Heap Leaching, Tank Leaching, and In-Situ Leaching of Copper Ores

Copper, a key metal supporting modern industry, is widely used in fields such as electricity, electronics, and construction. With the increasing depletion of high-grade copper ore resources, the efficient development of low-grade, refractory copper ores has become a core issue for the sustainable development of the mining industry.

Among the many copper ore separation technologies, wet leaching has become the mainstream choice for developing low-grade copper ores due to its adaptability to complex ores, cost controllability, and environmental friendliness. Based on ore particle size, occurrence, and mining conditions, mainstream copper ore leaching and separation processes can be divided into four categories: heap leaching, tank leaching, in-situ leaching, and agitation leaching. Each process is specifically adapted to the specific ore characteristics, achieving precise extraction and enrichment of copper resources.

I.Heap Leaching: A Large-Scale, Low-Cost Solution for Low-Grade Copper Ore Development

Heap leaching is a classic technology for treating low-copper, off-balance sheet ores and waste ore. Its core advantages lie in simple equipment, low investment, and adaptability to large-scale production. It is particularly suitable for highly permeable copper oxide ores (which can be mixed with small amounts of copper sulfide ores), enabling the revitalization of marginal resources at a low cost.

The separation process is structured around a three-step process: "Percolation - Reaction - Collection":

1. Crushing Pretreatment: The ore is crushed to an appropriate particle size (typically below 50mm). This ensures ample interstices between ore particles and increases the contact area between the copper minerals and the leaching agent, preventing the heap from compacting and reducing permeability due to excessively fine particles. 2. Pile Construction and Liquid Distribution: Crushed ore is evenly piled on a leaching site covered with an impermeable layer. The pile height is controlled between 3 and 30 meters, depending on the site's bearing capacity and permeability. A leaching agent, such as dilute sulfuric acid, hydrochloric acid, or nitric acid, is evenly sprayed onto the surface of the ore pile through a spray system. The leaching agent, driven by gravity, penetrates the ore pile and chemically reacts with the copper ore (for example, copper oxide reacts with sulfuric acid to form soluble copper sulfate), dissolving the copper ions into the solution.

3. Precious Solution Collection and Recovery: The copper-containing "precious solution" is collected from a collection ditch at the bottom of the ore pile and pumped through a pump station to the subsequent extraction, electrowinning, or precipitation stages. Extractants separate copper ions from impurities, and cathode copper with a purity exceeding 99.9% is obtained through electrowinning, or copper compounds are produced through precipitation, completing the final copper recovery.

This process requires high ore permeability. If the ore contains excessive mud, pre-processing is necessary. The leaching agent formulation requires precise control of its pH (typically 1.5-2.5) and concentration to avoid excessive acidity that corrodes equipment or excessive dilution that reduces reaction efficiency. It is suitable for large-scale mines with annual processing capacity of hundreds of thousands of tons, and the cost per ton of copper recovered is 15%-20% lower than other processes.

II. Tank Leaching: A Traditional, High-Efficiency Separation Technology for Fine-Grained Copper Oxide Ores

Tank leaching was one of the core processes of early hydrometallurgical copper smelting. Despite technical optimization, it remains the preferred option for processing fine-grained copper oxide ores (typically -1 cm) with a copper content of 1%-2%. It is particularly suitable for small and medium-sized mines or for separation applications with smaller ore volumes.

Its core process focuses on "static reaction - filtration separation," ensuring stable and controllable operation.

First, finely crushed ore is evenly packed into a leaching tank (or leaching trough) with an impermeable layer. A false bottom filter layer (typically a combination of sand, gravel, and filter screens) is laid at the bottom of the tank to prevent ore particles from being lost with the leachate. Leaching agents are then added by perfusion or spraying. For copper oxide ores, concentrated sulfuric acid, sodium cyanide, or ammonium sulfate solutions are commonly used. Sulfuric acid systems are milder and less expensive, while sodium cyanide systems are suitable for some insoluble copper oxide ores. The leaching agent comes into full contact with the ore in the tank, gradually dissolving the copper minerals into soluble copper compounds. After the reaction is complete, the tank valve is opened, and the leachate is filtered through a false bottom to remove impurities, resulting in a copper-containing precious solution. This solution is then sent to electrowinning, displacement (e.g., iron scrap displacement to produce sponge copper), or adsorption (resin adsorption of copper ions) to extract copper.

The advantages of tank leaching are its closed reaction environment and high leaching agent utilization. Reaction efficiency can be optimized by controlling the tank temperature (room temperature is sufficient, but special ores can be heated to 30-50°C) and agitation (some tanks are equipped with simple agitation devices). However, due to limited tank capacity, the processing scale is relatively small, making it more suitable for small- and medium-sized mines or laboratory-level copper separation tests.

