Generation of active polysulphide with manganese and bismuth catalysts

Polysulphide produced by oxidizing white liquor includes both active and inactive components. "Active" polysulphide is the only component that increases pulp yield. The amount of active polysulphide formed when manganese oxides are used as catalysts in the generating process is increased by adding a co-catalyst. Adding bismuth compounds and, in particular, bismuth oxide as a co-catalyst increases the total amount of polysulphide formed with all the manganese oxides and increases the amount of active polysulphide produced particularly when using the lower manganese oxides. The co-catalyst also increases the number of cycles in which the most active catalyst, manganese dioxide, can participate before losing efficiency. Other elements in the same group and adjacent groups in the periodic table are active but these other elements are more soluble than bismuth and are toxic.