Homogeneous reduction for heavy metals from pickling sludge with aluminum nitride from secondary aluminum dross in aluminosilicate melt ‘solution’ environment

Secondary aluminum dross (SAD) and pickling sludge were hazardous wastes . In this work, aluminum nitride (AlN) from SAD was used to reduce heavy metals from pickling sludge by pyrometallurgy . Reaction mechanism was studied after exploring transformation of heavy metals and AlN during reaction process. It was found that reduction reaction between heavy metals and AlN was homogeneous reduction reaction. When mixture was heated to 1000 °C, heavy metals and AlN were distributed independently, and reduction reaction had not occurred. When mixture was heated to 1300 °C, heavy metals and AlN entered aluminosilicate network, and homogeneous reduction reaction occurred. Half of the heavy metals were reduced into metallic state and mixed with the dross. When the mixture was heated at 1400 °C for 1 h, metal block separated from dross. Reduction rates of Fe, Cr and Ni were 94%, 88% and 100%. Like water solution, aluminosilicate melt could dissolve heavy metal oxides , aluminum compound (AlN, Al 4 C 3 , etc.) and silicon compound (Si 3 N 4 , SiC, etc.). This work proposed a novel homogeneous reaction environment, aluminosilicate melt ‘solution’ environment, which had a significant effect not only on heavy metals reduction, but also on other high temperature oxidation-reduction. • AlN in SAD was used to reduce heavy metals by pyrometallurgy. • Reduction rates of Fe, Cr and Ni were 94%, 88% and 100%. • Reaction mechanism was studied by exploring AlN and heavy metals transformation. • Reaction between AlN and heavy metals was homogeneous reduction reaction. • Aluminosilicate melt ‘solution’ was proposed for homogeneous reaction.