Synthesis and characterization of nesquehonite (MgCO3•3H2O) powders from natural talc

The feasibility of synthesis of nesquehonite powders from natural talc was evaluated both through theoretical and experimental approaches. The change of the Gibbs free energy was - 318 kJ/mol with its corresponding equilibrium constants (K) of 5.53 x 10(55), which indicated that the reaction could proceed spontaneously. Pure phase of nesquehonite was successfully obtained from natural talc at a low temperature and ambient pressure under the action of ammonia. The effects of reaction temperature and ammonia dosage on the precipitation of MgCO3 center dot 3H(2)O have been investigated. XRD and SEM results demonstrated that the reaction temperature had a significant impact on the crystal phase of the products, while the ammonia dosage showed no serious effect on the morphology of the products, but had important influence on the length of the crystals. With the optimization of operating conditions (reacted at 60 degrees C with 8 mL ammonia), the nesquehonite crystals were prepared and could grow up to a length of about 19.31 mu m and a width of 0.96 mu m. During the crystallization process, the nesquehonite crystals were transformed from magnesium bicarbonate obtained from magnesium, and have a preferential orientation growth in the (002) direction. The growth process of nesquehonite crystals accorded with the solution-liquid-solid mechanism. (C) 2016 Elsevier B.V. All rights reserved.