The role of natural clays in the sustainability of landfill liners

Engineered synthetic liners on their own are not the ideal solution to protect land, water and living beings against landfill leachate pollution. Despite their impermeability, engineered liners are susceptible to fail during installation and after a few years of landfill operation, and have no attenuation properties. Conversely, natural clay liners can attenuate leachate pollutants by reactions of sorption, dilution, redox, biodegradation, precipitation and filtration; resulting in a decrease of the pollution load over time. Depending on the clay, significant differences exist in the shrinkage potential, sorption capacity, erosion resistance and permeability to fluids; which would affect the suitability and performance of the potential clay liner. Here, the physical, chemical, mineralogical and geotechnical characteristics of four natural clayey substrata were compared to discuss their feasibility as landfill liners. All the studied clayey substrata had favourable properties for attenuation of leachate pollutants, although different management options should be applied for each one. London clay (smectite-rich) is the best material based on the sorption capacity, hydraulic conductivity and low erodibility, but has the greatest susceptibility to excessive shrinkage and easily alterable clay minerals that partially collapse to illitic structures. Oxford clay (illite rich) is the best material for buffering acid leachates and degrading organic compounds. The Coal Measures Clays (kaoline-rich) have the lowest sorption capacity, but on the plus side they have the lowest plasticity and most resistant clay minerals to alteration by leachate exposure