Methods for the production of potassium sulphate from potassium-containing ores at high ambient temperatures

A method for the production of potassium sulphate comprising the consecutive steps of:

• Ia) contacting an aqueous potassium- and sulphate-containing composition with magnesium chloride (MgCl2), thereby obtaining a composition comprising kainite (KCl.MgSO4.2.75H2O);
• IIa) optionally, concentrating the kainite from the composition, obtained in step Ia;
• IIIa) reacting the kainite, obtained in step Ia or IIa, with magnesium sulphate (MgSO4) and potassium sulphate (K2SO4) at a temperature of 45° C. to 55° C., so as to convert the kainite into leonite (K2SO4.MgSO4.4H2O), thereby obtaining a composition comprising leonite, wherein leonite is present in the composition comprising leonite at a concentration of at least 90% by weight;
• IVa) optionally, contacting the leonite, obtained in step Ma, with water to remove excess MgSO4;
• and
• Va) contacting the leonite obtained in step Ma or IVa, with water so as to leach the MgSO4 contained in the leonite and to at least substantially selectively crystallize potassium sulphate (K2SO4).