Characterization of brines and evaporite deposits for their lithium contents in the northern part of the Danakil Depression and in some selected areas of the Main Ethiopian Rift lakes

摘要

Lithium is a metal with increasing demand on the global market mainly for its application in lithium ion batteries for electric vehicles. Ethiopia has potential for lithium resources related to pegmatites and to rift-bound brine deposits.The current research focused on known brine lakes and hot springs in the Danakil Depression and the Main Ethiopian Rift. Lithium contents in water samples from rift-bound lakes like Abijata, Shala, Chamo, Abaya, and Chew Bahir show low concentrations consistent with background values for surface waters. Lithium concentrations are elevated in brine lakes, brine ponds, and hot springs of the Danakil Depression. Hot springs in the Dallol contain up to 20 ppm lithium. Lithium enrichment was also noted in residual brines from multi-stage solar evaporation pans during soda-ash production. However, brines produced during precipitation of trona and halite contain about 0.009 ppm lithium, which is well below economically extractable concentrations. Core samples from the Danakil Depression potash exploration reported up to 20-40 ppm in the carnallite and bischofite layers of the evaporite sequence.At least three potential sources for lithium are noted in the Danakil Depression. For example, lithium is leached and mobilized during water rock interactions by deeply circulating and cycling hot meteoric and possibly juvenile geothermal fluids related to the intense volcano-tectonic processes. The current hydrological condition also suggest the possibility of lithium mobilization during surface run off from the basement and Mesozoic sedimentary rocks exposed along the western rift margin of the Danakil Depression. Moreover, variable lithium contents in the different layers of the evaporite sequence suggests, that lithium originated from sea water evaporation before the Danakil Depression became a closed basin. The current research strongly indicates that more detailed investigation is required to evaluate the lithium resources as a primary product and/or as a secondary byproduct during potash mining.