核桃青皮生物炭对重金属的吸附效应分析

Adsorption Performance of Walnut Green Husk Biochar for Heavy Metals

以核桃青皮为原料,分别在300、500和700℃的条件下经过限氧热解制备了核桃青皮生物炭WP300、WP500和WP700,并应用于溶液中Pb^(2+)、Cu^(2+)和Cd^(2+)的吸附去除.结果表明,中等热解温度下的WP500具有最高的重金属吸附性能,且在溶液初始pH为8时吸附效果最佳,对Pb^(2+)、Cu^(2+)和Cd^(2+)的去除率分别为97.87%、99.78%和71.15%.不同吸附体系下所需的生物炭投加量不一致,在单一金属体系中,WP500对Pb^(2+)、Cu^(2+)和Cd^(2+)的最佳投加量为1.3、2.1和1.9 g·L^(-1),而在复合污染体系下,生物炭最佳投加量为5.1 g·L^(-1).此外,在单一和复合重金属反应体系中,WP500对3种重金属的吸附量均呈现出Pb^(2+)>Cu^(2+)>Cd^(2+)的规律,且在竞争吸附条件下,3种吸附质之间不存在协同或拮抗作用.等温吸附模型拟合结果显示,WP500对Pb^(2+)、Cu^(2+)和Cd^(2+)的固定方式较为多元,而动力学拟合结果则证明了WP500与Pb^(2+)、Cu^(2+)和Cd^(2+)之间主要是化学吸附.分析表明核桃青皮生物炭对3种重金属的吸附机制涉及孔隙填充、静电吸附、离子交换、矿物沉淀、官能团络合和π-π电子供体-受体相互作用.本研究为核桃青皮的资源化利用提供了一种新的视角.

The biochars of WP300,WP500,and WP700 were prepared by pyrolyzing walnut green husk under 300℃,500℃,and 700℃with the oxygen-free condition for removing Pb^(2+),Cu^(2+),and Cd^(2+)in an aqueous solution.The results revealed that WP500 prepared under the medium pyrolysis temperature achieved the best adsorption performance for heavy metals,and the highest removal efficiency was reached when the solution pH was 8,in which the removal efficiency of Pb^(2+),Cu^(2+),and Cd^(2+)were 97.87%,99.78%,and 71.15%,respectively.The required biochar dosage for heavy metal removal varied under different adsorption conditions.In the single-metal system,the optimal dosage for WP500 in the Pb^(2+),Cu^(2+),and Cd^(2+)solutions was 1.3 g·L^(-1),2.1 g·L^(-1),and 1.9 g·L^(-1),respectively,whereas in the pollution metals system,the optimal biochar dosage was 5.1 g·L^(-1).In addition,the adsorption capacity of WP500 for the three heavy metals followed the order of Pb^(2+)>Cu^(2+)>Cd^(2+)under the single and combined-metals system,indicating that there were no synergistic or antagonistic effects among these three adsorbates.The fitting results of the adsorption isotherm model suggested that various immobilization methods existed in adsorption process between WP500 and Pb^(2+),Cu^(2+),and Cd^(2+).The kinetic fitting results suggested that the main reaction between WP500 and Pb^(2+),Cu^(2+),and Cd^(2+)was chemical adsorption.The mechanisms of WP500 for heavy metals involved pore-filling,electrostatic attraction,ion-exchange,mineral precipitation,complexation,andπ-πelectron donor-accepter interaction.To conclude,this study offered a new insight for the resource utilization of the waste walnut green husk.