# Statistical Study for Leaching of Covellite in a Chloride Media

^{1}

^{2}

^{3}

^{4}

^{5}

^{6}

^{*}

## Abstract

**:**

^{2}= 0.99).

## 1. Introduction

^{2+}in solution. All copper sulfides require the presence of Fe

^{3+}and O

_{2}as oxidizing agents for leaching to occur. Copper sulfide is oxidized by the presence of Fe

^{3+}, and the resulting Fe

^{2+}is reoxidized to Fe

^{3+}by O

_{2}. The redox pair Fe

^{2+}/Fe

^{3+}act as a catalyst in these reactions. The following reactions occur with the main secondary copper mineral, chalcocite, when the temperature is high (Equation (1)), and the sulfur is in the form of sulfate and not of elemental sulfur, as in natural conditions (Equations (2) and (3)) [5]:

_{2}S

_{(s)}+ Fe

_{2}(SO

_{4})

_{3(aq)}= Cu

^{2+}

_{(aq)}+ SO

_{4}

^{2−}

_{(aq)}+ CuS

_{(s)}+ 2FeSO

_{4(aq)}

_{2}S

_{(s)}+ 2Fe

^{3+}

_{(aq)}= Cu

^{2+}

_{(aq)}+ 2Fe

^{2+}

_{(aq)}

_{(s)}+ 2Fe

^{3+}

_{(aq)}= Cu

^{2+}

_{(aq)}+ 2Fe

^{2+}

_{(aq)}+ S

^{0}

_{(s)}.

_{2}S

_{(s)}+ 2Fe

^{3+}

_{(aq)}= Cu

^{2+}

_{(aq)}+ CuS

_{(s)}+ 2Fe

^{2+}

_{(aq)}

_{(s)}+ 2Fe

^{3+}

_{(aq)}= Cu

^{2+}

_{(aq)}+ S

^{0}

_{(s)}+ 2Fe

^{2+}

_{(aq)}.

_{2}:

_{2}S

_{2(s)}= CuS

_{2(s)}+ Cu

^{2+}

_{(aq)}+ 2e

^{−}

_{2(s)}= Cu

^{2+}

_{(aq)}+ 2S

^{0}

_{(s)}+ 2e

^{−}.

_{2}is only achieved from media with high chloride concentrations or high potentials [25]. Copper leaching processes in a chloride media are especially adequate for leaching non-ferrous minerals such as chalcocite, djurleite, digenite, and covellite, since in these cases, the leaching solutions contain low levels of dissolved iron [3].

## 2. Materials and Methods

#### 2.1. Covellite

#### 2.2. Reagent and Leaching Tests

#### 2.3. Experimental Design

_{2}SO

_{4}concentrations variables on leaching covellite [37,38,39,40]. An experimental design was carried out considering three levels per factor, resulting in a total of 27 samples [41]. The fit of the multiple linear regression model was generated in the statistical software Minitab 18 (version 18, Pennsylvania State University, State College, PA, USA), studying the linear and quadratic effects and the interactions of the factors considered in the study [42], as shown in Equation (9).

_{1}, x

_{2}, and x

_{3}are time, chloride, and H

_{2}SO

_{4}concentration variables, respectively. Table 3 shows the parameters used in the experimental model, and Equation (10) shows the transformation between the real values (Z

_{i}) and coded values (X

_{i}) of the experimental design.

_{high}and Z

_{low}are respectively the highest and lowest levels of each variable [43].

^{2}, R

^{2}

_{adj}, and p-values statistics were used to indicate whether the model obtained is adequate to describe the dependent variable under the sampled domain. The R

^{2}statistics measures the proportion of total variability that is explained by the model, the predicted R

^{2}statistic determines the performance of the model predicting the response, and finally, the p-values indicate whether there is a statistically significant association between the dependent variable and a determined independent variable [43].

## 3. Results

#### 3.1. ANOVA

_{2}SO

_{4}} and {Chloride, H

_{2}SO

_{4}} and the curvature of time variable contribute to explain the variability of the model.

_{2}SO

_{4}.

_{2}SO

_{4}concentration and the interactions of time–H

_{2}SO

_{4}concentration and of chloride–H

_{2}SO

_{4}concentrations affected the Cu extraction rate.

^{2}(0.9945) and R

^{2}

_{adj}values (0.9925). The ANOVA indicates that all the factors influence the Cu extraction from CuS, as indicated in the F statistic, where F

_{reg}(371.42) > F

_{T,95%}confidence level F

_{7,19}(2.543). Additionally, the p-value was lower than the significance level, which indicates that the multiple regression is statistically significant.