III. In-situ Leaching: A Powerful Tool for "Secondary Development" of Residual Ore Bodies in Old Mines

In-situ leaching (in-situ leaching) is a "re-mining" technology for traditional mining resources. It primarily targets residual ore bodies in old mine goafs, unmined low-grade copper oxide ores, or lean copper ores. Removing the need for surface stripping and ore transportation significantly reduces mining costs and minimizes environmental disturbance. It is particularly suitable for mines where mining is difficult and surface development is uneconomical.

The core of this separation process is "wellbore delivery - in-situ reaction - solution reflux." The process design is closely integrated with the orebody's occurrence conditions:

1. Wellbore Design and Construction: Injection and recovery wells are drilled based on the orebody's distribution characteristics. Well spacing typically ranges from 15 x 7.5 m to 30 x 30 m, with a borehole diameter of 15 to 25 cm. Corrosion-resistant plastic pipes are buried in the holes, with one end extending directly into the orebody, ensuring precise delivery of the leaching agent to the target area and preventing loss to non-mineralized layers.

2. In-situ Leaching: A prepared leaching agent (such as dilute sulfuric acid or an ammonia solution) is pressurized and delivered to the orebody through an injection well. The leaching agent penetrates and diffuses within the orebody's pores, reacting with the copper minerals and dissolving the copper ions. The copper-containing leachate is then pumped back to the surface through a recovery well at the bottom of the orebody under gravity or negative pressure, forming a closed-loop "injection - reaction - recovery" system. 3. Solution Treatment: After the precious liquid returns to the surface and is purified and impurities removed, copper is extracted using an extraction-electrowinning process. Some of the leaching agents can be recycled, reducing reagent consumption and wastewater discharge.

The key to in-situ leaching lies in the permeability of the ore body. Preliminary tests assess the porosity and permeability coefficient of the ore body. If permeability is insufficient, it can be improved through methods such as fracturing. This technology not only enables the development of new ore bodies but also revitalizes "inactive resources" in older mines, making previously unprofitable ore bodies profitable.

IV. Agitation Leaching: An Efficient Separation Solution for Fine-Grained and High-Grade Copper Ores

The agitation leaching process is a highly effective technology for processing fine-grained, high-grade, or difficult-to-separate copper ores. It is particularly suitable for copper oxide ores with a particle size of more than 75μm, sulfide ore roasts, and lower-grade tailings (Cu<1%). By enhancing the mixing of the ore slurry and the leaching agent, it significantly improves copper leaching efficiency, achieving efficient resource utilization.

The separation process is centered around "intense mixing - precise temperature control - efficient reaction." The core equipment is a leaching tank equipped with a stirring device:

1. Slurry Preparation: The raw ore is finely ground to a particle size of -75μm, with a minimum of 90% copper minerals, to ensure complete dissociation of the copper minerals. The ore powder is then mixed with water at a specific liquid-to-solid ratio (typically 2:1 to 5:1) to create a slurry, which is then pumped to the leaching tank.

2. Agitation Leaching: A concentrated sulfuric acid solution (higher than in heap leaching and tank leaching) is added to the leaching tank. Air agitation (compressed air, which combines agitation and oxidation) or mechanical agitation (paddle agitation, with the speed adjusted according to the slurry viscosity) is used to ensure full contact between the slurry and the leaching agent. The reaction temperature (ranging from room temperature to 80°C, with elevated temperatures required for sulfide ore roasting), agitation intensity, and reaction time are controlled to promote rapid dissolution of the copper minerals. For example, the copper oxide and copper sulfate in the sulfide ore roast react with sulfuric acid to form soluble copper salts, while impurity ions (such as iron and aluminum) are precipitated and removed by adjusting the pH.

3. Solid-Liquid Separation and Recovery: After leaching, the slurry is filtered and washed to achieve solid-liquid separation. The copper-containing precious liquid is sent to the extraction-electrodeposition stage to extract the cathode copper. The filter residue (tailings) is tested for copper content and discharged or further utilized.

This process offers advantages in high leaching efficiency (copper leaching rates exceeding 90%), controllable reaction conditions, and the ability to process fine-grained ores that are difficult to process using heap or tank leaching. However, it requires high grinding fineness, resulting in slightly higher energy consumption and equipment investment than other leaching processes. It is therefore more suitable for applications requiring high copper recovery and fine ore size.

Summary: Development Trends in Copper Ore Separation Technology

Currently, copper ore separation technology is evolving towards "precise adaptation, high efficiency, low consumption, and environmentally friendly" approaches. Specifically, specialized leaching agents and process combinations (such as combined bioleaching and chemical leaching) are being developed for complex and difficult-to-separate copper ores (such as those containing arsenic and sulfur) to further improve copper recovery. Furthermore, intelligent transformation (such as real-time monitoring and automated control of pH and copper ion concentration during the leaching process) is being used to optimize process parameters and reduce labor costs and reagent consumption. In the future, with the integration of materials science and automation technologies, copper ore separation technology will more efficiently unlock low-grade, difficult-to-separate copper resources, providing technical support for the sustainable development of the copper industry.