Cd²⁺.The preferred adsorbed heavy metal on biochar was followed the order of Cu²⁺>Cd²⁺≈Zn²⁺in the aqueous solution.Cu²⁺was the most stable heavy metal in soil,and least affected by acid rain leaching and coexisting heavy metal,while Cd²⁺was easiest migrate in soil and greater affected by acid rain leaching and coexisting heavy metal.