^{2}and R

^{2}

_{pred}reduces the possibility that the model is over-adjusted, and the leaching, chloride, and H

_{2}SO

_{4}concentrations, and the interactions of time–H

_{2}SO

_{4}and chloride–H

_{2}SO

_{4}are the most critical factors in explaining the process.

#### 3.2. Effect of Chloride Concentration

_{2}is possible with any chloride concentration, but the oxidation of CuS

_{2}is only possible with very high potential or high chloride concentrations [25].

## 4. Conclusions

- The linear variables of time and chloride concentration have the greatest influence on the model.
- Under ambient conditions of pressure and temperature, H
_{2}SO_{4}concentration–time and chloride concentration–time have significant effects on copper extraction kinetics from covellite. - The ANOVA analysis indicates that the quadratic model adequately represents copper extraction, which was validated by the R
^{2}value (0.9945). - The highest copper extraction rate at ambient temperature of 71.2% was obtained with a low sulfuric acid concentration (0.5 M), high level of chloride (100 g/L), and extended leaching time (600 h).

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

- Klein, C.; Hurlbut, C.S. Manual de Mineralogía; Reverté: Madrid, Spain, 1996; ISBN 8429146067. [Google Scholar]
- Lundström, M.; Liipo, J.; Taskinen, P.; Aromaa, J. Copper precipitation during leaching of various copper sulfide concentrates with cupric chloride in acidic solutions. Hydrometallurgy
**2016**, 166, 136–142. [Google Scholar] [CrossRef] - Ruiz, M.C.; Honores, S.; Padilla, R. Leaching kinetics of digenite concentrate in oxygenated chloride media at ambient pressure. Metall. Mater. Trans. B
**1998**, 29, 961–969. [Google Scholar] [CrossRef] - Senanayake, G. Chloride assisted leaching of chalcocite by oxygenated sulphuric acid via Cu(II)-OH-Cl. Miner. Eng.
**2007**, 20, 1075–1088. [Google Scholar] [CrossRef] - Schlesinger, M.E.; King, M.J.; Sole, K.C.; Davenport, W.G. Extractive Metallurgy of Copper, 5th ed.; Elsevier: Oxford, UK, 2011; ISBN 9780080967899. [Google Scholar]
- Shuva, M.A.H.; Rhamdhani, M.A.; Brooks, G.A.; Masood, S.; Reuter, M.A. Thermodynamics data of valuable elements relevant to e-waste processing through primary and secondary copper production: A review. J. Clean. Prod.
**2016**, 131, 795–809. [Google Scholar] [CrossRef] - Turan, M.D.; Sari, Z.A.; Miller, J.D. Leaching of blended copper slag in microwave oven. Trans. Nonferrous Met. Soc. China
**2017**, 27, 1404–1410. [Google Scholar] [CrossRef] - Kelm, U.; Avendaño, M.; Balladares, E.; Helle, S.; Karlsson, T.; Pincheira, M. The use of water-extractable Cu, Mo, Zn, As, Pb concentrations and automated mineral analysis of flue dust particles as tools for impact studies in topsoils exposed to past emissions of a Cu-smelter. Chemie der Erde
**2014**, 74, 365–373. [Google Scholar] [CrossRef] - Afif, C.; Chélala, C.; Borbon, A.; Abboud, M.; Adjizian-Gérard, J.; Farah, W.; Jambert, C.; Zaarour, R.; Saliba, N.B.; Perros, P.E.; et al. SO
_{2}in Beirut: Air quality implication and effects of local emissions and long-range transport. Air Qual. Atmos. Heal.**2008**, 1, 167–178. [Google Scholar] [CrossRef][Green Version] - Dijksira, R.; Senyard, B.; Shah, U.; Lee, H. Economical abatement of high-strength SO
_{2}off-gas from a smelter. J. South. African Inst. Min. Metall.**2017**, 117, 1003–1007. [Google Scholar] [CrossRef][Green Version] - Dimitrijević, M.; Kostov, A.; Tasić, V.; Milosević, N. Influence of pyrometallurgical copper production on the environment. J. Hazard. Mater.
