Decolorizing method for waste kraft paper mill effluents

Abstract

Considerable reduction in color of a kraft paper mill effluent has been found with the addition of barium ions (Ba.sup..sup.+2) to the effluent. Unlike the familiar lime decolorization process for kraft paper mill effluents, decolorization using barium is substantially independent of the pH of the effluent and the color removing mechanism is in the form of an occlusion of the color bodies from the effluent into the barium sulphate precipitate (BaSO.sub.4) which forms from the sulphate (SO.sub.4) already present in or added to the effluent. The amount of decolorization produced by the process of the present invention depends upon the amount of sulfate ions in the effluent, the amount of barium ion containing material added to the effluent and the relationship of the amount of barium to the amount of sulphate in the effluent. A slight excess of sulphate over the stoichiometric equivalent of barium is desired, and the total amount of barium ion containing material and sulphate that must be added to the effluent depends on the initial color of the effluent and the degree of decolorization desired.

Dependencies are inferred from the claim text.