# Leaching of Pure Chalcocite in a Chloride Media Using Sea Water and Waste Water

^{1}

^{2}

^{3}

^{4}

^{5}

^{*}

## Abstract

**:**

^{2}value of 0.92 is valid. The highest copper extraction (67.75%) was obtained at 48 h leaching under conditions of 2 mol/L H

_{2}SO

_{4}and 100 g/L chloride. The XRD analysis shows the formation of a stable and non-polluting residue; such as elemental sulfur (S

^{0}). This residue was obtained in a leaching time of 4 h at room temperature under conditions of 0.5 mol/L H

_{2}SO

_{4}and 50 g/L Cl

^{−}.

## 1. Introduction

_{2}), which together, with NO

_{x}and CO

_{2}, can cause large problems; such as acid rain and increasing local pollution, therefore, the abatement of waste gases is an important task for the protection of the environment [7,8,9]. As a result, new hydrometallurgical alternatives are being developed in the mining industry, because they are more ecological and economic processes to recover copper [10,11].

_{2}S + 2Fe

^{3+}= Cu

^{2+}+ 2Fe

^{2+}+ CuS

^{3+}= Cu

^{2+}+ 2Fe

^{2+}+ S

^{0}

^{−1}) [19]. The second stage is slower and can be accelerated depending on the temperature [13,26].

^{3 +}, Cu

^{2 +}, etc.) and at room temperature.

_{2}at ambient pressure in a H

_{2}SO

_{4}-NaCl solution, where the leaching agents are Cu

^{2+}, CuCl

^{+}, CuCl

_{2}and Cu${\mathrm{Cl}}_{3}^{-}$, which are generated during leaching in a Cu

^{2+}/Cl

^{−}system. The general reaction of chalcocite leaching is as follows:

^{0}) with covellite residues or copper polysulfides (CuS

_{2}) that still contain valuable metals.

^{−}at room temperature, in a system of high concentrations of chloride (greater than 1 M). This Cu${\mathrm{Cl}}_{2}^{-}$ is stable in a range of potentials between 0–500 mV and pH < 6–7 (depending on the chloride concentration in the system) [20,28].

## 2. Materials and Methods

#### 2.1. Chalcocite

#### 2.2. Leaching and Leaching Tests

#### 2.3. Experimental Design

_{2}S leaching.

_{2}SO

_{4}concentration as independent variables. Minitab 18 software (version 18, Pennsylvania State University, State College, PA, USA) was used for modeling and experimental design, which allowed the study of the linear and quadratic effects of the independent variables. The experimental data were fitted by multiple linear regression analysis to a quadratic model, considering only those factors that helped to explain the variability of the model. The empirical model contains coefficients of linear, quadratic, and two-factor interaction effects.

_{2}SO

_{4}concentration, and $b$ is the variable coefficients.

_{i}) into a code value (X

_{i}) according to the experimental design:

_{2}SO

_{4}and chloride concentration.

^{2}, R

^{2}

_{adj}, p-values and Mallows’s Cp indicate whether the model obtained is adequate to describe Cu extraction under a given domain. The R

^{2}coefficient is a measure of the goodness of fit, which measures the proportion of total variability of the dependent variable with respect to its mean, which is explained by the regression model. The p-values represent statistical significance, which indicates whether there is a statistically significant association between the response variable and the terms. The predicted R

^{2}was used to determine how well the model predicts the response for new observations. Finally, Mallows’s Cp is a precise measure in the model, estimating the true parameter regression [36].

## 3. Results

#### 3.1. ANOVA

_{2}SO

_{4}concentration.

_{2}SO

_{4}and time-concentration of H

_{2}SO

_{4}in copper extraction, complying with the theory that the increase in sulfuric acid concentration does not have a great influence on the leaching of chalcocite above 0.02 mol/L [19,22]. Rather, it is only the time-concentration interaction of chloride that must be considered in the model. Additionally, the effects of curvature of the variable chloride concentration and H

_{2}SO

_{4}concentration do not contribute significantly to explaining the variability of the model. On the other hand, the linear effects of chloride time and concentration contribute to explaining the experimental model, as shown in the contour plot of Figure 2.

_{2}SO

_{4}concentration, as well as the interaction of time-H

_{2}SO

_{4}and Cl-H

_{2}SO

_{4}affected Cu extraction.

_{2}SO

_{4}and chloride-H

_{2}SO

_{4}is low.

_{2}SO

_{4}concentration.

_{2}S under the established parameter ranges. The model did not require adjustment and it was validated by the R

^{2}value (0.92) and R

^{2}

_{adj}value (0.90). The ANOVA analysis showed that the factors indicated influence Cu extraction from Cu

_{2}S (F

_{Regression}(22.73) > F

_{T,95% confidence level}= F

_{5,21}(2.68)). On the other hand, the p-value of the model (Equation (9)) is lower than 0.05, indicating that the model is statistically significant.

^{2}

_{pred}= 0.8684.

