Formation of Cross-linked Gel from Complex Water-Solution of Sodium Metasilicate Nonahydrate and Polyvinyl Alcohol to Inhibit Spontaneous Coal Combustion

This study presents a novel cross-linked gel to prevent coal spontaneous combustion. Complex Water-Solution (C-WS) of sodium metasilicate nonahydrate (SMN) and polyvinyl alcohol (PVA) was used to wet coal particles and reacted with CO2 from coal oxidation and natural atmospheric air to form the cross-linked gel (SMN/PVA gel), which was examined by measuring critical self-ignition temperature (CSIT) through the wire-mesh basket test. Baiyinhua lignite coal excavated from Inner Mongolia was used to investigate the inhibitory effect of SMN/PVA gel. Wire-mesh basket test results indicated the fire-prevention effectiveness of the SMN/PVA gel from C-WS was superior to those of pre-formed SMN/PVA gels. It snugly covered the coal particle surface and inlets of micropores to prevent oxygen ingress and water emission, and thus exhibited excellent performance in stability and compatibility. Based on the present tests, the concentrations of SMN-16 wt% and PVA-0.5 wt% in C-WS were best and increased the CSIT of raw coal by 26 degrees C. The effect of wetting C-WS on CSIT for different including coal pile volume and particle size has been presented as an empirical equation to estimate the CSITs for SMN and PVA concentrations to consider field applications.