The pulping industry generates great quantities of wastewaters (WW), where a small amount of black liquor accounts for more than 90% of its entire manufacturing process load in organics. Treatment of the black liquor from pulping manufacture in ThaiNguyen province (Vietnam) by catalytic wet oxidation (CWO) under mild reaction conditions (150-180 degrees C, 15 bar) using solid wastes containing iron oxide as heterogeneous catalysts is communicated herein. These solid wastes have been found to be active in the oxidation of pollutants in the black liquor and show a high application potential in CWO processes for the treatment of this kind of industrial wastewater.