In-situ stabilization/solidification of lead/zinc mine tailings by cemented paste backfill modified with low-carbon bentonite alternative

Abstract

The improper stockpiling of lead/zinc mine tailings results in significant toxic impurities releasing, which threatens both the surrounding environment and human health. Cemented paste backfill (CPB) is considered an effective in-situ remediation way for managing lead/zinc mine tailings. In this study, the mechanical performance and heavy metal retention of CPB were evaluated by comparing the different binder strategies of ordinary Portland cement (OPC), Ca-bentonite, and Na-bentonite. The engineering properties of the mixtures were verified by uniaxial compressive strength (UCS) tests. The phase composition and internal microstructure were obtained by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Toxicity characteristic leaching procedure (TCLP) was performed to ascertain the effectiveness of heavy metal retention capacity. The results showed that the use of bentonite effectively optimized the UCS at early ages. Despite the deterioration is observed at 28 days, the UCS values are still qualified for the engineering application. With XRD and SEM analysis, a great content of amorphous was quantitatively characterized, highlighting the importance of amorphous content in the regulation of mechanical properties. TCLP results indicate that all the Pb, Cd, and As are predominantly incorporated within the cementitious matrix, whereas the Zn is the only concern in which the leachability decreases with the Ca-bentonite proportion. The leachates met the regulation limits (0.1 mg/L) at the CPB samples with 1.28 wt% of Ca-bentonite. Overall, bentonite could be an attractive alternative for the in-situ remediation of lead/zinc mine tailings to revive the stockpile site and reduce the environmental influence of this solid waste.