Background: The increasing prevalence of the Galvanized and dry battery industries has led to a rise in zinc proportions in landfills, posing environmental risks. This study explores the potential of bentonite, renowned for its metal adsorption capability, as a landfill barrier material. Methods: Adsorption characteristics of Zn(II) in natural bentonite and Shanghai clay were investigated. Various factors affecting Zn(II) adsorption, including pH, Na ion strength, contact time, initial Zn(II) concentration, and adsorption temperature, were analyzed through batch-type adsorption tests. Results: The change in pH and Na strength demonstrates no significant impact on the adsorption of Zn(II) onto bentonite, highlighting the strong selectivity of bentonite for Zn(II). Conversely, the equilibrium adsorption capacity of Zn(II) onto clay increases with rising pH or decreasing ion strength. The Zn(II) adsorption onto bentonite is well-described by the pseudo-second-order, intra-particle diffusion, and Elovih models, each achieving an R² value exceeding 0.9. While both physical and chemical adsorption coexist in Zn(II) adsorption onto bentonite or clay, the primary determinant of the adsorption rate is chemical adsorption. The adsorption onto bentonite is spontaneous, whereas onto clay it is not. The mechanism involves van der Waals forces, ion exchange, and chemical actions such as inner-sphere complexation for Zn(II) adsorption onto both bentonite and clay.

Soil‐bentonite cutoff walls, consisting of excavated in situ soil and bentonite as backfills, are used extensively as vertical barriers for groundwater pollution control. Sand mixed with high‐quality natural sodium bentonite (NaB) is commonly used as a research object to investigate the hydraulic and compression properties of soil‐bentonite backfills. However, pure sand could rarely be found in real conditions, and natural NaB may not be available readily in some countries such as China, India, and Turkey. This paper presents a comprehensive laboratory investigation on the compressibility and hydraulic conductivity (k) of soil‐bentonite backfills created by simulated in situ soil and low‐quality sodium activated calcium bentonite (SACaB). The simulated in situ soils are prepared using sand‐natural clay mixtures with sand to natural clay mass ratios ranging from 0.5 to 6.0, and the bentonite content (BC) in the base mixture ranges from 0 to 15%. The result indicates that BC dominates the compression index (C_c) of the backfill, and a unique relationship between void ratio at effective vertical compression stress of 1 kPa and compression index is proposed for various types of soil‐bentonite backfills. An increase in either BC or clay size fraction (CF) in simulated in situ contributes to reducing k, but the impact of CF in simulated in situ soil on k tends to be insignificant for backfill with BC higher than 6%. A new characteristic parameter based on the concept of void ratio of bentonite (e_b), named apparent void ratio of clay size fraction (e_C), is developed for predicting soil‐bentonite backfills created by in situ soils and bentonites with various contents.

An empirical equation was proposed to predict compression index (C_c) of saturated reconstituted contaminated clays. Experimental data from 464 oedometer tests from literature were analyzed, aiding to develop a method for predicting the C_c of saturated reconstituted contaminated clays. The predictive capacity of three existing empirical equations of C_c with either liquid limit (w_L), plasticity index (PI) or initial porosity (n₀) was assessed. It was found that these equations previously used for clean soils roughly predict the C_c value of saturated reconstituted contaminated clays. To better predict the C_c, a series of empirical equations were established by regression analysis of the experimental data. Finally, the “best” equation was determined by an assessment of goodness of fit.