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Reference 90

Bruno, J., and A. Sandino. 1987. Radionuclide Co-precipitation, SKB Technical Report. no. 87-23. The Royal Institute of Technology, Department of Inorganic Chemistry, Stockholm. 19pp. NTIS No. :D£88754187

Submitted in accordance with 40 CFR §194.13, Submission of Reference Materials.

Radionuclide co-precipitation

.Jordi Bruno and Amaia Sandino

The Royal Institute of Technology Department of Inorganic Chemistry Stockholm

December 1987

·~

I

RADIONUCLIDE CO-PRECIPITATION

Jordi Bruno and Amaia Sandino

The Royal Institute of Technology Department of Inorganic Chemistry

Stockholm December 1987

\

This report concerns a study which was conducted for SKB. The conclusions and viewpoints presented in the report are those of the author(s) and do not necessarily coincide with those of the client.

In!ormation on KBS technical reports from

I

I

1977-1978 (TR 121), 1979 (TR 79-28), 1980 (TR 80-26), 1981 (TR 81-17), 1982 (TR 82-28), 1983 (TR 83-77), 1984 (TR 85-01), 1985 (TR 85-20) and 1986 (TR 86-31) is available through SKB.

\

\ I

RADIONUCLIDE

CO-PRECIPITATION

Jordi Bruno and Amaia Sandino

The Royal Institute of Technology Department of Inorganic Chemistry

Stockholm

December 198 7

I

i

CONTENT

SUMMARY

PART I - RADIONUCLIDE CO-PRECIPITATION IN THE NEAR FIELD

1. Introd;Jction 2. Cho1ce of Analogues 3. Thermodynarrics of Radior.~clide Co-pre=ip:tat:on 4. The Effect of Agir.g nn Co-precipitat~or. 5. Kinetics of Co-d~sso!~tio~ 6. Co~clusior.s

7. Ackno~ledgemer.ts e. References

PART II - RADIONUCLIDE CO-PRECIPITATION IN THE FAR FIELD

l. Introd;Jctior. 2. Radionuclide Co-ptecipi:atior. with Ca!cite 3. Radionuclide Co-precipitation with Iror. Ox:des 4. Concl;Jsior.s 5. References

i i

1

1

-4 5 t g

:c ' " _ ...

12

l2 ~3

~6

:7

I

ii

SUMMARY

Thf? therm(;dynarrjc and kinetic behav1our of the minor co~;por.ents o! the spent fuel matrix has been theoretica:ly and experimenta:ly investigated. Two d:~ferer.t situations ~ave been stud:ed: Part l, the near field ~cenario, where the release and migration cf the rr.inor corr.ponents is dependent on the so:'.lbility be::av1our c! uo2(s); Part II, the far field, where the solubility and transpcr: of the radior.'.lclides is related to the ma;or geoche~ica: processes occ'.lrring.

l<EY'WCRDS: cc-preciFi ta:ion/co-d~sso::.:::or., s~er.t nuclear f;.;e:, radion:.:c:ide solub:l:ty.

1

1

PART I: RADIONUCLIDE CO-PRECIPITATION IN THE NEAR FIELD

Introduction

A first estimate of the release and transport ?f radionuclid .. ·s f.rom spent nuclear fuel in contact with groundwater is genera:l~: made by using thermodynaznic models. The collection a::d critical evaluation of the necessary the~~yn~~lC data requires much work. Solubility limits ar@ often used as radionuclide St"lrce terms ir. the general sec~rity analysis and most of the solubility data used in these exercises relates to pur~. solid phases.

Spent nuclear fuel can .be coosidered as a multicomponent so:ic solutior. of varying homogeneity, dependioq on the conside:-ed radionuclide. It is now well established that. the release o! uranium, U·.e major componen~ of uo2 spent fuel. is so!ubili.ty limited [ 1]. It is reasonable to expect that the dissolution of the minor compone:1ts will be influenced by the release and cis­sol~t~o:: of uraniwm. Cor.te~~ently, the thermodyn&~ic and kinetic behavio~r of these c~ponents c6nnot be modelled only by using the data for the p~re individual phases.

