Experimental study on reinforcement of tailings sand by microbially induced carbonate precipitation at low pH

Experiments were conducted to investigate the effects of bacterial suspension concentration and pH on calcium carbonate production and the flocculation latency phase during microbially induced carbonate precipitation (MICP) reinforcement of tailings sand. The effectiveness of this method in reinforcing tailings sand was evaluated using tests for permeability, water retention, resistance to raindrop erosion, wind erosion resistance and penetration. By analyzing the influence of pH on urease activity and the equilibrium of the carbonate system, and observing the microstructure of tailings sand through scanning electron microscope and X-ray diffraction tests, the mechanism of MICP reinforcement of tailings sand at low pH was revealed. Results showed that the MICP method at low pH significantly improved the mechanical properties of tailings sand. After a single spray treatment, the wind erosion mass of tailings sand was reduced to zero, and the permeability coefficient decreased by an order of magnitude. Additionally, the raindrop and wind erosion mass of tailings sand treated with a high-concentration bacterial suspension at pH = 4 was also reduced to zero. Low pH temporarily inhibited urease activity and disrupted the carbonate system equilibrium, delaying calcium carbonate precipitation. This allowed calcite to uniformly fill the intergranular pores of tailings sand, cementing the sand particles together. This research presents a novel approach to tailings dam reinforcement and tailings sand treatment, elucidating its reinforcement mechanism and offering theoretical and experimental support for the application of low-pH MICP reinforcement of tailings sand.