A preliminary study of solid-waste coal gangue based biomineralization as eco-friendly underground backfill material: Material preparation and macro-micro analyses.

Solid-waste coal gangue (CG) mixed with cement as underground backfilling material is widely applied in coal mines throughout China. However, this material can pollute the environment during its production, preparation, and transportation, which is mainly caused by cement. As a cement-free eco-friendly technology, microbially induced carbonate precipitation (MICP) technology can produce biomineralization products to consolidate loose grains, and the microbial growth environment is adapted to underground temperature with no pollution. To this end, this study gets the Bacillus pasteurii with special resistance by strain domestication, proposes a CG-based bio-mineralized underground backfilling material without using cement, and analyses the characteristics of it from macro- to microscopic perspectives by dissolution test, scanning electron microscopy (SEM), Energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results indicate that strain domestication leads to B. pasteurii, which can withstand CG leaching solution and 1 M urea simultaneously. This satisfies the basic requirements of CG based mineralized material. Through the circulation perfusion method, the intact CG based biomineralized specimens are obtained. Macroscopically, the bacteria bind gangue grains into a whole with high biomineral content (11.66%). The utilization rate of mineralizing solution is up to 66.82% which makes good use of raw materials. Microscopically, a new crystal formation is observed, and CG particles are consolidated well where the crystals precipitate to fill the pores and bind the particles together. Hence this method has a significant influence on the deposition of biominerals. Meanwhile the biomineralization improves the microstructure considerably and bonds the CG particles as a whole. A comprehensive analysis of the test results shows that, from an environment viewpoint, the preliminary study of new CG based bio-mineralized material is successful.