PDF EXTRACTION & PURIFICATION OF RARE EARTH ELEMENT - Universiti Malaysia Sabah

EXTRACTION & PURIFICATION OF RARE EARTH ELEMENT

NURUL HASNI BINTI MD NOR

NOOR QHADRUNNADIA BINTI LUKHMAN

MUHAMMAD NUR RASHIDI BIN ROSLI

What is rare earth?

Discovery & History of rare earth

Rare earth element

Lynas Corporation's Rare Earth Extraction Plant in Gebeng, Malaysia

Extraction Purification

refferences

W HAT IS RARE EARTH ?



The term "rare earth" is the English

translation of French terre rare ( terre refers to an oxyde). It arises from the rare earth

minerals from which they were first isolated, which were uncommon oxide-type minerals

(earths) found in Gadolinite extracted from one mine.



The rare earth are not called rare because they’re truly rare. They’re called rare because it’s very difficult to isolate these elements

individually and it takes a lot of skill to do

that.

D ^ISCOVERY & H ISTORY OF RARE

EARTH

D ^ISCOVERY & H ISTORY OF RARE EARTH



The exact number of rare earth elements was unclear and a maximum number of 25 was estimated.



The use of x-ray spectra (obtained by diffraction in crystals) of Henry Moseley made it possible to

determine the atomic numbers.



In the 1940s Frank Spedding developed an ion

exchange procedure for separating and purifying

the rare earth elements.

CHARACTERISTIC



Rare earths are characterized by :

➢

high density,

➢

high melting point,

➢

high conductivity and

➢

high thermal conductance.



Several rare-earth minerals contain thorium and uranium in variable amounts, but thorium and

uranium do not constitute essential components in the

composition of the minerals.

T ^YPES R ARE EARTH ELEMENT

Z Symb ol

Name Usage

21 Sc Scandium Aluminum-scandium alloy

39 Y Yttrium YAG garnet, YBCO high-temperature superconductors

57 La Lanthanu

m

High refractive index glass, flint,

hydrogen storage, battery-electrodes, camera lenses

58 Ce Cerium Chemical oxidizing agent, polishing powder, yellow colors in glass and ceramics, catalyst for self-cleaning ovens, etc.

T ^YPES R ARE EARTH ELEMENT

Z Symbol Name Usage

59 Pr Praseodymium Rare-earth magnets, lasers, green colors in glass and ceramics, flint

60 Nd Neodymium Rare-earth magnets, lasers, violet colors in glass and

ceramics, ceramic capacitors 61 Pm Promethium Nuclear batteries

62 Sm Samarium Rare-earth magnets, lasers, neutron capture, masers

T ^YPES R ARE EARTH ELEMENT

Z Symbol Name Usage

63 Eu Europium Red and blue phosphors, lasers, mercury-vapor lamps

64 Gd Gadolinium Rare-earth magnets, high

refractive index glass or garnets, lasers, x-ray tubes, computer

memories, neutron capture 65 Tb Terbium Green phosphors, lasers,

fluorescent lamps

66 Dy Dysprosium Rare-earth magnets, lasers

L IGHT RARE EARTH

Lanthanum (La) Cerium (Ce)

Praseodymium (Pr) Neodymium (Nd)

Samarium (Sm)

H EAVY RARE EARTH

Europium (Eu) Gadolinium (Gd)

Terbium (Tb) Dysprosium (Dy)

Holmium (Ho) Erbium (Er) Thulium (Tm) Ytterbium (Yb)

Lutetium (Lu)

Yttrium (Y)

L

^YNAS

C

^ORPORATION

'

^S

R

^ARE

E

^ARTH

E

^XTRACTION

P

^{LANT IN}

G

^EBENG

, M

^ALAYSIA

 Australia's Lynas Corporation is building the world's

largest rare earth extraction plant at Gebeng near the city of Kuantan in Malaysia. The planned capacity is 22,000 tonnes per annum.

