Recovery of chemicals from smelt solutions

Claim 1

IN THE PREPARATION OF WOOD PULP, THE SOLUTION-PHASE PROCESS FOR RECOVERING CHEMICALS AND PREPARING PULP DIGESTION LIQUORS WHICH COMPRISES COMBUSTING SODA-BASE WASTE LIQUOR CONTAINING SULFUR COMPOUNDS FROM THE DIGESTION OF WOOD, FORMING A SMELT CONTAINING A SUBSTANTIAL QUANTITY OF SODIUM SULFIDE BY FURNACING THE WASTE LIQUOR UNDER REDUCING CONDITIONS AND FORMING AN AQUEOUS SOLUTION OF THE RESULTING SMELT, SUBJECTING ONE BODY OF THE SMELT SOLUTION TO CARBONATION WITH A GAS CONSISTING AT LEAST IN PART OF CARBON DIOXIDE UNDER A PRESSURE OF FROM 16 TO 165 POUNDS PER SQUARE INCH ABSOLUTE AND AT A TEMPERATURE OF FROM 50* TO 150*C., DIRECTING THE HOT CARBONATED SOLUTION WHILE UNDER PRESSURE INTO A CHAMBER MAINTAINED UNDER A VACUUM OF FROM 5 TO 29 INCHES OF MERCURY WHERE HYDROGEN SULFIDE AND STEAM FLASH OFF RELEASING A SUBSTANTIAL PROPORTION OF THE HYDROGEN SULFIDE AND THEN CONTACTING THE SOLUTION WITH STEAM TO STRIP OFF ADDITIONAL HYDROGEN SULFIDE WHILE UNDER THE VACUUM, WHEREBY HYDROGEN SULFIDE IS RECOVERED IN CONCENTRATED FORM AND A SMELT SOLUTION IS PRODUCED HAVING AN ENHANCED CONTENT OF SALTS OF CARBONIC ACID AND A DECREASED SULFIDE CONTENT, CAUSTICIZING WITH LIME THE SOLUTION HAVING AN ENHANCED CONTENT OF SALTS OF CARBONIC ACID AND A DECREASED SULFIDE CONTENT TO FORM AN ALKALINE LIQUOR CONTAINING SODIUM SULFIDE AND SODIUM HYDROXIDE, SUBJECTING ANOTHER PART OF THE SMELT SOLUTION TO MULTIPLE STAGES OF SOLUTION CARBONATION EACH FOLLOWED BY FLASH-STRIPPING AS AFOREMENTIONED FOR THE SUBSTANTIALLY COMPLETE REMOVAL OF HYDROGEN SULFIDE THEREBY SUBSTANTIALLY COMPLETELY REMOVING THE SODIUM SULFIDE THEREFROM AND ENHANCING THE CONTENT OF SODIUM SALTS OF CARBONIC ACID, REACTING SULFUR DIOXIDE WITH SAID LATTER SOLUTION TO FORM SODIUM SULFITE AND SODIUM BISULFITE, AND COMBINING THE CAUSTICIZED SOLUTION WITH THE SOLUTION CONTAINING SODIUM SULFITE AND SODIUM BISULFITE.