Patent ID: 7371307

Claim:
A method of producing an oxidized white liquor containing polysulphide comprising: i) oxidizing a white liquor with oxygen containing gas in the presence of lime mud, manganese dioxide or both to produce on oxidized white liquor containing polysulphide and having a first active polysulphide concentration measured at 285 or 286 nm (PS UV ) or a first active polysulphide concentration measured at 416 nm (PS VIS ) or a first PS UV /PS GR or PS VIS /PS GR ratio, and ii) storing said oxidized white liquor at a temperature of 50° C. to 90° C. for a time of 6 to 72 hours while monitoring the concentration of active polysulphide spectrometrically and the concentration of total polysulphide gravimetrically to produce an oxidized white liquor having a second active polysulphide concentration measured at 285 or 286 nm (PS UV ) or a second active polysulphide concentration measured at 416 nm (PS VIS ), wherein said second concentration is greater than said first concentration; or a second PS UV /PS GR or PS VIS /PS GR ratio, wherein said second ratio is greater than said first ratio.