^{2}and R

^{2}

_{pred}of the model was minimal, thus reducing the risk that the model was over adjusted. That means, the probability that the model fits only in the sample data is lower. The ANOVA analysis indicated that time, chloride concentration, H

_{2}SO

_{4}concentration and the interaction of time-chloride are the factors that explain to a greater extent the behavior of the system for the sampled data set.

_{2}), what it requires is even more demanding conditions to achieve its complete dissolution [37].

#### 3.2. Effect on the Chloride Concentration

^{−}), results similar to those presented in Figure 5a were obtained in a Cl

^{−}concentration of 50 g/L, so it is noted that the presence of calcium ions, fluorine, magnesium and calcium carbonate did not affect the dissolution of copper from the chalcocite. In the tests carried out with seawater, which has approximately a concentration of 20 g/L Cl

^{−}, obtained copper extractions of up to 63.4% at 48 h with a concentration of 0.5 mol/L of sulfuric acid. In previous investigations [13,20], it has been determined that leaching is independent of a chloride concentration between 0.5 and 2 mol/L, but a greater kinetic of dissolution is observed in the first minutes and then the difference decreases as a function of time and behavior similar to that of Figure 5.

^{−}and 0.5 mol/L H

_{2}SO

_{4}, in a leaching time of 4 h. The result of this XRD is useful to understand the behavior of the chalcocite in a short time and in low reagent conditions, and to observe which mineralogical species are forming. The results show a high formation of synthetic covellite (77.34 wt %), early formation of elemental sulfur (20.20 wt %) and a remaining chalcocite (4.46 wt %), which still does not dissolve. From this, it follows that the transformation of chalcocite to covellite is faster than the transformation of covellite to elemental sulfur, which is similar to that observed in Equations (4) and (5), also, according to Figure 5, the slope of the curve is decreasing slowly, which means less kinetics of copper dissolution as a function of time. In the investigation of Senanayake [28], it is reported that the dissolution of chalcocite in a chloride-iron-water system at 25 °C occurs at potentials greater than 500 mV with a pH < 4, while in the research of Miki et al. [13] it is reported that the chalcocite dissolution occurs rapidly at a potential of 500 mV but stops when it reaches 50% copper extraction. When the potential increases to 550 mV, this extraction increases again because once it reaches 50% copper extraction, the mineral present is mainly covellite, which has a dissolution kinetics lower than the chalcocite and that needs potentials greater than 600 mV to dissolve.

## 4. Conclusions

- The linear variables with the greatest influence in the model are: time, chloride concentration and sulfuric acid concentration, respectively.
- Under normal pressure and temperature conditions, only the chloride-time concentration exerts a significant synergistic effect on the extraction of copper from a chalcocite mineral.
- The ANOVA analysis indicates that the presented quadratic model is adequate to represent the copper extractions and the value of R
^{2}(0.92) validates it. - The highest copper extraction is achieved under conditions of low concentration of sulfuric acid (0.5 mol/L), high concentrations of chloride (100 g/L) and a prolonged leaching time (48 h) to obtain an extraction of 67.75% copper.
- The XRD analysis shows the formation of a stable and non-polluting residue; such as elemental sulfur (S
^{0}). This residue was obtained in a leaching time of 4 h at room temperature under conditions of 0.5 mol/L H_{2}SO_{4}and 50 g/L Cl^{−}.

## Author Contributions

## Funding

## Acknowledgments

^{®}and for facilitating the chemical analysis of the solutions. We are also grateful to the Altonorte Mining Company for supporting this research and providing slag for this study, and we thank to Marina Vargas Aleuy and María Barraza Bustos of the Universidad Católica del Norte for supporting the experimental tests.

## Conflicts of Interest

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**Figure 2.**Experimental contour plot of independent variables of Chloride and H

_{2}SO

_{4}concentration (

**a**); Time and H

_{2}SO

_{4}concentration (

**b**); and Time and Chloride concentration (

**c**) on the dependent variable Cu extraction.

**Figure 4.**Interaction effect plot of independent variables Time and H2SO4 concentration (

**a**); and Chloride and H2SO4 concentration (

**b**) on the dependent variable Cu extraction.

**Figure 5.**Effect of chloride concentration on Cu extraction from chalcocite (T = 25°C. H

_{2}SO

_{4}= 0.5 mol/L); (

**a**) Cl

^{−}added by NaCl; (

**b**) Cl

^{−}added by waste water and seawater.

**Figure 6.**X-ray diffractogram for solid residues (chalcocite mineral) after being leached at 25 °C in a time of 4 h with 0.5 mol/L H

_{2}SO

_{4}and 50 g/L Cl

^{−}.

