MAGNESIUM AS A STABILIZER FOR PEROXIDE BLEACHING OF MECHANICAL PULP

The effects of magnesium on brightness response and peroxide consumpti on during peroxide bleaching of a radiata pine thermomechanical pulp a re shown to be dependent on the level of magnesium used and the form i n which it is added. It is proposed that the active stabilizing agent is a soluble complex formed between magnesium and organic by-products of the bleaching reaction. Significant reductions in proxide consumpti on, together with increased brightness gains observed with optimum lev els of magnesium addition are comparable to those obtained using sodiu m silicate as the stabilizing agent, under conditions of constant pH. The quantity of magnesium needed would probably preclude its use in in dustrial bleaching.