Patent ID: 9682868
Date: 2017-06-20
CPC Classifications: C01C,C01F,C01P,C30B

Claim:
1. A partially continuous countercurrent flow process for converting gypsum to ammonium sulfate and calcium carbonate comprising the following steps: separating an aqueous slurry of gypsum to result in a gypsum liquid residue and a gypsum cake; feeding a flow of reactants being the gypsum cake and a solution of ammonium sulfate and ammonium carbonate into a first reactor for chemical reaction; stopping the flow of reactants into the first reactor for a retention time selected to achieve a preselected degree of chemical reaction to form an ammonium sulfate solution containing a first precipitate calcium carbonate and a gypsum remnant; discharging the ammonium sulfate solution containing a first precipitate calcium carbonate and a gypsum remnant; resuming the flow of reactants into the first reactor; separating the first precipitate calcium carbonate and gypsum remnant from the ammonium sulfate solution to result in a product ammonium sulfate solution and a remnant cake of first precipitate calcium carbonate and gypsum; retaining the product ammonium sulfate solution; feeding a flow of reactants being the remnant cake of first precipitate calcium carbonate and gypsum and ammonium carbonate solution into a second reactor for chemical reaction; stopping the flow of reactants into the second reactor for a retention time selected to achieve a predetermined degree of chemical reaction to form a second precipitate calcium carbonate and a solution of ammonium sulfate and ammonium carbonate; discharging the first and second precipitate calcium carbonate and a solution of ammonium sulfate and ammonium carbonate; resuming the flow of reactants into the second reactor; separating the first and second precipitate calcium carbonate from the solution of ammonium sulfate and ammonium carbonate to result in a product calcium carbonate cake and a residue solution of ammonium sulfate and ammonium carbonate; retaining the product calcium carbonate cake; and adding the residue solution of ammonium sulfate and ammonium carbonate to the first reactor.