Mining minerals and critical raw materials from bittern: Understanding metal ions fate in saltwork ponds

Seawater represents a potential resource for raw materials extraction. Although NaCl is the most representative mineral<br> extracted other valuable compounds such as Mg, Li, Sr, Rb and B and elements at trace level (Cs, Co, In, Sc, Ga and<br> Ge) are also contained in this “liquid mine”. Most of them are considered as Critical Raw Materials by the European<br> Union. Solar saltworks, providing concentration factors of up-to 20 to 40, offer a perfect platform for the development<br> of minerals and metal recovery schemes taking benefit of the concentration and purification achieved along the evaporation<br> saltwork ponds.<br> However, the geochemistry of these elements in this environment has not been yet thoroughly evaluated. Their knowledge<br> could enable the deployment of technologies capable to achieve the recovery of valuable minerals. The high ionic<br> strengths expected (0.5–7 mol/kg) and the chemical complexity of the solutions imply that only numerical geochemical<br> codes, as PHREEQC, and the use of Pitzer model to estimate the activity coefficients of the different species in solution<br> can be adopted to provide valuable description of the systems.<br> In the present work, for the first time, PHREEQC Pitzer code database was extended to include the target minor and<br> trace elements using Trapani saltworks (Sicily, Italy) as a case study system. The model was able to predict: i) the purity<br> in halite and the major impurities contained, mainly Ca,Mgand sulphate species; ii) the fate of minor components as B,<br> Sr, Cs, Co, Ge and Ga along the evaporation ponds. The results obtained pose a fundamental step in critical raw materials<br> mining from seawater brine, for process intensification and combination with desalination.