Research on technology and process for moderate desalination of high-salinity mine water by nanofiltration

High-salinity mine water is widespread in mining areas in western China. In recent years, with the implementation of the westward coal strategy, the drought, water pollution, and ecological degradation in the region have become increasingly prominent, forcing more stringent policies and regulations on high-salinity mine water to re-use as water resources and meeting discharge standards, which has forced the continuous development of energy-saving and high-efficiency desalination technology for high-salinity mine water. In order to further improve the resource utilization level of high salinity mine water in western mining areas and reduce the cost of desalination, this research is based on extensive surveys of mine water quality and quantity, distribution status, and status quo of desalination technology, in response to the current mainstream technology of high salinity mine water desalination due to the use of non-selective desalination and the pure pursuit of high desalination rates, problems such as excessive desalination, process complexity, high energy consumption, membrane pollution, et al., a moderate desalination process is proposed for the graded and qualitative reuse of brackish mine water in the range of 1 000～3 000 mg/L in coal mine area. The core of the so-called moderate desalination is the selective removal of specific ions （such as Ca2+, Mg2+, SO2-4, et al.） in mine water, minimizing the cost of desalination, and achieving energy-saving desalination and cost reduction and efficiency enhancement under the premise of meeting relevant water quality requirements. This study takes the moderate desalination of brackish mine water as the goal, and takes the screening of nanofiltration（NF）membranes and the Donan effect as the theoretical basis. Through indoor water distribution experiments, field tests, laboratory characterization, etc., the systematic study of the brackish mine water moderate desalination process and its key operating parameters. The results show that NF membranes can intercept high-valence characteristic ions in mine water while allowing part of the monovalent ions to pass through. Its wider range of desalination rate（37.4%～98.25%） is more advantageous than reverse osmosis in the moderate purification of brackish mine water; due to the low operating pressure and large membrane pore size, NF have stronger anti-pollution ability than reverse osmosis. The moderate desalination process of NF has greater application prospects in the purification of brackish mine water with heavier inorganic pollutants.