 Lynas attempts to promote the view that the plant would be beneficial to the Malaysian economy as it would be

dealing with rare earths – essential elements used in high technology manufacturing and also in "green" technology such as wind turbines used to generate electricity.

EXTRACTION

Extraction process REE is done after the concentration of REE

bearing minerals. In this process, the REE will be

extracted from the concentrate.

Solvent extraction Liquid Emulsion Membranes

Extraction

S ^OLVENT E ^XTRACTION



Liquid-liquid solvent extractions are often performed to separate a mixture of rare earths from each other,



i.e., tributyl phosphate, which selectively extracts one rare earth from the others.



Several stages of extractions are needed to separate each rare earth metal.



Example extractants are shown in the next slide.

Commercially used extractants for rare earth separation (Thakur 2010)

 The process uses: chemical agents

 to break down the components within a substance.

 Those materials which:

 more soluble or

 react more readily to a particular acid or base

➢ get separated from the rest.

 The separated materials are then removed

 the process begins all over again with the introduction of more chemicals to leach out more components.

 When it comes to Rare Earths,

 these steps need to be repeated and again

 depending on which REE are trying to produce.

The solvent extraction method used today to separate REEs relies on the slightly different solubilities of rare earth compounds between two liquids

that do not dissolve in each other (in essence, oil and water).

For example, one process has bastnaesite repeatedly treated with hot sulphuric acid to create water-soluble sulphates.

•More chemicals are added to neutralize acids and remove various elements like thorium.

•The mineral solution is treated with ammonium to convert the REEs into insoluble oxides.

Another chemical technique for separating monazite into RE compounds is called alkaline opening.

•This process uses a hot sodium hydroxide solution that makes thorium precipitate out as a phosphate.

•The remaining mixture of thorium and lanthanides (REEs) is further broken down when treated with a hydrochloric acid that creates a

•liquid solution of lanthanide chlorides

•and a sludge made up of thorium hydroxide.

•One advantage solvent extraction has is that it can be continuous

• a counter-current system can be employed in which the many, many extraction steps are carried out in a continuous stream, progressively increasing the degree of separation until the substance in one phase in nearly pure.

Advantage

•The time required for solvent extraction can vary widely;

• it can be very lengthy in some cases where materials need to be allowed to mix and sit for a time for the components to separate out.

•many of the chemicals used as well as some by-products of solvent extraction are extremely hazardous and must be handled (and disposed of) with great care.

Disadvantages

L ^IQUID E ^MULSION M ^EMBRANES E ^XTRACTION



In liquid emulsion membrane (LEM) extraction a stable emulsion between two immiscible phases is first formed,

then the emulsion is dispersed into a third continuous phase by agitation.



The organic membrane phase consists of an:

 organic solvent that contains an extracting agent and an emulsifier,

 the internal aqueous phase (droples) contains a stripping agent

 and the external continuous phase is the aqueous feed solution containing the species to be extracted.



The target species can then be recovered from the aqueous feed into the organic phase and then stripped into aqueous droplets in the emulsion.



The emulsion is broken by typically electrostatic coalescence

and then the target species can be recovered by for example

electrowinning or precipitation. (Hasan et al, 2009)

LEM over LLE

provides a much larger interfacial

area than conventional

liquid-liquid extraction

it carries out the extraction and

stripping operations in one

step.

It can reduce the amount of expensive extractant about 10 times (Hanapi

et al. 2006).

are high selectivity and

simple.



The technique is not fully developed, and more

research is needed before large scale and widespread application in industry can occur.



The main problem associated with the LEM process is emulsion stability.



Another problem is osmotic swelling, which occurs when water in the external phase diffuses through the organic membrane phase and swells in the

internal aqueous phase.



The internal phase is being diluted and the

increased volume of the internal phase leads to an increased breakage of the droplets (Hanapi et al., 2006).



