Rare earth elements are most simply defined as those chemical elements ranging in atomic numbers between 57 and 71 and include lanthanum, from which rare earth metals get their collective name of lanthanides and range through to lutetium with an atomic number of 71. Yttrium (atomic number of 39) due to its chemical similarity to lanthanides (it is placed as a transition metal on the periodic table) is commonly found in rare earth deposits and is generally classed as a heavy rare earth metal.
Light rare earths make up the first seven elements of the lanthanide series (atomic number 57-62) and include lanthanum one of the more reactive of the rare-earth metals, cerium the most abundant of the rare earth metals, praseodymium, neodymium, promethium (not found naturally) and samarium.
Heavy rare earths are typically more valuable relative to light rare earths and have a higher atomic number ranging from 63-71. Heavy rare earths include europium (which together with terbium is the most valuable rare earth valued at US $600-700 per kilo at today’s prices) gadolinium, terbium dysprosium, holmium, erbium, thulium, ytterbium and lutetium.
The rare earths range in crustal abundance from cerium, the most abundant at 60 parts per million, which is more abundant than nickel, to thulium and lutetium which are the least abundant rare earth elements at about 0.5 parts per million.
Other metals are also often found associated with rare earth deposits and these include uranium, thorium, beryllium, niobium, tantalum and zirconium.
Most rare earth deposits that are mined will comprise a complex mix of oxides that will include monazite, allanite, bastnasite and cerite which are the main rare earth minerals. These minerals then require complicated techniques to separate and to refine the metals from the oxides. The rare earth oxides are then sold at an individually negotiated contract as there is no central clearing or pricing facility for rare earth metals or oxides.
Estimated demand for Rare Earths by element in 2012
Source: Roskill (presentation dated August 2012, titled: "Global Demand for Rare Earths")
Rare earth metals are used in a variety of modern technologies with applications in the military, medical, scientific, aerospace and consumer sectors plus in the increasingly important "green" sector. For many of their applications there is currently no known appropriate substitute. The use of rare earths as magnets in electrical motors is likely to become the major driver for growth for the whole rare earths industry and this use together with phosphors will soon make up over 65% of rare earth oxides (by value) consumed. The main uses of rare earths are the following:
Rare-earth alloy magnets are very powerful permanent magnets which are particularly useful in the automotive and wind power generation industries due to their light weight compared to magnetic strength. In addition these magnets are also used in computer disc drives plus in mobile phones, IPods, etc. The key rare earth metals used in magnets are neodymium, praseodymium and dysprosium.
A traditional use of rare earths is to provide colour phosphors in televisions and more recently in cathode ray tubes, plasma screens and liquid crystal displays with europium, terbium and yttrium being able to emit red, green and white light respectively
The main battery use is in nickel metal hydride batteries (NiMH) that have a large component of lanthanum and cerium due to their hydrogen storage properties. Hybrid electric vehicles represent more than half the usage of NiMH batteries with these hybrid vehicles combining a conventional internal combustion engine propulsion system with an electric propulsion system.
Another traditional use is as a polishing powder used in the manufacture of television and computer screens and in the production of precision optical and electronic components.
Fluid Catalytic Cracking
Rare earths, particularly lanthanum, are used in oil refining in a process called Fluid Catalytic Cracking catalysts.
Cerium is often used in gasoline autocatalysts as it improves vehicle performance, increases thermal stability, extends durability and will also reduce precious metals consumption.
Other uses of these metals that have an increasingly wide range of applications include metallurgical alloying agents, within the nuclear industry as control rods and in shielding, as energy efficient low temperature fluorescent lamps and within fiber-optic cables.