The imbalance between raw materials of high economic importance and their supply has increased the search for new approaches to obtain valuable elements from mining tailings. In this study, the extraction of copper, zinc, and lead from sulfidic tailing in sulfate–chloride media was investigated. A 33 Box–Behnken design was applied to evaluate three variables over a 4-h testing period: sulfuric acid concentration (0.01–1.0 mol/L H2SO4), sodium chloride (10–60 g/L NaCl), and temperature (20–70 °C). The design showed two optimum working regions: a combination of a high NaCl level, low H2SO4 level, and medium temperature level for lead leaching, while for copper and zinc, a combination of a medium–high H2SO4 level and a high temperature level. The concentration of NaCl had only a slight impact on their leaching. Based on these results, two-stage leaching was performed. The first stage was carried out under an experimental condition that favored the leaching of lead (60 g/L NaCl, 0.01 mol/L H2SO4, 45 °C, 1 h, 10:1 liquid-to-solid ratio), whereas the second stage maximized the leaching of copper and zinc (60 g/L NaCl, 0.5 mol/L H2SO4, 70 °C, 24 h, 10:1 liquid-to-solid ratio). The global leaching rate was 66.8 ± 3.0% copper, 84.1 ± 5.2% zinc, and 93.9 ± 3.2% lead. The iron and arsenic content were also leached by about 20 and 50% at the end of the second stage. The study demonstrated that the use of sulfate–chloride media in a two-stage leaching considerably improved the extraction of the desired metals and was, therefore, suitable for their recovery. Graphical Abstract
RESUMO -A produção nacional de potássio fertilizante supre cerca de 10% do consumo interno brasileiro. O desenvolvimento de rotas alternativas para a obtenção de potássio, como a solubilização biológica do elemento a partir de rochas, configura-se como uma opção frente à necessidade de importação e produção de fertilizantes comerciais. Neste estudo utilizou-se a bactéria gram-negativa Burkholderia sp. em ensaios iniciais de solubilização de potássio a partir da rocha verdete. Foi utilizado um planejamento fatorial 2³ tendo como variáveis a granulometria da rocha, concentração de glicose do meio de cultivo e o tempo de ensaio. A extração máxima de potássio (0,26%) ocorreu quando foram estudados os valores máximo (+1) de granulometria (100#) e glicose (5 g/L) e mínimo (-1) de tempo (30 dias). Comparativamente aos controles, a ação microbiana elevou a extração desse elemento cerca de três vezes. Portanto, a estirpe de Burkholderia sp. foi capaz de elevar a extração de potássio a partir do verdete, mostrando potencial para estudos de otimização do processo de biossolubilização.
<p>The recovery of valuable metals such as copper (Cu), zinc (Zn) and lead (Pb) from mine tailings has gained attention in recent years, mainly for the environmental risk of tailings storage facilities and the demand of such elements in different industrial sectors. Many sulphide tailings deposits are spread worldwide, and some of them belong to active mines, which produce tons of material per year. Leaching is a well-known technology for metal extraction. However, two aspects must be considered: the dissolution of metals involves the use of fresh water and, the tailings contain low metal concentrations and high impurities. As a result, leaching is too expensive due to energy input in water purification and high acid consumption. The use of salt water in mineral extraction processes is becoming more attractive in the mining sectors over the years, especially in regions where fresh water is scarce. The presence of salt water in metal leaching has demonstrated a great capacity to increase metal extraction from ore, for example, by increasing the surface and porosity of copper containing minerals. This phenomenon plays an important role in metal leaching. The formation of a passive layer on the surface of the mineral in oxidizing conditions is a strong barrier in the extraction of the target metal. Conditions that overcome this obstacle are of utmost importance for the mining industry. Furthermore, a combination of conventional leaching systems with biological methods (bioleaching) is shown to be a good strategy in tailings leaching. Bioleaching has been applied to the treatment of poor ores and tailings, since acidophilic bacteria can oxidize Fe<sup>2+</sup> with the regeneration of Fe<sup>3+</sup> ions, together with the reduction of sulphur species to sulfuric acid, leading to the extraction of metals. Moreover, it is considered a more environmentally friendly technology than traditional extraction methods, as it occurs naturally, more economical and results in significantly less pollution. Therefore, some studies have been applying biological leaching as a pre-treatment for chemical leaching of mining tailings. The aim of this work is to present and discuss possibilities to conventional metal extraction processes, combining the two strategies of bioleaching and brine-leaching.</p>
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