Removal of Chloride in the Kraft Chemical Recovery Cycle of Pulp Mills Using the Ion-Exchange Process

Abstract

High levels of chloride in the kraft recovery cycle of pulp mills can cause serious problems, particularly in recovery boiler operation. The treatment of ash collected from the electrostatic precipitator (ESP) for chloride removal was investigated experimentally using the ion-exchange process based on an amphoteric resin (BIORAD AG 11 A8). Saturation and regeneration experiments in a fixed bed were carried out for different flow rates. Experimental adsorption results obtained in the saturation step were well predicted with a mathematical model that takes into account dispersed plug flow for the bulk liquid, external mass-transfer resistance, intraparticle mass transfer by pore diffusion, and instantaneous equilibrium of adsorption at the pore/wall interface. The equilibrium was modeled using an extended Langmuir−Freundlich isotherm for three components (Cl-, SO42-, and CO32-) based on single-component equilibrium data. The resin performance was tested during cyclic operation, in which a chloride removal efficiency of higher than 89% was achieved, along with a sulfate recovery of 67−74%.