Recovery of cooking liquor from spent semi-chemical pulping liquors

Claim 1

IN A PROCESS FOR THE RECOVERY OF SODIUM SULFITE FROM SPENT SEMI-CHEMICAL PULP LIQUOR, THE STEPS COMPRISING: PULPING WOOD CHIPS WITH A BUFFERED SOLUTION OF SODIUM SULFITE; SEPARATING PULP AND A SPENT SEMI-CHEMICAL PULP LIQUOR; OXIDIZING SUBSTANTIALLY COMPLETELY THE ORGANIC AND INORGANIC CONSTITUENTS OF SAID LIQUOR WHILE MAINTAINED UNDER THE VAPOR PRESSURE OF THE REACTION MIXTURE AND SUBSTANTIALLY IN THE LIQUID PHASE IN A REACTION ZONE TO OBTAIN A SODIUM-CONTAINING CONCENTRATE; INTRODUCING SULFUR DIOXIDE AND A SOLUBLE CALCIUM-CONTAINING MATERIAL WHICH WILL FROM INSOLUBLE CALCIUM SULFATE WHEN CONTACTED WITH AN AQUEOUS SOLUTION OF SODIUM SULFATE; SEPARATING CALCIUM SULFATE THUS PRECIPITATED AND TREATING THE RESULTING FILTRATE WITH A CALCIUM-CONTAINING MATERIAL WHICH WILL FORM SODIUM SULFITE AND CALCIUM SULFITE WITH SAID FILTRATE; SEPARATING THE CALCIUM SULFITE SO-FORMED AND RETURNING IT TO SAID SODIUM-CONTAINING CONCENTRATE; AND RETURNING THE SODIUM SULFITE SO-FORMED TO THE PULPING STEP.