Mineral Processing and Extractive Metallurgy
Mineral processing and extractive metallurgy are at the heart of many industrial processes, from the extraction of ore to the production of the final product. This means the engineering that is involved in processing ores, concentrates, and finished products must be a precise and specialized process. There are many types of processes employed in mineral processing, such as crushing, grinding, screening, leaching, flotation, thickening and filtration.
At the heart of all mineral processing operations is the need to separate valuable minerals from the host rock, known as ore. Ore must be crushed and screened to the appropriate size before it can be processed, and the desired concentrate is obtained from the ore through a variety of methods such as leaching, flotation and gravity separation. In some cases, the ore can be separated into two main groups known as the valuable fraction, which contains the minerals with economic value, and the reject fraction, which contains unwanted impurities.
Crushing is the process of reducing the size of the ore particles, typically by a combination of compression, impact and attrition. The aim of this process is to reduce the size of the ore to a size that is suitable for grinding, while also reducing the amount of undesirable material in the ore. The size of ore crushed by crushers is further reduced by the use of grinding, which uses a variety of tools such as mills, autogenous grinders and crushers, to break down the ore into smaller pieces.
Screening is used to separate large particles from the smaller particles of the ore. This is done by passing the ore through a series of screens with varying mesh sizes. The screen separates the ore into two fractions according to particle size. The smaller particles are then sent to the grinding stage, while the larger particles are sent to the next processing stage in the circuit or discarded as waste.
Once the ore is suitably crushed and screened, further processing depends largely on the mineral being processed. In the case of metallic ores, leaching processes can be used to remove the metal from the feed ore, while in the case of industrial minerals, flotation and gravity separation are the main separation techniques employed.
During leaching, a solution is used to extract metal compounds from the ore in a chemical reaction. The metal compound goes into solution, while the remaining ore has to be removed and deposited in a waste heap. In flotation processes, a solution is used to separate minerals from gangue, which is the unwanted part of the ore. The ore is mixed with a special solution, usually containing a surfactant, or a chemical that reduces the surface tension of the water to help separate the minerals from the waste. This process is also used in the production of coal, where coal particles are separated from ash.
In gravity separation processes, a difference in the density of the ore and gangue determines which material is separated. Gravity concentrators use gravity to separate heavy minerals from lighter particles. The process works by adding water to the ore mixture, along with a dense reagent that causes the heavier minerals to sink. The lighter particles are then removed and a concentrate is produced.
Finally, thickening and filtration allow the concentrate to be purified. In thickening, the solids are allowed to settle and some of the liquid is removed. The remaining liquid is then subjected to filtration, where the water is separated from the solid particles that form the concentrate.
Mineral processing and extractive metallurgy are both complex and precise technology-based fields that require the expertise of engineers with a specialized knowledge. A number of technologies are used to ensure the end product is produced to the highest quality, including crushing, grinding, screening, leaching, flotation, thickening, and filtration. By leveraging these techniques, minerals can be efficiently, safely and economically extracted from ore.
