Geoeconomic Interest Versus Environmental and Health Issues of the Mineralogical Assemblage of Sebkha Oum El Khialate, Southeastern Tunisia

Abstract

This work focuses on the formation of evaporite minerals through a progressive evaporation of water of Sebkha Oum El Khialate. The precipitated salt is variable along the evaporation path. Weights of evaporite before each phase of precipitation indicate a heterogeneous evaporation process with a final cumulative amount of 294 g L−1. With an increasing evaporation of Oum El Khialate brine, the number of precipitated mineral species is increased. The cumulative number of species along the evaporation process reaches eight in the following depositional sequence: calcite (CaCO3) (29%), Vaterite (CaCO3) (10%), Potassium Pentasulphate (K2S5O16) (9%), thenardite (Na2SO4) (33%), beryllium sulfate (BeSO4) (10%), brucite (Mg(OH)2) (4%), gypsum (CaSO4·2H2O) (2%) and mirabilite (Na2SO4·10 H2O) (3%). The sebkha can provide 86 kt of evaporite deposits per year at 100% evaporation. These evaporite minerals have variable industrial, medical and military uses. However, beryllium sulfate may cause a health risk to the population including lung cancer. The study shows that the use of a fractional crystallization may decrease the cost of salt extraction and the environmental risks by localizing the crystallization domains of valuable and hazardous minerals.