Experimental research on biochemical consolidation of bauxite tailings clay

Microbially induced carbonate precipitation (MICP) is rarely applied to clay. With the aim of tailings reservoir reclamation, measurements for compression tests, scanning electron microscope (SEM) observations and mercury intrusion porosimetry (MIP) tests were conducted to study the macroscopic strength and microstructure of the over-wet bauxite tailings clay with different water contents (w) after biochemical consolidation and quicklime solidification. These tests indicate that the compressibility (a(v1-2)) of tailings clay with w = 60% after biochemical consolidation is less than that obtained with w = 80% and can reach the index of low compressibility. In addition, the cumulative pore volume is also less than that with w = 80%, but the volume percentage of small pores for tailings clay with w=60% is larger than that with w = 80%. As the quicklime content increases, the compressibility (av1-2) and cumulative pore volume of tailings clay with w = 60% and after biochemical consolidation decreases at first and then increases, but the volume percentage of small pores first increases and then decreases. Quicklime solidification can expand soil pores and provide space for the microorganisms to survive, while the microbial mineralization fills soil pores and bonds with soil particles; therefore, biochemical consolidation will make the soil more compact. However, when the water content or quicklime content is too high, an intense hydration reaction releases a large amount of heat, making the temperature too high (up to 50.5 degrees C) and increasing the concentration of OH-. The excessive temperature and alkaline environment markedly inhibits the microbial activity, resulting in a large number of microbial death, and the biochemical consolidation effect is no longer apparent.