Extraction of strategic materials from the concentrated brine rejected by integrated nuclear desalination systems

Abstract

Seawater usually contains sixty elements from the Periodic Table. The brine, rejected by a desalination unit, is a concentrate of all compounds contained by seawater. However, some of the elements are very scarce on land and/or are very expensive. There is thus a strong motivation for extracting these materials. Current practice in countries using large-scale desalination is to reject brine back to the sea. Increasing ecological objections are now being voiced since this rejection leads to a degradation of local fauna and flora. Extraction of materials and subsequent brine conditioning for surface storage would therefore be also another advantage for these integrated desalination plants, making them more environmentally friendly. This paper summarizes our preliminary investigations to achieve the above objectives. Elements of interest were first selected on the basis of several economic, physical-chemical and technical criteria. Research was then undertaken to elaborate a common extraction method. After several different solutions, the protocol finally retained comprises a first extraction of Phosphorus through purification by alum. The next step is the recovery of Caesium through an innovative liquid–liquid extraction approach, based on the use of Calixarenes. Indium is then recovered by another liquid–liquid extraction with the help of organic acids. In the final phase germanium and magnesium are extracted. The remaining solution is principally composed of sodium and potassium chlorides, which are separated by hot lixiviation techniques, using the different solubilities of NaCl and KCl. The protocol of extraction thus elaborated would now require exhaustive economic evaluation and experimental verification. These are currently in progress.