Processing of spent cooking liquors

Claim 1

A CYCLICAL METHOD FOR CHEMICAL RECOVERY FROM A PULPING PROCESS WHEREIN AN AMMONIA-BASE SULPHITE COOKING LIQUOR IS EMPLOYED WHICH COMPRISES COMBINING SPENT COOKING LIQUOR WITH AN AQUEOUS SOLUTION CONTAINING SODIUM CARBONATE AND SODIUM SULPHIDE DERIVED FROM PROCESSED SPENT COOKING LIQUOR IN AMOUNTS SUFFICIENT FOR THE SUSTANTIALLY COMPLETE LIBERATION BY DISTILLATION OF THE AVAILABLE AMMONIA CONTENT OF SAID SPENT COOKING LIQUOR AND TO PROVIDE SUCH LIQUOR WITH A PH OF AT LEAST ABOUT 7 AFTER REMOVAL OF AMMONIA THEREFROM, STRIPPING THE AVAILABLE AMMONIA FROM SAID ALKALIZED SPENT LIQUOR AND CONVERTING VOLATILE SULPHUR COMPOUNDS IN SAID LIQUOR TO NONVOLATILE SULPHUR COMPOUNDS IN A HEATED STRIPPING ZONE BY MEANS OF AN OXYGEN-CONTAINING STRIPPING GAS, RECOVERING SAID AMMONIA, CONCENTRATING BY EVAPORATION SAID ALKALIZED SPENT LIQUOR AFTER STRIPPING TO INCREASE THE SOLIDS CONTENT THEREOF TO AT LEAST ABOUT 40 PERCENT BY WEIGHT, SUBSEQUENTLY BURNING SAID CONENTRATED LIQUOR UNDER SELFSUSTAINING AND REDUCING CONDITIONS FOR REDUCTION OF THE SODIUM SULPHUR COMPOUNDS PRESENT THEREIN WITH THE GENERATION OF VOLATILE SULPHIDES AND THE FORMATION OF A SMELT CONTAINING SODIUM CARBONATE AND SODIUM SULPHIDE, OXIDIZING THE VOLATILIZED SULPHIDES TO SULPHUR DIOXIDE BY MEANS OF AN OXYGEN CONTAINING GAS, RECOVERING SAID SULPHUR DIOXIDE, FORMING AN AQUEOUS SOLUTION OF THE SMELT, COMBINING THE SMELT SOLUTION WITH SPENT COOKING LIQUOR AND FORMING A FRESH COOKING LIQUOR CONTAINING AN AMMONIUM SULPHITE FROM SAID RECOVERED AMMONIA AND SULPHUR DIOXIDE FOR USE IN A SUCCEEDING CYCLE.