Study On The Preparation Of High Pure Magnesium Carbonate And Magnesium Oxide From Byproduct Containing Magnesium Chloride

The production of magnesium salts are at the primary stage in our country. Many are raw material products or just lower grade products. Comparatively, high grade products are deficient, and needed to be imported from abroad for great demand. Therefore, it is a significant tendency to explore high grade, multi-functional, fine magnesium salts in this fields. Recently , Magnesium chlorides, as a industrial byproduct, gradually are a high quality main magneisum resources. The resources of this kind, which have a advantage of higher purity and non-complicated recycle pretreatment process compared to natural magnesium resources, are generally saled at a very low price though. It is a urgently necessary as well as a good way to reuse this resurce for improving the quality level in magnesium fields.Basic magnesium carbonate and magnesium oxide are two important products in magnesium salts. They have a great demand in recent years, especially due to the increasing development of high inorganic funtional materials as a efficient additive. But the performance indexes of the two products can't wonderfully meet the related demand standards, which are the gap in this fields. Based on the background, this thesis gives a study on the prepared technology of high pure basic magneisum carbonate and magnesium oxide from the industrial byproduct. And further the morphological forming way of the two salt is also tentatively researched. The main work includes three parts as follows.(1) The industrial byproduct, magnesium chlorides are a simple purified treatment. Then intermediate products, magnesium hydroxides are prepared with ammonia as a precipitant. After carbonizing and pyrolysising technology, high pure basic magnesium carbonates are synthesized. The technological parameters are all detailedly given research under the guidance of reaction kinetics theory and industrial amplification perspective. The transformation rate of raw materials is about 87.6%. The molecular formula of as-sythesized basic magnesium carbonate is 4MgCO₃·Mg(OH)₂·4H₂O. And the total contents of impure metal are 10 ppm below. The purity is above the related international standard of high pure electronic basic magnesium carbonate.(2) High pure grade active magnesium oxide are prepared using high pure as-synthesized basic magnesium carbonate as a precursor by controlling the calcining technology parameters (heating rates, calcining time, calcining temperature). The prepared magnesium oxde has as the following characters: over 99.99% of purity, about 120m²/g of the specific surface area, 8 s of citric acid active value, 18.5ml/g of the apparent specific cubage.(3) Based on the characteristics of solution homogeneous nucleation and the influence factors on crystal growth, different morphological magnesium carbonates (whisker, ellipsoid, sphere, rod, shell and leaf like) are respectively prepared by a solvent-induced method (ethylene glycol, triethanolamine as induced solvents), a template-mediated method (cetyltrimethylammonium bromide as template agent) and adoptting different way of pyrogenation. And using the obtained magnesium carbonate as precursors, magnesium oxides with the similar morphologies as precursors' are prepared by controlling the sectional program calcinations regulation according to thermal gravimetric analysis of precursor. The morphology relations between magnesium oxide and its precusors are also further studied. Finally, the transformation rules from precursor to magnesium oxide were intentatively summed up.