Temperature and concentration dependence of ammonium migration in bentonite-clay mixtures: A case study in Hanoi,Vietnam

Groundwater in southern Hanoi, Vietnam has been recently detected to possess high concentration of ammonium ion (NH₄⁺). Otherwise, one of the abundant sources of NH₄⁺ comes from municipal solid waste landfills. Bentonite-clay mixtures (BCMs) widely utilized as landfill bottom barriers in various countries, but limited in Vietnam should perform well to isolate NH₄⁺ from groundwater. This study is to evaluate combined effects of temperature and initial ammonium concentration on adsorption, diffusion, and permeability through mixtures of indigenous clay with 0 %, 5 %, 10 %, 15 % bentonite. The results indicated more effective NH₄⁺ adsorption capacity for low initial concentration than high initial concentration in all temperatures (20, 35, and 50 °C). The temperature dependency showed an increase in adsorption coefficient from 20 °C to 35 °C and a decrease in the range of 35 °C and 50 °C. Whereas diffusion coefficient and hydraulic conductivity for all cases keep increasing gradually in both temperature ranges. The reasonable mass of bentonite content of 15 % should be added into local clay for landfill bottom liners in such conditions of elevated temperature at 50 °C and interaction of ammonium solution 1000 mg/L. The micro-structures via SEM images of these materials provided the proofs of both improvement of hydraulic barrier properties for indigenous clay owing to bentonite presence and NH₄⁺ effects on their micro-structures.