液/固体系Cu2+、Zn2+、Mn2+在硅藻土表面的吸附行为与特性

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.

Adsorption behavior and characteristics of Cu2+, Zn2+, Mn2+ onto diatomite in liquid/solid system

In order to well understand adsorption behavior and characteristics of Cu²⁺, 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/diatomite 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 min, 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.