Hydraulic conductivity of compacted manufactured sand tailings–bentonite mixtures: a new hydraulic barrier material

The valorization of manufactured sand tailings (MST) with annual production of 4 billion tons is crucial to the healthy development of manufactured sand industry. The feasibility of compacted MST–bentonite mixtures as hydraulic barrier in landfill cover system was studied herein. A series of rigid-wall permeation tests were carried out to measure the saturated hydraulic conductivity (ks) of compacted MST–bentonite specimens, considering bentonite content, mixing method, sieving treatment, and degree of compaction (DOC). The ks of specimens prepared by different methods were listed as follows: without water < water pouring < gradual water addition. It was because the specimen prepared without water had a unimodal pore-size distribution and had the least macro-pores, while the specimens prepared by the other two methods had bimodal pore-size distributions. Sieving helped reduce the ks, due to less macro-pores. The effect of sieving on ks decreased at higher DOC. The decrease of ks was more significant with the increase of bentonite content at lower DOC. Accordingly, it is suggested to mix MST with 10% bentonite and then compacted without water at DOC no less than 90%, so that the allowable ks of 10–9 m/s required by design guideline of hydraulic barrier of landfill cover can be met.