Magnesium oxysulfate (MgSO4·5Mg(OH)2·2H2O) flake powders with an average diameter of 2 μm and a thickness of 0.052 μm were prepared using magnesium sulfate and sodium hydroxide as raw materials by hydrothermal synthesis process. The composition, morphology and structural features of the hydrothermal products were examined with X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The experimental results indicate that in the conditions of n(NaOH)/n(MgSO4) of 1.25, the dosage of w(Na3PO4) crystal additives of 1.0% w(MgSO4), stirring for 5 h at 180 °C, the morphology of MgSO4·5Mg(OH)2·2H2O products is flaky and laminar, which is a kind of complex magnesium single- crystal. The recycling of MgSO4 mother liquor was also investigated to make a full use of the materials and reduce disposal. The results prove that there is no adverse effect on the yield and purity of the products.
Chemical Manganese Dioxide (CMD) was prepared by an alkali-oxidation method. There are several virtues to this environmental friendly and clean process, including the nontoxic and harmless reagents and products, easy operations, no pollutants, easily obtained raw materials and moderate reaction conditions. The synthesized manganese dioxide was characterized by XRD and SEM. The particles were small, consisting primarily of α-MnO2 and γ-MnO2. Experimental results showed that the optimum conditions were: MnSO4?H2O to NaOH ratio, 1.0:2.4; catalyst concentration (catalyst TF-2), 6% of the MnSO4; initial solution pH, 11; reaction time and temperature, 20 min and 80 °C; air flow, 0.20 m3/h; and, agitation rate, 700 r/min. The conversion of MnSO4 can exceed 80% under these optimum conditions.
FU Jiangang, HE Zhangxing, WANG Hui, LIANG Wei, GUO Chao College of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China
The dissolution of molybdenite concentrate in NaCl electrolyte was investigated. The results show that the dissolution rate increases with the increase in liquid-to-solid ratio, stirring speed, NaCl concentration and temperature. When the liquid-to-solid ratio is 30:1, stirring speed is 400 r/min, concentration of NaCl is 4 mol/L at pH=9 and room temperature, the leaching efficiency of molybdenite concentrate will reach 99.5% in 240 min. Molybdenite concentrate cannot be electro-oxidized directly on the anode. The kinetic studies show that the dissolution of molybdenite concentrate is represented by shrinking core model with diffusion through a porous product layer of element sulfur, and the apparent activation energy for the dissolution reaction is 8.56 kJ/mol.
