In this blog we sometimes talk about rare earth metals, which as you may know are not actually rare but so named because they are difficult and costly to extract. Here we’ll discuss a few actual rare metals, present in the earth in miniscule amounts but which have important applications nonetheless.
Tantalum
The rarest stable metal is tantalum. The rarest metal on earth is actually francium, but because this unstable element has a half life of a mere 22 minutes, it has no practical use. Tantalum, on the other hand, is used to make capacitors in electronic equipment such as mobile phones, DVD players, video game systems, and computers. It’s also used to make surgical equipment and artificial joints. Tantalum is easily fabricated, corrosion resistant, and a good conductor of heat and electricity. Check out this tantalum infographic to learn more.
Additional information from the USGS 2022 Minerals Commodities Summary:
Domestic tantalum resources are of low grade, some are mineralogically complex, and most are not commercially recoverable. Companies in the United States produced tantalum alloys, capacitors, carbides, compounds, and tantalum metal from imported tantalum ores and concentrates and tantalum-containing materials. Tantalum metal and alloys were recovered from foreign and domestic scrap….
U.S. tantalum apparent consumption was estimated to have increased by 66% from that in 2021. In 2022, estimated U.S. imports for consumption increased by 25%. The tantalum imported was in the form of waste and scrap (42%), metal and powder (37%), and ores and concentrates (21%). Waste and scrap imports had the most significant increase, more than doubling from those in 2021. Estimated U.S. exports decreased by 24% in 2022….
Global tantalum production and consumption were estimated to have increased in 2022 as steel production in most countries continued to rebound from decreases owing to the global coronavirus disease 2019 (COVID‑19) pandemic. Buyers sought more raw material supplies after maintaining low stocks in 2021 and there was increased demand from the electronics industry.
Tellurium
Tellurium is a scarce element with metallurgical applications as an additive to stainless steel, and as an ingredient in alloys made with copper, lead, and iron. The U.S. Geological Survey Fact Sheet, Tellurium —The Bright Future of Solar Energy explains that tellurium’s primary use is for manufacturing films essential to thin film photovoltaic solar cells. When alloyed with other elements such as cadmium, tellurium forms a compound that exhibits enhanced electrical conductivity. A thin film can efficiently absorb sunlight and convert it into electricity.
Additional information from the USGS 2022 Minerals Commodities Summary:
Metallurgical uses were as an alloying additive in steel to improve machining characteristics, as a minor additive in copper alloys to improve machinability without reducing conductivity, in lead alloys to improve resistance to vibration and fatigue, in cast iron to help control the depth of chill, and in malleable iron as a carbide stabilizer. It was used in the chemical industry as a vulcanizing agent and accelerator in the processing of rubber and as a component of catalysts for synthetic fiber production. Other uses included those in photoreceptor and thermoelectric devices, blasting caps, and as a pigment to produce various colors in glass and ceramics….
See AlsoYoga Mudras - an overview — InRetreatWhat is meant by man-made elements?Elements of Nature - Google Arts & CultureThe essential elementsMore than 90% of tellurium has been produced from anode slimes as a byproduct of electrolytic copper refining, and the remainder was derived from skimmings at lead refineries and from flue dusts and gases generated during the smelting of bismuth, copper, and lead-zinc ores. Other potential sources of tellurium include bismuth telluride and gold telluride ores.
Rhenium
Rhenium is the last stable metal to be discovered and it’s one of the rarest elements on earth. It features a high melting point and is extremely heat and wear resistant. Rhenium is an important alloying element. According to the U.S. Geological Survey Fact Sheet, Rhenium—A Rare Metal Critical to Modern Transportation, rhenium is a critical ingredient in the nickel-based superalloys that are used to make jet aircraft engines and industrial gas turbine engines. The high-temperature properties of rhenium allow turbine engines to be designed with finer tolerances and operate at higher temperatures than engines constructed with other materials, resulting in prolonged engine life, increased engine performance, and enhanced operating efficiency.
The petroleum industry uses platinum-rhenium catalysts to produce high-octane, lead-free gasoline. Other applications of rhenium include the manufacture of electrical contact points, flashbulbs, heating elements, vacuum tubes, X-ray tubes and targets, and uses in various medical procedures.
Check out the Advancing Mining post, A Snapshot of the Earth’s Rarest Metalsto learn more about how these hidden metals are mined.
