Water-rock interaction experiments with acidic aqueous solution and iron bearing broken rocks and characteristics of water permeability decline

Aiming at the self-healing phenomenon that the water permeability capability of mining-induced broken rock was prone to decrease in some chemical environment with water-rock interaction,the process and mechanism of perme- ability reduction that happened during soaking and water-passing process in the acidic aqueous solution,taking iron- bearing broken sandy mudstone as rock samples,was experimentally investigated and theoretically studied. The results showed that the permeability reduction of rock samples was significantly influenced by the blocking function of iron bearing sediment and secondary mineral which formed during ion-replacement reaction,in addition to the traditional view of claystone expansion when interacted with water. Furthermore,the permeability of broken rock samples showed different levels during the process that solution transformed from acid to neutral. During the initial phase with low pH value,rock samples were significantly dissolved and corroded. Aluminosilicate minerals,such as feldspars,exchanged ion with H+ ,generating secondary mineral,such as kaolinite,sericite,quartz and so on,which caused slight permeabili- ty reduction and the particular increase of pH value. Based on the findings above,the process was greatly improved that Fe2+ ,separated from illite and chlorite,was oxidized into Fe(OH)3 ,which entailed a rapidly reducing trend in the mid-stage trial. Therefore,the iron-bearing sediment had a stronger effect on the permeability reduction of rock sam- ples. However,when the dissolution and corrosion of solution rapidly declined,the generation of iron-bearing sediment and secondary mineral,and the function of solution on permeability reduction would decreased simultaneously,even ended. The results provided an important inspiration for underground broken rock repairment by artificially controlling chemical environment with water-rock interaction,and gave a theoretical reference to water resource conservation and ecological restoration in coal mining.