Complexation Chemistry and Precipitation/Crystallization Processes

32 Pages·2009·1.64 MB·English

Complexation Chemistry and
PPrreecciippiittaattiioonn//CCrryyssttaalllliizzaattiioonn PPrroocceesssseess
Gordon Jarvinen
Associate Director, Glenn T. Seaborg Institute
Stockpile Manufacturing & Support Directorate
Los Alamos National Laboratory
LA-UR 09-04900
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Outline
11)) EElleeccttrroonniicc ssttrruuccttuurree ((oorrbbiittaall eenneerrggiieess aanndd ssppaattiiaall eexxtteenntt)) ooff eeaarrllyy
actinides gives chemical properties resembling transition metals,
but later actinides more like lanthanides
22)) PPrreecciippiittaattiioonn aanndd ccrryyssttaalllliizzaattiioonn - ggeenneerraattee ssuuppeerrssaattuurraattiioonn, ee.gg., bbyy
reagent addition (K ), ΔT, redox; followed by nucleation, growth
sp
(agglomeration, aging)
33)) BBaattcchh vvss ccoonnttiinnuuoouuss pprreecciippiittaattiioonn//ccrryyssttaalllliizzaattiioonn ooppeerraattiioonnss;; ssoolliidd--
liquid separations: filtration, centrifugation
4) Co-precipitation or carrier precipitation - very important tool in
aannaallyyttiiccaall mmeetthhooddss ffoorr rraaddiioonnuucclliiddeess
5) Plutonium first isolated as weighable compound and first
production performed by multiple stages of co-precipitation using
LLaaFF aanndd bbiissmmuutthh pphhoosspphhaattee, rreessppeeccttiivveellyy
3
6) Examples of Pu and U purification and product preparation using
oxalate, peroxide, fluoride, hydroxide; Cs and Sr separations at
HHaannffoorrdd
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The Periodic Table of Elements
Systematic changes in chemical properties
result from filling of s, p, d, and f orbitals:
1 2
H lanthanides 4f, actinides 5f He
33 44 55 66 77 88 99 1100
Li Be B C N O F Ne
11 12 13 14 15 16 17 18
Na Mg Al Si P S Cl Ar
1199 2200 2211 2222 2233 2244 2255 2266 2277 2288 2299 3300 3311 3322 3333 3344 3355 3366
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86
CCs BBa LLa HHff TTa WW RRe OOs IIr PPtt AAu HHg TTll PPbb BBii PPo AAtt RRn
87 88 89 104 105 106 107 108 109 110 111 112 114 116 118
Fr Ra Ac Rf Db Sg Bh Hs Mt

Lanthanide 58 59 60 61 62 63 64 65 66 67 68 69 70 71
series Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Actinide 90 91 92 93 94 95 96 97 98 99 100 101 102 103
series Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