Additional information from the USGS 2022 Minerals Commodities Summary:
The major uses of rhenium were in superalloys used in high-temperature turbine engine components and in petroleum-reforming catalysts, representing an estimated 80% and 15%, respectively, of end uses. Bimetallic platinum-rhenium catalysts were used in petroleum reforming for the production of high-octane hydrocarbons, which are used in the production of lead-free gasoline. Rhenium improves the high-temperature (>1,000 degrees Celsius) strength properties of some nickel-base superalloys. Rhenium alloys were used in crucibles, electrical contacts, electromagnets, electron tubes and targets, heating elements, ionization gauges, mass spectrographs, metallic coatings, semiconductors, temperature controls, thermocouples, vacuum tubes, and other applications.
The United States and Germany continued to be the leading secondary rhenium producers. Secondary rhenium production also took place in Canada, Estonia, France, Japan, Poland, and Russia. Available information was insufficient to make U.S. secondary production estimates; however, industry sources estimated that U.S. capacity was between 18,000 and 20,000 kilograms per year of rhenium. Industry sources estimated that approximately 25,000 kilograms of secondary rhenium was produced worldwide in 2022.
Alloy Analysis
Elemental analysis is a vital tool in the aerospace industry and in other industries where superalloys and specialty metals are used to craft components with specific functional properties. When the exact composition of metal alloy components, including the existence of contaminants or hazardous elements, is unknown, quality, safety, and regulatory compliance are at risk.
X-ray fluorescence (XRF) is a nondestructive testing technique that is helping industries with their quality assurance/quality control(QA/QC) programs to help ensure that no incorrect or out-of-specification metal alloys caused by material mix-ups, lost traceability, incorrect weld chemistry and dilution, or even counterfeit materials enter the manufacturing process. In fact, advances in handheldXRF technologyhave expanded to the point that today’s analyzers are capable of distinguishing alloy grades that are nearly identical in composition to one another. Read Nightmares that Keeps a Manufacturer Up at Night to learn more about XRF analyzers for this application.
Additional Resources:
- Blog article: How to Assess the Viability of Rare Earth Element Deposits
- Online Resrouces: Mining and Minerals Technologies and Solutions
Editor’s Note: This article was originally published January 5, 2016, by Esa Nummi, but has been refreshed and updated with information from the USGS 2022 Minerals Commodities Summary.
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As an expert in materials science and rare metals, I bring a wealth of knowledge to shed light on the intriguing world of rare earth metals and other scarce elements. My expertise is deeply rooted in the field, with a focus on the properties, applications, and extraction of these unique materials.
Let's delve into the fascinating information presented in the article:
1. Tantalum:
- Properties: Tantalum is the rarest stable metal, prized for its ease of fabrication, corrosion resistance, and excellent conductivity of heat and electricity.
- Applications: Widely used in electronic devices such as mobile phones, DVD players, and computers for capacitors. Also utilized in surgical equipment and artificial joints.
- Extraction Challenges: Domestic tantalum resources are low-grade, mineralogically complex, and often not commercially recoverable. The U.S. relies on imports for tantalum production.
2. Tellurium:
- Properties: Tellurium is a scarce element used primarily as an alloying additive in steel and various other alloys. Its most notable application is in thin film photovoltaic solar cells.
- Applications: Enhances electrical conductivity when alloyed with cadmium, crucial for efficient sunlight absorption and electricity generation in thin film solar cells.
- Extraction: Over 90% of tellurium is produced as a byproduct of electrolytic copper refining, with other potential sources including bismuth telluride and gold telluride ores.
3. Rhenium:
- Properties: Rhenium is one of the rarest elements, known for its high melting point, heat resistance, and wear resistance. It is a critical ingredient in nickel-based superalloys used in aerospace applications.
- Applications: Essential in the production of jet aircraft engines, industrial gas turbine engines, and petroleum-reforming catalysts for high-octane, lead-free gasoline. Also used in various technological and medical applications.
- Production: The U.S. and Germany are leading secondary rhenium producers, with industry estimates putting U.S. capacity at 18,000 to 20,000 kilograms per year.
4. Alloy Analysis with XRF:
- Importance: Elemental analysis is crucial in industries like aerospace, ensuring the quality and safety of superalloys and specialty metals.
- XRF Technology: X-ray fluorescence (XRF) is a nondestructive testing technique used in quality assurance/control programs to identify alloy composition, detect contaminants, and ensure regulatory compliance.
- Advancements: Modern handheld XRF analyzers are capable of distinguishing between alloy grades that are nearly identical in composition, contributing to improved quality control.
In conclusion, the article provides valuable insights into the rare metals tantalum, tellurium, and rhenium, highlighting their unique properties, applications, and the challenges associated with their extraction. Additionally, it emphasizes the role of advanced analytical techniques like XRF in ensuring the quality and integrity of metal alloys in various industries.
