Aggregation Process And Mechanism Of DCS Interferent In Papermaking White Water Circuit

Within the pulp and paper industry, the recycling of white water to reduce fresh water consumption and effluent discharge leads to accumulation of dissolved and colloidal substances?DCS? in white water, which easily gather together when operating conditions change, or form non-ionic DCS interferent?pitch deposits and depositions? with electrolytes, especially Ca²⁺, thus adversely affecting papermaking. An understanding of aggregation process and mechanism of DCS interferent is important in applications of DCS and electrolytes control.Py-GC-MS was employed to identify the composition and origin of DCS separated from white water in a fine paper mill, the basic properties and stability of DCS upon electrolytes addition were analyzed. The aqueous dispersions of individual colloidal substances?CS? simulacra, dissolved substances?DS? simulacra, and the mixture of CS or DCS simulacra were prepared. The aggregation process and mechanism of interferent were analyzed as a function of various kinetic parameters. The fixation efficiency of DCS simulacra and the wet-end properties were evaluated under varying conditions in pulp with addition of polyethyleneimine?PEI?.The results showed that DCS in white water primarily originated from chemical additives and wood extractives, and among which sizing agents and wood resin predominated. The DCS were negatively charged with an average particle size of 1.656 ?m after dialysis, and presented higher stability at higher pH value and lower temperature. Destabilization of DCS caused by Ca²⁺ and Na⁺ was susceptible to electrolytes valency and concentration. The conductivity of white water should be controlled under 1887?S/cm to minimize the destabilization of DCS.The simulacra achieved higher stability at higher pH value. The sticky and hydrophobic pitch deposits with small size and high agglomerating tendency can be produced with addition of Ca²⁺ at low CS simulacra concentration. When CS simulacra accumulated to a certain concentration, the micelles were formed and pitch deposits with larger size were produced then by particle-particle collision and “layer by layer” adsorption. More severe destabilization occurred in the mixture of CS simulacra than in individual ones. Depositions can be produced by DS simulacra with addition of Ca²⁺, while they can stabilize the pitch by steric stabilization.To reduce the amount of interferent, the pH value of white water and the DCS concentration should be reduced, and the electrolytes concentration should be controlled, with Na⁺ under 40 mmol/L, Ca²⁺ under 5 mmol/L and Al³⁺ under 0.1 mmol/L, respectively.The fixation and retention efficiency of DCS simulacra were improved, the drainage rate and the Zeta potential of pulp increased, and the cationic demand of pulp filtrate decreased as increasing PEI dosage. The key point of DCS interferent prevention and control is reducing the concentration of multivalent metal ions, such as Ca²⁺.