Hydraulic Conductivity Characteristics of Iron-Ore Tailings–Bentonite Mixtures Exposed to Landfill Leachate

Abstract

Landfill liner materials are required to provide reliable hydraulic performance for very long times after construction, and at least for the design lifespan of the facility. To meet this objective, liner systems must retain their low hydraulic conductivity over their service lives. In this paper, we report on the durability aspects of iron-ore tailings (IOT)–bentonite mixtures in extended hydraulic conductivity experiments. The hydraulic conductivity tests were conducted on mixtures containing 20%, 25%, 30%, 35%, and 40% bentonite, compacted at 2% wet of optimum by the British standard light (BSL) effort, and permeated with municipal solid waste (MSW) landfill leachate (electrical conductivity = 25.60 mS/m, pH = 7.94) with or without prehydration for a duration of 120 days. Under these influences, permeation with leachate showed no detrimental effect on mixtures with 25% and 30% bentonite, but was rather beneficial in reducing the hydraulic conductivity (k) values of the two mixtures at the end of testing by two orders of magnitude to 4.19 × 10−8 and 9.25 × 10−9 cm/s for the prehydrated specimens and 2.4 × 10−8 and 9.9 × 10−9 cm/s for the nonprehydrated specimens. For mixtures containing 20%, 35%, and 40% bentonite, k values representing a 1.6 times decrease from the average were recorded for both the prehydrated and nonprehydrated conditions at the end of testing. Further analysis showed that prehydration had a slightly substantial effect on those specimens containing 20%, 35%, and 40% bentonite, whereas it had a minor effect, if any, on mixtures with 25% and 30% bentonite. In terms of durability, only mixtures containing 25% and 30% bentonite that consistently maintained low k values up to the end of testing are projected to be effective as liner materials in the construction of geological repositories for MSW. Regarding the hydraulic conductivity characteristics of the mixtures upon exposure to the combined effects of leachate and the elevated temperatures expected in landfill conditions, all mixtures maintained relatively good hydraulic performance, exhibiting a decrease in hydraulic conductivity with time.