This paper reports on a study of column bioleaching of a low-grade chalcopyrite ore that is currently dump-leached under natural biological conditions without any control over microbial populations. The experimental methodology was focused on the effect of managing the bacterial populations in a raffinate solution sourced from a dump-leach operation. This study presents results from columns of two heights (0.45 and 1.0 m). We demonstrated that intermittent irrigation enhanced the chalcopyrite dissolution during column leaching, but excessively long rest periods negatively affected the chemical and bacterial activity due to the shortage of oxidizing agents and/or nutrients for microorganisms. The recovery of low-grade chalcopyrite ore was enhanced by increasing the microbial cell density. The addition of 1.5 × 10⁸ cells/mL to the 0.45 m column and 5.0 × 10⁷ cells/mL to the 1 m column resulted in increased extraction, with the copper dissolution increasing from 32% to 44% in the 0.45 m column and from 30% to 40% in the 1.0 m column over 70 days of leaching. Under these conditions, the pH level remained constant at ~1.8, and the redox potential was around 840 mV vs. the SHE throughout the experiment. These results provided useful insights for evaluating a sustainable controlled dump-based technology for mineral bioprocessing.

An option to improve the leaching efficiency of chalcopyrite is pretreatment prior to leaching. Pretreatment variables, such as the curing time and the addition of chloride, can increase the kinetics of copper extraction, particularly for sulphide ores. However, there has been little research on the topic. The reactions that govern this phenomenon have not been clearly identified. In this study, the effects of sulphuric acid and sodium chloride agglomeration and curing on chalcopyrite leaching were evaluated at various temperatures: 25, 50, 70, and 90 °C. The pretreated ore and leach residues were characterised by X-ray diffraction, scanning electron microscopy, and reflected light microscopy. Under the conditions of 15 kg/t of H₂SO₄, 25 kg/t of NaCl, and 15 days of curing time (as pretreatment), the following products were identified: CuSO₄, NaFe₃(SO₄)₂(OH)₆, Cu₂Cl(OH), and S⁰. Increasing the curing time and leaching temperature increased copper leaching. The copper extraction was 94% when leaching at 90 °C after pretreatment with 50 g/L of Cl⁻ and 0.2 M of H₂SO₄. Elemental sulphur, jarosite, and copper polysulphide (CuS₂) were detected in the leaching residues.

Although the main cause of hydrometallurgical plant closures is the depletion of oxidized copper minerals reserves, the lack of new hydrometallurgy projects also contributes to these closures. One solution is to be able to process copper sulphide ores hydrometallurgically. However, it is widely known that sulphide copper ores—and chalcopyrite in particular—have very slow dissolution kinetics in traditional leaching systems. An alternative to improve the extraction of copper from sulphide ores is the use of a pretreatment process. Several investigations were developed evaluating the effects of pretreatment, mainly in the extraction of copper from chalcopyrite in chloride media. This study presents a review of various pretreatment methods prior to heap leaching to aid in the dissolution of copper from sulphide ores. Different variables of pretreatment that affect the extraction of copper were identified, including the type of salts used in agglomeration, curing time, and curing temperatures. Successful cases such as the implementation of the CuproChlor^® process (use of calcium chloride), and various pilot studies using sodium chloride and temperature, show that pretreatment is an alternative that aids in the dissolution of copper from sulphide ores.

Black copper oxides are amorphous materials of copper-bearing phases of manganese. They are complex mineral compounds with difficult to recognize mineralogy and have slow dissolution kinetics in conventional hydrometallurgical processes. This study evaluates the effects of various leaching media on copper dissolution from black copper minerals. Leach of a pure black copper sample from Lomas Bayas Mine and another from a regional mine were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), scanning electron microscopy (SEM), Qemscan and mechanically prepared for acid leaching under standard, oxidizing and reducing conditions through the addition of oxygen, iron sulfate or sulfur dioxide, respectively. Standard and high potential leaching (770 mV (SHE)) results in a copper dissolution rate of 70% and manganese dissolution rate of 2%. The addition of potential reducing agents (FeSO₄ or SO₂) decreases the redox potential to 696 and 431 mV, respectively, and favors the dissolution of manganese, thus increasing the overall copper extraction rate. The addition of SO₂ results in the lowest redox potential and the highest copper extraction rates of 86.2% and 75.5% for the Lomas Bayas and regional samples, respectively, which represent an increase of 15% over the copper extract rates under standard and oxidizing conditions.