Experimental study on the effect of cementation curing time on MICP bio-cemented tailings

Abstract

Tailings dam break and leakage accidents usually threaten the safety of people around the mining area. In addition, tailings leakage seriously pollutes the surrounding environment. In view of the above problems, the tailing sand is solidified based on the microbial induced calcite precipitation (MICP). This method can not only enhance the strength of tailing sand, but also solidify heavy metals in tailings. In order to optimize the curing time of MICP bio-cemented tailings, improve the strength and cost-effectiveness, this study used the layered injection method to cement the tailings. Combined with the unconfined compressive strength, calcium carbonate content and heavy metal leaching effect of MICP bio-cemented tailings, the effect of MICP curing time on bio-cemented tailings was analyzed. The results showed that the curing time of MICP bio-cemented tailings has a great influence on the strength of tailings, and has little effect on the fixation of heavy metals in tailings. The curing time of the optimized MICP biocemented tailings is 10 days. The unconfined compressive strength of the MICP bio-cemented tailing sand specimen is 1.01 MPa. When the cementation curing time is greater than 10 d, the cementation curing time will no longer be the main factor affecting the MICP bio-cemented tailings. After the MICP bio-cemented tailings samples were leached for 5 days, the fixation rates of Pb2+, Zn2+, total Fe, Mn2+, Cu2+, Cd2+ and total Cr in the leaching solution were 100%, 100%, 100%, 94.80–98.45%, 100%, 100%, 93.34–95.56%, respectively. The results of FTIR, XRD, SEM and EDS showed that when the tailings were cemented and solidified many times the cementation liquid metabolized by Sporosarcina pasteurii was mainly used for the growth of existing calcium carbonate crystals rather than the formation of new calcium carbonate crystals. The deposition of these larger calcium carbonate crystals can stably fill the gaps between the tailings particles, cement the tailings particles together and improve the strength of the tailings.