Application Of H₂O₂Catalized By Molybadate On The Bleaching Of Pulp Of Waste Official Paper

H₂O₂bleaching of deink pulp of MOW（mixed official waste paper） catalyzed bymolybdate was studied in this paper. The emphasises are on the single stage bleaching ofacidic H₂O₂catalyzed, two stages bleaching of alkaline extraction following acidic H₂O₂bleaching and the combined bleaching of acidic H₂O₂with FAS（Formamidine Sulfinic Acid）as TCF bleaching.The results indicats that adding molybdate to the bleaching stage of acidic H₂O₂can workas catalyzer, only with a little bit amounts present, the bleaching efficiency of acidic H₂O₂canget improvement effectively by increasing ISO brightness of bleached pulp. For the deinkingpulp of MOW, after the Q+PM+Q+EPbleaching, the kappa number of bleached pulp decreasesby34.1%but for the deink pulp of ONP（old newsprint paper）, after the same bleachingsequences, the kappa number of bleached pulp decreases by28.3%, from which it can beobserved that delignification of MOW has more obviously effective than it is of ONP withQ+PM+Q+EPbleaching sequences.The initial properties of unbleached deinking pulp of MOW are as follows: brightness70%ISO, viscosity850ml/g, PC number4.41. After the process of combined acidic H₂O₂catalized by molybdate with alkaline extraction, the properties of bleached pulp are changingas follows: brightness76.5%ISO, viscosity701ml/g，yield89.57%, PC number1.03. And theoptimal conditions of this bleaching experiment are as follows: temperature80℃, time90min,NaOH7%, MgSO41%, H₂O₂2%, pH5, molybdate700mg/kg, silicate200mg/kg.In order to screen the optimal conditions and study delignification behaviour in the stageof acidic H₂O₂catalyzed by Molybdate, the orthogonal experiment has been used to study twostages process of acidic H₂O₂catalized by molybdate followed with alkaline extraction. Thefinal pulp properties are as follows: brightness76.5%ISO, viscosity of710ml/g, Kappa5.08,and the optimal conditions are: temperature80℃, thedosage of sodium molybdate700mg/kg,time1.5h, the dosage of H₂O₂2%, pH value5, the dosage of Na2Si03500mg/kg.In addition, the effect of single stage bleaching of sodium hydrosulfite and FAS has also been compared in this research. Among which FAS has better effect of bleaching than theothers two single-stage bleaching. The optimum conditions of single-stage bleaching of FASare as follows: dosage of FAS1.0%, ration of m（NaOH） to m（FAS）=1:2, pulp consistency10%, EDTA dosage0.2%, the temperature60℃, bleaching time60min.After treatment of thisoptimum condition, the properties of bleached pulp are as follows: brightness76.8%ISO,viscosity803ml/g, yield95.00%, PC value1.27.Based on the results of single stage bleachings, we organize the optimal conditionstogether to study the effect of multi stages bleachings on deink pulp of MOW. Among thedifferent multistage bleaching sequences, the bleaching sequence of PMSi+EP+F has the bestproperties of bleached pulp as follows: brightness81.7%ISO, viscosity of672ml/g, yield85.02%, PC value of1.12, tensile index22.4N m/g, tear index7.11m N m²/g, which qualitycan meet the demand of ordinary printing and cultural paper. The residual COD of wasteliquor of bleaching is1696mg/L.