Magnesium salts as compounds of the preparation of magnesium oxide from Tunisian natural brines

Abstract

Magnesium oxide is one of the most important magnesium compounds used in industry. The production of MgO is often done from calcined magnesium carbonate or from natural magnesium saline solutions (sea water and brines). In the case of these solutions, magnesium oxide is precipitated after the addition of a strong base (eg. Ammonia). Magnesium hydroxide is calcined after its separation from the excess resulting from the strong base through filtration. Thus, magnesia qualities may differ depending on several physical parameters and particularly on the nature of the compound. Consequently, two different compounds were selected: magnesium chloride and magnesium sulphate which can be recovered from Tunisian natural brines. Three physical factors were considered: calcination temperatures, precipitation temperatures and calcination time of Mg(OH)2. The decomposition of Mg(OH)2 was investigated by DTA/TGA. Mass losses vary in the range (23.0%-29.9%). Starting decomposition temperatures are between 362?C and 385?C. The MgO produced from MgSO4 under 1000?C within 48 hours of calcination time and with 40?C as a reaction temperature for Mg(OH)2 shows a good crystallinity and is of a cristallyte size of 86.3 nm and has a specific surface area equal to 16.87 m2g-1. Finally, morphological differences between MgO agglomerates at different temperatures were observed by SEM. Consequently, magnesium sulphate as precursor for preparing MgO is selected.