Investigation | Leaching Agent | Parameters Evaluated | Reference | Cu Ext (%) |
---|---|---|---|---|

The kinetics of leaching chalcocite (synthetic) in acidic oxygenated sulphate-chloride solutions | NaCl, H_{2}SO_{4}, HCl, HNO_{3} and Fe^{3+} | Oxygen flow, stirring speed, temperature, sulfuric acid concentration, ferric ions concentration, chloride concentration and particle size. | [20] | 97 |

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. | [13] | 98 |

Leaching kinetics of digenite concentrate in oxygenated chloride media at ambient pressure | CuCl_{2}, HCl and NaCl | Effect of stirring speed, oxygen flow, cupric ion concentration, chloride concentration, acid concentration and temperature effect. | [27] | 95 |

Leaching of sulfide copper ore in a NaCl–H_{2}SO_{4}–O_{2} media with acid pre-treatment | NaCl and H_{2}SO_{4} | Chloride concentration, effect of agitation with compressed air, percentage of solids and particle size. | [22] | 78 |

Component | Cu | S^{0} |
---|---|---|

Mass (%) | 79.83 | 20.17 |

Compound | Concentration (g/L) |
---|---|

Fluorine (F^{−}) | 0.01 |

Calcium (Ca^{2+}) | 0.80 |

Magnesium (Mg^{2+}) | 2.65 |

Bicarbonate (HCO_{3}^{−}) | 1.10 |

Chloride (Cl^{−}) | 39.16 |

Calcium carbonate (CaCO_{3}) | 13.00 |

Experimental Parameters | Low | Medium | High |
---|---|---|---|

Time (h) | 4 | 8 | 12 |

Concentration | 20 | 50 | 100 |

Cl^{−} (g/L) | |||

Concentration | 0.5 | 1 | 2 |

H_{2}SO_{4} (mol/L) | |||

Codifications | −1 | 0 | 1 |

Exp. No. | Time (h) | Cl^{−} (g/L) | H_{2}SO_{4} (mol/L) | Cu Ext. (%) |
---|---|---|---|---|

1 | 4 | 20 | 0.5 | 31.63 |

2 | 4 | 20 | 1 | 33.25 |

3 | 4 | 20 | 2 | 37.00 |

4 | 4 | 50 | 0.5 | 32.25 |

5 | 4 | 50 | 1 | 33.38 |

6 | 4 | 50 | 2 | 38.00 |

7 | 4 | 100 | 0.5 | 44.75 |

8 | 4 | 100 | 1 | 44.88 |

9 | 4 | 100 | 2 | 46.19 |

10 | 8 | 20 | 0.5 | 35.75 |

11 | 8 | 20 | 1 | 38.75 |

12 | 8 | 20 | 2 | 43.00 |

13 | 8 | 50 | 0.5 | 48.13 |

14 | 8 | 50 | 1 | 49.50 |

15 | 8 | 50 | 2 | 50.63 |

16 | 8 | 100 | 0.5 | 51.50 |

17 | 8 | 100 | 1 | 53.00 |

18 | 8 | 100 | 2 | 54.88 |

19 | 12 | 20 | 0.5 | 52.25 |

20 | 12 | 20 | 1 | 52.75 |

21 | 12 | 20 | 2 | 52.63 |

22 | 12 | 50 | 0.5 | 53.13 |

23 | 12 | 50 | 1 | 53.13 |

24 | 12 | 50 | 2 | 53.00 |

25 | 12 | 100 | 0.5 | 53.25 |

26 | 12 | 100 | 1 | 53.88 |

27 | 12 | 100 | 2 | 55.63 |

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

Regression | 22.73 | 0 |

Time | 123.15 | 0 |

Cl^{−} | 45.25 | 0 |

H_{2}SO_{4} | 5.44 | 0.03 |

Time × Time | 2.06 | 0.17 |

Cl^{−} × Cl^{−} | 0.13 | 0.72 |

H_{2}SO_{4} × H_{2}SO_{4} | 0.00 | 0.97 |

Time × Cl^{−} | 10.27 | 0.01 |

Time × H_{2}SO_{4} | 1.18 | 0.29 |

Cl^{−} × H_{2}SO_{4} | 0.31 | 0.59 |

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## Share and Cite

**MDPI and ACS Style**

Toro, N.; Briceño, W.; Pérez, K.; Cánovas, M.; Trigueros, E.; Sepúlveda, R.; Hernández, P.
Leaching of Pure Chalcocite in a Chloride Media Using Sea Water and Waste Water. *Metals* **2019**, *9*, 780.
https://doi.org/10.3390/met9070780

**AMA Style**

Toro N, Briceño W, Pérez K, Cánovas M, Trigueros E, Sepúlveda R, Hernández P.
Leaching of Pure Chalcocite in a Chloride Media Using Sea Water and Waste Water. *Metals*. 2019; 9(7):780.
https://doi.org/10.3390/met9070780

**Chicago/Turabian Style**

Toro, Norman, Williams Briceño, Kevin Pérez, Manuel Cánovas, Emilio Trigueros, Rossana Sepúlveda, and Pía Hernández.
2019. "Leaching of Pure Chalcocite in a Chloride Media Using Sea Water and Waste Water" *Metals* 9, no. 7: 780.
https://doi.org/10.3390/met9070780