The solubility behavi~ur of uo2(s) depends on the recox potentie: of the aq'.leous medium in ce>nt.act with th• fuel. Hence, t.,.o dlf­ferer:~ situations shou~.d be studied. In the first case a prelimi­nary solubiliz5tion of the spent nuclear ft•el caused by oxidat ior. in the near field, te.g. due to radiolysis), is followed by a re­precipita~ion in the far field when reducing conditions are res­tored. In the second case, co-dissolu•io~ of the minor component rt1dionuclides may occur in relation to the dissolution of uo2 under reducing con~itions. In both cases, the solubility of these radionuclides will be ~ffected by the behaviour of uo2 . The syste~ is no lonqe. dependent only on tt.e thermodynamic and kinetic properties of the various individual phues for the different radionuclid~s. but un the distri" .. :i"'" of the components in the &?lid phase, •·9· the formation of solid solutions.

The attachmer:t of a certain metal ion to a host solid phase n:ay occur J.n several forms, from adsc•rption of the ion at the sur!ace of the solid to true ideal solid solutions, where the foce.'-.gn

2

metal ion is regularly placed in the host lattice. There is a sequential transition from surface co-precicit~tion to idea: so:~c solution formation through these three processes:

a) Surface co-precipitatio~ b) Lattice dlffusion c) Solid solution

At room temperature, diffusion in a solid matrix is generally very ~low and the first process, surface co-precipitation, is the o~e expected to occur. In this case, there is no major structural arrange~ent and the radionuclide distribution equilibria i~

established between the solid surface and the solution. However, the initial source (U02 spent fuel), may be considerec as an ~dea: solid soll<tion tor most of its components.

All these phenomena can be included under the term co-precipita­tion. Co-precipitation has been defined as "the conta~ir.atic~ o! a precipitate by substances that are normally so2.uble under tt.e conditions of tt:e precipitation [2)". This concept is lir::itec since there are sorre cases which cannot be explair.~d by tt-.:.s definition. Therefore, Gon!on [3) rede!int:d co-precipitatio:-: as "the precipitation of a compound in cor.junction wlth one or m~re components". We will use the concept co-precipitation in tt::s sense. Four types of co-precipitation have been characterized:

a) Isomorphous rr..ixed crystal !ormation a) Anomalous mixed crysta: formation c) Adsorption d) Occlusi•

where the first two cases are different degrees of so:id so:~t:cr.s [3].

The constituents of isomorphous mixed crystals t:ave Sl~:~ar

chemical and crystallographic properties. In the case of ano:r.a:o·.s rr.ixed crystal formation, the characteristics are the sa':'le as ir. the former case, but •. heir formation cannot be explained on t::e same besis. Adsorption can be cor:sidered to some extert, as anoMalous mixed crystal fo~~tion at tne surface of the precip:­tate. The term occlusion is usually applied for the case where adsorbe-'~ species on crystal planes are subsequently covered with ~ther crystal layers.

Co-precipitation is a wel: known chemic:lll phenorner:on. It has beer. extensively applied in analytical chemistry for the separation of trace ele1nents [3,4]. Also in radioar:alytical applications, particularly in enrichment processes [ 5 ,& ] , and for mixed oxide fuel production [7,8,9]. In the field of geochemistry, there are many processes which should be explained by means of co-precipita­tion, for instance the anomalous behaviour of the Sr-Ca carbonate cystem [10], or the Ba2•, Sr2• system in calcite [11].

I !

•

2

3

In a previo~:s work ( 12] we have studied the co-precipita'::a~

behaviour of the La{OH)ruo2 system at roorr. tempera~ure. In u.:s communication we preser.t some recent results on the therrr.ociyr.ar.-.:cs of co-precipitation at room temperature of so~e rad1on~cl1des. Tr.e effect of hyllrotherrr.al aging on the co-prec1ri tatlon/co-c:sso:t.<­tion distribution lS also studied, by using Th4 ·, La3• ar.d Ba2 • as radionuclide analogues.

