A large-scale study on solidification of gold tailings based on microbially induced carbonate precipitation (MICP)

One of the major challenges in the application of microbially induced carbonate precipitation (MICP) is achieving "bacteria freedom", as it necessitates a substantial volume of bacterial solutions. Nevertheless, both in-situ bacterial cultivation and transportation of bacterial solutions have proven to be inefficient. In this study, we suggested the utilization of bacteria in the form of dry powder, enabling easy on-site activation and achieving a relatively high urease activity. We conducted MICP curing experiments on gold mine tailings (GMT) using steel slag (SS) as an additive. The results showed that the average unconfined compressive strength (UCS) values of the tailings treated with MICP and MICP+SS reached 0.51 and 0.71 MPa, respectively. In addition, the average leaching reduction rates of Cu, Pb, Cr, Zn, and T-CN in GMT after MICP treatment reached 98.54%, 100%, 70.94%, 59.25%, and 98.02%, respectively, and the average reduction rates after MICP+SS treatment reached 98.77%, 100%, 88.03%, 72.59%, and 98.63%, respectively. SEM, XRD, FT-IR analyses, and ultra-deep field microscopy results confirmed that the MICP treatment produced calcite-based calcium carbonate that filled the inter-tailing pores and cemented them together, and the hydration mechanism was the main reason for the increased curing efficiency of SS. Our research findings demonstrate that bacterial powder can efficiently achieve the objectives of heavy metal removal and tailing solidification. This approach can substantially decrease the expenses associated with bacterial cultivation and solution transportation, thereby playing a crucial role in advancing the practical implementation of MICP.