Effective reuse of waste material as an amendment in composite landfill liner: Assessment of geotechnical properties and pollutant retention capacity

The effective reuse silica fume (S), a by-product from the silicon manufacturing industry, as an amendment in the composite landfill liner along with natural clay (C) and bentonite (B) was investigated in the present study. Experiments were conducted with various proportions of silica fume (10%-50%) to clay and bentonite to get mixtures C-B-S1 to C-B-S5. The study indicated significant improvement in the geotechnical and pollutant retention capacity by silica fume addition. The maximum dry density of the mixtures ranged from 1.568 to 1.732 g cm(-3). Permeability was in the order of C-B<C-B-S1 to C-B-S5<clay. Unconfined compressive strength of the C-B mix increased with the addition of silica fume from 10% to 25%, with a maximum value of 241.31 kPa. The free swell index decreased to 3.6 and the cation exchange capacity increased to 83 meq/100 g with the addition of 50% silica fume. The percentage removal of copper with C-B-S1 to C-B-S5 was 91.2%, 92%, 93.5%, and 95.2%, respectively, when the initial copper concentration was about 30 mg L-1. Based on the assessment of geotechnical and pollution abatement capacity C-B-S3 with 25% silica fume addition was proposed as the composite liner material for the naturally available clay at the landfill site.