Understanding the Deposition and Surface Interactions of Gypsum

Abstract

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 γeff = 32.8 and 7 mJ/m2 for gypsum surfaces with an rms roughness of ∼8 and ∼100 nm, respectively, which increase with a decrease of the rms roughness, approaching the thermodynamic value ∼48 mJ/m2 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 CaSO4 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.