From waste to barrier: A mini-review of geopolymer-modified soil as environmentally sustainable landfill liner material

Effective liner materials must be installed in landfills to prevent leachate leakage. Traditional liner layers are typically composed of compacted clay (CCL) or geosynthetic materials (or a combination of both). Due to limited clay resources in many areas and the relatively high cost of geosynthetic materials, landfill managers are seeking suitable alternative materials. In recent years, geopolymer materials (GPMs), as an environmentally sustainable soil modification material, have become a candidate for landfill liner materials due to their ability to significantly enhance the engineering properties of soil and their excellent adsorption performance for various pollutants. This study evaluates data from existing literature and assesses the suitability of geopolymer-modified soil as landfill liners based on three factors: strength, permeability and adsorption performance. The study results indicate that the strength of geopolymer-modified soil exceeds 200 kPa, meeting the requirements for landfill liner layers; The permeability coefficient <i>k</i> of geopolymer-modified soil decreases with increasing geopolymer content and curing age. As the geopolymer content increases and the curing time extends, it meets the minimum requirement of 1 × 10^-7 cm s^-1 specified by the U.S. Environmental Protection Agency (EPA) for landfills. Geopolymers have good adsorption effects on a variety of pollutants. Among them, the removal rate of heavy metal ions generally exceeds 90%, and the removal rate of organic dyes generally exceeds 80%. This mini-review provides a reference for the selection of landfill barrier materials and the assessment of the long-term safety of barrier layers.