New insights into coal slime water in backfill materials: A fundamental study of pretreatment methods to enhance curing time

Abstract

Treatment of coal slime water (CSW) faces a major challenge: an increased difficulty due to higher ash content and finer particle size with the improvement of mechanization, which could cause environmental pollution and resource waste. CSW prepared for backfilling material can avoid existing disadvantages in procedures for treating CSW. As a backfilling material, the curing rate is extremely important for preventing bleeding and supporting roofs effectively, which can be achieved by pretreatments. However, there are no reports involving CSW-based backfill materials. Therefore, pretreatment methods, including NaOH treatment (A), combined ultrasonic-NaOH (C-A), and plasma electrolysis (P), were carried out to explore the effect on curing time. The results show that: (1) pretreatments can accelerate the curing time of the backfill slurry and significantly shorten the initial curing time by half; (2) a new composite of calcium silicate and calcium metaaluminate was generated from A and C-A pretreatments, thus promoting hydration and cementation performance; (3) improved hydrophobicity of coal slime can be obtained after A and C-A, which can speed up the curing rate; and (4) active species in plasma thin coal flakes and increased interlayer spacing lead to the ability to absorb water interlayers being enhanced and the initial curing time being shortened. The results showed that the pretreatments can effectively improve the curing rate of CSW slurries due to changes in the functional groups, microstructure and chemical composition, providing technical support for the rapid and efficient preparation of backfilling materials with CSWs.