Reinforcement of Tailings Sand by Stimulation of Native Microorganisms Induces Mineralization

Reinforcement of tailings sand requires both improving mechanical properties and immobilizing heavy metals, while also considering cost, microbial environmental impacts, and applicability in practical engineering. Biostimulation of a microbially induced carbonate precipitation process can achieve in situ immobilization of heavy metals without the introduction of exogenous bacteria while reinforcing tailings sand. In this study, a single-factor experiment together with Plackett-Burman and central composite design were conducted to optimize a biostimulation strategy to screen and enrich native ureolytic microorganisms for tailings sand reinforcement. Different concentrations of cementation solution and treatment cycles were set to evaluate and compare the reinforcement effects and economic-environmental benefits of native ureolytic bacteria and Sporosarcina pasteurii for biomineralization. The results showed that (1) the urease activity in the optimal stimulation strategy for tailings sand is 1.944 times that in the non-optimized condition; (2) with the same treatment cycles, native ureolytic bacteria demonstrate stronger ability to immobilize heavy metals, along with better reinforcement depth and uniformity; (3) the mechanical properties of tailings sand reinforced by native ureolytic bacteria for 15 cycles are equivalent to those reinforced by Sporosarcina pasteurii for 10 cycles, with a cost reduction of two-thirds; and (4) biostimulation induces calcite crystals filling the pores between sand particles and transforms exchangeable heavy metals into metal carbonates precipitates, metal-calcium carbonate co-precipitates, or is adsorbed by iron and aluminum oxides. This process achieves both improved mechanical properties and in situ immobilization of heavy metals.