Contact angle and bubble attachment studies in the flotation of trona and other soluble carbonate salts

Trona, Na₂CO₃ · NaHCO₃ · 2H₂O, is mined as the primary source for sodium carbonate production in the United States. Recent studies have shown that the flotation method can be used for pre-processing of trona ore to remove insoluble mineral contaminants for the production of soda ash (sodium carbonate). Studies with carbonate salts suggest that certain important factors can affect their flotation response, including viscosity of the brine and interfacial water structure. Flotation studies showed that contrary to the strong flotation of NaHCO₃ with both anionic and cationic collectors, Na₂CO₃ does not float at all. Based on the analysis of interfacial water structure in saturated brines, Na₂CO₃ was found to act as a strong water structure maker, whereas NaHCO₃ acts as a weak water structure maker. Bubble attachment time measurements suggest that collector adsorption at the surface of NaHCO₃ induces flotation; this is not the case for Na₂CO₃. Contact angle measurements indicated that the surface of Na₂CO₃ is hydrated to a great extent, whereas the NaHCO₃ salt surface is less hydrated. These results reveal that there is a strong relationship between the interfacial water structure and the contact angle of these salts. The less stable NaHCO₃ surface is ascribed to the interfacial water structure which allows for NaHCO₃ flotation with both anionic and cationic collectors.