The flotation chemistry of potassium double salts: Schoenite, kainite, and carnallite

Abstract

It is known from soluble salt flotation practice that the K, Mg double salts of kainite (KClMgSO 43H 2O), and carnallite (KClMgCl 26H 2O) are difficult to float and must be converted to other salts such as schoenite (K 2SO 4MgSO 46H 2O) and sylvite (KCl) in order to recover potash values. The flotation characteristics of these double salts have now been confirmed in some detail by carefully controlled laboratory experiments with both cationic and anionic collectors. The experimental results are discussed in view of recent experimental findings regarding the flotation characteristics of simple salts, in which the flotation response was shown to be determined by the interfacial water structure and whether the salt could be considered to be a water structure maker or a water structure breaker. The same approach can be use to explain the flotation response of the potassium double salts; schoenite, kainite, and carnallite. In addition, the sign of the surface charge of schoenite (K 2SO 4MgSO 46H 2O), was determined as a function of pH from nonequilibrium electrophoretic mobility measurements. Schoenite appears to exhibit three charge reversals (CR) which can be explained based on surface hydrolysis reactions. The flotation behavior of schoenite is further considered based on solution chemistry calculations, electrophoretic mobility measurements, and microflotation results.