Characterization of brines and evaporites of Lake Katwe, Uganda

• Lake Katwe brines and evaporites were characterized.
• The brines are of carbonate type, with high amounts of Na, Cl, SO4 and HCO3 + CO3.
• Evaporites from the deposit are composed of mainly Na and Cl with other impurities.
• Mineralogical analysis shows that salts contain halite, hanksite, burkeite and trona.
• The work provides information towards sustainable extraction of salts from the lake.

Lake Katwe brines and evaporites were investigated to determine their chemical, mineralogical and morphological composition. 30 brine samples and 3 solid salt samples (evaporites) were collected from different locations of the lake deposit. Several analytical techniques were used to determine the chemical composition of the samples including Inductively Coupled Plasma–Atomic Emission Spectrometry (ICP–AES), Inductively Coupled Plasma–Sector Field Mass Spectrometry (ICP–SFMS), ion chromatography, and potentiometric titration. The mineralogical composition and morphology of the evaporites was determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Physical parameters of the lake brines such as density, electrical conductivity, pH, and salinity were also studied. The results show that the lake brines are highly alkaline and rich in Na+, Cl−, CO32-, SO42-, and HCO3- with lesser amounts of K+, Mg2+, Ca2+, Br−, and F− ions. The brines show an intermediate transition between Na–Cl and Na–HCO3 water types. Among the trace metals, the lake brines were found to be enriched in B, I, Sr, Fe, Mo, Ba, and Mn. The solid salts are composed of halite mixed with other salts such as hanksite, burkeite and trona. It was also observed that the composition of the salts varies considerably even within the same grades.