Comprehensive utilization of reverse osmosis concentrated brine in coal mines in the arid areas of Western Inner Mongolia

The western region of Inner Mongolia has an arid climate and abundant coal resources, but the high degree of mineralization of groundwater and mine water in mining areas leads to a severe shortage of freshwater resources. Reverse osmosis technology is utilized by some sewage treatment plants in the mining areas to treat considerable highly mineralized mine water. This technology solves the problem of domestic water shortage in the mining areas and improves the comprehensive utilization of mine water, whereas, it raises a new issue about the storage and comprehensive utilization of the concentrated brine continuously produced by reverse osmosis plants. Various treatment technologies for reverse osmosis concentrated brine and their advantages and disadvantages are discussed, including discharge into the sea, evaporation pond concentration, zero discharge technology, and ion extraction technology. Taking the reverse osmosis concentrated brine from the Shanghai Miao mine in the western arid region of Inner Mongolia as an example, based on the water quality and quantity characteristics of the concentrated brine, the natural conditions and the principle of solar ponds in the mine, the study provides a comprehensive assessment of the feasibility of recycling concentrated brine ions and the prospects for the application of solar ponds. The results has shown that the Na⁺, K⁺ and Mg²⁺ ions in mine reverse concentrated brine are 1−2 orders of magnitude lower than that in salt lake and seawater. The extraction of sodium salt, potassium salt, and magnesium oxide is technically mature, but economically unfeasible. Although the Li⁺ ion content in reverse osmosis concentrated brine is higher than that in seawater and seawater concentrate, it is 30 times lower than the lowest industrial extraction concentration (30 mg/L) and lithium concentration in the salt lake. The technology of recycling and extracting lithium in concentrated brine needs to be improved in the near future. The uranium content in the concentrated brine of the mining area is also higher than that of seawater and seawater concentrate, but it is one order of magnitude lower than that of the salt lake. The western part of Inner Mongolia, where the mining area is located, belonging to the“abundant solar resource area”, with a total annual solar radiation above 6 300 MJ/m², has the inherent advantage of building solar power plants. In the meantime, reverse osmosis concentrated brine provides a sufficient source of salt for the solar pond. The utilization of reverse osmosis concentrated brine for solar pond construction can provide very substantial thermal energy and is very economically viable.