Conversion of alkali metal sulfate to the carbonate

A process for converting potassium sulfate to potassium carbonate comprising passing a mixture of potassium sulfate and calcium oxide to a reducing station and there reacting said mixture for a time not to exceed about one hour to convert not less than about 80% of the sulfate potassium sulfide, potassium bisulfide, or potassium hydroxide at a temperature of about 750.degree. C. with a gaseous mixture having a minor amount of up to about 20 volume percent reductants selected from the group consisting of hydrogen, carbon monoxide and mixtures thereof in an inert diluent wherein the calcium oxide is present in an amount not greater than about 20 percent by weight of the potassium sulfate to produce a liquid mixture of said potassium sulfide, potassium bisulfide or potassium hydroxide and calcium sulfide and a gaseous mixture of steam and hydrogen sulfide;

• passing the liquid mixture to a quenching station and there adding water to produce an aqueous slurry of soluble potassium salts and insoluble calcium salts and a gaseous mixture of steam and hydrogen sulfide;
• passing the slurry to a filtering station and there separating the insoluble calcium salts from the aqueous solution of soluble potassium salts;
• passing the calcium salts to a drying station operated at a temperature of about 100.degree. C. to produce calcium sulfide, calcium bisulfide and steam;
• passing the calcium sulfide and calcium bisulfide to a calcining station operated at a temperature of between about 800.degree. C. and 1000.degree. C. and introducing air thereto to produce calcium oxide for recycle to the reducing station and sulfur dioxide;
• passing the soluble potassium salts from the filtering station to a carbonating station operated at a temperature of about 80.degree. C. and introducing carbon dioxide gas to the aqueous solution of potassium salts to produce potassium carbonate and hydrogen sulfide;
• passing the potassium carbonate solution to an evaporating station to concentrate the potassium carbonate to precipitate potassium carbonate from solution and to produce steam containing potassium salts recycled to the quenching station;
• passing the liquid phase containing precipitated potassium carbonate from the evaporating station to a filtering station to separate solid potassium carbonate therefrom and recycling the concentrated potassium-containing filtrate to the quenching station.