**2009**, 164, 892–899. [Google Scholar] [CrossRef] - Sánchez de la Campa, A.M.; de la Rosa, J.D.; Sánchez-Rodas, D.; Oliveira, V.; Alastuey, A.; Querol, X.; Gómez Ariza, J.L. Arsenic speciation study of PM2.5 in an urban area near a copper smelter. Atmos. Environ.
**2008**, 42, 6487–6495. [Google Scholar] [CrossRef] - Serbula, S.M.; Milosavljevic, J.S.; Radojevic, A.A.; Kalinovic, J.V.; Kalinovic, T.S. Extreme air pollution with contaminants originating from the mining—Metallurgical processes. Sci. Total Environ.
**2017**, 586, 1066–1075. [Google Scholar] [CrossRef] [PubMed] - Balladares, E.; Jerez, O.; Parada, F.; Baltierra, L.; Hernández, C.; Araneda, E.; Parra, V. Neutralization and co-precipitation of heavy metals by lime addition to effluent from acid plant in a copper smelter. Miner. Eng.
**2018**, 122, 122–129. [Google Scholar] [CrossRef] - World Health Organization. World Health Statistics 2018: Monitoring Health for the SDGs, Sustainable Development Goals; WHO: Geneva, Switzerland, 2018; ISBN 9789241565585. [Google Scholar]
- Baba, A.A.; Balogun, A.F.; Olaoluwa, D.T.; Bale, R.B.; Adekola, F.A.; Alabi, A.G.F. Leaching kinetics of a Nigerian complex covellite ore by the ammonia-ammonium sulfate solution. Korean J. Chem. Eng.
**2017**, 34, 1133–1140. [Google Scholar] [CrossRef] - González, C.; Parra, R.; Klenovcanova, A.; Imris, I.; Sánchez, M. Reduction of Chilean copper slags: A case of waste management project. Scand. J. Metall.
**2005**, 34, 143–149. [Google Scholar] [CrossRef] - Lü, C.; Wang, Y.; Qian, P.; Liu, Y.; Fu, G.; Ding, J.; Ye, S.; Chen, Y. Separation of chalcopyrite and pyrite from a copper tailing by ammonium humate. Chinese J. Chem. Eng.
**2018**, 26, 1814–1821. [Google Scholar] [CrossRef] - Rabadjieva, D.; Tepavitcharova, S.; Todorov, T.; Dassenakis, M.; Paraskevopoulou, V.; Petrov, M. Chemical speciation in mining affected waters: The case study of Asarel-Medet mine. Environ. Monit. Assess.
**2009**, 159, 353–366. [Google Scholar] [CrossRef] - Reilly, I.G.; Scott, D.S. The leaching of cupric sulfide in ammonia. Ind. Eng. Chem. Process Des. Dev.
**1976**, 15, 60–67. [Google Scholar] [CrossRef] - Fisher, W.W. Comparison of chalcocite dissolution in the sulfate, perchlorate, nitrate, chloride, ammonia, and cyanide systems. Miner. Eng.
**1994**, 7, 99–103. [Google Scholar] [CrossRef] - Vračar, R.Ž.; Vučković, N.; Kamberović, Ž. Leaching of copper(I) sulphide by sulphuric acid solution with addition of sodium nitrate. Hydrometallurgy
**2003**, 70, 143–151. [Google Scholar] [CrossRef] - Cheng, C.Y.; Lawson, F. The kinetics of leaching covellite in acidic oxygenated sulphate-chloride solutions. Hydrometallurgy
**1991**, 27, 249–268. [Google Scholar] [CrossRef] - Miki, H.; Nicol, M.; Velásquez-Yévenes, L. The kinetics of dissolution of synthetic covellite, chalcocite and digenite in dilute chloride solutions at ambient temperatures. Hydrometallurgy
**2011**, 105, 321–327. [Google Scholar] [CrossRef][Green Version] - Nicol, M.; Basson, P. The anodic behaviour of covellite in chloride solutions. Hydrometallurgy
**2017**, 172, 60–68. [Google Scholar] [CrossRef] - Donati, E.; Pogliani, C.; Boiardi, J.L. Anaerobic leaching of covellite by Thiobacillus ferrooxidans. Appl. Microbiol. Biotechnol.
**1997**, 47, 636–639. [Google Scholar] [CrossRef] - Monteiro, F.V.; Garcia, O.; Tuovinen, O. Oxidative dissolution of covellite by Thiobacillus ferrooxidans. Process Metall.
