## 1 Introduction  
Mine tailings are the slurries that remain after the treatment of minerals by separation processes (crushing, grinding, or flotation) and other physicochemical techniques in order to extract the valuable minerals from the less valuable rocks. Worldwide, mine tailings are produced at a rate of anywhere from five to fourteen billion tons per year [1]. Their storage in tailing dam basins represents an important environmental issue [1]. The generation and dispersal of dust from mine tailings can contaminate air and surrounding soils. In addition, metals and soluble salts present in these wastes could pollute groundwater and surface water. Finally, some mine tailings include sulfide minerals that can induce the formation of acid mine drainage (AMD) and acid rock drainage (ARD) [2]. The mining area of Cartagena-La Union is one of most degraded areas of Spain, exploited for centuries until its closure in the early 1990s. The main minerals obtained are galena (PbS with small amounts of Ag), sphalerite (ZnS), cerussite (PbCO\({}_{3}\)), cassiterite (SnO2), and iron oxides (Fe\({}_{2}\)O\({}_{3}\)) [3]. During some years, these mines represented 40% of Pb, 60% of Ag, and 12% Zn of the Spanish production [4]. These former mining activities have produced important amounts of mine wastes deposited in dumps, ponds, and tailings, without sealing or reforetesting, which have been and continue to be eroded and dragged through watercourses that make up its orography [5; 6; 7]. Four watercourses have their basins in the mountain range of Cartagena-La Union that flow into the Mar Menor: Rambla de las Matildes, Rambla del Beal, Rambla de Ponce, and Rambla de la Carrasquilla. Among these four watercourses, Rambla del Beal is considered to be one of the most polluted in this region [8]. Watercourses constitute a method of transport for waste materials from mining sites through the peaks and valleys to the Mar Menor and the Mediterranean Sea. These mining wastes also contaminate the surrounded soils with heavy metals [3]. Taking into account the low but torrential rainfall in this region [9], the great amount of sediment deposition with high concentration of metals and sulfates, and the erosion and overland flow, important human health and environmental risks can emerge. According to previous works [10; 11; 12], the lagoon is still being affected by trace elements such as Ni, Cu, Zn, As, Cd, Pb, Fe, and Mn [6]. They are contained in the sediments from the watercourses of the mining mountain range and from rock pools located in the surroundings. The influence of this abandoned mining site on the associated ecosystems, land degradation, and its human and environmental risks has been widely studied [3; 5; 9; 10; 13]. They highlight the need to work on solutions to counteract the environmental problems associated with mining waste dispersion through the watercourses of this area. The recovery of metals from mine tailings and surrounding soils can contribute to minimize environmental risk and to achieve a circular economy model [14]. Different approaches to economic tailings valorization can be taken, such as reprocessing to extract residual metals and minerals and the use of final waste matrix as backfill or construction materials. In addition, in some cases, the presence of valuable metals could make mining wastes an appreciable resource with economic benefit [15; 16]. However, pyrometallurgical treatment of mine tailings is limited by low metal grade and their minerallurgical concentration by classical technologies is limited by the surface modifications of minerals [17; 18]. It is well established that hydrometallurgy is one of the most efficient leaching technologies to recover valuable metals from low-grade ores and wastes, sulfuric acid being the most employed leaching system due to price, availability, and dissolution capacity [19; 20; 21]. Some mine tailings related to the exploitation of metallic deposits like Cu or Zn are rich in sulfide minerals, which show low dissolution rates [22; 23].