The investigation of the basic processes relateo to radionuclide co-dissolution/co-prt?c.:ipitation, req-.Jin:s well contro_:Oed ex­perimental conditions. The study of the actual radionuclldes has experimental difficulties ~ue to their radioactive nature. Because of this, proper ar:elogues have to be chosen. One of t.he a:.~s of this rE<search program has been to ir.vestigate the deper . .jer.ce of the degree of co-precipitation/co-disso!~tion with tte ctarge c~

the radionuclide ion. Cor.seq..iently Th4 •. La3• a:1d aa2• l":ave be~~. selected as ana~ogue ions for this p~rpose.

The co-precipitatlon and co-dissolution p~enomer.a are cor.trcl!e~

by ~"lny dHf erent var iaoles: terr.perat~re, the co:-.:er.trat ior. of t:.e IT!inor compone:1ts, the rate of the process, t~e io:-.:..c rad:us a:-.ci the ionic charge (3]. Tl":e two rrair. factors are t~e !or.:c cl":ar~e

ar.d size, since the fo~ation of iso~orph::~us ~:.xed crysta:s :s depe:1dent on si::-.!larities in both the che~ical properties ar.d t:-.e size of the substltuting ions. Tl":e prooabi:ity that co-preciplta­tion/co-dissolutior. occurs is larger .,..her. t!",ese para.~e:ers a:-e si:r.ilar for both the host a:1d the :r~~.cr corT:poner.t. lr. Ta:::e !-: we have s~~arized the io~ic rac~i for varlous ior.s of 1~:eres:.

Table 1-1. Effective ionic radii (13] of some ions of interest.

Ion 1 COordination number

u6• 1.00 8

u4• 1.14 8

Th4• 1.19 e Pu4• 1.10 8

Pu3+ 1.14 6

Ln3• 1. 00-l. 21 6

Ra2• 1.62 8

sa2• 1. 56 8

3

4

In the case of Pu4• and Th4• an isomorphous subs~itution o: u<O• in the uo2 lattice is obviously possible since both charge and si~e

are very &imilar.

For pu3• and the lantr.anide ions (here syrr.bolized by Lr. 3 •) t:-:e ionic radii are in a range of values wr.ich indicates the pos· sibility of isomorphous subst.itution of u4 •, altho":Jgh this w::J:.::d imply a readjustment of the charg~. We fou~d it would be interes­ting to test to which extent a larger ion like Ba 2• (analog:.:e to Ra2•), wou:d behave in the co-prec~pltation system.

Thermodynamics of Radionuclide Co-precipitation

The equilibriwr. distribution of the components A, B of a so.1c solution between the solid and the aqueous phases can be described in two different ways.

If eq-.;ilibr!u.-:: is attained between the bulk of the so~:d so:..:::.::Jn •u;d the aq~.:eous pr.ase the syste:r. fo~lows the Be!:'the:o:-se:-~.s:

ho~ogeneous distribution law (1.;). !his car. be expressed as:

When equilibriu.-r. is only reached bet weer. the surface of the so. :c and tt.e aq:.:ccus sol~.:tior., t.t:e d:str~b..:t:or. of t!'Je co:--pc::e:-.:~

between the solid and the aq":Jeows phases follows the Doer::e:-· Hoskins logaritr~ic law (15]. This is fo:rm":Jlated as:

log ---- = k log ( 2)

The 'co-precipitation eq11ilibna ln the system La(Ill)/U(IV). 112) and Ba( II)/U( IV) have been studied under well controlled co!"ldi­t ions at 25°C. The exper imenta 1 details have been prev io:.:sl y descr i.oed (12) .

