Waste liquid recirculation-driven hydrolysis mechanism of secondary aluminum dross (SAD) in the hydrometallurgical processes

Abstract

The presence of toxic components (AlN and salts) was the major reason why secondary aluminum dross (SAD) was hard to utilize effectively. Hydrometallurgy can effectively realize the removal of AlN and salts, but it will produce large amounts of acid or alkali wastewater. In this study, a new idea of waste liquid recirculation-driven hydrolysis of SAD in the hydrometallurgical processes without acids or alkalis added was proposed to enhance deep denitrification. The results showed that AlN was readily hydrolyzed to Al(OH)₃ and released NH₃. The encapsulation of Al(OH)₃ inhibited the deep removal of AlN. Fortunately, ammonia dissociated to OH^-, making the disruption of the core-shell structure possible. Through leaching solution recirculation, ammonia was significantly enriched in the solution, which increased the pH and intensified the dissolution of Al(OH)₃, thereby enhancing the denitrification of SAD. In addition, salts were also accumulated, which facilitated the subsequent recovery and promoted the dissociation of ammonia, thus further increasing the pH. The denitrification was increased from 70.56 % to 87.62 % with a residual nitrogen content of 0.71 % after 10 times of leaching solution recirculation. The leaching residue was a valuable aluminiferous raw material with an Al content of 40.23 %.