FLUORIDE CONTAMINATION AND MINERALOGICAL COMPOSITION OF EAST AFRICAN MAGADI (TRONA)

Magadi from Lake Magadi, Kenya, Lake Natron, Tanzania, Lake Katwe, Uganda and lake El Atrun, Sudan, are analysed along with efflorescent crust magadi from the surface soil from Northern Tanzania. The fluoride and carbonates concentrations are measured chemically and the mineralogical composition is determined through X-ray diffraction analysis. Magadi from Lake Natron and Lake Magadi are found to be very similar consisting mainly of trona (CO_(3)^(2-) + HCO_(3)^(-) ->10.4 meq/g magadi), mixed with halite and either kogarkoite or villiaumite respectively. This is resulting in fluoride concentrations up to 8.7 mg F-/g magadi. The scooped magadi is less pure with respect to trona, but its fluoride content is of the same order of magnitude (0.23-5.1 mg F-/g magadi). The scooped magadi consists of trona (CO_(3)^(2-) + HCO_(3)^(-) = 3.5 - 9.5 meq/g magadi) with different mixtures of halite, quartz, villiaumite, kogarkoite, and thermonatrite. No fluoride containing minerals are identified in magadi from Uganda and Sudan, probably due to the very low fluoride concentrations, = 0.02 and < 0.24 mg/g magadi respectively. The Sudanese magadi consists of different mixtures of trona, halite, and quartz resulting in a variation its alkaline strength (CO_(3)^(2-) + HCO_(3)^(-) = 4.6-11.9 meq/g magadi). The magadi from Lake Katwe consists of trona (CO_(3)^(2-) + HCO_(3)^(-) = 7.0 meq/g magadi) mixed with burkeite and halite.