The effect of metal ions with different valences on the retardation of soil-bentonite barrier materials and its mechanism

In this paper, with K⁺, Ca²⁺ and Fe³⁺ as the objects of study, retardation of soil–bentonite (SB) barrier materials for metal ions with different valences is investigated, and the adsorption mechanism, migration patterns and permeation behavior are explored so as to provide a theoretical basis for their application. The results show that the adsorption process for metal ions with different valences by SB barrier materials is fast, and the higher the valence, the greater the adsorption capacity. The fitting of the adsorption process conforms to pseudo-second-order adsorption kinetics and Langmuir–Freundlich adsorption equation, which explains that chemical adsorption is the dominating state and that the SB surface has certain heterogeneity. The permeability coefficient of K⁺, Ca²⁺ and Fe³⁺ in SB each has a maximum and the higher the valence, the sooner the maximum appears. Also the higher the valence, the more obvious the effect on SB retardation performance; and the sooner the ion breaks through the barrier wall completely, that is, the wall's retardation performance for higher valent ions may decline.