**1999**, 9, 283–290. [Google Scholar] - Falco, L.; Pogliani, C.; Curutchet, G.; Donati, E. A comparison of bioleaching of covellite using pure cultures of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans or a mixed culture of Leptospirillum ferrooxidans and Acidithiobacillus thiooxidans. Hydrometallurgy
**2003**, 71, 31–36. [Google Scholar] [CrossRef] - Lee, J.; Acar, S.; Doerr, D.L.; Brierley, J.A. Comparative bioleaching and mineralogy of composited sulfide ores containing enargite, covellite and chalcocite by mesophilic and thermophilic microorganisms. Hydrometallurgy
**2011**, 105, 213–221. [Google Scholar] [CrossRef] - Niu, X.; Ruan, R.; Tan, Q.; Jia, Y.; Sun, H. Study on the second stage of chalcocite leaching in column with redox potential control and its implications. Hydrometallurgy
**2015**, 155, 141–152. [Google Scholar] [CrossRef] - Ruiz, M.C.; Abarzúa, E.; Padilla, R. Oxygen pressure leaching of white metal. Hydrometallurgy
**2007**, 86, 131–139. [Google Scholar] [CrossRef] - Senanayake, G. A review of chloride assisted copper sulfide leaching by oxygenated sulfuric acid and mechanistic considerations. Hydrometallurgy
**2009**, 98, 21–32. [Google Scholar] [CrossRef][Green Version] - Ruan, R.; Zou, G.; Zhong, S.; Wu, Z.; Chan, B.; Wang, D. Why Zijinshan copper bioheapleaching plant works efficiently at low microbial activity-Study on leaching kinetics of copper sulfides and its implications. Miner. Eng.
**2013**, 48, 36–43. [Google Scholar] [CrossRef] - Ruiz, M.C.; Montes, K.S.; Padilla, R. Chalcopyrite leaching in sulfate-chloride media at ambient pressure. Hydrometallurgy
**2011**, 109, 37–42. [Google Scholar] [CrossRef] - Padilla, R.; Jerez, O.; Ruiz, M.C. Hydrometallurgy Kinetics of the pressure leaching of enargite in FeSO
_{4}–H_{2}SO_{4}–O_{2}media. Hydrometallurgy**2015**, 158, 49–55. [Google Scholar] [CrossRef] - Ruiz, M.C.; Gallardo, E.; Padilla, R. Copper extraction from white metal by pressure leaching in H2SO4-FeSO4-O2. Hydrometallurgy
**2009**, 100, 50–55. [Google Scholar] [CrossRef] - Aguirre, C.L.; Toro, N.; Carvajal, N.; Watling, H.; Aguirre, C. Leaching of chalcopyrite (CuFeS
_{2}) with an imidazolium-based ionic liquid in the presence of chloride. Miner. Eng.**2016**, 99, 60–66. [Google Scholar] [CrossRef] - Bezerra, M.A.; Santelli, R.E.; Oliveira, E.P.; Villar, L.S.; Escaleira, L.A. Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta
**2008**, 76, 965–977. [Google Scholar] [CrossRef] - Dean, A.; Voss, D.; Draguljic, D. Response Surface Methodology. In Design and Analysis of Experiments; Springer Nature: Cham, Switzerland, 2017; pp. 565–614. [Google Scholar]
- Toro, N.; Herrera, N.; Castillo, J.; Torres, C.; Sepúlveda, R. Initial investigation into the leaching of manganese from nodules at room temperature with the use of sulfuric acid and the addition of foundry slag—Part I. Minerals
**2018**, 8, 565. [Google Scholar] [CrossRef][Green Version] - Toro, N.; Saldaña, M.; Gálvez, E.; Cánovas, M.; Trigueros, E.; Castillo, J.; Hernández, P.C. Optimization of parameters for the dissolution of mn from manganese nodules with the use of tailings in an acid medium. Minerals
**2019**, 9, 387. [Google Scholar] [CrossRef][Green Version] - Saldaña, M.; Toro, N.; Castillo, J.; Hernández, P.; Trigueros, E.; Navarra, A. Development of an analytical model for the extraction of manganese from marine nodules. Metals
**2019**, 9, 903. [Google Scholar] [CrossRef][Green Version] - Montgomery, D.C. Design and Analysis of Experiments; John Wiley & Sons: New York, NY, USA, 2012. [Google Scholar]

