Process related to pulp bleaching effluent purification using ion

Abstract

A process for purifying the effluent from a pulp bleaching process which includes a chlorine treatment, an alkali extraction, and a final bleaching is disclosed, wherein a number of washing steps are connected in counter-current series from a final wash step in the final bleach section to the wash step of the first alkali extraction stage, the strongly polluted effluent from the wash step of the first alkali extraction stage is passed through a first column containing a bed of particulate porous resin which traps and retains organic pollutants in the effluent, and a combined effluent which includes an acidic polluted liquor from the chlorine bleaching stage and a partly purified filtrate from the first column is fed through a second column which contains a bed of particulate porous resin which traps organic pollutants fed therethrough, with the resin bed in the second column being activated by the acidic nature of the combined effluent, with chloride ions in the combined effluent essentially passing through the resin bed without being trapped by the resin, so that the chloride ions are discharged with the purified filtrate from the second column. The purified filtrate is the final wash liquor effluent of the system of counter-current washing steps. By this process the organic pollutants are efficiently separated from the wash liquors, with the chemical purification cost kept at a low level. The separated pollutants are obtained in a relatively concentrated form which facilitates evaporation and burning. The main portion of the chloride ions arising from the chlorination stage are removed with the final wash liquor effluent, which is an important advantage for further processing.