Study On Methods Separation Of Impurity From CaSO₄ Mixture System

The research focused upon purification and separation of CaSO4 from natural gypsum (from Chaohu, Anhui Province, P. R. China). Two kinds of impurities, MgO and SiO2, were chosen to simulate the process. Leaching and foam flotation were selected as two methods for purification of CaSO4. The thermodynamics, kinetics and main working conditions were investigated in detail. Furthermore, ceramic membrane microfiltration for separation of CaSO4 from the simulated mixture was also investigated. Thus, these studies are supposed to provide basic dada for non-metal mining manufacturing and utilization.MgO was separated from the simulated system of CaSO4-MgO by leaching, 5.0wt.% MgO was separated with H2SO4 leaching. Under optimized working conditions: slurry concentration of 10 g·L-1, H2SO4 concentration of 0.015 mol·L-1, temperature 298 K, stirring speed 700 r·min-1 and leaching time 90 min, the result showed that removal rate of MgO was 91.18%. Under the same working conditions, the removal rate of MgO was 59.49% in natural gypsum. The raffinate of leaching meets the national standard after treatment. The leaching behavior could be described by liquid film diffusion model and the leaching rate of MgO obeyed the first order kinetic model.5.0wt.% SiO2 was separated from the simulated system of CaSO4-SiO2 by foam flotation. Under the optimized conditions: pH value of 7.0, slurry concentration 10 g·L-1, average diameter of bubble 2.0 mm, the flotation liquid height of 28.0 cm, CTAB concentration of 0.2 mmol·L-1, gas quantity 0.6 L·min-1 and temperature 298 K, the result showed that removal rate of SiO2 was 74.53%. Under the same condition, the removal rate of SiO2 was 73.36% in natural gypsum. Freundlich model can be utilized to describe the adsorption process of CTAB by SiO2, the pseudo second-order kinetic model can describe well the adsorption process. The process was found to be controlled by the intra-particle diffusion. In the process of flotation, the CTAB was adsorbed by the bubble, the adsorption can be described by the apparent first order kinetics. The adhesion between the particle and the bubble was spontaneous, the surface adsorption was an exothermic process.The ceramic membrane microfiltration was utilized in the CaSO4 slurry processing, the optimum operation conditions was determined as follows: pH value of 7.0, slurry concentration of 10 g·L-1, cross-flow velocity of 1.45 m·s-1, operation pressure of 0.15 MPa and temperature 308 K. Turbulence promoter and the hydrophilic polymer materials could reduce fouling in microfiltration of CaSO4 slurry, the enhancement effect of turbulence promoter was better than the hydrophilic polymer. The membrane separation process was enhanced by helical turbulence promoter, the results showed that the inner ring channels and the outer ring placed the different helical distance (4 mm and 8 mm), the diameter of 3.4 mm, the placement can make combined helical turbulence promoter obtained the better effect on microfiltration process, the permeation flux was enhanced 23.76% by, and the mechanical energy loss was only 26.06 J·kg-1.