#
Dynamic of Mining Systems: Impact of Cl^{−} Ion Concentration on Heap Copper Leaching Process at Industrial Scale

^{1}

^{2}

^{3}

^{4}

^{5}

^{*}

## Abstract

**:**

_{2}SO

_{4}) and a second operation mode, where Cl

^{−}is added to accelerate the reaction kinetics of sulfide minerals (secondary sulfides). Mineral recovery was modeled for the different modes of operation, dependent on the independent variables/control parameters time, heap height, leach flow rate, and feed granulometry. The results indicate that the recovery of ore from sulfide minerals is proportional to the addition of Cl

^{−}, reaching recovery levels of approximately 60%, very close to 65% recovery in conventional oxide leaching, using only H

_{2}SO

_{4}as leaching agent. Additionally, high copper recoveries from sulfide ores are achieved at medium Cl

^{−}concentrations, but the increase in recovery at high Cl

^{−}concentrations is marginal.

## 1. Introduction

_{2}emissions into the atmosphere, generating serious environmental problems [11]. However, there is development of the concept of an electrochemical device that can reduce the emission of SO

_{2}gas based on SO

_{2}-Despolarized Water Electrolysis forming H

_{2}and H

_{2}SO

_{4}as products, which can be performed in the same metallurgical process using solar energy [12] integrating the concept of green mining. This technology is considered as an alternative for the control of fugitive emission in the pyrometallurgy process, according the following reactions [13]:

^{−}) concentrations, has not been studied in depth. Additional leaching studies in chloride media include modeling the kinetics of chalcocite leaching in acidified cupric chloride (CuCl

_{2}) [21] or ferric chloride (FeCl

_{3}) [22] media under fully controlled pH and potential or analyses of copper speciation and activities in high chloride leaching solutions [23]. In salty solutions, the dissociation of H

_{2}SO

_{4}is according to the following reaction [24].

_{4}

^{−}) is also called bisulfate, is a salt based of sulfuric acid. In the solution is an ion and it contributes to generate Acid Chloride (HCl). That is the response to the improvement in the leaching process. The formed of HCl promotes a rapid kinetic the dissolution of the mineral according to corrosion phenomena during the anodic subprocess [25].

_{2}SO

_{4}), while the second case represent the proposed situation (changes in the operating modes of leaching process), leaching copper oxides with H

_{2}SO

_{4}, and copper sulfide minerals, adding chlorides ions (Cl

^{−}) [28]. The inclusion of uncertainty (associated with parameters of the feed mineral such as granulometry or type of mineral, or operational variables such as the type of leaching agent to be used) in operational planning optimization models of heap leaching has the potential to become an important advance in the way in which mining projects are managed, and specifically, the modes of operation of the threads of the mineral processing industry.

## 2. Materials and Methods

#### 2.1. Heap Leaching

_{2}SO

_{4}leach through large heaps or ore dumps under normal atmospheric conditions. Oxide minerals and chalcocite are easily leached [29,30], while that bornite and native copper are leached under conditions of biological oxidation. Chalcopyrite, on the other hand, is not leached significantly under ordinary heap leach conditions [31].

#### 2.2. Modeling of Heap Leaching Process

- Process controlled by diffusion through the product layer: formation of a product layer around the material that resists diffusion of the oxidant to the surface of the material and slows down leaching.
- Chemically controlled process: the product layer is absent or its presence does not affect the free movement of the oxidant to the surface and the reaction between the surface and the reagent is much slower than the diffusion of the oxidant.
- Film Diffusion Process—Bulk leach solution resists movement of oxidant to the surface and this can slow leach kinetics.

