Download Lecture 1: RDCH 710 Introduction

Lecture 4: Thorium Chemistry
• Chemistry of actinides
 Nuclear properties
 Th purification
 Metal
 Compounds
 Solution chemistry
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Nuclear Properties
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Thorium Isotopes
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Thorium isotopes
•
232Th




main isotope of Th
228Th from 232Th decay
Other isotopes from decay of U isotopes
227,231Th (from 235U decay)
230,234Th (from 238U decay)
Isotopes can be isolated from U ore
Free from 232Th
Other isotopes from nuclear reactions with
Pb and Bi targets
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Th ore processing
• Main Th bearing mineral is monazite

Phosphate mineral
 strong acid for dissolution results in water soluble salts
 Strong base converts phosphates to hydroxides
* Dissolve hydroxides in acid
• Th goes with lanthanides

Separate by precipitation

Lower Th solubility based on difference in oxidation state
 precipitate at pH 1
* A number of different precipitation steps can be used
 Hydroxide
 Phosphate
 Peroxide
 Carbonate (lanthanides from U and Th)
 U from Th by solvent extraction
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Th atomic spectroscopy
• Electronic states of Th can provide information on higher actinide states

Neutral atom has available valence orbitals
 5f, 6d, 7s, 7p
 Stable 6d27s2 (3F2)
• Term symbol

abbreviated description of angular momentum quantum numbers
2S+1L

J

S from unpaired electrons
 2 d electrons, S=1, 2S+1=3

L from orbitals of unpaired electrons
 2 d electrons (5 orbitals; 2,1,0,-1,-2): 3
 3 is F
* S=0, P=1, D=2, F=3

J has some rules
 Less than half filled, J=|S-L|
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 J=|3-1|=2
Th atomic spectroscopy
• Wide range of values based on configurations
• Singly ionized states

d2s, ds2, fs2, fds, d3, fd2
 Energy range from 1859 cm-1 to 12485 cm-1

p orbital occupation starts at 23372 cm-1
 dsp

Double f occupation at 24381 cm-1
 f2s
• Increase in ionic charge increases f orbital stabilization, decreases p
orbitals
• Odd or even electron parity

sum of p and f electrons defines parity

Strong spectral lines result only from transitions between
configurations of unlike parity
• Actinide data

http://www.lac.u-psud.fr/Database/Introduction/Table1-dir.html
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Th levels (cm-1)
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Th levels (cm-1)
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Thorium metal synthesis
• Reduction of ThO2 with Ca
• Electrolysis of anhydrous ThCl4 in a fused
mixture of sodium and potassium chlorides
• Ca reduction of ThCl4 mixed with anhydrous
ZnCl2
 Formation of Th2Zn17
Distillation of Zn
• reduction of ThCl4 with an alkali metal
• Reduction of ThCl4 by DyCl2
• Decomposition of ThI4 on hot W surface
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Th metal properties
• silvery-white metal which is air-stable

Oxide slowly forms, to gray and
finally black.
• Changes structure with temperature

ffc to bcc at 1360 ºC
 High pressure forms body
centered tetragonal
• Metal is paramagnetic (2 d electrons)
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Th metal reactivity
• Attacked by oxygen, hydrogen, nitrogen, halogens, and
sulfur at elevated temperatures
• Dissolved by HCl
 Can form ThOClH
• Numerous alloys
 Mag-Thor magnesium alloys containing thorium
 magnesium-thorium-zirconium
 magnesium-thorium-zinc-zirconium
 magnesium-silver-thorium-rare earth metalzirconium
* Alloys have high strength, creep resistance
at high temperatures, and light weight
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Th compounds
• Hydrides
 Formed by reaction with H2
Powdered Th at room temperature
 ThH2 and Th4H15
ThH2 tetragonal
Th4H15 cubic
* Th in center of 12 H
* 1st metal hydride superconductor
 Hydride forms oxide
 Range of ternary hydrides
Fe, Zr, Mn, Al
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Borides, Carbides, Silicides
• Borides
 Formed from chlorides with
MgB2
 ThB6 (octahedra), ThB4, ThB12
 A few higher borides reported
 Ternary borides are known
• Carbides
 Formed from oxide with carbon
 ThC, ThC2, and Th2C3
 Boride-carbides also formed
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Th silicides
• Four Th-Si compounds