Many metal ions have been reported to be

successfully extracted by liquid emulsion membrane extraction such as



Pd, Cu, Cr(VI), Th, U, Co, In, Ni, Ag and Mo (Hasan

et al., 2009, Yadav and Mahajani, 2007).

P URIFICATION

 The rare earth elements have a history of intriguing scientist with their rich variety of physical properties.

 Early attempts to investigate these properties were hampered, however, by a lack of suitably pure samples, for it soon come to be realized that the intrinsic properties of these notoriously reactive metals could only be measured if their typical impurity levels

were significantly reduced

 for the past few decades, purification and property measurement have gone hand in hand, a process that is still not complete, as is regularly demonstrated by the discovery of new phenomena as higher purity samples are produced

purification method

Vacuum melting

Zone refining

Vapor technique Solid State

Electro- transport

(SSE)



Since the aim of preparing very high purity metal is normally to perform some sort of experiment, rather than purification, consideration is also given to sample preparation and crystal growth, for these operations generally take place alongside the purification and can sometimes be combined with it



The choice of purification technique for a rare earth

metal will depend upon the species of impurities to be

removed and the properties of the rare earth element

itself

properties relevance of purification to

Vapour pressure

Melting point

Crystal structure

Transformation temperatures

density

V ACUUM MELTING AND DEGASSING

 Many rare earth are vacuum melted as part of their preparation, but improvements in purity can often be made by re-melting

using a better vacuum, and possibly at a higher temperature

 Residual fluoride and certain other volatile impurities can be removed by melting of rare earth at 500-1000 °C above their melting points, where vapor pressures permit.

 To reach such temperatures, a hot crucible will probably be

necessary; the favored crucible material is tungsten, since this is less soluble in liquid rare earth than tantalum.

Z ONE REFINING

 When zone refining the rare earth, it is essential that the

environment within the refining system is sufficiently clean to

prevent degradation of the sample during its supposed purification.

 Early zone refining of rare earth using high vacuum, rather than UHV-rated apparatus, successfully moved many metallic impurities, but any potential for purification with respect to interstitial

impurities was negated by contamination

 During zone refining, any one part the sample spends a significant amount of time at or close to its melting point, so zone refining in UHV is only possible with the lower-vapor-pressure rare earths.

V APOR TECHNIQUES



The essence of vapor technique is that the metal to be

purified is heated in a container under vacuum conditions and vapor from it is collected by condensation on to a cooler surface



Impurities with lower vapor pressures than the host metal will tend to remain in the container, leaving the condensed metal of enhanced purity; thus, vapor technique are most effective with the higher-vapor-pressure metals.



2 main technique-sublimation and distillation

S ^OLID S ^TATE E ^LECTRO - ^TRANSPORT

 Based upon the electrostatic force between ions in the metal and the applied electric field, it was subsequently realized that the

momentum transfer that occurs when current carriers collide with ions is an important factor

 The force exerted on the ions by the current carriers is commonly called the “electron drag force” or “electron wind”

 The actual rate and direction of migration of an ion during SSE is determined by the balance of the drag and electrostatic forces on the ion

 Thus, electro-transport force vary in magnitude and direction

according to the species of host and impurity atoms, meaning that in any host it is possible for different impurities to migrate at different velocities in different directions.

REFFERENCES

 Kai-Lit Phua^1*, Saraswati S. Velu^1, Lynas Corporation's Rare Earth Extraction Plant in Gebeng, Malaysia, 2012, licensee Herbert

Publications Ltd.

 Yoshio Waseda, Minoru Isshiki. Purification Process and

Characterization of Ultra High Purity Metals: Application of Basic Science to Metallurgical Processing. Springer, Oct 9, 2001

 Hanapi Bin Mat, Norasikin Binti Othman, Chan Kit Hie, Chiong Tung, Hii King Hung, Ng Kok Sum, Selective emulsion liquid membrane extraction of silver from liquid photographic waste

industries, report, Department of Chemical Engineering Faculty of Chemical and Natural Resources Engineering Universiti Teknologi Malaysia