From these experimental data we conclude that the dist!:'ibutior. of the different ions involved between the aqueou:. phase and the solid solution follows the logarit~~ic law. From these data it is possible to calculate conditlonal solubility product~£ (12} of La(OH)3(s) and Ba(OH) 2 (s), in the presence of uo2 (s). Fror"" a few data obtained (16), in the Pu(Ill)/U(IV) sys:~m. we hav~ a:so estimated a conditio~al solubility prod.;ct for Pu(OH) 3(s) in t~e

freser:.:e of uo2< s). In Table 1·2 we make a conparison be~~o·eer: these conditional solubility prodJcts anC: the values for the individJal phases.

4

Table I-2.

Mn+

Pu 3"

La3•

Ba2 •

5

A comparison bet~een conditional (K• ) and individual solubility products for the equilib~~a:

Mn+ + n E2o ..>. M(OH)n(s) + n H+ ~

log Jt• log ltso so

- 2.4 -19.3

-12.5 -20.5

- 9.1 -24.4

From these data it is possible to conclude that:

Tile solubility of the mi. !"lor co:::por.ent s is stror.:;: y rec..:cec !:;j'

the presence of uo2 (s).

At low te:-perat'..lre the co-preclp:.tat1on eq'.Jilibriurr obe~·s t::e Doerner-Hosk.:.ns dl~trib'.Jtlon law. Thls indica:es tl':a: eq.:­libr:~ is or.ly attained be:&een tr.e surface o! the so::.c a:-.:: the aq..:eous phase.

The Effect cf !ging on Co-precipitation

Because of tl':e long-ter~ pred!ct1o::s necessary for tl':e sa~e:y e::~

·per!or~·a:-.ce assessr:-e:-:t of n-.;c lear waste repos: tor:.es, i: :.s i:::portan':. to cor.s•der the ef!ect o! aging of tne co-prec:.p::. ta:e o:. the dis:r1b·..::1or. eq-..:Llbr:a.

I!"' order to St;.:dy this, a solu-:.ior. :.n:.tia:.ly con~al.~i.ng

!U(VI)] a 1.00 10-2 mol dr.1- 3

1 :-r.( :vJ l l.O::l 1c-4 mol dro- 3 '

I La (II I) ] .. 5.00 10-5 mol dr..-3

[ Ba< I1 J I .. 5.00 10-5 mel dro-3

in 0.5 mol dm- 3 NaClo4 was reduced with H2/Pd(g) at pH • 3 by using the same experimental approach as previously des:ribed (12]. A black precipitate was formed which wu characterized by X-ray powder diffraction (XPD), (see Figure I-1). The broad lines ob­served, showed the presence of a microcry:o;tallint> solid. Tlus solid was kept in contact with the mother solution for six months, at T • 110 to l20°C under N2 (g) atmosphere. After this time the solution and the solid phase ,..,~re anal yzcd. In Table I- 3 W\! S'.lm­

mar ize the percentagt>s of the different col":por.ents both in t!'le aqueous and the solid phases.

s

b

Fiqure I -1. XfD pat tern of the solid used in our experiments where thP. theoretical assiqned distances (19), are in ( J.) :

a: 3.234 (Th02) b: 3.157 (U,Th)02 c: 2.73 (U,Th}02 d: 1.98 (Th02 ) e: 1.93 (U02) f: 1.&5 (U,Th}o2

Table I-3. Relati•1e composition of the aqueous phat:e and the co­precipitate after aginq.

Metal ion

U( IV) Th ( :v) La( I::) Ba(I:)

\ in solution

98.0 l.C 0.5 0.5

\ in solid

'P.5 1.7 0.4 0.4

The results in Table I-3, i~dicate a co~gr~e~t co-precip~:a::=~ o! La(II:) a.1d Ba(!l) ar:d an er:rich.-,ent of Th(:V) in the so::d.

Xlnetics of Co-dissolution

A portion of this solid phase 01as put in contact with a 0. 5 mol dm-3 NaCl04 solution at pH s 4.5 under N2(g) atmosphere. The time dependence and the equilibrium distrlbu~ion between the solid and the aqueous phase were studied. Several sa:nples were taken at different times, and 01e ana: yzed tl":e urar: iu.r:1, lanthar.:.l:r., t!lor i~~ and bar:u.~ contents ir. the init1al solid an~ in the liquld sa~p:e~ by induced coupled p~asma spec~rophotorr.etry, ( IC). These ana:ysi!: were performed by using a Perkin Elmer !CF/5500 spectrop~o:ome:er.

