Recovery of manganese oxides from spent alkaline and zinc-carbon batteries. An application as catalysts for VOCs elimination

摘要

Manganese, in the form of oxide, was recovered from spent alkaline and zinc-carbon batteries employing a biohydrometallurgy process, using a pilot plant consisting in: an air-lift bioreactor (containing an acid-reducing medium produced by an Acidithiobacillus thiooxidans bacteria immobilized on elemental sulfur); a leaching reactor (were battery powder is mixed with the acid-reducing medium) and a recovery reactor. Two different manganese oxides were recovered from the leachate liquor: one of them by electrolysis (EMO) and the other by a chemical precipitation with KMnO_4 solution (CMO). The non-leached solid residue was also studied (RMO). The solids were compared with a MnO_x synthesized in our laboratory. The characterization by XRD, FTIR and XPS reveal the presence of Mn_2O_3 in the EMO and the CMO samples, together with some Mn~(4+) cations. In the solid not extracted by acidic leaching (RMO) the main phase detected was Mn_3O_4. The catalytic performance of the oxides was studied in the complete oxidation of ethanol and heptane. Complete conversion of ethanol occurs at 200 ℃, while heptane requires more than 400 ℃. The CMO has the highest oxide selectivity to CO_2. The results show that manganese oxides obtained using spent alkaline and zinc-carbon batteries as raw materials, have an interesting performance as catalysts for elimination of VOCs.