Abstract:Backfilling is widely used to control surface subsidence and stope stability to improve pillar recovery. Furthermore, it is also an effective way to process and dispose of mining waste such as coal gangue and tailings. In this study, the hydraulic-mechanical properties of cemented paste backfill materials (CPB) were investigated. Twenty-eight cemented coal gangue-fly ash backfill mixtures were prepared with different water, cement, fly ash and coal gangue content and the slump, segregation and water bleeding ratio tests were conducted. Increasing fly ash content increased the slump value and decreased the segregation value of the slurry. The uniaxial compressive strength (UCS) of the cemented coal gangue-fly ash backfill samples were tested at different curing times. Based on the test results, an optimized recipe was used for the field trial. Longwall cut and backfilling mining method was used in the 2300 mining district to recycle the coal pillar between longwall 2301 and 2302. Both stress and displacement meters were installed in the goaf and their performance was monitored continuously. An increase in stress and displacement values were observed to occur with the working face advanced (up to 325 m and 375 m, respectively); thereafter, a trend of stabilization was observed. The monitoring results suggest that the backfills can efficiently control the roof movement and surface subsidence as well as improve pillar recovery.

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A series of unique morphologies of ZnO were synthesized by a simple mild solvothermal process using equimolar of Zn(NO 3 ) 2 /Zn(AC) 2 -hexamethylenetetramine (HMT) acting as precursors and ethylene glycol (EG) and triethylamine (TEA) as the dispersant and surfactant additive, respectively. When the as-prepared particles were further treated in 0.02 M HMT solution for such a long time as 72 h, screw-like and rose-like crystals with three-dimensional and developed structure could be formed. The deNO x photocatalytic activity was characterized and the analysis results showed that the modified ZnO crystals possessed a three-dimensionally developed structure and had higher deNO x photocatalytic activity compared to that of the as-prepared untreated ZnO.

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