FTIR analysis of water structure and its significance in the flotation of sodium carbonate and sodium bicarbonate salts

Abstract

Abstract The production of soda ash from trona resources (sodium sesquicarbonate, Na 2 CO 3 ·NaHCO 3 ·2H 2 O) has completely displaced the production of synthetic soda ash in the USA. Further, the utilization of other trona resources is under consideration in China, Turkey, etc. Recent research has been concerned with the development of flotation technology for the trona industry. In this regard studies on the flotation behavior of sodium carbonate salts: trona, sodium carbonate monohydrate and decahydrate, as well as the flotation behavior of sodium bicarbonate, are reported for both cationic (dodecyl ammonium hydrochloride) and anionic (sodium dodecyl sulfate) collectors. It has been found that strong flotation of sodium bicarbonate (NaHCO 3 ) can be achieved with 100% recovery, while the other sodium carbonate salts do not float well. These results have been explained by FTIR analysis of aqueous solutions of Na 2 CO 3 and NaHCO 3 in a range of concentrations from very dilute to saturated conditions. The changes in the shape of the O–H stretching band of water are correlated with the flotation behavior of Na 2 CO 3 salts and NaHCO 3 . In addition, the absorption band of the carbonate ion at ca. 1385 cm −1 is used to monitor its interactions with water and/or other ions in solution. The infrared results demonstrate that Na 2 CO 3 acts as a water structure maker, leading to an extensively hydrated surface that accounts for the poor flotation of most sodium carbonate salts. In contrast, NaHCO 3 does not have this characteristic and consequently complete flotation is possible with both cationic and anionic collectors. These results support the previous water structure analysis for soluble salt flotation of alkali halides and other oxyanion salts.