Recovery of Fe, Cr and Ni in pickling sludge with aluminum nitride in secondary aluminum dross

Abstract

Secondary aluminum dross (SAD) is a hazardous solid waste due to containing aluminum nitride (AlN). In this work, AlN was used to reduce heavy metals in pickling sludge by pyrometallurgy. Reduction extent of Fe, Cr and Ni was up to 97, 91 and 100%. However, it was found that some AlN was oxidized by oxygen. AlN oxidization could be decreased by shortening melting process. The AlN oxidization would be restricted after aluminosilicate was melted. Reduction extent of heavy metals increased from 51% to 86%, when treatment temperature was increased from 1350 to 1400 °C. Meanwhile, AlN oxidization could be exacerbated by increasing CaF2 and soda. The CaF2 and soda could corrode the alumina protective layer on AlN and promote AlN oxidization. Reduction extent of heavy metals decreased from 48% to 19% after adding soda. The AlN oxidization could be restrained by cutting down the air during melting process. After covering the crucible, reduction extent of heavy metals was increased from 48% to 92%, and reduction extent of Fe, Cr and Ni was increased from 58, 18 and 83% to 97, 91 and 100%. After evaluating environment benefit of AlN reducing heavy metals, it was found that utilizing a ton SAD replacing carbon to reduce heavy metals in pickling sludge could reduce carbon emissions of 279 kg. In addition, SAD could be used as reductant to replace Al for chromium metallurgy. Using a ton SAD to replace Al for chromium metallurgy could reduce carbon emission of 3961 kg.