Preparation and Characterization of Manganese and Zinc Oxides Recovered from Spent Alkaline and Zn/C Batteries Using Biogenerated Sulfuric Acid as Leaching Agent

Abstract

Manganese, zinc and mixed manganese-zinc oxides were synthesized after a biohydrometallurgical process to recycle alkaline and Zn/C batteries. A mixture of alkaline and Zn/C batteries was leached with biogenerated sulfuric acid. The effect of pulp density, time and use of additives, namely, H2O2 and Na2SO3, was studied. Using an S/L = 0.04 g ml−1, 2 h, 5 vol.% H2O2 or 1 wt.% Na2SO3 at 30°C and in one step, 99% Zn and 90–98% Mn were extracted. After leaching, manganese (MnOx) and zinc oxides (ZnO) were obtained by sequential precipitation first with KMnO4 and then with Na2CO3, recovering 90% Mn and 95% Zn. Additionally, a mixed manganese-zinc oxide was obtained by precipitation with NaOH until pH = 8 (ZM) recovering 28% Mn and 95% Zn. The Mn/Zn ratio was higher for the MnOx catalysts. Characterization by x-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed the presence of α-MnO2 in MnOx with globular shape, wurtzite in ZnO oxide with spherical shape and a mixture of ZnO wurtzite and ZnMn2O4 in the ZM sample with platelet-type shapes.