Platinum group

The platinum-group metals, or PGMs, are a cluster of six precious metallic elements. These elements are transition metals located in the d-block of the periodic table. Specifically, they occupy groups 8, 9, and 10 across periods 5 and 6. The six metals are ruthenium, rhodium, palladium, osmium, iridium, and platinum. They are known as noble metals because they share similar physical and chemical properties. Because of these similarities, they often occur together in the same mineral deposits.

Scientists categorize these metals into two distinct subgroups based on their geological behavior. The first is the iridium-group platinum-group elements, or IPGEs. This group consists of osmium, iridium, and ruthenium. The second subgroup is the palladium-group platinum-group elements, known as PPGEs. This group includes rhodium, platinum, and palladium. Interestingly, the three elements located directly above the platinum group are iron, nickel, and cobalt. These three, along with the lanthanide gadolinium, are the only transition metals that show ferromagnetism near room temperature.

These metals are highly valued for their catalytic properties. A catalyst is a substance that helps a chemical reaction occur more easily. In the automotive industry, vehicle exhaust catalysts (VECs) use solid platinum, palladium, and rhodium. These are installed in exhaust systems to reduce harmful emissions. For example, they convert carbon monoxide (CO) into less harmful gases. Beyond cars, PGMs have many diverse applications. They are used in electronics, dentistry, and the production of anticancer drugs.

Platinum is also prized in fine jewelry because it is resistant to wear and tarnish. It possesses high mechanical strength, excellent high-temperature characteristics, and stable electrical properties.

Human history with these metals spans centuries. Pre-Columbian Americans used platinum and platinum-rich alloys long before European contact. The first European reference to platinum appeared in 1557. An Italian humanist named Julius Caesar Scaliger described a mysterious metal found in Central American mines. He noted that it was impossible to melt using Spanish methods of that time. The name "platinum" comes from the Spanish word "platina," meaning "little silver." Spanish settlers in Colombia used this name because they viewed the metal as an unwanted impurity in silver. Later, in 1815, rhodium and palladium were discovered by William Hyde Wollaston. His collaborator, Smithson Tennant, discovered iridium and osmium around the same time.

Extracting these metals is a complex and difficult process. Because they are often found in very low concentrations, they are frequently recovered as by-products. For instance, platinum is produced commercially during the processing of nickel ore. Even though platinum may only make up two parts per million of the ore, the massive volume of nickel processed makes recovery profitable.

Purification often begins with the anode residues from gold, copper, or nickel production. This is a very energy-intensive process. Classical methods use differences in chemical reactivity and solubility to separate the metals. Modern technology has moved toward using solvent extraction. To separate them, a sample might be dissolved in aqua regia to produce chloride complexes. These are then turned into specific compounds like volatile osmium tetroxide (OsO4) or ruthenium tetroxide (RuO4).

Geologically, these metals are found in specific environments. They are most common in mafic and ultramafic igneous rocks. These rocks have high concentrations of platinum-group elements, whereas granites have low amounts. The Bushveld Complex in South Africa is a major source, as its mafic layered intrusions outweigh all other geological settings. South Africa is the world's largest producer of platinum, followed by Russia. Other significant producers include Canada, Zimbabwe, and the United States. Rhodium is particularly rare; in 2003, the total annual world production was only 7 or 8 tons.

While these metals are useful, they also present environmental and health challenges. Mining can cause significant damage, such as the acidic water drainage and environmental degradation seen in Zimbabwe. There is also the concern of bioaccumulation. This occurs when metals like platinum enter water sources and soil, eventually moving up the food chain into animals and humans. Additionally, workers in industrial catalyst production may face health risks. Exposure to certain platinum salts can lead to allergic reactions, including dermatitis and asthma. As global demand for these metals rises, researchers continue to study how to manage these environmental impacts.