Fine Processing Technology And Application Of Anhydrite

In our country, the resources of natural anhydrite are abundant and widely distributed, but the exploitation of anhydrite is not much in the past. From the existing research report, the main application of anhydrite was in cementing and construction materials field, with low value-added. According to the application of anhydrite in polymer is still in the initial stage, this study aims to explore the use properties of anhydrite in plastic and broaden the anhydrite application field.In this paper, modified anhydrite powder was prepared by dry ultra fine processing method and surface modification. The different formula anhydrite/PVC composite materials were prepared by amplified experiment. Considering the anhydrite with low whiteness degree, smooth surface and sharp edges, surface nanocrystallization modification of anhydrite was also studied. Whiteness, XRD, SEM, EDAX, FT-IR, N2adsorption were used to characterize the samples properties. The results were as follows:(1)In addition, the silane, titanate, aluminate coupling agent were used to modify different particle size of the anhydrite powders, the results showed aluminate coupling agent was most effective to anhydrite. When the activation index above90%, different particle size of anhydrite powder need different amount aluminate coupling agent, the1000mesh and425mesh anhydrite powder need1.2%,0.6%aluminate coupling agent respectively.(2)Anhydrite/PVC composite pipes were prepared by melt extrude, through blending modified anhydrite powder, polyvinyl chloride (PVC) matrix and all kinds of additives. Testing and analysis showed that, with the right proportion of modified anhydrite powder as filler in PVC matrix, the compatibility of anhydrite and PVC was well, the modified filler also distributed uniformly in the PVC matrix. The composite material had compact structure and well combined interface. The properties of anhydrite/PVC composite pipe met the enterprise standards, especially, the vicat softening point (90.2℃) and ring stiffness (11.90kN/m2) were obviously better than the enterprise standards(80℃,8.0kN/m2). Furthermore, compared with PVC resin, the filling amount of modified anhydrite could reach250%.(3)Surface nanocrystallization modification of anhydrite was studied using carbonation method in the Ca(OH)2-H2O-CO2system. Test analysis showed that, the nanosized CaCO3of70nm in average size was uniformly coated on the surface of anhydrite, the surface of the CaCO3/anhydrite composites became rough without sharp edges, meanwhile, the whiteness of anhydrite increased significantly. Especially when the mass ratio of CaCO3:anhydrite was1:1, the whiteness of the CaCO3/anhydrite composites could reach85.8%, much higher than that of the original anhydrite (63.1%). The specific surface area (26.25m2/g) of CaCO3/anhydrite composites was nearly three times larger than the original anhydrite (6.65m2/g).