## 3. Results and Discussions

#### 3.1. Adjustment of Analytical Models

_{2}SO

_{4}, and Cl

^{−}ions addition for sulfide minerals at concentration levels of 20 g/L (Equation (4)), 35 g/L (Equation (5)) and 50 g/L (Equation (6)). In addition, its assumption that in an infinite operating time the mineral recovery is equal because chalcocite and others secondary copper sulfides are not refractory to conventional leaching processes [30,51]. Copper recovery from oxides and sulfide minerals by adding only H

_{2}SO

_{4}is shown in Equations (2) and (3), while that copper recovery from sulfide minerals by adding H

_{2}SO

_{4}+ Cl

^{−}at concentrations of 20, 35 and 50 g/L are shown in Equations (4)–(6), respectively, where the random variables of the models are $Z,{\mu}_{s},r$ and $t$ (whose domain is indicated in Table 1), the parameters ${\epsilon}_{b}$, ${D}_{Ae}$, ${\epsilon}_{0}$ and $\omega $ were set from historical measurements and contrasted with the literature [50], and the mathematical fit parameters were calculated using least squares.

^{−}ion concentrations added. Additionally, goodness-of-fit indicators of the recovery models presented in Equations (2)–(6) are shown Table 2. Error measures (MAD and MSE) indicate that all the analytical models fitted present a good fit to operational data.

#### 3.2. Scenarios Modeling

- Mode 1: Leaching of oxidized and secondary sulfides minerals only with H
_{2}SO_{4}as a leaching agent. Leaching of oxides and secondary sulfides with sulfuric acid (leaching of secondary sulfides with H_{2}SO_{4}slows down mineral extraction from the rock, increasing the time required until one is marginal, or a smaller proportion of the valuable mineral is recovered, if considering the constant leaching time (how it usually works under operational conditions in the mining industry) [17]. Then, Mode 1 consists of two operation strategies:- ◦
- Strategy 1: leaching of oxidized copper mineral using only H
_{2}SO_{4}. - ◦
- Strategy 2: leaching of sulfide copper mineral using only H
_{2}SO_{4}.

- Mode 2: Leaching of oxidized minerals by H
_{2}SO_{4}and sulfide minerals at different levels of Cl^{−}ions concentration (20, 35 and 50 g/L). Leaching of secondary sulfides with Cl^{−}ions accelerates copper recovery from sulfide mineral [52,53,54,55]. Different chloride addition configurations are considered in order to determine the levels that improve mineral extraction.- ◦
- Strategy 3: leaching of oxidized minerals with H
_{2}SO_{4}and sulfide minerals by adding chloride at a concentration of 20 g/L. - ◦
- Strategy 4: leaching of oxidized minerals with H
_{2}SO_{4}and sulfide minerals by adding chloride at a concentration of 35 g/L. - ◦
- Strategy 5: leaching of oxidized minerals with H
_{2}SO_{4}and sulfide minerals by adding chloride at a concentration of 50 g/L.

^{−}ions, copper recovery from the sulfide minerals over time is increased, tending to obtain recovery curves like the oxidized minerals (copper recovery being proportional to Cl

^{−}ions concentration).

_{2}SO

_{4}. From Figure 3, a low expected mineral recovery is observed when leaching sulfide minerals only with H

_{2}SO

_{4}, which is due to a lower leaching kinetics, while the recovery from oxides is considerably higher (considering heaps duration times is constant in 120 days). Then, the weighted mineral recovery for both types is 64.7% in the case of oxidized minerals and 43.4% in the case of sulfide minerals. As an alternative scenario (operation mode varying leaching agents), the leaching phase presents two modes of operation: operation of oxidized minerals and sulfides minerals (secondary sulfides) at different Cl

^{−}ion concentrations. In the second operation mode, in 64% of the cases, the leaching was carried out on oxides minerals, while in 36% of the cases it was on sulfide minerals. On the other hand, the average mineral recovery for oxides minerals was 64.7%, while for operation scenarios for sulfide minerals with Cl ions added it was 53.1%, 59.5% and 60.9%, for Cl

^{−}concentrations of 20, 35 and 50 g/L, respectively.

#### 3.3. Uncertainty Analysis

#### 3.3.1. Descriptive Statistics Base Case

#### 3.3.2. Descriptive Statistics Proposed Case

^{−}ions and leaching time.

