Low-Energy Method for Water-Mineral Recovery from Acid Mine Drainage Based on Membrane Technology: Evaluation of Inorganic Salts as Draw Solutions.

In this work, a novel study for acid mine drainage remediation and reutilization by means of a forward osmosis technology is addressed. The proposed process is a potential alternative path, which allows to recover high-quality water and to concentrate metals for its possible reutilization as synthetic minerals. This novel process will help in the mining industry evolving toward more sustainable processes and favors circular economy policies. Four inorganic salts (NaCl, KCl, CaCl2, and MgCl2) were evaluated as draw solutions from 1 to 5 M concentrations, in terms of water flux, water recovery, and metal rejection, using a thin-film composite (TFC) membrane. Water flux obtained was in the range of 14-53 L/(m2 h). The highest water flux was found for MgCl2, whereas the lowest correspond to KCl. The metal rejection obtained was greater than 99%. After a discussion and comparison of the results, MgCl2 was chosen for evaluating long-term assay performance. Scanning electron microscope images of the thin-film composite membrane after long-term assays were taken. The tendency of Mg-Ca and Al-Fe fouling was observed over the membrane surface. The energy consumption was estimated from 4.84-22.3 kWhe/m3, assuming that osmotically assisted reverse osmosis is used to regenerate the draw solution.