Kaya Abidin, Oren Ali Hakan
URS Corporation, 615 Piikoi Street, 9th Floor, Honolulu, HI 96814-3141, USA.
J Hazard Mater. 2005 Oct 17;125(1-3):183-9. doi: 10.1016/j.jhazmat.2005.05.027.
The adsorptive properties of natural and Na-enriched bentonite in zinc rich aqueous environment have been studied. The results show that adsorption behavior of both bentonites was strongly depending on the pH. At low pH values, the mechanisms that govern the adsorption behavior of bentonites are dissolution of crystal structure and competition of the metal ions with the H+. Between pH 4 and 7, the basic mechanism is an ion exchange process. The alkaline and alkaline earth metals located in the exchangeable sites of bentonites are replaced with Zn2+ cations present in the aqueous solution. At higher pH values (i.e. pH 8), formation of zinc hydroxyl species may result either participation to the adsorption or precipitation onto the bentonites. Therefore, a rapid increase in the equilibrium removal of zinc was obtained above pH 7. Increase in the initial metal ion concentration led to the increase in equilibrium adsorption to a certain degree; then, a plateau was obtained at higher concentrations. The rate of zinc removal depends also on the solid concentration of the suspension. Reducing the slurry concentration allows particles to get in the more dispersed form, resulting higher available sorption sites for zinc. As a result, the adsorption performance of Na-enriched bentonite is better than the natural bentonite in all physical and chemical changes. The data were fitted both Langmuir and Freundlich isotherms.
研究了天然膨润土和富钠膨润土在富锌水环境中的吸附特性。结果表明，两种膨润土的吸附行为都强烈依赖于pH值。在低pH值下，控制膨润土吸附行为的机制是晶体结构的溶解以及金属离子与H⁺的竞争。在pH值为4至7之间，基本机制是离子交换过程。膨润土可交换位点中的碱金属和碱土金属被水溶液中存在的Zn²⁺阳离子取代。在较高的pH值（即pH 8）下，锌羟基物种的形成可能导致其参与吸附或在膨润土上沉淀。因此，在pH值高于7时，锌的平衡去除率迅速增加。初始金属离子浓度的增加导致平衡吸附在一定程度上增加；然后，在较高浓度下达到平稳状态。锌的去除速率还取决于悬浮液的固体浓度。降低浆料浓度会使颗粒以更分散的形式存在，从而为锌提供更多可利用的吸附位点。结果，在所有物理和化学变化中，富钠膨润土的吸附性能均优于天然膨润土。数据符合朗缪尔等温线和弗伦德利希等温线。
