REEs are separated?NO!>>>>>On May 10th, 2011, posted in: Kidela Capital Group by Kidela
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Rare Earth ProcessingCell phones, iPods, LCD screens, hybrid cars – just some of the many devices containing Rare Earths, that we’ve come to rely on in this green, information age. While there’s a growing awareness of the importance of Rare Earths (REs) in these new technologies, the same can’t be said for the illusive question of just how Rare Earth Elements (REEs) end up in these products.
Mining REs is relatively simple – but producing individual elements from the ore is tremendously difficult. Rare Earth processing often requires dozens of procedures – each resulting in minute changes in the complex RE stream. Separating and extracting a single Rare Earth Element– especially one of the Heavy Rare Earths – takes a great deal of time, effort and expertise. Not to mention money – processing facilities cost hundreds of millions of dollars to build.
It’s something to think about, next time you text a friend or take your Prius out for a spin. But wrapping one’s head around the vast array of separation and extraction techniques for REEs, is far easier said than done. It’s terribly complex, and there just isn’t much information out there. For your benefit, here’s a basic primer on RE processing.
Milling
After rocks containing REEs are removed from the ground, they go to a facility where the valuable mineral material in the ore is separated from impurities. This process is known as milling or beneficiation. Here’s how it works:
The mined ore is crushed into gravel, which in turn is ground up into progressively smaller particles. These particles are sifted and sorted by such means as flotation and electromagnetic separation to extract usable material and set the waste products – called tailings – aside. This milling process is usually carried at or near the mine site, with the tailings stored in special facilities built to rigorous engineering and environmental standards.
For scarce resources like Heavy Rare Earths, this beneficiation process could be considered critical, “because it takes advantage of every scrap of material available. This practice can also make a marginal mining facility more practical than it might otherwise be, and may in fact be used to extract ore from a facility previously believed to be exhausted.”1
Electromagnetic Separation
This milling method uses magnetic principals to separate Rare Earth bearing minerals from other materials in the mined ore. Monazite – along with bastnaesite, the primary commercial source of REs mined around the world – is highly magnetic, meaning it can be separated from non-magnetic impurities in the ore through repeated electromagnetic separation.
This technique uses a magnetic separator device that consists of a belt moving on two rollers, one of which contains strong magnets. When powdered ore is dropped onto the belt, magnetic and non-magnetic particles within the ore will fall away differently from the magnetic roller as this diagram illustrates.
Flotation Process
This is another beneficiation method that’s used to separate bastnaesite from other minerals. First, the ore is ground into a fine powder and added to liquids in flotation tanks. Chemicals are added to cause impurities to settle out, and air is pumped in to create air bubbles. The finer bastnaesite particles stick to the bubbles, which rise to the top and form a froth that is then skimmed off.2 The following diagram shows how this works:
Gravity Concentration
Although they are commonly used in the gold industry, devices called Falcon Concentrators are also used in Rare Earth extraction at the milling stage. These concentrators contain rotating cones or bowls that are spun at high speed to generate a gravitational or centrifugal force, which acts to separate small particles by exploiting minute differences in density and specific gravity between the valuable minerals and waste products. Compared to other beneficiation technologies, gravitational separation offers lower installed and operating costs. It also tends to also have less environmental impact as gravity concentration does not require the use of chemicals.3
All of these milling processes produce mineral concentrates that contain a substantially higher proportion of REs. But there’s still much work to be done to separate the concentrate into its constituent REEs, and this is why things start to get really tricky.
Hydrometallurgy
As the generations of scientists who have tackled the problem can attest, isolating REs safely and effectively is not only a very long and costly exercise, but extremely complicated. The complex separation and extraction techniques in use today, like ion exchange and solvent extraction, are rooted in of a branch of geologic science known as hydrometallurgy.
In hydrometallurgy, mineral concentrates are separated into usable oxides and metals through liquid processes, including leaching, extraction, and precipitation. By these means, the elements are dissolved and purified into leach solutions. The RE metal or one of its pure compounds (such as an oxide) is then precipitated from the leach solution by chemical or electrolytic means.
Although hydrometallurgy originated in the 16th century, its principal development took place in the 20th century. The development of ion exchange, solvent extraction, and other processes now permits more than 70 metallic elements to be produced by hydro metallurgy, including the REEs.4 Here is a run-down on some of these techniques.
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