Leaching behaviour of arsenic in coal under the action of mine water

Arsenic, a potentially harmful element in coal, has a detrimental effect on the quality of groundwater and the water cycle. There is a significant safety risk to the drinking water and overall health of residents living near mining areas. It is of great significance to explore the leaching pattern of arsenic in coal under the influence of mining and identify the main controlling factors for the prevention and control of groundwater pollution in mining areas. In this paper, we selected long flame coal and non-caking coal from Wulanmulun Mine, along with four types of water samples from the mine area, as the research subjects. Our aim was to investigate the leaching mechanism of arsenic in groundwater under the influence of coal–water interaction in the mine area. To achieve this, we conducted indoor batch coal–water leaching simulation experiments. The results were as follows. (1) The four leaching solutions, which correspond to four groundwater types at the coal mine production site, exhibit similar trends in the presence of arsenic ions after water–coal interaction. The leaching process can be divided into three distinct zones: a rapid descent zone, a dissolution shock zone and a dissolution linear stable zone. The initial decline rate of arsenic content in different water samples is proportional to the initial concentration of arsenic in the water samples. (2) The dissolution of arsenic has a strong negative correlation with dissolved oxygen, and the lower the oxygen content in the solution, the higher the arsenic ion content. There is a relatively strong negative correlation with pH value, a strong positive correlation with the leaching of Mg, K, V, Cr and Fe, and a relatively small positive correlation with the leaching of Mn and Cu. The leaching degree of Mg, K, V, Cr and Fe can be used as an indicator to explore the leaching or content change of arsenic in the actual mining environment. (3) Most arsenic in coal occurs in pyrite in the form of isomorphism or solid solution, and the dissolution of arsenic is related to pyrite content and its oxidative dissolution behaviour. The higher the pyrite content, the greater its oxidation degree, and the higher the arsenic content in the solution. (4) Clay minerals, predominantly kaolinite, found in different coal samples demonstrate varying capacities for arsenic adsorption in the leaching solution. The results of this experiment indicate that the adsorption capacity of clay minerals in long flame coal is considerably higher than that observed in non-caking coal, leading to a substantial decrease in the concentration of arsenic ions in the solution. This reduction is associated with a notable decline in the arsenic concentration within the groundwater associated with the coal samples collected on-site. The results suggest that the leaching of arsenic from the coal samples will not lead to arsenic contamination in four distinct categories of groundwater. This finding holds considerable importance for the management and remediation of water pollution in mining contexts.