Evolution law of conductivity value in wet-end system of recycled pulp and its regulation strategy

Abstract

The closed cycle of white water in the paper-making process is an important way to reduce material loss, water consumption, and wastewater discharge. However, how to improve the quality of white water and increase the efficiency of white water recycling is still a challenge. Faced with the increasing conductivity value of white water in the process of white water circulation, in this study, the factors affecting the conductivity value of white water for recycled pulp and the strategies for regulating the conductivity value were investigated by simulating the white water circulation during the paper-making process. The experimental results indicate the accumulation of inorganic salts is one of the reasons for the increasing conductivity value of white water. When inorganic salts accumulate to dynamic equilibrium, the increase amplitude of conductivity caused by inorganic salts does not exceed 5% of the initial conductivity. Under the white water circulation, the polyelectrolytes formed by degradated starch are the main factor for the continuous increasing conductivity value of white water. The retention of starch, during the paper-making process, can be improved by adding in-situ generated aluminum hydroxide colloids and the polyelectrolytes from starch degradation in white water can also be adsorbed by aluminum hydroxide precipitates. The effects of soluble organic matter and dissolved inorganic matter on white water conductivity were revealed, and the formation pattern of conductivity value in the wet-end system of recycled pulp was derived. At the same time, methods for removing organic matter and polyelectrolytes were proposed. Both are helpful to improve the quality of white water for paper-making industry and reduce the pollution of the wastewater.