Performance of a salt-resistant mixture of bentonite and field soil as impermeable material in solid waste landfills

Abstract

Leachate in landfill contains a great number of toxic and harmful substances and results in long-term contamination of the underground environment once it leaks. Therefore, constructing an impermeable layer at the bottom of sanitary landfills is the key to preventing the contamination induced by leachate leakage. Bentonite is an impervious liner material that is currently widely used in landfills. However, the performance of bentonite as an impervious material is likely to be greatly affected when leachate contains a high salt content. By modifying additives using bentonite, a salt-resistant bentonite can be acquired which satisfies the impermeability requirement imposed by a saline environment. Additionally, by carrying out various tests (including a free swell index test, compaction, hydraulic conductivity, heavy metal adsorption, and direct shear tests), the performance of developed bentonite and the mixture of weathered soil and modified bentonite were verified. The swelling capacity of saltresistant bentonite in saline water was nearly equal to that in a fresh water environment. After salt-resistant bentonite was mixed with weathered soil in a proportion of 1:9, the hydraulic conductivity of the mixture in saline water was less than 1 x 10(-7) cm x s(-1), satisfying the basic requirement for use as a landfill liner material. Moreover, the relationship between the shear strength or the cracks in the liner soil and the initial moisture content of the mixed soil can be obtained by conducting direct shear and drying shrinkage tests on the mixture of weathered soil and modified bentonite. The results are expected to provide data support for the design of engineering construction works in a gee-environmental context.