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Actinide 5f electrons - itinerant versus localized
• Outer 7s and 6d electrons
overlap strongly & have
metallic behavior
• Light actinides have metallic-
Metallic electrons Atomic electrons
like 5f electrons
• Heavy actinides have atomic-
R. C. Albers, Nature, 2001, 410,
like 5ff electrons
759
• The transition from delocalized
to localized 5f electrons takes
ppllaaccee aatt PPuu ffoorr tthhee mmeettaallss
• Pu appears to undergo an
intermediate transition that is
oonnllyy ppaarrttllyy llooccaalliizzeedd!!
Savrasov, Kotliar, Abrahams, Nature, 2001, 410, 759
Wills, Eriksson, 2000, Los Alamos Science, 26, 128
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Oxidation States & Valence Electronic Configurations
00 II IIII IIIIII IIVV VV VVII VVIIII VVIIIIII VVIIIIII VVIIII VVII VV IIVV IIIIII IIII II 00
Boxes – known oxidation states
Ac La
Blue shading – most stable in
Th Ce
aqqueous acid solutions
Pa Pr
U ? Nd
Np Pm
Pu ?? n Sm
f
?
Am Eu
f0 f0
? ? f1 f1
Cm Gd
f2 f2
Bk f3 f3 TTbb
f4 f4
?
Cf Dy
f5 f5
Es f6 f6 Ho
f7 f7
FFmm f8 n f8 EEr
Valence f
f9 f9
Md Electronic Tm
f10 f10
Configuration
No f11 f11 Yb
f12 f12
LLr f1133 f1133 LLuu
f14 f14
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Oxidation State Characteristics of the Actinides
• IInn aacciiddiicc ssoolluuttiioonn, tthheerree aarree ffoouurr ttyyppeess ooff ccaattiioonnss, lliinneeaarr OO=AAnn=OO ccaattiioonnss
found in aqueous solution for V and VI oxidation states:
III IV V VI
An33+ An44+ AnO2++ AnO222++
• Metal ion affinity to form complexes with “hard” donor ligands:
4+ 3+ ~ 2+ +
An > An ~ AnO2 > AnO2
•• RReeddooxx rreeaaccttiioonnss aarree rraappiidd && rreevveerrssiibbllee wwhheenn tthheerree iiss nnoo mmaakkiinngg//bbrreeaakkiinngg
of An=O bonds
4+ 3+ 2+ +
AAnn AAnn AAnnOO AAnnOO
22 22
• Redox reactions are slow & irreversible when making/breaking An=O bonds
44+ +
An AnO
2
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Chemical Bonding in f-element 7
Comppounds
• BBonddiing iin 44ff ellementts offtten regarddedd
as ionic or “hard” Lewis acids
• Core-like nature of f orbitals limits
oovveerrllaapp ttoo ffoorrmm bboonnddss
• Extent of involvement of 5f electrons
of actinides in bonding has been
widely debated since 1950s
44ff 44dd
• Examination of covalency in 5f
complexes has indicated involvement
44ff
of s, p, d, and f orbitals, UO 2+ Radial Functions
2
ccoonnttaaiinnss UU-OO ttrriippllee bboonnddss
Pu3+/Sm3+
55ff
• Trivalent actinides can be separated
00..88
Schrekenbach, Hay, Martin,
from Ln(III) using ligands with “soft” 55dd J. Comp. Chem. 1999, 20, 70.
donor sites,, e.gg. N or S vs O or F,, PP((rr)) 6666dddd
PPPP((((rrrr))))
suggesting stronger covalency in the
00..44
actinides
G. Seaborg, J. Am. Chem. Soc. 1954, 76, 1461
H. Taube, J. Chem. Phys. 1962, 76, 1461
R. Hoffman, Inorg. Chem. 1980, 19, 2656
00..00
R. Denning, Struct. Bonding, 1992, 79, 215
00 11 22 33
RR((ÅÅ))
Oxidation-reduction properties of plutonium
AAmmoonngg tthhee mmoosstt iinnttrriiccaattee iinn tthhee ppeerriiooddiicc ttaabbllee
VI V IV III 0
0.99V
0.94V 1.03V 1.05V -2.00V
Acid PuO 2+ PuO + Pu4+ Pu3+ Pu0
2 2
J. Fuger, J. Chem. Thermodyn, 1992, 24, 337 -1.24V
R.J. Lemire, Chem Thermodynamics 4, 2001, OECD-NEA
• Redox potentials that couple the four common oxidation states in acid solution
aarree aallll rreemmaarrkkaabblly ssiimmiillaarr, ccaa. 11.00 VVoolltt
• Appreciable concentrations of 3 or 4 oxidation states can exist together at
equilibrium
• The equilibria depend on H+ concentration, and are quite complicated
• Complexation can stabilize a given oxidation state against redox
-- ee.gg., PPuu((IIVV)) iiss vveerryy ssttaabbllee iinn HHCCll ((CCll- ccoommpplleexxaattiioonn))
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Redox Stability and Equilibrium Concentrations
44++ 33++ ++ ++
22PPu + 22HH2OO PPu + PPuOO2 + 44HH
4+ + 3+ 2+
Pu + PuO Pu + PuO
2 2
+ + 4+ 2+
2PuO2 + 4H Pu + PuO2 + 2H2O
0.8
1.0
Ave ox= IV
m=11.00MM,pHH=11.00
IV
IV
0.8
0.6
[Pu]=0.002M,t =2.7hrs.
1/2
0.6
0.4
III
0.4
III
00.22 VVII
0.2 VI
V V
0.0
0.0
00.00 00.55 11.00 11.55 22.00 00 2200 4400 6600 8800 110000
pH M•sec
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Oxidation States of Plutonium in Aqueous Solutions
f5 f4 f3 f2 f1
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