GB1117380A - Process for the production of alkali metal sulphates - Google Patents

Abstract

An alkali metal sulphate or alkali metal Mg sulphate is prepared by reacting an alkali metal chloride with MgSO4 or an alkali metal Mg sulphate in the presence of an organic solvent selective for MgCl2. The solvent may be methanol, ethanol, acetone, or dimethyl formamide, alone or mixed, or with water. Starting materials referred to are KCl, NcCl, KCl-NaCl, anhydrous MgSO4, MgSO4.7H2O, kieserite, and K2SO4.MgSO4.6H2O (shoenite), and the end product may be K2SO4, Na2SO4 (themardite), shoenite, Na2SO4.MgSO4.4H2O (astrakanite), or Na2SO4.3K2SO4 (glaserite). These processes are described (with reference to Figs. 1, 2 and 3 resp.) each using methanol and water as solvent: (1) Reaction of KCl and MgSO4 to give a mixture of K2SO4.MgSO4 and KCl. MgCl2.2H2O is recovered by spray-drying. (2) Reaction of K2SO4.MgSO4 and KCl to give K2SO4. The methanolic MgCl2 solution is mixed with MgSO4 and brine (obtained in the decomposition of camallite) to give the K2SO4.MgSO4 required. (3) A solid mixture of K2SO4.MgSO4 and KCl is suspended in methanol to obtain K2SO4. The MgCl2 solution is mixed with KCl and MgSO4 and a NaCl-KCl mixture to give the required starting mixture and further MgCl2 solution, which is mixed with camallite brine to give the required NaCl-KCl. The reactions are effected in stirred vessels followed by thickeners. Products are recovered in a centrifuge or on a water sprayed band filter, and the liquid recycled. The final MgCl2 solution may be passed through a vacuum evaporator and then to a steam-injected distillation column. The vaporized methanol is condensed and recycled.