(U(!Vi} :~ols/1

• 1 o- .t~ s

4

3

2

7

A A1 ~ ~

l

~ J 0~-_..____..,_-~-

~0:J 3:JD 0 100 t(I"IOI.II"'IIi

P~qure I-2a. Values of u1anium concentration vs t.iJDe.

The results are s;J..~arized in Fig-..:re 1-2. The plot of [C(:V)j :::!· contact time, (Fig;Jre l-2a) shows tha~ steady state conc~r.tra: :.c~,s are reach~d a!ter 50 hours. Tne average steady state cor.cer.tra­tio~s of U( !V), is of the same r.-:ac;::i tude "s t:1e expected [.; ( :v) J in equilibrium with a~orphous uc2 (s) (3.0 1C-~ mo: ~-3), [:7).

The plots o! the norrr.a: ized concer.: rat ~ons of ~he r.-::.no::- co~p:::~.er.: 5

with respect to the ura::iu.:r: cor.cer.~ratio:-: in so:u~ic-: ~· :::-e (Figure 1-2b-c-d), indica~e that the release of these rr: r.c:- cc:-­poner.ts from the so:ic matri.x is tota! ly cor.':. rolled by the u:-a:-.: ~­dissolution, e.g., congruent release. Thls ber.a·.r:our is la:-s;e~y

time independent (see Flc;ure l-2b-d). Finally. a ca:c.:la·~:o:J o: the distribution factors D accord inc; to the Be:-the:c.,t-!'e:-:-:s: distribution law (Eq. 1):

l M I ( aq) G D ----------- ( 3)

(U(IV)J(s) {t.:(lVlJ(aq)

9ives DTh4+ • DL8 3• • 1, while DBa2• • 2. This strongly suggests that hydrothermal aging of the co-precipitate has caused the initlal logarithmic distribution to shift to a norr.1al type of distribution.

/

8

[M)/[UJ

•10-~ ~ ~~----------~----~------------~------------

-A [ 11 J : Th I I Y)

A 02 -;

A A A

~~ A A &

A

c :J 100 <:O:J 3::::i

t l Mo ul"' £ :'

Figure I-2b. Plot of the nol'111i:1lized concentration of (Th(IV)) \.O"S

(U(IV)).

r ~ J _, r u J

A [ I'!) : Lc: I I I I ;

A

300

Figure I-2c. Plot of the normalized concentration of (La(III)) vs (U(IV)].

[MJ/[U]

•10-~

-~

~

c :J

.:..

iP L 6 ~

100

9

[ 1'1 J : Be ( I I)

L:. L.-.::.

;co~ 300 t(h::ur'"S.'

Figure I-2d. Plot of the normalized concentration c..f (Ba( II)) ~ (U(IV)).

Conclusions

!~ this work we have a::e~p:ed a ge~eral s:udy o! th~ so:~=:l!ty behavio~r o! the m!nor co~po~ents of the nuc~e~r ~aste ~a:r:x i~

relation to the major comp~ne~t uo2 .

As we ~ave shown in this and previous ~tud;es [l2,l6], the so:~b!­lity of the minor components cannot be only predicted on basis of the ind1vid~al solid phases. Co-precipltatior. occ~rs, ar.d a: lo•: temperatures the distribution of the co~ponents between the sol1d and the aque;:,•.-s phases follows the logarithmic distrib-..::ion la~.

Hydrothermal aging causes the co-precipitation syste:r: to shift from the logarithmic ( Doerner-Hosldns) to a normal (Berthelot­Nernst) distribution. This is in agreement with previous observa­tions in other co-precipitation systems (3].

At the same time, we have also sho~n that the dissolution of the minor components from a U(Th,La,Ba)o2 solid solution is ~lne:ical­ly and thermodynamically controlled by the behaviour of the rr.ajor component, uranium dioxide.

