Pulping parameters in neutral deinking of old newsprint (ONP) and its impacts on deinking efficiency were investigated with RPE as deinking agent in this paper. The results showed that the mechanical actions had intensive impacts on deinking efficiency. The low pulping consistency and short pulping time mostly contributed to the removal of ink as well as middle or high rotating speed of pulper in neutral pulping stage. The optimum pulping conditions of ONP were as follows: deinking agent, 0.6%-1.0% (all the agents were added into pulping stage); pulping consistency, 6%similar to 8%; pulping time, 15min; pulping temperature, 40 C; pulping speed, 2100r/min. The low temperature in pulping stage of ONP neutral deinking process could greatly improve the deinking efficiency and reduce heat energy consumption.
