Platinum, a rare and valuable metal, is used in automotive, jewelry, and electronics. Its properties, like corrosion resistance and a high melting point, contribute to its wide applications. Extracting platinum from the Earth is a complex process, requiring specialized geological understanding and advanced technology. This article details the methods employed to bring platinum to the surface and prepare it for its diverse uses.
Where Platinum is Found
Platinum deposits occur in mafic and ultramafic igneous rocks, rich in magnesium and low in silica. These rocks are found in ancient continental crust or ophiolite complexes. Platinum is often associated with other platinum group metals (PGMs) like palladium, rhodium, iridium, osmium, and ruthenium, and with sulfides of nickel and copper. While native platinum can be found, it is generally part of an ore, meaning it is mixed with other minerals.
Most platinum reserves are in a few regions. South Africa accounts for over 70% of the world’s supply, with deposits in the Bushveld Igneous Complex, which includes the Merensky Reef, UG2 Reef, and Platreef. Other substantial sources include the Norilsk-Talnakh region in Russia, the Stillwater Complex in Montana, USA, and the Great Dyke in Zimbabwe. These geological settings provide the necessary conditions for the formation and concentration of platinum-bearing minerals.
Extracting Platinum from the Earth
Platinum extraction begins with exploration to identify viable deposits. This initial phase involves geological mapping, geophysical surveys, and geochemical sampling to pinpoint areas with potential platinum mineralization. Once a promising site is identified, mining operations commence, primarily utilizing two distinct methods depending on the depth and characteristics of the ore body.
Underground mining is the predominant method for platinum extraction, especially for deeper deposits that form long, thin “reefs” within the Earth. Techniques such as mechanized mining, cut-and-fill mining, room-and-pillar, or narrow vein stoping are employed. Miners drill holes into the rock, pack them with explosives, and then blast the ore into smaller pieces. The broken rock is subsequently collected using equipment like load-haul-dump (LHD) vehicles and transported to the surface for further processing.
For shallower, larger deposits, open-pit mining may be used, though it is less common for platinum due to the typical geological occurrence of the metal. This method involves removing layers of overburden, the soil and rock covering the ore, to access the deposit. Blasting is also a common practice in open-pit operations to break up the ore. The choice between these methods depends on factors such as the depth, shape, and size of the platinum deposit.
Processing Platinum Ore
Once extracted, platinum ore undergoes a multi-stage processing sequence to separate the valuable metal from waste rock.
Crushing and Grinding
The initial step involves crushing and grinding the ore into a fine powder. This mechanical reduction liberates the platinum-bearing minerals from the surrounding gangue, which is the non-valuable material.
Flotation
Following size reduction, the fine ore material is subjected to flotation, a common beneficiation technique. In this process, the crushed ore is mixed with water and chemical reagents that selectively attach to the platinum particles, making their surfaces hydrophobic. Air bubbles are then introduced into the mixture, adhering to the treated platinum particles and carrying them to the surface to form a froth. This platinum-rich froth is skimmed off, dried, and forms a concentrate containing platinum group metals.
Smelting and Refining
The concentrate then proceeds to smelting, where it is heated to extremely high temperatures, often around 1,500 degrees Celsius. This intense heat melts the concentrate, separating the metals from many impurities, forming a molten “matte” that is rich in PGMs, nickel, and copper. Air is often blown over the matte to eliminate unwanted elements like iron and sulfur.
The final stage is refining, a complex purification process that isolates pure platinum from other PGMs and remaining base metals. This can involve hydrometallurgical methods, such as dissolving the material in aqua regia (a mixture of hydrochloric and nitric acids), followed by precipitation and filtration. Electrolysis or solvent extraction methods may also be used to achieve high purity levels, often exceeding 99.5%.
Challenges and Environmental Impact
Platinum mining presents operational challenges, primarily due to the metal’s rarity and the geological complexity of its deposits. The process is capital-intensive, requiring specialized equipment and substantial energy consumption. Labor costs are also a major expense, particularly in South Africa where many operations are labor-intensive. The low yield of platinum from ore, where it can take 7 to 12 tons of ore to produce a single troy ounce of pure platinum, further adds to the cost and complexity.
The environmental footprint of platinum mining and processing is considerable.
Land and Water Impacts
Land disturbance and habitat destruction are direct consequences of both underground and open-pit mining activities. Water usage is substantial, with platinum group metal production being among the most water-demanding processes in the mining sector. This includes water consumed through evaporation from processing plants and tailings storage facilities. There is also a risk of water contamination from the release of chemicals like cyanide and sulfuric acid used in processing, which can negatively impact aquatic ecosystems.
Waste and Air Pollution
Waste generation is another significant concern, with large volumes of tailings, fine rock, and chemical residues often deposited in dams. These tailings dams pose risks of dust generation and potential water pollution. Air pollution is also a factor, as the extraction and processing of platinum can release harmful pollutants such as sulfur dioxide, nitrogen oxides, and particulate matter. The energy-intensive nature of mining, concentrating, and smelting contributes to greenhouse gas emissions. While efforts are made to mitigate these impacts through regulations, cleaner technologies, and wastewater treatment, the industry continues to navigate these complex environmental considerations.