# Monitoring and Controlling Saturation Zones in Heap Leach Piles Using Thermal Analysis

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## Abstract

**:**

## 1. Introduction

^{2}) [3]. The solution leaches copper mineral species while it flows downward along the ore bed, and is finally collected in perforated tubes placed at the bottom of the heap for that purpose. In the case of heap bioleaching, a supply of air could be included through tubes located at the bottom of the heap, but above the phreatic level. The simplicity and low cost of this technology has promoted its use at large scale for the extraction of different metals [2]. However, the high variability of particle size distribution, ore mineralogy, and stacking methods determine a variable bulk porosity distribution along the heap, promoting channeling and preferential flows in the heap [4]. These consequences not only affect the wetting uniformity of the ore, reducing the metal extraction, but it could also promote saturated zones that can increase the risk of landslide stability. In this regard, different methods have been studied and applied to monitoring the fluid flow, moisture distribution, and liquid spread in heap leaching, such as electrical resistivity [5], X-ray computed tomography imaging [6], or UV fluorescence-based image analysis [7]. However, these techniques are still limited to application at the laboratory scale (X-ray tomography and UV fluorescence) and the possibility to have results in real time, dynamically (electrical resistivity), in order to have results that allow the taking of operational decisions immediately. In order to tackle these problems, an alternative method is the monitoring and control of irrigation on the surface of the heap during operation.

## 2. Materials and Methods

#### 2.1. Heap Leaching Characteristics

- Length: 48.4 m. Width: 24.4 m. Height: 2.5 m.
- Separation of the drip irrigation grid: 3 m.
- Separation of the drip irrigation line: 3 m.
- Leaching flow: 23 m
^{3}/h. - Application rate: 14 L/m
^{2}. - Temperature of the leaching solution: 30 °C.
- Temperature gradient: 20 °C.
- −
- Dry zone temperature: 40 °C.
- −
- Wet zone temperature: 20 °C.

- Leaching cycle: 15 days. Irrigation time: 8 days.
- Material: Leached ore; 100% under 1/2 inch.
- Type of leaching: Acid leaching with H
_{2}SO_{4}. - Chemical composition of the solution:
- −
- Irrigation: 0.2 g/L Cu and 10 g/L H
_{2}SO_{4}. - −
- Drainage: 1.5 g/L Cu and 3 g/L H
_{2}SO_{4}.

#### 2.2. UAV and Thermal Camera Integration

- Capacity: 5000 mAh
- Voltage: 3S1P / 3S Cell / 11.1V
- Discharge: 35 C (175 A) Constant / 70 C (350 A) Burst
- Weight: 409 g

#### 2.3. Image Processing and Analysis

**Training Stage**: The process of defining criteria by which patterns were recognized and developing a numerical description for each class.**Classification Stage**: Each pixel in the image data set was categorized and placed into the class it most closely resembles based on a mathematical decision rule.**Output Stage**: Results were commonly presented through tables, graphics, etc.

_{1}),…,P(CK) [16], the class label c can be assigned to an unknown example with features X = (x

_{1},…,x

_{N}) such that:

_{c}P(C = c ‖ x

_{1},…,x

_{N})

_{1},…,x

_{N}, which is independent given the class. This simplifies the numerator to become:

_{1},‖C = c) for each pixel.

## 3. Results

- Black (0): For saturated zone.
- Gray (127): For optimal zone.
- White (255): For dry zone.

## 4. Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Acknowledgments

## Conflicts of Interest

## Abbreviations

PLC | Programmable Logic Controller |

UAV | Unmanned Aerial Vehicle |

IMU | Inertial Measurement Unit |

GPS | Global Positioning System |

RF | Radio Frequency |

DF | Direction Finding |

DoF | Degree of Freedom |

GYRO | Gyroscope |

MPU | Motion Processing Units |

ROM | Run on the Mine |

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**Figure 4.**Thermal image. Deep blue zones are the saturated areas, while white zones correspond to dry areas inside the heap leach pile.

**Figure 7.**Some examples of the segmentations. (

**a**,

**c**) The thermal images, and (

**b**,

**d**) the segmented images.

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**MDPI and ACS Style**

Daud, O.; Correa, M.; Estay, H.; Ruíz-del-Solar, J.
Monitoring and Controlling Saturation Zones in Heap Leach Piles Using Thermal Analysis. *Minerals* **2021**, *11*, 115.
https://doi.org/10.3390/min11020115

**AMA Style**

Daud O, Correa M, Estay H, Ruíz-del-Solar J.
Monitoring and Controlling Saturation Zones in Heap Leach Piles Using Thermal Analysis. *Minerals*. 2021; 11(2):115.
https://doi.org/10.3390/min11020115

**Chicago/Turabian Style**

Daud, Omar, Mauricio Correa, Humberto Estay, and Javier Ruíz-del-Solar.
2021. "Monitoring and Controlling Saturation Zones in Heap Leach Piles Using Thermal Analysis" *Minerals* 11, no. 2: 115.
https://doi.org/10.3390/min11020115