Heap leaching process of copper oxide ore
The heap leaching process and equipment for copper oxide ore involves spraying a leaching solution onto the ore heap, allowing it to seep downward, selectively leaching the valuable components from the ore. The valuable components are then recovered from the rich solution flowing out from the bottom of the heap. Depending on the grade of the copper oxide ore, heap leaching can be categorized as either ore heap leaching or waste rock heap leaching; depending on the location of the heap, heap leaching can be categorized as surface heap leaching or underground heap leaching. The heap leaching process and equipment for copper oxide ore are simple, require minimal equipment, and consume low energy, resulting in low capital investment and production costs. However, its main disadvantage is a low leaching rate of the valuable components in the ore.
The heap leaching process and equipment for copper oxide ore include ore preparation, pad construction, heap building, leachate preparation, leachate distribution and collection, and rich solution (precious solution) processing. For copper oxide ore, satisfactory leaching results are generally achieved by properly controlling the ore particle size. However, leaching results for copper sulfide ore vary significantly depending on the mineral type.
The heap leaching process and equipment for copper oxide ore are detailed below:
1. Ore Preparation
This includes crushing, screening or granulation, and pretreatment. To improve the ore's leachability and the permeability of the heap, avoid uneven liquid flow, blockage, and channeling, increase metal recovery, reduce solution consumption, and enhance leaching efficiency, the ore must be crushed to a suitable size and achieve a suitable particle size composition. Requirements for the particle size and composition vary depending on the ore type, mineral composition, and fracture rate. For example, in heap leaching of copper and uranium ores in the United States, the ore size should range from 25 to 100 mm, with no more than 20% larger than 100 mm. For gold and silver ores, the ore size should be between 2.5 and 25 mm, whichever is greater. Ores containing a high amount of clay or mineral fines should be crushed to less than 6 mm for pelletizing. This is done by adding a certain amount of water (30 to 40 kg/t) and leaching solution (25 kg/t) to the crushed ore. The mixture is then stirred in a pelletizer to bond the clay and mineral fines to the coarse particles, forming a granular aggregate. After drying, it can be used for heap leaching. If the ore contains a high content of clay (<0.075 mm) and mineral fines (8% to 10%), a binder is also required. Common binders include cement (2 to 4 kg/t) or lime (1.5 to 5 kg/t). Leaching solution is sometimes added during the pelletizing process to pre-treat the ore. The primary purpose of granulation and pretreatment is to improve the permeability of the leaching pile and the leaching rate of the ore's useful components.
2. Leaching Pad Construction
To collect the rich solution and prevent solution leakage, the bottom of the leaching pile needs to be finished and paved (also known as a bedding layer) before construction. Materials used for the leaching pad include clay, sand, gravel, tailings, asphalt, reinforced concrete, plastic film, or rubber-plastic sheeting. Depending on the material, the bedding layer is generally 300-600 mm thick. On top of the bedding layer, longitudinal and transverse drainage trenches are paved with lumps of ore. Finally, a layer of large lumps of ore is laid across the entire floor to protect the bedding layer.
3. Pile Construction
The purpose of the pile construction is to ensure good and uniform permeability and prevent slope collapse. The height of the ore pile depends primarily on the ore's permeability, the leaching agent content in the leaching solution, and the equipment and methods used for construction. Gold ore piles are typically 1-4 meters high, while copper and uranium ore piles are typically 3-30 meters high. Ore stockpiles typically range from several hundred to several hundred thousand tons, with some containing millions of tons of lean copper ore. Construction methods include multi-layer construction, multi-stack construction, slope construction, and mobile bridge construction. Construction equipment primarily includes scrapers, front-end loaders, dump trucks, bulldozers, belt conveyors, and specialized stockpiling machines.
4. Leachate Preparation
Water and a leaching agent are combined according to a specific formula to create a solution, or leachate, used to extract useful components from the ore. The leachate formulation and dosage are primarily determined by the ore type, its mineral composition, and its chemical composition. In industrial-scale heap leaching, available leaching agents include H₂SO₄, HNO₃, HCl, Na₂CO₃, NaHCO₃, (NH₄)₂CO₃, NH₄HCO₃, Fe₂(SO₄)₃, NaCl, KCl, Na₁, K₁, (NH₄)₂SO₄, air, oxygen, permanganates, nitrogen oxides, hydrogen peroxide, and chlorates. To accelerate the leaching of valuable components from sulfide ores and certain oxide ores, bacterial solutions are added to the leachate. Bacterial leaching has been successfully used in production for certain uranium, copper, and gold ores.
