Study on the green disposal of industrial high salt water and its performance as activator to prepare magnesium-coal based solid waste backfill material for mine

The significant production of bulk solid waste from metallurgy or coal and industrial high-salt wastewater (SW), coupled with limited disposal capacity, high disposal expenses, and uncertain environmental impact, poses technical challenges that impede the green advancement of the metallurgical or coal sector. Based on the aforementioned industry challenges, this study suggests creating an all-solid waste mine backfill material known as magnesium-coal slag (MCBM). The technical requirements of coal mine backfill are assessed through relevant experimentation and microscopic analysis techniques, including fluidity, uniaxial compressive strength, microstructure, and toxicity leaching tests. Additionally, the synergistic reaction mechanism of MCBM is expounded upon. The results show that: (1) The rheological curve of the freshly prepared MCBM slurry is in strong agreement with the Herschel-Bulkley (H-B) model, and the viscosity meets the necessary pumping specifications for coal mine backfilling. It was observed that the fresh MCBM slurry's slump ranges from 134 mm to 146 mm, whereas the yield stress falls between 25 Pa and 37 Pa. (2) The mass concentration and SW content exert a significant influence on the uniaxial compressive strength (UCS) of MCBM specimens, primarily governed by the degree of hydration reaction and pore structure characteristics. (3) The leaching of toxic heavy metal elements such as Ni, Pd, and As in bulk metallurgical or coal-based solid waste greatly surpasses the standard levels. Nevertheless, by mixing such waste within the coal mine backfill materials, the resulting hydration products can achieve stable consolidation of these heavy metal elements through chemical bonding and physical adsorption and storage. Magnesium-coal slag backfilling technology for solid waste is aligned with the primary research objective of supporting green and safe mining, as well as facilitating the clean and efficient usage of coal resources. It represents a popular research topic, aimed at promoting high-quality coal resource development and green, low-carbon growth.