Abstract: Oxidation and fixing of sulfur and sulfur compounds in weak black liquor is accomplished by methods which insure minimal odorous sulfur emissions and which facilitate the collection of sulfate soaps. By critical adjustment of certain parameters substantially complete oxidation of sulfur and sulfur compounds is achieved, with maximum utilization of oxygen, while enhancing the collection of sulfate soaps and minimizing the production of foam. Various methods are disclosed for the oxygenation of weak black liquor, including the utilization of reaction columns, conical reactors, and venturis.