Th3Si5

Th3Si2
 Si bond distance 2.33 Å

ThSi
 Zig-zag structure

ThSi2
 Hexagonal and tetragonal
 Th in 12 fold coordination with Si
• Numerous ternary compounds

ThM2Si2
 Mn, Cr, Fe, Co, Ni, Cu, Tc

Th2MSi3
 Mn, Fe, Co, Ni, Cu, Rh, Rh, Pd, Os, Ir, Pt, Au
 From modification of ThSi2
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Oxides and hydroxides
• Oxides of ThO2 and ThO

ThO postulated as defect
 Surface of metal exposed to air
 fcc lattice

Dioxide can form colloids
 Sintered dioxides are extremely refractory
 Dissolves in nitric acid with HF
 Hot HF or gaseous HF converts oxide to tetrafluoride

Dioxide produces blue light when heated
• Hydroxide

Converted to oxide above 470 ºC

Absorbs atmospheric CO2

Environmentally important specie
• Peroxide formed by hydrogen peroxide and Th salts
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Th halides
• Tetrahalides have been formed
 ThF4
 Precipitation with fluoride and dehydration
with HF or F2
 Th metal or carbide with F2
 Other Th halides, oxalates, or oxides with HF
 ThO2 with NH4HF2
* NH4ThF5 that decomposes to ThF4 above
300 ºC
* Requires excess NH4HF2 (8x)
 Structure is square antiprism
• Mixed fluorides are also formed
 Th(OH)F3, ThOF2
• Hydrate of Th6F24.H2O
 Water centered 6 Th
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Th chlorides
• Crystallized from aqueous solution

Hydrated form, removal of water upon heating greater than
100 ºC

Reaction of ThH4 with HCl

Th metal or carbide with Cl2

Th metal with NH4Cl
• 2 phases

Transition at 405 ºC

Low temperature a-ThCl4

High temperature b-ThCl4 (metastable)
 Both dodecahedra, 8 fold coordination
 Difference due to relationship between dodecahedra
• Mixed chlorides

ThOCl2
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Th bromides and iodides
• Similar synthesis to the chlorides
 i.e., HBr instead of HCl
 Solution synthesis yields hydrates and mixed
oxide (ThOBr2)
• Also dimorphic, similar to chlorides
 Transition temperature at 426 ºC
• ThI4 from the reactions of the elements
 No water or O2; (forms ThOI2)
 ThH4 with HI
 Distorted square antiprism
• Lower valent ThI3 and ThI2 known
 Formed from ThI4 with Th
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S, Se, and Te complexes
• Heavier analogs of the oxides
• All form compounds
 Some simple fluorite or NaCl structures
 Electronic properties of S, Se, and Te can yield
complex structures
• Synthesis
 H2S with metal, Th halide, or hydride
• Se form series similar to S
 Se on metal, halides for synthesis
• Te slightly different structures
 CsCl structure for TeTh
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Nitrides, P, As, Sb
• Range of binary compounds

ThN, Th3N4, Th2N3

ThP, Th3P4, Th2P11, ThP7

ThAs, Th3As4, ThAs2

ThSb, Th3Sb4, ThSb2

ThBi2
 Heavier compounds form similar binary phases to
nitrides
 Bi blanket with ThBi2
• Th3N4

Heating of metal in N2

Under NH3, hydride intermediate forms

Heating nitrides under O2 produces oxides
• Reaction of binary compounds with Th halides leads to ThNX
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Complex ions
•
•
•
Th(ClO4)4

Tetrahydrate, decomposes to mixed oxide at 280 ºC, then dioxide at
335 ºC

Prepare from ThCl4 and Cl2O6

Used as starting material since ClO4- weakly binds
Sulfates (Th(SO4)2)

Prepared from salts with sulfuric acid
 Different hydration states
* Lower temperature 9 waters
 8 waters also found
 Tetrahydrate also stated to form
* 10 coordinate to Th(IV)
 2 sulfates, 6 waters
 Distorted bicapped squared antiprism
Mixed species formed

