Geochemical processes in compacted clay in contact with an acid landfill leachate: laboratory experiments and modelling results

Abstract

Clays are commonly used as liners in urban landfills. However, the reactive processes with landfill leachates, and in particular the role of accessory minerals is poorly known. The aim of this work is to evaluate the diffusion of a synthetic urban landfill leachate through compacted natural smectite-illitic clays containing carbonates and sulfates and to predict the functioning of the clay liner for different minor mineral proportions. The leachate, characterized by acidic pH conditions and high organic matter content, is a typical aqueous solution formed in the acetogenic phase of organic matter degradation in urban landfill areas. Medium-scale (11 cm) laboratory diffusion tests were performed over 77 days. Chloride diffusion coefficients, porosity changes, cation exchange constants and the sulfate reduction rate were quantitatively assessed by means of reactive transport modelling. The exchange capacity of the clays is responsible for NH4+ retention. However, the presence or absence of gypsum in the initial clay rock controls the functioning of the liner. Gypsum dissolution ensures a high sulfate concentration in the porewater and enhances the acetate consumption via sulfate reduction. Gypsum dissolution and the concomitant calcite precipitation do not significantly alter the porosity of the clay rock.

Effect of solid waste landfill leachate contaminants on hydraulic conductivity of landfill liners

“…Contaminants in leachate can be classified into five groups; dissolved organic substances, inorganic macro components, heavy metals, microorganisms, and xenobiotic organic compounds (Kjeldsen et al 2002;Zhang et al 2013;Luo et al 2020). Interactions between clay liners and leachates are solute diffusion, cation exchange, anion exclusion, redox reactions, and dissolution/precipitation (De Soto et al 2014). There may also be differences in hydraulic permeability performance due to the decomposition of the clay liner itself or the shrinkage or cracking of the clay (Spooner & Giusti 1999).…”

Investigation of the Effect of Leachate on Permeability and Heavy Metal Removal in Soils Improved with Nano Additives

“…Clayey soils are widely used in landfill areas due to their low permeability [4]. However, the properties of the clay change as a result of interactions such as cation exchange, dissolution/precipitation, and redox reactions between the clay and leachate [5]. It has been reported by many researchers that pH [6], salt solutions [7,8], organic matter [9,10], and heavy metals [9,11,12] increase the permeability of clayey liners used in landfills.…”