摘要:
研究了酸性条件下Pb在可变电荷土壤表面的反应动力学.结果表明,在酸性条件下,从一级动力学方程拟合的参数可知,三种土壤的最大吸附量依次为砖红壤赤红壤红壤,Pb最大吸附量随酸度的增加显著下降.红壤、赤红壤和砖红壤在pH5.5处理的半反应时间(t1/2)分别为231 min,266 min和182min;pH3.3处理的t1/2分别为43 min,26 min和32 min.用Elovich方程和抛物线扩散方程常数(b)解释离子的表观扩散速率,三种土壤的b值依次为砖红壤赤红壤红壤,且随酸度的增大而降低.在Pb的吸附过程中,pH值为5.5和4.3时,红壤和赤红壤流出液中有质子释放;当原液pH值为3.3和3.8时,都存在质子的消耗.三种土壤H+的消耗过程有较大的区别,砖红壤快速消耗的H+量远远大于红壤和赤红壤.反应初期,H+的消耗是快速反应,主要包括土壤交换阳离子的缓冲作用、土壤表面的质子化及硫酸根专性吸附释放的羟基中和H+;而后反应中H+对矿物的溶解是一个缓慢过程.
关键词:
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酸化
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土壤
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反应动力学
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铅离子
Abstract:
Characteristics of the reaction kinetics of Pb adsorption by three variable charge soils under acidic conditions were investigated.Results showed that maximal amounts of Pb adsorption fitted by the first order equation remarkably were the order of LatosolLatosolic red soilRed soil,and decreased with increase in acidity.The halF-time values(t1/2)were 231 min,266 min and 182 min for the pH 5.5 treatment of the influent,and 43 min,26 min and 32 min for the pH 3.3 treatment of the influent in the Red soil,Latosolic red soil and Latosol,respectively.The b values of the rate constant of Elovich and parabolic diffusion equation,by explaining the apparent diffusion rate of ions,were in the sequence of LatosolLatosolic red soilRed soil and decreased with increase in acidity.In the processes of Pb adsorption,the pH values of effluent were lower than that of pH 4.3 and pH 5.5 of influent in latosolic red soil and red soil,and higher than that of pH 3.3 and pH 3.8.It showed that the former released H+ and the latter consumed H+.The amounts of H+ consumption in Latosol were bigger than that in Latosolic red soil and Red soil.At the initial stage,H+ consumption was the rapid reaction,which could be cation exchange,and the specific adsorption of SO42- to release OH-for neutralizing H+ in the solution,and surface protonation of soil minerals,and then H+ dissolution to minerals was a slow processes.
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