Mineral Precipitation Sequence During Evaporation of Lake Katwe Brine
Lwanyaga, Joseph Ddumba (1,2); Kasedde, Hillary (2); Kirabira, John Baptist (2)
1: Department of Mining and Water Resources Engineering, Faculty of Engineering, Busitema University, P.O. Box, 236, Tororo, Uganda.; 2: School of Engineering, College of Art, Design and Technology, Makerere University, P.O.Box, 7062, Kampala, Uganda.
Traditional salt mining techniques that yield salts of both low quality and quantity have been practiced for centuries at Lake Katwe in Uganda. To change this trend, the thermodynamics of the salt reserve should be well understood. This in turn will facilitate the design of a salt extraction process that will improve the quality and quantity of the salt and thus increase the incomes of the salt miners. The effect of temperature on the mineral precipitation sequence during evaporation of the natural brine from lake Katwe was studied. Laboratory isothermal evaporation experiments at temperatures (30, 40, 50, 60 & 70) using the original Katwe surface brine were undertaken. PHREEQC, a solubility software was used to predict the crystallization paths at the different study temperatures. The mineralogy and morphology of the precipitates were determined by the XRD and SEM techniques respectively. The precipitation majorly started with Thenardite followed by Halite, Trona and lastly Glaserite at all temperatures. Halite emerged the most dominant mineral, with Thenardite, Trona and Glaserite following respectively. Higher temperatures (50, 60 & 70) favoured precipitation whereas lower temperatures favoured Halite precipitation. Increase in temperature moved the constituent phase boundaries making them more distinct thus reducing the possibility of coprecipitation. The study showed that the solubility of the precipitating minerals is sensitive to temperature change and therefore it can be used as a variable in the design of separation process.