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.

Sustainable management of spent fluid catalytic cracking catalyst from a circular economy approach.

For sustainable growth, an economic model must tend toward a circular system, especially in the field of waste management. This work focuses on the valorization of spent fluid catalytic cracking catalyst from oil refineries, which generate 400,000 metric tons of spent catalyst per year worldwide, most of which is sent to landfills. A new alternative to landfilling is proposed for this waste, based on the combination of acid leaching for the recovery of lanthanum, a valuable rare earth, and the reuse of the leached solid residue as a cement substitute. A comparative life cycle assessment was made, including four environmental impact categories, i.e. global warming, fossil resource scarcity, mineral resource scarcity and water consumption, in order to quantify the potential environmental benefits of secondary lanthanum recovery from industrial waste with respect to primary lanthanum extraction from mineral resources. A maximum of 85.6% La recovery was achieved and 15 wt% of cement can be substituted with leached solid residue without changing the original cement classification. The waste management process presented in this paper promotes the sustainable management of the spent fluid catalytic cracking catalyst and contributes to the development of a new resource for a critical material such as lanthanum. The implementation of this novel waste management process could reduce global warming and mineral resource scarcity but would increase fossil resource scarcity and water consumption in comparison with primary La extraction.