Method for producing oxidized white liquor

Claim 1

In the cyclic process for utilizing sodium values in sulfate cellulose pulping, in which sodium losses normally are less than sodium additions to the process, thus tending to build up a sodium surplus, and which includes the steps of pulping cellulosic material with a pulping liquor comprising sodium hydroxide and sodium sulfide, separating spent pulping black liquor containing sodium values, evaporating and combusting the black liquor to recover sodium values as sodium sulfide and sodium carbonate, dissolving the sodium sulfide and sodium carbonate in water to form green liquor, causticizing the green liquor with calcium hydroxide to form white liquor, and recycling white liquor to form pulping liquor, the improvement which comprises maintaining sodium balance at least in part by removing sodium values as white liquor, oxidizing the white liquor with a free oxygen-containing gas at a temperature within the range from about 50° to about 130° C by injecting a free oxygen-containing gas at a flow to maintain the white liquor in motion within the range from about 50 to about 500 Nm 3 /hm 2 while maintaining the aqueous solution at a depth of least 2 meters above the point at which the gas is injected into the solution for a time to convert substantially all sodium sulfides to sodium thiosulfates, and utilizing the oxidized sodium thiosulfate-containing white liquor as a source of alkali outside the cyclic process for sulfate cellulose pulping.