Process for recovery of pulp mill chemicals

Claim 1

In a method for regenerating and recovering pulp mill chemicals which comprises feeding black liquor to a recovery and regeneration operation including a recovery boiler, smelt dissolver for forming green liquor, and causticizer for converting the green liquor into white liquor containing sodium hydroxide and sodium sulfide useful for cooking wood chips, preparing an oxidized liquor by contacting an aqueous alkaline pulp mill liquor selected from the group consisting of green liquor, white liquor and weak white liquor with a gas containing molecular oxygen and absorbing waste gases containing sulfur compounds, carbon dioxide and dust in said oxidized liquor, the improvement comprising (a) contacting said aqueous alkaline pulp mill liquor with said gas containing molecular oxygen while maintaining said aqueous alkaline pulp liquor at a pH of 8.3 to 9.0, a temperature of 20° to 95° C. and a sodium ion concentration, derived from sodium carbonate and sodium bicarbonate in said aqueous alkaline pulp mill liquor, of from 0.1 to 1.0 moles/l, in the presence of from 10 to 100 mg/l of a catalyst consisting of at least one water-soluble iron salt, (b) absorbing the sulfur compounds including hydrogen sulfide and sulfur dioxide, and dust in said waste gases with said oxidized liquor containing said water soluble catalyst without substantial absorption of carbon dioxide in said oxidized liquor while the pH of said oxidized liquor is maintained between 8.3 and 9.0, (c) recirculating a portion of the oxidized liquor from step (a) to the black liquor, while (d) recirculating the liquor from the gas absorption step (b) to the oxidation step (a).