Modules 4+5

Question 1

which is the only Ln not to occur naturally

Answer 1

Pm

Question 2

in what state are the Ln elements found

Answer 2

In ore

all found together

Question 3

what are the 4 common ores

Answer 3

monazite
xenotime
bastnaesite
rare earth laterites

Question 4

give details about monazite

Answer 4

LnPO4
9 coord
contains thorium
mostly early Ln

Question 5

give details about bastnaesite

Answer 5

LnCO3F
9 coord
mostly early Ln

Question 6

give details about xenotime

Answer 6

LnPO4
8 coord
mostly late Ln

Question 7

give details about rare earth laterites

Answer 7

rich in late Ln

Question 8

why do monazite and bastnaesite favour early Ln

Answer 8

9 coord - favour large ions

Question 9

why did US ramp up production in early 2010s

Answer 9

china had a near monopoly on rare earths

Question 10

what are 4 main applications of rare earths

Answer 10

magnets
alloys
polishing powders
catalysts

Question 11

which are the 3 elements with the most applications

Answer 11

La, Ce, Nd

Question 12

what are the 2 key factors leading to supply problems

Answer 12

growth in consumption

china introducing quotas

Question 13

what is the process for extracting bastnaesite

Answer 13

LnCO3F roast -> LnOF + CO2 Ce(III) ox. to Ce(IV)

Aq. HCl -> LnCl3(aq) + Ce(IV) residue

Question 14

what is the process for extracting monazite

Answer 14

LnPO4 + NaOH —>
Ln(OH)3 +Th(OH)4
HCl/HNO3 —–>
LnCl3/Ln(NO3)3 + Th(IV) residue

Question 15

what is the next step after extraction of Ln ore

Answer 15

separation

Question 16

what happens in separation by redox

Answer 16

oxidation -> Ce(IV)—-hydrolyse –> Ce(OH)4

reduction -Zn->Eu2+—-SO42—–> EuSO4

Question 17

what are the 2 methods of further separation beyond redox

Answer 17

classical methods

fractional crystallation

Question 18

what happens in fractional crystalisation

Answer 18

Ln(NO3)3.2NH4NO3.4H2O

solubility varies with Ln3+ radius

Question 19

how does ion exchange chromatography work

Answer 19

cationic resin has different affinities for different ions

Question 20

how do affinities of the ion exchange resin change across the series

Answer 20

resin has greater affinity for larger ions (early)

- smaller ions eluted first

Question 21

how are ions processes after ion exchange chromatography

Answer 21

Ln(HEDTA) —C2O42—>Ln(C2O4)3 ——> Ln2O3

Question 22

what is the reaction that takes place in industrial solvent extraction

Answer 22

3H2L2 + Ln£+ —-> [Ln(HL2)3]

Question 23

how does industrial scale solvent extraction work

Answer 23

Ln moves to org layer
forms complex with HL
can be separated and repeated
late Ln prefer org layer

Question 24

what is the main way that phosphors can be recycled

Answer 24

hydro metalurgy - similiar to ore extraction

Question 25

what are the 3 ways magnets can be recycled

Answer 25

reuse them (only for larger magnets) separate the alloy - H2 decrepitation hydrometalurgy

Question 26

where are the 3 main sources of uranium

Answer 26

kazakhstan australia canada

Question 27

where is thorium extracted from

Answer 27

occurs as Th3PO4 in monazite

Question 28

where is uranium extracted from

Answer 28

occurs mainly as pitchblend U3O8

Question 29

how can ultra pure U be obtained

Answer 29

further extraction if U3O8 with (BuO)P=O

Question 30

what isotope of uranium is required for nuclear reactors

Answer 30

235U

Question 31

what is the natural compostions of uranium isotopes

Answer 31

99. 3% 238U | 0. 7% 235U

Question 32

what uranium compound is used in isotope separation

Answer 32

UF6

Question 33

what are the advantages of using UF6 in isotope separation

Answer 33

gas - sublimes at 56 C | F only has 1 isotope

Question 34

what are the disadvantages of UF6

Answer 34

it is corrosive and forms HF in water

Question 35

how is UF6 made

Answer 35

UO2 + 4HF -> UF4 +2H2O ---F2---> UF6

Question 36

what is the formula for rate of diffusion

Answer 36

rate = 1/root(Mr)

Question 37

what is the formula for separation factor

Answer 37

rate of diffusion 235UF6/ rate of diffusion 238UF6

Question 38

what are the 3 methods of isotope separtation

Answer 38

Gas diffusion gas centrifuge laser isotope separation

Question 39

why is gas diffusion no longer used

Answer 39

too expensive

Question 40

explain how a gas centrifuge works

Answer 40

spins at 70000 rpm 0.001atm so UF6 stays gaseous 238 is pushed towards the edge of the centrifuge - reused 235 stays in centre and is removed

Question 41

what is the separation factor of gas centrifuge

Answer 41

1.2

Question 42

what is a separative work unit

Answer 42

unit of measurement of the amount of work needed to separate uranium

Question 43

how does laser isotope separation work

Answer 43

UF6 forms dimers thriugh vdw interactions | selective excitation of U235 breaks U235 dimers and moves them to the side of the chamber - u 238 dimers are unaffected.

Question 44

what Kwh per SWU are required for each method

Answer 44

Gas Diff 2500 Gas cent 40 Laser 10-15

Question 45

how does uranium work in a reactor

Answer 45

split by thermal neutrons | forms lighter fragment and more neutrons

Question 46

how does a pressurised water reactor work

Answer 46

35% thermal efficency need 2.5-3.5% U235 water acts as moderator and coolant moderator slows reaction to enhance fission

Question 47

how is mixed oxide fuel made

Answer 47

239Pu + depleted U

Question 48

how is 239Pu made

Answer 48

238U absorbs a neutron followed by B- radiation

Question 49

what are the advantages of using thorium as a nuclear ful

Answer 49

abundant occurs as single isotope unlikely to produce trans uranium products ThO2 is easier to handle than UO2

Question 50

what are the disadvantages of using thorium as a nuclear fuel

Answer 50

not fissile - needs fissile material added | 232U is produced - gamma emitter

Question 51

how much energy does Th contain relative to U

Answer 51

200x more

Question 52

why does nuclear fuel need to be reprocessed

Answer 52

power output diminishes fuel rods become U235 depleted conc of fission products increases - capture neutrons

Question 53

how are nuclear fuels reprocessed

Answer 53

U and Pu separated from fission products | U separated from Pu

Question 54

what does spent nuclear fuel compose of

Answer 54

97% U/Pu | 3% fission products

Question 55

how are fission products dealt with

Answer 55

``` stored for weeks or months evaporated to powder mixed with molten glass stored in stainless steel cannister long term storage ```