Hydromagnesite, the most stable of the basic magnesium carbonates, can be obtained by mining or by synthesis. Existing synthetic procedures have certain drawbacks which include, undesirable environmental effluents or high pressure and/or temperature requirements. Due to the lack of information in the literature, the aim of this study was to develop a cost effective procedure for the synthesis of basic magnesium carbonate from Mg(OH)2, not hampered by the above mentioned drawbacks. Following an extensive investigation into various parameters that influenced the final product, a simple procedure, based on sparging CO2 through a slurry of magnesium hydroxide in water until the pH reached 7.5-8.5, was developed. The solid portion of the slurry is dried at 80 or 120°C to deliver an unidentified basic magnesium carbonate and hydromagnesite respectively. The products were characterised by XRD, TG-DTA, surface area determination, SEM and FT-IR. The rehydration characteristics of the products were also investigated. By combining the information obtained by each technique, valuable information could be obtained. The synthesised products were evaluated for flame retardant application, due to the demand of mineral flame retardants which could compete with Mg(OH)2 and AI(OH)3. Compared to the traditionally used halogenated flame retardants, the mineral flame retardants deliver non-toxic, non-corrosive decomposition products and contributes in suppressing the emission of smoke in a fire. Results indicated that the basic magnesium carbonates compared favourably to Mg(OH)2 and AI(OH)3 and presented several advantages in terms of flame retardant applications. Further tests will be necessary to accurately assess the flame retardant effect of the basic magnesium carbonates. The possibilities however seem promising.
Thesis (PhD (Chemistry))--University of Pretoria, 2006.