EN
Ore leaching
The process of leaching is the transfer of ore into a solution of one or more components (usually an aqueous solution) of a solid material. Leaching plays a key role in flotation processes based on the use of particle friction forces, sedimentation of denser particles, etc., since these processes occur in liquid solutions.
Leaching is quite widely used in the production of uranium, gold, copper, zinc, molybdenum, tungsten, aluminum and other elements. If required by further enrichment processes as well as the leaching process itself, the ore is subjected to grinding and crushing at the preliminary stages.
Leaching is often carried out using aqueous solutions of inorganic acids (sulfuric, hydrochloric, nitric) or alkalis (caustic soda, ammonia), as well as salts (ammonium, cyanides, etc.). It is easy to guess that the solvent is selected based on the properties of the ore, the presence of certain elements in it, as well as the requirements for the final product. The leaching stages are, in most cases, accompanied by the presence of three processes:
- Complex formation (during gold cyanidation or during the treatment of nickel sulfides with ammonia solutions).
- Exchange reaction (during leaching of oxides and carbonates with acidic solutions)
- Redox reaction (leaching of electronegative metals with acids)
And also divided into three stages: first, reactants are supplied to the solid surface, then chemical reactions occur, after which the soluble reaction products are removed into the solution. To accelerate the rate of obtaining homogeneous solutions, containers equipped with mechanical, pneumatic or pneumomechanical mixing devices (various mixers and airlifts) are used.
Leaching is used not only to prepare ore for further enrichment processes, but also to extract ore located in the bowels of the earth. This technology is called in-situ leaching (ISL) . When using this method, the ore remains in place and liquids are pumped through it to leach minerals from the ore. However, not every deposit can be developed in this way, since the ore body must be permeable to the liquids used, that is, not prevent it from passing through the ground rock, and the ore body must also be located so that the liquids do not pollute the groundwater located far from the ore body.
This method was developed independently in the USSR and the USA in the mid-1970s, and at the first stages was used to extract uranium from roll-type deposits. The leaching process itself in this method, namely the choice of solvents, is determined by the geological features of the rock occurrence, for example, if there is a significant amount of calcium in the ore zone, alkaline (carbonate) leaching should be used. Today, the ISL technology is quite well developed and has a number of advantages in the development of deposits, as it is a controlled, safe and environmentally acceptable method of extraction.
This method is widely used in uranium mining in Kazakhstan and Australia, using leaching with alkaline leaching agents such as sodium bicarbonate or carbon dioxide.
