Investigation on Bleaching of Mixed Old Newspaper and Magazine Deinked Pulp with Hydrogen Peroxide

In the present research, the effect of different peroxide charges and reaction times were investigated in hydrogen peroxide bleaching of mixed old newsprint and old magazine deinked pulp. In the beginning, mixed recycled papers were pulped using conventional method and then deinked by flotation. In addition, deinked pulps (mixture ratio of 70% ONP and 30% OMG) were bleached with hydrogen peroxide at different charges of 0.5, 0.75 and 1% from peroxide and times of 30, 60 and 90 min under constant process conditions. The bleached pulps refined with laboratory PFI mill to freeness of 300 ml, CSF and then standard handsheets (60gm-2) were made from them. The residual peroxide existing in bleaching liquor, chemical oxygen demand (COD) of bleaching effluent and also the paper quality properties (optical, physical and strength properties) were measured according to respected standards. Obtained results indicated that with increase in bleaching times, the residual peroxide in liquor was decreased but the differences of them was insignificant (P<0.01) with increase in peroxide charge. Also effluent COD was enhanced significantly with increase in the both peroxide charges and bleaching times. When the peroxide charge and also the bleaching time were added, the paper brightness had increased significantly but opacity was not significantly changed (P<0.01). Increasing the bleaching agent of peroxide has not been shown any significant influence on the paper strength properties. However increasing the bleaching time led to significant improve in these properties.