Hydrogen as Carbon-Free Reducing Agent in Non-ferrous Slag Fuming

Abstract

In this work, pyrometallurgical treatment of non-ferrous iron residue was studied. This approach aimed to recover the valuable metals and convert the residue into reusable benign slag using hydrogen as a non-fossil reducing agent. The pyrometallurgical treatment for this type of residue involves pretreatment prior to two stages, oxidation and reduction. Hydrogen was employed as a reducing agent in slag cleaning. The reduction tests were performed at temperatures of 1200 °C, 1250 °C, and 1300 °C using H2 and N2 gases to form the reducing gas atmosphere. The results show that H2 is an effective reductant because reduction proceeded rapidly, forming speiss droplets within the slag already after 10 minutes. The laboratory-scale experiments suggest that slags or other residues obtained from metallurgical processes can be further cleaned in a fuming process using hydrogen and its mixtures to obtain environmentally friendly cleaner slag with respect of volatile metals. The results also show that one can tune the reduction and control the formation of metallic iron during the process. Thermodynamic modeling was also performed to simulate the fuming stage, i.e., reduction of the slag. Metal alloy formation as well as elemental distributions between metal and slag were studied, and results from thermodynamic modeling agree well with experimental results.