Reduction kinetics of zinc powder from brass converter slag by pyrometallurgical method using hydrogen gas

Abstract

A pyrometallurgical reduction process for the recovery of copper and zinc from brass secondary slag (BSS) was studied. Specifically, the effect of reduction temperature and time on the conversion to metallic phases was investigated. The brass secondary slag was characterized by X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, automatic elemental analysis, thermogravimetric analysis, and field emission scanning electron microscopy. A two-step reduction of BSS was identified. The step 1 comprised the reduction of ZnO, while the step 2 featured the reduction of Zn0-Al203. Furthermore, the application of a first-order reaction model with Arrhenius analysis, indicated a conversion of ZnO to Zn(g) that had a rate constant increasing from 1.4 ±0.13 x 10-3s-1 at 900 °C to 2.18 ±0.15 x 10-2>s-1 at 1050 °C. This reaction had an activation energy of 233.2 ± 26.1 kJ/mol. Secondly, the conversion of Zn0-Al203 to Zn(g) and A1203 increased from 1.54 ± 0.21 x 10-5s-1 at 900 °C to 1.09 ±0.19 x 10-3s-1 at 1050 °C, and the activation energy was 376.7 ±22.4 kJ/mol. This reaction mechanism and its associated kinetic data can be applied to optimize the operation conditions of recycling processes for Cu-containing wastes.