Evaluation of two-step processes for the selective recovery of Mn from a rich Mn residue

Abstract

Abstract In this work, effective two-step processes for recovering manganese (Mn), as well as zinc (Zn), from a rich Mn residue, that mainly consists of Mn and carbon with lesser amounts of Zn and Fe, are proposed. First, three different methods (conventional, ultrasound- and microwave-assisted) were evaluated for reductive acid leaching of the residue. Subsequently, two different strategies for purification of Mn from the leachate were considered: oxidative precipitation of Mn with persulfate and solvent extraction with Cyanex 302 as the extractant. The results showed that microwave-assisted leaching was the most effective in terms of the percentage of metal leached (with 98 and 100% of Mn and Zn, respectively) as well as the effectiveness of time and reagent consumption. Both Mn purification strategies were effective; with the oxidative precipitation, a 99.7% pure MnO2 precipitate and 3.30\u202fg/L Zn solution with a purity of 99.9% were obtained at a global yield of 97.4 and 94.8%, respectively. Solvent extraction resulted in a 32.6\u202fg/L Mn solution with a purity of 99.9% and 35.2\u202fg/L Zn solution with a purity of 98.4%, with global yields of 96.3 and 100%, respectively. Based on these results, a sequential two-step procedure for recovering all valuable products (Mn, Zn and graphite) with high efficiency from a Mn rich residue is proposed.