液/固体系Cu^(2+)、Zn^(2+)、Mn^(2+)在硅藻土表面的吸附行为与特性

Adsorption behavior and characteristics of Cu^(2+),Zn^(2+),Mn^(2+) onto diatomite in liquid/solid system

为了深入了解液/固体系Cu^(2+)、Zn^(2+)、Mn^(2+)在硅藻土表面的吸附行为与特性,为硅藻土在含重金属离子废水处理上的应用提供充分的理论依据,采用静态吸附试验对Cu^(2+)、Zn^(2+)、Mn^(2+)在硅藻土表面的吸附条件、性能、行为与特性进行了系统的研究.结果表明,硅藻土投加量和离子初始浓度对硅藻土吸附Cu^(2+)、Zn^(2+)、Mn^(2+)的影响均可归结为液/固比(液相离子与硅藻土的质量比)的影响,过高或过低的液固比均不利于吸附,硅藻土吸附Cu^(2+)、Zn^(2+)、Mn^(2+)所需的最佳液/固比分别为0.025、0.100和0.100.溶液初始pH值对硅藻土吸附Cu^(2+)、Zn^(2+)、Mn^(2+)的影响主要与溶液初始pH值与硅藻土等电点(2.0)之间的距离有关,接近或低于硅藻土等电点都不利于吸附,过高的pH值会使Cu^(2+)、Zn^(2+)、Mn^(2+)发生沉淀,也不利于吸附,硅藻土吸附Cu^(2+)、Zn^(2+)、Mn^(2+)所需的最适溶液初始pH值区间分别为4.0~6.0、4.0~7.0和4.0~7.0.溶液温度对硅藻土吸附Cu^(2+)、Zn^(2+)、Mn^(2+)的液膜扩散、颗粒扩散和吸附反应3个过程的影响不一致,导致对吸附量的影响无明显规律.硅藻土对Cu^(2+)、Zn^(2+)、Mn^(2+)的吸附分别符合Langmuir、Tenkin、Freundlish等温吸附模型,以物理吸附为主,吸附反应容易进行,在40 min达到平衡,吸附容量(25℃时)理论值分别为4.335、23.031、3.844 mg·g^(-1).吸附是自发的、吸热的、无序性增加,符合二级动力学模型.吸附速率的控制步骤为发生在孔道内部的吸附反应.

In order to well understand adsorption behavior and characteristics of CH2＋ , Zn2＋ , Mn2＋ onto diatomite in liquid/solid system, and provide sufficient theoretical basis for application of diatomite in treatment of wastewater containing heavy metal ions, a series of static adsorption tests were conducted to investigate adsorption condition, property, behavior and characteristic of Cu2＋, Zn2＋, Mn2＋ onto diatomite comprehensively. As result indicate, the effect of diatomite adding quantity and ion initial concentration on adsorption of Cu2＋ , Zn2＋ , Mn2＋ onto diatomite can be attributed to the effect of liquid/solid ratio （ion/diatomite mass ratio）, excessive or too low ion/diatomite mass ratio is not favorable for adsorption, the best ion/diatmnite mass ratio for adsorption of Cu2＋ , Zn2＋ , Mn2＋ onto diatomite is 0.025, 0.100 and 0.100, respectively. The effect of solution initial pH value on adsorption of Cu2＋ , Zn2＋ , Mn2＋ onto diatomite is related to the gap between solution initial pH and diatomite isoelectric point （ 2.0）, close to or lower than diatomite isoelectric point are both unfavorable for adsorption, excessive initial pH value will lead to precipitate of Cu2＋ , Zn2＋ , Mn2＋ , and it is also umfavorable for adsorption, the best interval of solution initial pH value for adsorption of Cu2＋ , Zn2＋ , Mn2＋ onto diatomite is 4.0 - 6.0, 4.0 - 7.0 and 4.0 - 7.0 respectively. Solution temperature has different effect on three processes of liquid film diffusion, particle diffusion and adsorption reaction of adsorption of Cu2＋, Zn2＋, Mn2＋ onto diatomite, it leads to uncertain effect of solution temperature on adsorption quantity. The most suitable isotherm models for describing adsorption of Cu2＋ , Zn2＋ , Mn2＋ onto diatomite are Langmuir, Tenkin and Freundlish, respectively, the adsorption of each ion onto diatomite is mainly a physical process, the adsorption reaction is easy and will reach equilibrium in 40 rain, theoretical value of adsorption capacity of Cu2＋ , Zn2＋ , Mn2＋ onto diatomite is 4.335, 23.031, 3.844 mg·g-1. It also can be find that, the adsorption of Cu2＋, Zn2＋, Mn2＋ onto diatomite is spontaneous, endothermic and disorder enhancing, the adsorption kinetics fit well with the pseudo-second-order model, and the control step of adsorption process is adsorption reaction in pores of diatomite.