Dihydroxide

Monooxide

Dimer (Th2(OH)2(SO4)8
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Complex ions
•
•
Wide range of sulfates

A2Th(SO4)3
 A=Na=Cs, NH4

Fluoride species
 Th(SO3F)4
Nitrates

Prepared from Th(OH)4 in nitric acid

Soluble in water

Nitrate extracted into tributylphosphate
 Nucleophilic
 Metal ion interaction through oxygens on TBP
* 2-3 TBP per thorium nitrate

Polymeric

Th4(OH)10(NO3)6TBP4

A2Th(NO3)4
 A=monovalent
* 12 coordination by O

Also with divalent cations
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Complex ions
•
•
Carbonate

From the hydroxide
 ThO(CO3)2 then dicarbonate under high CO2

Numerous mixed species
 Metal ion with extra carbonate
* MTh(CO3)x
Phosphate

ThO2/P2O5
 Range of sulfates
* 3,4 (may not exist, as Th4(PO4)4P2O7
 4 monodentate, one chelating
* ThO3(PO4)2
* (ThO)2P2O7
* ThP2O7

Range of MTh2(PO4)3
 M monovalent
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Complex ions
• Range of metal oxides with Th
 Vanadates
 M2Th2(VO4)3
 Th(VO4)(VO)3
 Molybdates
 Th(MoO4)2
 Chromates
 Th(CrO4)2
• Prepared from salts
• Range of hydrates
 Higher temperature, lower hydrates
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Coordination compounds
• Range of compounds examined
 TBP for extraction
 Ligands with
C-O, N-O, P=O, As=O, S=O
• Th tetrakis(acetylacetone) [Th(acac)4]
• 8-hydroxyquinoline
• Thorocene
 2 cyclo-octatetraene
• Cyclopentadienyl (Cp-)
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Solution chemistry
• Only one oxidation state in solution
• Th(III) is claimed
 Th4+ + HN3  Th3+ +1.5N2 + H+
 IV/III greater than 3.0 V
* Unlikely based on reduction by HN3
 Claimed by spectroscopy
* 460 nm, 392 nm, 190 nm, below 185 nm
* Th(IV) azido chloride species
• Structure of Th4+
 Around 11 coordination
 Ionic radius 1.178 Å
 Th-O distance 2.45 Å
 O from H2O
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Solution chemistry
• Thermodynamic data

Eº= 1.828 V (Th4+/Th)

ΔfHº= -769 kJ/mol

ΔfGº= -705.5 kJ/mol

Sº= -422.6 J/Kmol
• Hydrolysis

Largest tetravalent actinide ion
 Least hydrolyzable tetravalent
 Can be examined at higher pH, up to 4
 Tends to form colloids
* Discrepancies in oxide and hydroxide solubility

Range of data
 Different measurement conditions
 Normalize by evaluation at zero ionic strength
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Solubility
• Large variation with preparation
 Average OH- 2.5 without delayed precipitation
 Polymerization
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Solution chemistry
• Complexing media
 Carbonate forms soluble species
 Mixed carbonate hydroxide species can
form
Th(OH)3CO31,5
 Phosphate shown to form soluble species
Controlled by precipitation of
Th2(PO4)2(HPO4).H2O
* logKsp=-66.6
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Complexation
• Inorganic ligands
 Fluoride, chloride, sulfate, nitrate
 Data is lacking for complexing
 Re-evaluation based pm semiemperical approach
* Interligand repulsion
 Decrease from 1,4 to 1,5
 Strong decrease from 1,5 to 1,6
• Organic ligands
 Oxalate, citrate, EDTA, humic substance
 Form strong complexes
 Determined by potentiometry and solvent extraction
 Choice of data (i.e., hydrolysis constants) impacts
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evaluation
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Analytical
• Low concentrations
 Without complexing agent
• Indicator dyes
 Arzenazo-III
• ICP-MS
• Radiometric methods
 Alpha spectroscopy
 Liquid scintillation
May require preconcentration
Need to include daughters in evaluation
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