Understanding the Deposition and Surface Interactions of Gypsum

Using a surface forces apparatus (SFA) and an atomic force microscope (AFM), we have studied the deposition of gypsum on a silicate mineral (mica) and their surface interactions. An exponential force-distance repulsion relation was obtained for two rough (gypsum) crystal surfaces with root-mean-square (rms) roughness between 4 and 200 nm on approach and separation after the initial contact. The effective surface energies were estimated as gamma(eff) = 32.8 and 7 mJ/m(2) for gypsum surfaces with an tins roughness of similar to 8 and similar to 100 nm, respectively, which increase with a decrease of the rms roughness, approaching the thermodynamic value similar to 48 mJ/m(2) estimated by a three-probe-liquid contact angle measurement. The repulsive force observed for rough gypsum surfaces was found to be a mainly elastic force due to asperity interactions. The surface forces measured between two silicate mineral surfaces (mica) in CaSO(4) solutions were fitted well by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory at low concentrations (10(-4)-10(-2) M) but deviated at higher concentration. Our results have provided insight into the basic surface interaction mechanisms of gypsum and silicates in many mineral flotation processes and industrial operations.