**Figure 1.**Experimental contour plot of Cu extraction versus time and chloride (

**a**), time and H

_{2}SO

_{4}concentration (

**b**), and chloride concentration and H

_{2}SO

_{4}concentration (

**c**).

**Figure 3.**Interactions of time–chloride (

**a**), time–H

_{2}SO

_{4}concentration (

**b**), and chloride–H

_{2}SO

_{4}(

**c**) on Cu extraction.

Research Title | Dissolution Agents | Parameters Evaluated | Ref. | Maximum Cu Extraction (%) | Type of Covellite |
---|---|---|---|---|---|

The kinetics of leaching covellite in acidic oxygenated sulfate—chloride solutions | HCl, HNO_{3}, NaCl, H_{2}SO_{4} | Temperature, oxygen partial pressure, particle size, stirring speed, and sulfuric acid concentration | [23] | 85% | Synthetic covellite |

The kinetics of dissolution of synthetic covellite, chalcocite, and digenite in dilute chloride solutions at ambient temperatures | HCl, Cu^{2+} and Fe^{3+} | Potential effect, chloride concentration, acid concentration, temperature, dissolved oxygen, and pyrite effect | [24] | >90% | Synthetic covellite |

Element | Cu | S | Ca | O | H |
---|---|---|---|---|---|

Mass (%) | 56.14 | 31.08 | 3.66 | 8.76 | 0.36 |

Experimental Variable | Low | Medium | High |
---|---|---|---|

Time (h) | 48 | 72 | 144 |

Chloride Concentration (g/L) | 20 | 50 | 100 |

H_{2}SO_{4} Concentration (M) | 0.5 | 1 | 2 |

Codifications | −1 | 0 | 1 |

**Table 4.**Experimental configuration and Cu extraction data (at T = 25 °C, Stirring rate = 600 rpm, P = 1 atm).

Exp. No. | Time (h) | Cl (g/L) | H_{2}SO_{4} (M) | Cu Extraction Rate (%) |
---|---|---|---|---|

1 | 48 | 20 | 0.5 | 2.50 |

2 | 48 | 50 | 0.5 | 3.50 |

3 | 48 | 100 | 0.5 | 6.00 |

4 | 48 | 20 | 1 | 3.00 |

5 | 48 | 50 | 1 | 3.63 |

6 | 48 | 100 | 1 | 9.13 |

7 | 48 | 20 | 2 | 3.25 |

8 | 48 | 50 | 2 | 5.50 |

9 | 48 | 100 | 2 | 11.38 |

10 | 72 | 20 | 0.5 | 5.13 |

11 | 72 | 50 | 0.5 | 8.75 |

12 | 72 | 100 | 0.5 | 11.25 |

13 | 72 | 20 | 1 | 5.88 |

14 | 72 | 50 | 1 | 9.25 |

15 | 72 | 100 | 1 | 13.88 |

16 | 72 | 20 | 2 | 6.38 |

17 | 72 | 50 | 2 | 11.63 |

18 | 72 | 100 | 2 | 18.75 |

19 | 144 | 20 | 0.5 | 24.63 |

20 | 144 | 50 | 0.5 | 24.88 |

21 | 144 | 100 | 0.5 | 28.75 |

22 | 144 | 20 | 1 | 26.25 |

23 | 144 | 50 | 1 | 29.75 |

24 | 144 | 100 | 1 | 35.00 |

25 | 144 | 20 | 2 | 28.75 |

26 | 144 | 50 | 2 | 31.25 |

27 | 144 | 100 | 2 | 38.75 |

Source | F-Value | p-Value |
---|---|---|

Regression | 371.42 | 0.000 |

Time | 2624.36 | 0.000 |

Cl | 257.04 | 0.000 |

H_{2}SO_{4} | 105.5 | 0.000 |

Time × Time | 9.7 | 0.006 |

Cl × Cl | 0.56 | 0.466 |

H_{2}SO_{4} × H_{2}SO_{4} | 3.39 | 0.083 |

Time × Cl | 0.81 | 0.379 |

Time × H_{2}SO_{4} | 11.22 | 0.004 |

Cl × H_{2}SO_{4} | 22.6 | 0.000 |

© 2020 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 (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Pérez, K.; Toro, N.; Saldaña, M.; Salinas-Rodríguez, E.; Robles, P.; Torres, D.; Jeldres, R.I. Statistical Study for Leaching of Covellite in a Chloride Media. *Metals* **2020**, *10*, 477.
https://doi.org/10.3390/met10040477

**AMA Style**

Pérez K, Toro N, Saldaña M, Salinas-Rodríguez E, Robles P, Torres D, Jeldres RI. Statistical Study for Leaching of Covellite in a Chloride Media. *Metals*. 2020; 10(4):477.
https://doi.org/10.3390/met10040477

**Chicago/Turabian Style**

Pérez, Kevin, Norman Toro, Manuel Saldaña, Eleazar Salinas-Rodríguez, Pedro Robles, David Torres, and Ricardo I. Jeldres. 2020. "Statistical Study for Leaching of Covellite in a Chloride Media" *Metals* 10, no. 4: 477.
https://doi.org/10.3390/met10040477