Abstract
Currently, there is a large amount of mineral resources not being exploited in large copper minings, a clear example are black copper minerals. These resources are generally not incorpo-rated into the extraction circuits or are not treated, either in stocks, leach pads, or debris. These exotic minerals have considerable amounts of Cu and Mn, which are commercially very attractive. They are refractory to conventional leaching processes, therefore, the use of reducing agents is necessary for treatment of these minerals in order to dissolve the present MnO2, which in turn allows Cu extraction. In this research, iron scrap Fe0 was used as a reducing agent for the dissolution of Mn from a black copper mineral in an acidic medium and compared to previous studies of the use of Fe2+ under the same conditions. In addition, the effects of a pretreatment process (agglomeration and curing) by adding NaCl are investigated in order to favor the reduction of MnO2. Finally, it was discovered that there is a higher kinetics of dissolution of Mn when working with Fe0 in short periods of time, although similar extraction efficiencies are obtained after prolonged times. The pretreatment process by adding NaCl resulted in increased Mn extraction in short periods of time (30 min). At applying high concentrations of the reducing agent, the effect of particle size on the dissolution rate of MnO2 was shown to be insignificant.
Highlights
19.7 Mt of copper are produced worldwide [1]
It can be observed that higher Mn extraction percentages are obtained in general, when working with Fe0 over Fe2+, which agrees with our results reported previously [26] for dissolution of MnO2 from manganese nodules with the use of Fe0
It can be seen that, for both reducing agents, high Mn extractions are obtained in short periods of time, which is similar to the results obtained in previous studies published in literature [16,18], for this type of minerals in stirred reactors under similar conditions
Summary
In Chile, large-scale copper mining is the main economic activity, generating 10 % of GDP (gross domestic product) [2] as Chile is the largest producer of copper in the world (27.7 % of the world production) [3]. Among the possible treatment processes, pyrometallurgical processes are mainly used (75 %), and to a lesser extent hydrometallurgical processes (25 %) [4]. Pyrometallurgical processes generate more pollution to the environment because flotation processes generate the tailings dams [5], where acid drainage is generated by oxidation of minerals with high pyrite contents. Along with large emissions of sulfur dioxide, NOx and CO2 are generated in the smelting plants [6,7]. It should be mentioned that hydrometallurgical methods have lower operating, energy, and water consumption costs [8,9,10]
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