5. Liquid Distribution and Collection
Liquid distribution involves evenly spraying the leachate onto the top surface of the ore heap. The distribution (spraying) system consists of a distribution tank, pumps, liquid delivery pipes, and spray pipes and sprinklers installed above the ore heap. Spray pipes are typically plastic, and sprinklers are often swing-type. The requirements for spraying are, first, that the leachate be evenly distributed over the ore heap, and second, that the required spray intensity be achieved—that is, the spray volume per unit area per unit time, typically 0.1 to 0.4 L/m·min. During the heap leaching process, spraying accounts for approximately one-third to one-half of the total time. In addition to spraying, other distribution methods include irrigation and drip irrigation. The heap leaching liquid collection method is relatively simple: rich liquid from the bottom of the heap is collected through a liquid ditch into a collection tank, from which it is pumped to a processing workshop.
6. Rich Liquid Processing
The technology used to recover metals from rich liquid varies depending on the ore type. For uranium extraction, extraction and ion exchange precipitation, as well as solvent extraction-electrodeposition, are commonly used. For gold extraction, activated carbon (or ion exchange resin) adsorption-desorption-electrodeposition, and displacement precipitation are commonly used.
Advantages of the heap leaching process and equipment for copper oxide ore: Compared with conventional hydrometallurgy, heap leaching offers the following advantages: 1) Low investment and rapid results (approximately one-third of conventional methods); 2) Simple process and low cost (approximately one-third of conventional methods); 3) Depending on the conditions and characteristics of the ore deposit, heap leaching can be conducted on the surface or underground, and waste materials can be used as filler; 4) Minimal environmental pollution; and 5) High resource utilization.
Disadvantages of the heap leaching process and equipment for copper oxide ore include: 1) Relatively low leaching rates, 5-15% lower than agitation leaching; 2) Open-pit heap leaching is susceptible to climate (wind and rain) production, resulting in uneven production; 3) Long leaching cycles of approximately one year, hindering capital turnover; and 4) Optimized leaching methods are difficult to implement for heap leached ore.
Suitable conditions for the heap leaching process and equipment for copper oxide ore: ① Easily leachable ore; ② Low-grade ore with large reserves; ③ High-grade ore with small reserves, poor accessibility, and dispersed locations.
Heap leaching of copper oxide ores and its equipment are fully capable of processing mixed ores and high-grade secondary sulfide ores. It has achieved large-scale production and a high degree of mechanization, becoming a mature copper leaching process. In recent years, with the increasing scale of heap leaching equipment and the increasing scale of hydrometallurgical copper smelting mines, heap leaching has become one of the primary copper leaching processes in hydrometallurgical copper smelting mines.
The technical features of heap leaching of copper oxide ores and its equipment primarily focus on the following three aspects: ① Ore pile—geometric properties of the pile; ore particle size and distribution, porosity, and permeability; ore acidity and oxidation level; valence and grade of the main metal elements; and the type and content of associated elements. ② Leachate—primarily referring to the type, concentration, acidity or pH value, redox properties, volatility, and corrosiveness of the solution. ③ Description and exploration of the phenomena and laws governing the interaction between the leachate and the ore pile.
In the beneficiation process of copper oxide ore, in order to improve the beneficiation efficiency of the ore, based on the existing beneficiation technology, continuous research and development have found that the copper ore can be processed through processes such as leaching, extraction and electrowinning, which can greatly improve the output rate of copper ore. With the continuous innovation and development of domestic science and technology, the beneficiation technology of copper oxide ore has been effectively improved, and the attention on the heap leaching process and equipment of copper oxide ore has been continuously increasing, and the scope of application is becoming wider and wider, but the relevant use is relatively small. At the same time, this technology has an advantage in cost. Compared with other copper ore beneficiation technologies, the heap leaching process and equipment of copper oxide ore are relatively low in cost, so the development prospects are very broad. In particular, during the use of this technology, the oxidation process of the ore is significantly improved, which greatly improves the treatment effect of the ore. For some ore processing plants, it can effectively ensure that they meet their economic indicators.
Among copper ore resources, in addition to the oxidation zones found above most copper sulfide deposits, there are also vast reserves of independent copper oxide deposits. Among copper ores with industrial mining value, oxide copper ores and mixed copper ores account for approximately 25% of my country's copper resources. Oxide copper ore is a crucial component of my country's copper resources and possesses abundant reserves. However, with the continued mining and utilization of copper sulfide ore resources, copper sulfide resources are becoming increasingly depleted, and the relatively easy-to-process copper sulfide ore resources are decreasing year by year, while the proportion of difficult-to-process oxide copper ore resources is increasing. Therefore, developing rational, efficient, and environmentally friendly heap leaching processes and equipment for oxide copper ore is of great significance.
