Geoeconomic interest of minerals assemblage of sebkha El Melah, southeastern Tunisia

Abstract

AbstractThis work aimed to study the formation of salt through a progressive evaporation of sebkha El Melah brine. The precipitated salt in the case of sebkha El Melah is variable along the progressive evaporation. Weights of salt after each phase of precipitation indicate a heterogeneous evaporation process cumulating at 315 g L−1. With an increasing evaporation of El Melah brine, the number of precipitated mineral species increased. The cumulative number of species along the evaporation process reached 20, including principally: Halite (NaCl) (73–95%), epsomite (MgSO4·7H2O) (7–14%), bischofite (MgCl2:6H2O) (1%), Kieserite Mg(SO4)(H2O) (0–2%), magnesite (MgCO3) (1–4%), polyhalite (K2Ca2Mg(SO4)4,2H2O). Also, the thermodynamic theoretical modeling of the El Melah brine shows convergence with geochemical and mineralogical experimental data. At an evaporation rate of 60%, the sebkha of El Melah annually provides with 315,000 tons of salt. The majority of salt (80%) is halite. The remaining 20% contains different species having a huge economic interest. From an industrial viewpoint, our study shows that the purity of halite is guaranteed at low rates of evaporation. Evaporation between 50 and 75% produces a mixture dominated by halite. Evaporation higher than 75% needs further studies to find the mineralogical composition and the phase of each mineral precipitation. The saline system of El Melah represents a geoeconomic interest due to the cheap natural process of production, its large quantity of halite with varieties of other accessory minerals, and cheap procedure of exportation.