Optimizaiton of Neutral Deinking Process and Comparison with Alkaline Deinking of Old Newsprint

Pulping parameters in neutral deinking of old newsprint (ONP) and its impacts on deinking efficiency were investigated as well as comparison with alkaline deinking in this paper. The results showed that the low pulping consistency and short pulping time mostly contributed to the removal of ink in neutral pulping stage. The optimum pulping conditions of ONP were as follows: deinking agent, 0.6%similar to 1.0%; pulping consistency, 6%similar to 8%; pulping time, 15min; pulping temperature, 40 degrees C. The low temperature in pulping stage of ONP neutral deinking process could greatly improve the deinking efficiency and reduce heat energy consumption. The comparison of neutral deinking and alkaline deinking of ONP showed that low pulping consistency contributed to the ink removal for neutral deinking, however, high pulping consistency benefit the alkaline deinking. Neutral deinked pulp had better H2O2 bleachability than alkaline deinked pulp, and could save 60% H2O2 usage, when the brightness was similar to that of alkaline pulp.