Lianman Xu, Kaixuan Lu, Yajing Li , Yuwei Li, Yishan Pan , Hao Wei, Fengshuo Yang, School of Environment

Na Li, Liaoning Technical University

Xiangfeng Lv, Beijing University of Science and Technology

Abstract: Coal seam water injection technology which provides a guarantee for coal mine safety production is significant for the prevention and control of coal mine disasters. The selection of additives is very important for the  implementation of coal seam water injection technology. Although the research on additives has been extensive  in recent years, the mechanism of additives which can increase the permeability of coal and change mechanical  properties of coal is still unclear. After selecting the chelating agent as the water injection additive, we characterized the pore structure of coal by low temperature N2 adsorption, mercury injection, scanning electron  microscopy, etc., and tested the strength of coal by uniaxial hydraulic testing machine, as a result, several  interesting results were found. Firstly, the minerals in the coal seam will damage the permeability of the coal  seam and impede the flow of water in the coal seam. Secondly, the chelating ligand can interact with minerals  like calcite and dolomite. When the concentration of the chelating agent is 500 mg/L, Ca²⁺ can be detected in the  immersion solution and the leaching concentration of Ca²⁺ is 43.76 times greater than that in the ultra-pure water immersion solution. The change of pH has a greater impact on the leaching concentration of Fe and Mg, while the change of solid–liquid ratio has a smaller impact on their leaching concentration. Thirdly, as the dissolution of minerals, the size and volume of pore in coal increase, specific surface area decrease, connectivity of pore become better, the permeability of coal increase by an average of 129%, which has a promoting effect on water injection. Fourthly, the existence of minerals will affect the mechanical strength of coal. The uniaxial compressive strength of coal decreases after the chelating ligands interacted with the coal and the pH of the solution and soaking time also obviously affect the strength of coal. These results are helpful to open up a new direction for the selection of water injection additives that can realize the green and safe mining of coal.

Read the article here:   126-Study on the infiltration mechanism of injecting chelating agent into deep low permeable coal seam.pdf