The problem of mine water pollution from abandoned mines after integration is becoming increasingly serious with the integration of coal resources and the merger and reorganisation of coal companies. An accurate understanding of the development mechanism of mine water quality in abandoned coal mines is an important prerequisite for the protection and use of mine water and the effective prevention and control of groundwater pollution. The leaching behaviour of Fe³⁺ and Mn²⁺ and the changes of related water quality indices were investigated by the long-term indoor water-coal immersion test based on the project practice of Shendong mining area. The results show that the solubility of Fe³⁺ is “wave-like”, and the solubility of both samples reaches the lowest value at the 84th day after immersion, while the solubility of Mn²⁺ remains relatively stable after a rapid reaction (the first day). The causes of solubility variations were further analysed by ion ratio coefficient method and Pearson correlation coefficient method, and it was found that mine water in goaf may be affected by mining activities, and the water quality of mine water is strongly influenced by the dissolution of silicate rocks and gypsum. The main water-rock interactions in mine water in the goaf area include the dissolution of silicate rocks and evaporative rocks and the alternating adsorption of cations. For the rational development and utilisation of mine water in China, it is of great importance to study the characteristic pollutant ion change law of mine water in the goaf area.