Citation: Maltrana, V.; Morales, J. The Use of Acid Leaching to Recover Metals from Tailings: A Review. Metals 2023, 13, 1862. https:// doi.org/10.3390/met13111862 Academic Editors: Petros E. Tsakiridis and Long Meng Received: 10 October 2023 Revised: 26 October 2023 Accepted: 3 November 2023 Published: 8 November 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). metals Review The Use of Acid Leaching to Recover Metals from Tailings: A Review Valeria Maltrana and Jaime Morales * Escuela de Ingeniería Química, Pontificia Universidad Católica de Valparaíso, Avenida Brasil 2162, Valparaíso 2362854, Chile; valeria.maltrana@pucv.cl * Correspondence: jaime.morales@pucv.cl Abstract: Mine tailings deposits are often overlooked by the industry, posing significant environ- mental challenges due to chemical hazards and inadequate maintenance. Nevertheless, such mineral deposits hold considerable economic potential for processing, and the adoption of innovative tech- nologies may also address critical chemical and physical stability issues. Existing research has demonstrated the feasibility of recovering target metals—i.e., copper, iron, manganese, cobalt, zinc, and others—through the application of acid leaching techniques with consistently high yields and metal recovery rates. Therefore, a compilation was carried out from 2008 onwards, on working conditions such as leaching agent, acid concentration, oxidizing-reducing reagent, particle size, O 2 pressure, stirring speed, solid–liquid ratio, temperature, and leaching time. At present, there are no reviews on the recovery of metals via acid leaching in tailings, so this study can serve as support for future researchers who want to project themselves in this area, ordering the procedures and the results obtained by the research carried out. Regarding the evaluation, it can be commented that research has shown that acid leaching of tailings has achieved recoveries of over 90% in different metals, such as Zn, Cu, and Fe, which indicates that the treatment is efficient and recommended for different types of tailings. Keywords: mine tailings; tailings reprocessing; acid leaching; hydrometallurgy; metal recovery 1. Introduction In copper mining, various physicochemical processes [1,2] are employed to treat ores and extract valuable commercial materials. The choice of ore processing depends on mineral composition, whether oxide or sulfide-based; though for both, material liberation processes must involve different particle sizes. Generally, oxide-rich materials are subjected to hydrometallurgical treatment, while sulfide-rich materials are concentrated [3] before undergoing pyrometallurgical treatment. Both processing routes yield the desired products but generate mining waste [4], much of which poses environmental and human health hazards [3,5–12]. One particularly significant and recently studied waste stream is mine tailings, a byproduct of sulfide ore concentration procedure [13]. These tailings are transported to tailings deposits [14] with a focus on achieving chemical and physical stability [2,6]. To meet these objectives, it is imperative to remove toxic agents and potential sulfuric acid producers, including pyrite, which is the precursor of acid mine drainage (AMD) formation due to oxygen and water exposure, where it is a serious environmental problem for industries due to its low pH, less than pH 3, coupled with a high concentration of heavy metals such as cadmium (Cd), Cu, iron (Fe), manganese (Mn), lead (Pb), and zinc (Zn), and toxic metalloids such as arsenic (As) and selenium (Se) [15], and to ensure a robust structural integrity to prevent spillage and leakage within the deposit. Further, emphasizing the chemical stability of mine tailings is paramount since insufficient stability within a tailings deposit significantly heightens the risk of environmental contamination [6]. The Metals 2023, 13, 1862. https://doi.org/10.3390/met13111862 https://www.mdpi.com/journal/metals