**Lan-Huong Tran \*, Kulchaya Tanong, Ahlame Dalila Jabir, Guy Mercier and Jean-François Blais**

Institut National de la Recherche Scientifique (Centre Eau, Terre et Environnement), Université du Québec, 490 rue de la Couronne, Québec, QC G1K 9A9, Canada; kulchaya.tanong@ete.inrs.ca (K.T.); ahlame\_dalila.jabir@ete.inrs.ca (A.D.J.); guy.mercier@ete.inrs.ca (G.M.); jean-francois.blais@ete.inrs.ca (J.-F.B.) **\*** Correspondence: lan.huong.tran@ete.inrs.ca; Tel.: +418-654-2550; Fax: +418-654-2600

Received: 17 July 2020; Accepted: 26 August 2020; Published: 1 September 2020

**Abstract:** An innovative, efficient, and economically viable process for the recycling of spent alkaline batteries is presented herein. The developed process allows for the selective recovery of Zn and Mn metals present in alkaline batteries. The hydrometallurgical process consists of a physical pre-treatment step for separating out the metal powder containing Zn and Mn, followed by a chemical treatment step for the recovery of these metals. Sulfuric acid was used for the first leaching process to dissolve Zn(II) and Mn(II) into the leachate. After purification, Mn was recovered in the form of MnO2, and Zn in its metal form. Furthermore, during the second sulfuric acid leaching, Na2S2O5 was added for the conversion of Mn(IV) to Mn(II) (soluble in the leachate), allowing Mn to be recovered as MnCO3. Masses of 162 kg of Zn metal and 215 kg of Mn (both in the form of MnO2 and MnCO3) were recovered from one ton of spent alkaline batteries. The direct operating costs (chemicals, labor operation, utilities, energy) and indirect costs (amortization, interest payment) required for a plant treating 8 tons of spent batteries per day was calculated to be \$CAD 726 and \$CAD 534 per ton, respectively, while the total revenue from the sale of the metals was calculated at \$CAD 1359.6 per ton of spent batteries. The development of this type of cost-effective industrial process is necessary for a circular economy, as it contributes to addressing environment- and energy-related issues, and creates opportunities for the economic utilization of metals.

**Keywords:** spent alkaline battery; recycling; leaching; electrowinning; hydrometallurgy; techno-economic evaluation; metal recovery
