Effect of Temperature on Mineral Precipitation Sequence of Lake Katwe Brine during Evaporation
Joseph Ddumba Lwanyaga *
Department of Mechanical Engineering, College of Engineering, Design, Art and Technology, Makerere University, P.O.Box 7062, Kampala, Uganda and Department of Mining and Water Resources Engineering, Faculty of Engineering, Busitema University, P.O.Box 236, Tororo, Uganda.
Hillary Kasedde
Department of Mechanical Engineering, College of Engineering, Design, Art and Technology, Makerere University, P.O.Box 7062, Kampala, Uganda.
John Baptist Kirabira
Department of Mechanical Engineering, College of Engineering, Design, Art and Technology, Makerere University, P.O.Box 7062, Kampala, Uganda.
*Author to whom correspondence should be addressed.
Abstract
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 and 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 sequence majorly started with sulphates followed by chlorides and lastly carbonates at all temperatures after precipitation of the calcium-magnesium carbonates. Halite emerged the most dominant mineral, with thernadite, trona and glaserite following respectively. Thenardite, glaserite and burkeite precipitation flourished at lower temperatures (30 and 40 ) whereas soda ash precipitation flourished at higher temperatures (60 and 70 . Halite equally precipitated at all temperatures thus not showing a temperature preference in this study. Temperature variation is a key design parameter in the extraction of mineral salts from the Brines of Lake Katwe.
Keywords: Lake Katwe, evaporation temperature, PHREEQC, precipitation