SURFACE-CHEMISTRY AND FLOTATION OF SCHEELITE .1. SOLUBILITY AND SURFACE CHARACTERISTICS OF PRECIPITATED CALCIUM TUNGSTATE

A method of preparing microcrystalline calcium tungstate with a scheelite structure and a large specific surface area has been developed. Solubility studies on this material have given a solubility product of 4.9 × 10-10 (mollliter)2 at 25°C, valid for the pH range 5-13. An unexpected result, namely, that [WO42-] ≠ [Ca2+] in pure water, has been ascribed to anion exchange adsorption of OH-. The ζ-potential of scheelite is primarily controlled by concentrations of the lattice ions, with an iep at pCa 3.1; but many electrolytes have some effect. pH has an influence both direct and indirect, and it appears that net adsorption of OH- occurs in alkaline media. Silicates, phosphates, and (particularly) polyphosphates are markedly adsorbed, enhancing the (usually negative) potential on scheelite. © 1979.