Innovative solution for the recovery of clean water and high-purity minerals from the coal mine sector

Abstract

Coal mining activities generate massive volumes of highly saline wastewater that cause significant ecological damage once they end up in the environment. Saline discharges contribute to the salinization of soil, the disruption of the aquatic flora and fauna, and the degradation of surface water quality. To address this issue, a near-zero liquid discharge (near-ZLD) system has been designed and constructed to treat coal mine wastewater before its discharge into the environment. The pilot system included membrane, precipitation, and thermal technologies to desalinate the water and to recover valuable products, including Europe's critical material, magnesium, as magnesium hydroxide with >84 % purity. Calcium carbonate, calcium sulphate, and sodium chloride were also recovered from the wastewater with high purity: over 96 % for CaCO₃ and CaSO₄, and >99.9 % for NaCl. The recovered water showed high purity with a conductivity below 400 μS/cm. The pilot system energy consumption was 421 kWh/t of salt with >90 % overall water recovery. The results show that the proposed technology, if implemented in a much larger scale, has a potential to decrease the salt load discharged into surface water.