^{−}ions, in addition to the configurations of 0, 20, 35 and 50 g/L, it can be concluded that there are significant differences between the 4 means considered in the hypothesis testing. However, when developing the hypothesis test considering only the configurations with the highest concentration (35 and 50 g/L), there is not enough evidence to ensure that the means of both scenarios differ, so it is possible to conclude that the increase in the Cl

^{−}ions concentration from 35 to 50 g/L does not necessarily increase the efficiency of copper recovery from secondary sulfides.

#### 3.3.3. Scenarios Comparison

_{2}SO

_{4}as the only leaching agent, and the copper recovery using H

_{2}SO

_{4}for oxidized minerals and H

_{2}SO

_{4}+ Cl

^{−}ion for copper sulfides, whose individual distributions are presented in Figure 4. Developing the t-test for two samples, the difference between the population means is greater than the hypothetical difference (µ = 0), i.e., the value of the average copper recovery considering a dynamic structure of leaching agents (H

_{2}SO

_{4}+ Cl

^{−}) is significantly higher than in the base case (H

_{2}SO

_{4}), validated by a p value less than the significance level (p < 0.001), indicating that the model is statistically significant.

## 4. Conclusions

^{−}levels), very close to the expected recoveries from acid leaching of oxidized minerals (approximately 65%).

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 2.**Recovery from oxidized copper minerals (leaching agent: H

_{2}SO

_{4}) and sulfur copper minerals (H

_{2}SO

_{4}+ Chloride at concentrations levels of 0, 20, 35 and 50 g/L).

Variable/Level | Low | Medium | High |
---|---|---|---|

$Z$ (cm) | 600 | 800 | 900 |

${\mu}_{s}$ () | 9 | 28 | 57 |

$r$ (mm) | 1.0 | 2.5 | 3.5 |

$t$ (days) | 90 | 105 | 120 |

Equation | MAD | MSE | p Value (Residuals Normality) |
---|---|---|---|

(2) | 0.136464313 | 0.041459923 | <0.01 |

(3) | 0.041547655 | 0.003484736 | <0.01 |

(4) | 0.028614690 | 0.002489411 | <0.01 |

(5) | 0.136871445 | 0.042610117 | <0.01 |

(6) | 0.120720494 | 0.031967063 | <0.01 |

Ores/Stats | Mean | Standard Deviation | Normality (p Valor) |
---|---|---|---|

Oxides | 64.655 | 1.367 | <0.005 |

Sulfide | 43.416 | 1.784 | 0.149 |

Cl Conc./Stats | Mean | Standard Deviation | Normality (p Value) |
---|---|---|---|

Cl 20 g/L | 53.107 | 1.693 | 0.125 |

Cl 35 g/L | 59.489 | 1.704 | 0.058 |

Cl 50 g/L | 60.935 | 1.601 | 0.010 |

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**MDPI and ACS Style**

Saldaña, M.; Gálvez, E.; Gallegos, S.; Madrid, F.M.G.; Robles, P.; Toro, N. Dynamic of Mining Systems: Impact of Cl^{−} Ion Concentration on Heap Copper Leaching Process at Industrial Scale. *Metals* **2023**, *13*, 465.
https://doi.org/10.3390/met13030465

**AMA Style**

Saldaña M, Gálvez E, Gallegos S, Madrid FMG, Robles P, Toro N. Dynamic of Mining Systems: Impact of Cl^{−} Ion Concentration on Heap Copper Leaching Process at Industrial Scale. *Metals*. 2023; 13(3):465.
https://doi.org/10.3390/met13030465

**Chicago/Turabian Style**

Saldaña, Manuel, Edelmira Gálvez, Sandra Gallegos, Felipe M. Galleguillos Madrid, Pedro Robles, and Norman Toro. 2023. "Dynamic of Mining Systems: Impact of Cl^{−} Ion Concentration on Heap Copper Leaching Process at Industrial Scale" *Metals* 13, no. 3: 465.
https://doi.org/10.3390/met13030465