Characterization of Dolomitic Lime as the Base Reagent for Precipitation of Mg(OH)2 from Seawater

J. Jakić, M. Labor and V. Martinac

Abstract
The process of obtaining magnesium hydroxide from seawater involves precipitation of magnesium ions with suitable basic reagents, such as calcined dolomite. The purity of the magnesium hydroxide precipitate depends on dolomite characteristics; therefore, it is necessary to find high purity dolomite with good physical properties. The aim of this study was to characterize the specific dolomite from the location of Đipalo-Sinj (Croatia), its quality, and the favourable conditions for calcination. Certain physical and chemical characteristics were determined by pure chemical analysis, as well as by using TG/DTG-DTA, FTIR and SEM/EDS analysis. Good chemical quality of dolomitic lime (59.03 wt. % CaO, and 40.69 wt. % MgO) with low content of impurities was confirmed with the TG/DTG-DTA thermal analysis. In the atmosphere of air + CO2, dolomite decomposes to CaCO3 and MgO in a temperature area between 415 and 824 °C; thereafter, another reaction begins – the decomposition reaction of calcium carbonate, completed at 897 °C. In air, the simultaneous decomposition of two carbonates occurs between 657 –840 °C. The FTIR and EDS analyses confirmed the complete breakdown of carbonates at 950 °C. The main components (Mg, Ca, and O) confirmed the purity of the dolomite lime.

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Keywords
dolomitic lime, Mg(OH)2, seawater, TG/DTG-DTA, ATR-FTIR, SEM/EDS