Major Ionic Evolution of Na–Mg–Cl Brines in Solar Saltworks and Their Processing Optimization: A Case Study From Chott Melrhir Salt Lake, Algeria

Abstract

Solar saltworks often face challenging production conditions, including drastic thermodynamic condition changes. The major ionic evolution of the inland brine in Chott Melrhir saltwork has been studied with an indoor polythermal and isothermal at 35°C evaporation simulation, using phase diagrams and forward geochemical modelling. Hydrochemical and mineralogical analysis indicated that the brine under investigation exhibits an oceanic chemical character and follows a metastable evaporation path similar to that of seawater at 35°C. During the transport to the surface, the brine undergoes a drastic concentration, depositing major calcium content as gypsum. Evaporation yields significant quantities of kainite, magnesium sulphate salts and halite, the latter of which precipitates predominantly at the outset of the process along with minimal gypsum contents. Raw salt and washing brine analysis indicated that the interstitial brine was the source of the major ionic impurity, along with clay and sand, while gypsum and calcium ions were identified as solar evaporation impurities. The use of PHREEQC (pH-Redox Equilibrium C-programme) geochemical simulation software and Pitzer's database has enabled the precise proposal of a shift in pumping densities for solar evaporation feed brine of approximately 1.221 and for washing brine of approximately 1.227. This methodology may be tested for the purpose of overcoming significant challenges posed by major ionic impurities that producers may encounter during production in such environments. Moreover, the results have the potential to facilitate the expansion of production through the separation of other salts that may possess greater economic value, such as kainite in this case.