In this paper

the effect of modes introducing Mg(OH)2 on hydrogen peroxide(H2O2)bleaching processes was investigated for the eucalyptus kraft pulps.There are three ways to introduce Mg(OH)2 into the bleaching system

i.e.

the direct-addition

or fresh-formed Mg(OH)2 by adding magnesium sulfate into a pulp slurry pre-mixed with sodium hydroxide

or vice verse.The results showed that the particle size distributions of Mg(OH)2 were quite different for the three cases.The average particle sizes are much smaller for fresh-formed Mg(OH)2 than for direct-addition.As a consequence

the processes with fresh-formed Mg(OH)2 were proved more effective for the pulp bleaching

and there were more hydrogen peroxide found in the bleaching effluents and the favorable pulp qualities.The time-dependent pH profiles of the process effluents also indicated that the decomposition of H2O2 for direct-addition or for no addition of Mg(OH)2 was very significant

especially during the early stage of the bleaching processes.