酸性条件下红壤表面Zn^2＋-H^＋反应动力学的能量特征

用自行设计的动力学装置研究了酸性条件下Zn在红壤表面的反应动力学能量特征。结果表明,酸性条件下,Zn吸附分为快反应和慢反应。用一级动力学方程拟合的Zn最大吸附量：pH5.5处理Zn的最大吸附量在289 K时为1.79 mmol.kg^-1,在313 K时为2.62 mmol.kg^-1;pH3.3处理Zn的最大吸附量在289 K时为0.12 mmol.kg^-1,在313 K时为0.16 mmol.kg^-1。即吸附量随酸度增加显著下降,随温度升高明显增加。用扩散速率常数计算的活化能（ΔE＊）：pH5.5处理Zn的ΔE＊为9.05 kJ.mol^-1,pH3.3处理Zn的ΔE＊为12.02 kJ.mol^-1,随酸度的增加ΔE＊增加,Zn扩散需克服的能障加大,Zn吸附量降低。ΔH值为正,温度升高可促进Zn的扩散;ΔS值均为负,说明吸附反应使体系有序度增加。原液pH为5.5时,流出液的pH急剧下降;pH4.3、pH3.8和pH3.3时流出液比流入液的pH高,是由于土壤的缓冲作用和土壤表面质子化;当溶液中H＋超过一定数量后,反应初期的H＋消耗是快反应过程,H＋对矿物的溶蚀成为速率控制步骤。

Energy Characteristics of Reaction Kinetics of Zn^2＋-H^＋ on Red Soil Surface Under Acidic Conditions

Energy characteristics of the reaction kinetics of Zn on red soil surface under acidic conditions were investigated by using a home made dynamic device. The results showed that Zn adsorption could be divided into rapid and slow reactions. The maximum amount of Zn adsorption fitted by the first order equation was 1.79 and 2.62 mmol·kg^-1 at 289 K and 313 K in pH5.5 treatment, and 0.12 and 0.16 mmol·kg^-1 at 289 K and 313 K in pH3.3 treatment, respectively. It remarkably decreased with increase in acidity and increased with increase in temperature. Activation energy （△E^＊）of Zn diffusion calculated by using b value of the rate constant of parabolic diffusion taw was 9.05 and 12.02 kJ·mol^-1 in pH5.5 and pH3.3 treatments, respectively. It increased with increase in acidity, which reflected that the energy barrier to be overcome by Zn diffusion would rise up and the rate of diffusion in Zn adsorption decrease accordingly. Enthalpy of activation （AH）was positive in value and rising temperature could contribute to Zn diffusion. Entropy of activation （△S）was negative in all cases, suggesting that system could improve its degree of order. The effluent pH drastically dropped when the influent solution was pH5.6. There was the consumption process of H^＋ by using influent of pH4.3 and pH3.8 and pH3.3, which was attributed to soil buffer mechanism. H＋ consumption was rapid at the initial stage of the reaction. Since H^＋ dissolution of minerals became a controlling process.