Can Brine from Seawater Desalination Plants Be a Source of Critical Metals?

Desalination removes salts of various metals and impurities from seawater. It is used to obtain fresh water for human consumption and for domestic/industrial use. Extracted salts and other metal compounds present in the desalination mix form a hyper-saline mixture commonly referred to as brine. This waste by-product contains mainly sodium chloride (NaCl) and water. Its composition depends on the type of desalination process and the area where the desalination takes place. The economic growth and global competitiveness of the European Union require the availability of vital raw materials of strategic relevance—critical raw materials or CRMs—to strengthen long-term industrial leadership. The extraction of minerals from hypersaline brines generated as by-products of seawater desalination plants has attracted the interest of scientists. About 18,200 desalination plants operate worldwide with a global cumulative capacity near 90 million m3/day [1]. This capacity is expected to grow at an increasingly rapid pace in the near future because of the water shortage crisis around the world and increasing water demand [2]. Brine generated in seawater desalination (SWD) is currently discharged into the sea, generating negative environmental impacts and posing a potential danger for marine ecosystems due to its high salinity. Furthermore, if the brine is discharged, the energy used for its production will be lost as well as the benefit of using it as a potential source of metals and critical metals. For the recovery of the brine, however, a lot of research is required. In particular, a European project with the acronym SEA4VALUE is working on how to extract metals and critical metals while minimizing the negative environmental impact. The vision of the project is to create a multimineral and modular process to separate, concentrate, and crystallize molybdenum, magnesium, scandium, vanadium, gallium, boron, indium, lithium, and rubidium in seawater desalination plants. A first challenge is the removal of the large amounts of calcium from brine. Another issue is the amount of energy required.