Improvement effect of organic ligands on chalcopyrite leaching in the aqueous medium of sulfuric acid‑hydrogen peroxide-ethylene glycol
Introduction
The addition of organic polar solvents in the aqueous solution of hydrogen peroxide and sulfuric acid increases the percentages of copper and iron leaching from chalcopyrite (Solís-Marcial and Lapidus, 2013), the most abundant copper sulfide in nature. Among the different polar organic solvents that have been studied, methanol and ethylene glycol give the best results. However, the low boiling point of methanol compared to ethylene glycol represents a practical disadvantage. For that reason, the ethylene glycol is considered the most suitable polar organic solvent for a leaching process that operates at moderate temperatures (20–50 °C) and pressure (101.325 kPa). However, application at the industrial level for the leaching system formed by sulfuric acid‑hydrogen peroxide-ethylene glycol has not been possible due to the following disadvantages: the use of high concentrations of ethylene glycol (3.5 M) and sulfuric acid (0.7 M) (Ruiz-Sánchez and Lapidus, 2017), as well as the low efficiency (less than 2%) in the purification process (by solvent extraction) of copper as a result of highly acidic levels (0.7 M H2SO4) of the resulting leaching solution.
To optimize the copper leaching process and increase the efficiency in the solvent extraction process, leaching studies with low concentrations of sulfuric acid (0.007 M) and ethylene glycol (0.1 M) with 1 M H2O2 have been carried out. The results have shown that the use of 0.007 M H2SO4 promotes, on the one hand, the decomposition of hydrogen peroxide as a result of Fenton reaction, which takes place between hydrogen peroxide and ferric or ferrous iron, catalyzed by the cupric ion (Barb et al., 1951; Pestovsky and Bakac, 2006; Ruiz-Sánchez and Lapidus, 2017); and on the other hand, the mineralization of ethylene glycol due to the OH* radicals formed in the Fenton reaction. However, it has been found that the presence of EDTA in the leaching solution 0.007 M H2SO4–1 M H2O2–0.1 M EG helps to decrease the decomposition of hydrogen peroxide due to the formation of highly stable copper-EDTA and iron-EDTA complexes; thus, favoring a greater dissolution of chalcopyrite (Ruiz-Sánchez and Lapidus, 2018).
Despite the significant increases in the percentages of copper and iron reported by Ruiz-Sánchez and Lapidus (2018), until today it has not been possible to purify copper by solvent extraction due to the elevated stability of the complexes of copper-EDTA and iron-EDTA in the leach liquor. Furthermore, in this leaching system, the studies by Ruiz-Sánchez and Lapidus (2018) and by Mahajan et al. (2007) used samples of pure chalcopyrite at low pulp densities (maximum 3.75 g/L). Consequently, the experimental conditions adequate for processing of high pulp densities (greater than 10 g/L) have not been established nor has this system been used on copper flotation concentrates. Therefore, there is a need to conduct a systematic study on the H2SO4-H2O2-EG-EDTA leaching solution, either to purify the copper from the resulting leach liquor or to design a new approach to the leaching process that suppresses the dissolution of iron and allows the processing of high pulp densities, in such a manner that a copper-rich leaching liquor is obtained that can be sent directly to the electrowinning process.
To achieve the aforementioned goal, a copper leaching process from a chalcopyrite concentrate is presented which obtains a copper-rich PLS and with a low iron content. The proposed process consists of two consecutive stages, the first of which uses a H2SO4-H2O2- EG-oxalic acid leaching solution for the selective dissolution of iron and the formation of solid copper oxalate; the second stage employs a H2SO4-H2O2-EG-EDTA leach solution to dissolve the copper oxalate and react with the remaining chalcopyrite from the first stage.
Section snippets
Copper concentrate characterization
The sample of copper concentrate used in this work originated from the state of Sonora, Mexico. A kilogram of copper concentrate was sieved to determine its particle size distribution. The different fractions obtained, as well as the original copper concentrate were digested with aqua regia and analyzed by atomic absortion spectrometry (AAS, Varian SpectrAA220fs), according to the methodology described by Ruiz-Sánchez and Lapidus (2017).
Copper concentrate characterization
Table 1 shows the elemental composition obtained by AAS for the copper concentrate according to the particle size distribution corresponding to the fractions +106 μm, + 53 μm and + 38 μm. As can be seen, the contents of Pb, Zn, Cu and Fe increase as the particle size decreases, due to the liberation of mineralogical phases (shown below Table 1) during the milling process, which precedes the flotation process.
Due to the variation of the elementary composition with the particle size (Table 1), an
Conclusions
- 1)
An increase in pulp density (from 3.75 to 22.5 g/L) for the sulfuric acid‑hydrogen peroxide-EG-EDTA leaching solution confirmed a rapid and quantitative decomposition of hydrogen peroxide as a consequence of the Fenton reaction between Fe(II, III)-EDTA complexes and H2O2.
- 2)
The use of oxalic acid decreases the decomposition of hydrogen peroxide and favors the selective leaching of iron and the transformation of copper to solid copper oxalate; However, in the presence of this ligand, it was not
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Ángel Ruiz Sánchez is grateful for the financial support of the UASLP Metallurgy Institute through the postdoctoral fellowship (UASLP-4528 project), as well as the National Council of Science and Technology (CONACyT) for the postgraduate scholarship # 284302.
References (15)
- et al.
Modern SEM-based mineral liberation analysis
Int. J. Miner. Process.
(2007) - et al.
Passivation of chalcopyrite during oxidative leaching in sulfate media
Hydrometallurgy
(1995) - et al.
Energetics of interconversion reactions of oxyradicals
Adv. Free Radic. Biol. Med.
(1985) - et al.
Enhanced leaching of copper from chalcopyrite in hydrogen peroxide–glycol system
Miner. Eng.
(2007) - et al.
Study of chalcopyrite leaching from a copper concentrate with hydrogen peroxide in aqueous ethylene glycol media
Hydrometallurgy
(2017) - et al.
Improvement of chalcopyrite dissolution in acid media using polar organic solvents
Hydrometallurgy
(2013) - et al.
Oxidation menagee de la chalcopyrite en solution acide: Analyse cinetique des reactions: I. Modeles chimiques
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