Saharan lithium: Brine chemistry of chotts from eastern Algeria

摘要

Salt pan brines in desert areas are globally known to be rich sources of lithium. This study reports the results of a regional survey of brine chemistry in chotts (salt pans) conducted along a 550 km long valley in the northeast Algerian Sahara, one of the major desert areas on Earth. A dataset composed of 50 samples, including brine, river, and aquifer, is integrated and discussed in order to study the characteristics of Sahara brines. Brines contain up to 66 mg L-1 of lithium, salinities up to similar to 400 g L-1, and magnesium concentrations similar to 690 times greater than that of lithium. The primary source of major ions would occurr by dissolution of ancient evaporites of the substrate by aquifer waters. Near surface lithium concentration of brines in chotts across the study area and in the aquifer Complexe Terminal defines a pattern of increasing values to the north, where maximum values coincide with chotts (Melghir and Merouane) having the largest sizes (up to 1,840 km(2)) and placed at the lowest altitudes (36 m below sea level). This pattern coincides with the northwards plunging structured substrate. Lithium grades increase consistently with salinity during the concentration through evaporation. However, lithium continues to concentrate beyond evolved brines whether due to the precipitation of lithium-free salts leading to lithium increases in residual brine, and/or by unknown processes supplying additional lithium. Discussed aspects are expected to drive an increasing interest on chotts, which would reveal in the future, as a stimulating opportunity for Algeria and the Saharan region.