| Brucite is a high-grade mineral, only few countries have brucite mineral resources, which have been found in China. Brucite has been widely in refractory, environmental protection, building materials, ceramics and nuclear industry, as an industrial mineral. Brucite is mainly used to be exported as a raw material and prepare refractory in China, due to undeveloped technology, which is a great waste and limit high efficiency utilization of brucite. Brucite should be used to prepare high value-added and high technological functional materials to avoid waste.More and more attention has been paid to prepare magnesium hydroxide by brucite. In recent years, Magnesium hydroxide has been widely used in polymers, electric cables, building and decoration materials, as an economic and environment-friendly inorganic flame retardant, due to flame retardency, smoke-repressive property, low or zero evolution of toxic or hazardous byproducts and high decomposition temperature. The morphology and particles size of crystals play an important role in flame retardency of Mg(OH)2.It was reported that preferred flame retardant features Mg(OH)2 purity>97%, particles thickness>80nm, average particle size at 0.5-1μm, the microstain of (101) polar plane is small. However, products prepared with brucite as raw materials by physical method have bad flame retardency, due to low purity and irregular morphology. Good magnesium hydroxide was mainly prepared by chemical methods, with magnesium and magnesium salts as raw materials, which is high cost. So, preparation of magnesium hydroxide by brucite can remarkably improve competitiveness of magnesium resource of China.Superfine high pure, different morphological Mg(OH)2 particles with uniform particle size and good dispersion were prepared by hydrothermal synthesis and treatment with brucite as raw materials in this paper. The crystal phase, morphology and particles size of the Mg(OH)2 particles as prepared were characterized with X-ray(XRD) and scanning electron microscopy(SEM). Mechanistic interpretation of crystal growth was postulated based on experiment result. Conclusions can be drawn as follow:(1)Geological conditions of brucite deposit in Liaoning Province, formation of different morphological brucite and mineralogical characterization were researched through field investigation and data analysis, which provide geological proof for utilization of brucite. Technological methods of preparing form stable magnesium hydroxide were presented based on characterization of brucite resources in Liaoning Province.(2)The high pure Mg(OH)2 crystals of good dispersion were prepared by hydrothermal synthesis and hydrothermal treatment, which exhibited hexagonal lamellar morphology with thickness of 80-100nm and diameter of 200-400nm and fibrous morphology of diameter of 100-500nm and lengths of 1-20μm. All the diffractive peaks of each sample were in agreement with the standard data, no peaks arising from impurities were observed, the microstain of (101)polar plane<3.0×10-3, which indicated the obtained Mg(OH)2 particles were preferred inorganic flame retardant.(3)The influence of speed of stirring, degree of filling, precursor concentration, time, temperature, pH values, KOH, SO42-, solvent and surfactant on Mg(OH)2 particles were systemically researched. The preferential orientations of different crystal facet were estimated by calculating I001/I101.(4)The relationship of filtration efficiencies and crystal morphology and crystallinity was discussed. The results indicated that hexagonal lamellar morphological crystals had better filtration efficiencies than whiskers, which indicated controlling crystal morphology and crystallinity of Mg(OH)2 could satisfy filtration efficiency.(5)Based on the experimental data, started from knowledge of modern physics, solution chemistry and crystallography, according to the theoretical model of anionic coordination polyhedron growth units, the growth mechanism of Mg(OH)2 crystals under hydrothermal conditions were investigated. It concluded that the final morphology of a crystal was dependent on the intrinsic crystal structure and external growth conditions, growth units connected to crystal facet determined the process of crystal growth, which was affected by crystal structures and external growth conditions.Mg(OH)64- is the basic growth unit of Mg(OH)2 crystals. The intrinsic crystal structure make Mg(OH)2 be in favor of formation of hexagonal lamellar crystals, according to bond valence model. The process of Mg(OH)64- growth units connected to crystal facet is determinated by the number of Mg-O-Mg and OH groups at the three-centered bringing position.The formation of growth units and process of growth units connected to facet are affected with external growth conditions, which play an important role on crystal growth.Theoretical analysis is in agreement with experimental result. The work of this paper shows that growth unit connects the crystal structure, external growth conditions and growth morphology together for a better understanding of intrinsic relationships between them. Therefore, growth unit model is correct and thus is powerful.This study provides theoretic basis and technological method for preparation of form stable magnesium hydroxide crystals by brucite. |
