Effects of ammonium ion and bentonite content on permeability of bentonite-clay mixture

Sanitary landfill is a common method for the treatment of municipal solid waste. The landfill leachate contains a large amount of NH₄⁺, which will affect the physicochemical properties of bentonite, and subsequently change the anti-seepage function of the bentonite enhanced cutoff wall. The permeability tests were carried out on bentonite-clay mixed soil infiltrated by the ammonium salt solutions using a head pressure control permeameter. The results show that saturated permeability coefficient of the bentonite-clay mixture increases with the decrease of bentonite content and with the increase of NH₄⁺ concentration. Moreover, the reasonable mass content of bentonite is about 10% if the studied bentonite-clay mixture are used in vertical cutoff wall. The scanning electron microscope (SEM) and the nuclear magnetic resonance (NMR) measurements were conducted on the bentonite-clay mixed soil samples with different bentonite contents, and samples infiltrated by the ammonium salt solutions with different concentrations, and afterwards the variations of the micro pore structure and pore-size distribution were obtained. Connecting the Donnan osmotic pressure with saturated permeability of bentonite-clay mixed soils, the effect mechanism of bentonite content and ammonium solution concentration on the permeability of the bentonite-clay mixture was analyzed.