A study of the kinetics of conversion of natural langbeinit mixed with carnallite

Abstract

The dependence of the process of conversion of natural langbeinite with carnallite in the presence of a carnallite solution on the process duration, temperature, and particle size was studied. The mechanism and kinetics of the process were analyzed.The most valuable component of Precarpathian polymineral potassium ores is a sulfate mineral, langbeinite, whose content in the ore may be as high as 20 330%. In the mineral-salt technology of ore processing, used in practice, only 20 323% of the difficultly soluble langbeinite passes into solution, with the rest remaining in the halitelangbeinite residue, which is the waste. Because of the low solubility of langbeinite, the recovery of K + into fertilizer does not exceed 60%, and the content of chloride ions in the finished product is not higher than 25% [1]. Therefore, a study of how the solubility of langbeinite components can be raised is a matter of current interest.A method for processing of langbeinite ores is known. This method consists in washing-out with water of well-soluble salts to give a langbeinite concentrate. Drying of the concentrate yields a compound that contains 18 wt % MgO, 22 wt % K 2 O, and <2.5 wt % Cl ! [2]. Polymineral ores are also processed using electrostatic separation [3]. However, these methods are not applicable to processing of Precarpathian polymineral ores because of the high content of readily soluble potassium3magnesium minerals kainite, sylvine (20 330%), and clayey admixtures (up to 20%) [2].Also known is a method for processing of polymineral ores with preliminary conversion of langbeinite into schoenite [4] by the reaction K 2 SO 4 . 2MgSO 4 + 13H 2 O 6 4 K 2 SO 4 . MgSO 4 . 6H 2 O (1) + MgSO 4 . 7H 2 O. The recovery of components of the polymineral ore into fertilizer is 80 382%. This technique cannot provide a >85% conversion of langbeinite into solution, because an increase in the concentration of the reaction product, MgSO 4 , in the liquid phase leads to a shift of the point corresponding to the solution composition into the region of langbeinite crystallization. Kainite present in the polymineral potassium ore also enters into the conversion reaction to give schoenite [3]: 2[KCl .MgSO 4 .3H 2 O] 6 4 K 2 SO 4 .MgSO 4 .6H 2 O + MgCl 2 .(2)The forming MgCl 2 hinders the course of reaction (2). The negative effect of kainite on the conversion of langbeinite into schoenite was noted in [5]. In addition, conversion of langbeinite into schoenite requires a large amount of water, which is bound into crystal hydrates, and soluble salts crystallize entrapping particles of the ore. In dissolution of a schoenitecontaining ore, there occurs crystallization of secondary leonite, which gives no way of achieving a high saturation of the solution with sulfate potassium3magnesium salts.Also, a method for conversion of langbeinite with a magnesium chloride solution into kainite has been developed [1]. The process occurs in a suspension and can be represented as K 2 SO 4 . 2MgSO 4 + 9H 2 O + MgCl 2 + KCl (3) 6 4 3[KCl . MgSO 4 . 3H 2 O].The...