酸性条件下H^+-Cu^(2+)在红壤表面反应的能量特征

ENERGEY CHARACTERISTICS OF THE REACTION KINETICS OF H^+-Cu^(2+)ON RED SOIL SURFACE UNDER ACIDIC CONDITIONS

研究了酸性条件下H+-Cu2+在红壤表面反应动力学的能量特征,结果表明:酸性条件下Cu2+的吸附分为快反应和慢反应两个阶段.用一级动力学方程拟合,Cu2+的最大吸附量随酸度的增加而显著下降,随温度的升高提前达到平衡.用双常数方程描述Cu2+在吸附点位能量分布的不均匀性,用扩散速率常数b计算,活化能(Eb*)随酸度的增加而增加,Cu2+扩散需要克服的能障变大;ΔH*值为正,温度升高可促进Cu2+的扩散;ΔS*均为负值,表明吸附反应使体系的有序度增加.原液pH值为3.8和3.3时,流出液的pH值高于原液,这是由于土壤的缓冲作用、土壤表面质子化和硫酸根专性吸附释放的羟基中和;反应初期H+消耗是快反应过程,反应后期H+对矿物的溶蚀为速率控制步骤.

Energy characteristics of the reaction kinetics of H^＋- Cu^2＋ on red soil surface under acidic condition were investigated by using a home-made dynamic device. The results showed that Cu^2＋ adsorption could be divided into rapid and slow reactions. The maximal amount of Cu^2＋ adsorption fitted by the first order equation remarkably decreased with increasing acidity and reached equilibrium earlier at higher temperature. A two-constant equation could be used to describe unevenness of the energy distribution of Cu^2＋ adsorption on soil surface. Activation energy （ △Eb＊ ） of Cu^2＋ diffusion was calculated by using b value of the rate constant （ b value） of parabolic diffusion equation and increased with increasing in acidity, which reflected that the energy barrier to be overcome by Cu^2＋ diffusion would rise up and the diffusion rate in Cu^2＋ adsorption decrease accordingly. Enthalpy （△H ＊ ） was positive in value and rising temperature could enhance Cu^2＋ diffusion. Entropy （△S＊ ） was negative in all cases, suggesting that system could improve its degree of order. There was the consumption process of H ^＋ ion on soil surface by using influent of pH3.3 and pH3.8, which was attributed to soil buffer mechanism and specific adsorption of SO4^2-. H^＋ consumption was rapid at the initial stage of the reaction, then the slow dissolution of minerals caused by H ^＋ became a controlling process.