In this work we have only studied the co-pre~ipitation/co-dissolu­tion systems in connection with a near field situation, w~ere

uranium ~an be the major component in case of oxidat1on a~d

container failure. In the far field, the co-precipitation/co­dissolution systems have to be related to the major geoche::-.ica: processes occurring in granitic groundwaters. Possible systems

7

8

10

affecting the "individual solub.ility" of radion>lclides are the precipitation/dissolution of calcite, Fe(III)-hydrox:de, ~nc2 a~c

feldspars n•odification ( 18]. Future work lliill be foc'.lsed to an understanding of these processes.

Acknowledga~~ents

This investigation was financially supported by SKB (Swed:sl". Nuclear Fuel and Waste MC\nagemer.t Co.). Prof. I. Grer.the is thanked for valuable criticism. Dr. Inga-Kar i Bj()rner is grateL~l­ly acknowledged for carrying out the ICP measurements.

References

l. FORSYTH, R., WERME, L.O., BR:J~G. J.: (!986).

N-.Jcl. r.a:. De,

2. KC:i.. THCFF, I. f.:., SA~:::r:.L, E. E. : TE:xtbook of q~,;c:r::: ta:.: ·:e inorgan1c ar.a:ysis, 3rd ed, Kac ~:::an, New York :95~.

3. GCi'JO~, l.., SI.:.:.JTSK'.', I':.:.., w::.:J.::<:::, H. H.: free ipi ta: :o~. !:ro:­horrcc;er.eo:.;s sc:~,;t:.o:-:, :o!':n ;;::.er a:-.d So::s, ::nc., ~e·..: Ycrk 1959.

4. K:!-':;;1\A, T., KO:SAY:.S:i:, Y., A!\h:-S:.;, K.: Radio:::!' . .:.~. A::a :!?, (!986).

·-:. - ' J

5. SA:...:JTSKY, M.L., s:::ES, J .G., IV..A..;::~. A. W.: A::a:. Che:-.. :;:5, 1677 (1953).

6. HER~ANN, J.A.: U.S. Atorric Energy Corrrrisior., AECC-3f~7,

(1954).

, SCHNEIDER, V. W. , HERI-'.A~N, F. , DR:.'CKEK:SR::::;:, W. G. : '!rar:s. A::'. ll:'.lcl. Soc. 176 (197'1).

8. ~FvRD, K.C., BRATTON, R.S.: J. Nucl. Mat. 57, 28 (!975).

9. D'ANNUCCI, F., SARI, C., SCHUIV~CHER, G.: Nucl. Techr.ol. ~5. 80 (1977).

10. KlNS~AN, D.J., HOLLAND, H.D.: Geochim. Cosmochirr. Acta 33 (1969).

11. PINGITORE, N.E.: Geochemical Processes at M.ineral Surfaces, ACS, S~p. Ser. 323, Washington D.C., 19e6.

~2. BR\.:NO, J., GRENTHE, I., Mt:NOZ, M.: Ma~. Res. Soc. S)~p. Proc. 50, 717 (1985).

/

11

13. SHANON, R.D.: Acta Cryst. A32, 751 (197o).

14. HENDERSON, L .M. , KRACEl<. F. C.: J. Air.. Chern. Soc. 49, 738 (1927).

15. DOERNER, H.A., HOSKINS, W.M.: J. Am. Chern. Soc. 47, c62 (1925).

1o. GRENTHE, I., PUIGDOMENECH, I., BRUNO, J.: KBS-Technica1 Report 83-02. SKB/KBS, Stockholm (1983).

l7. BRUNO, J., CASAS, I., LAGERMAN, B., ~U~OZ, M.: Mat. Res. Soc. Symp. Proc. 84, 153 (1987).

lB. STUMM, W., MORGAN, J.J.: Aq..1atic Cherr.istry, 2nd ed., Jo:-.r. Wiley and Sons, New York 1981, p. 536.

19. J.C.P.o.s. Diffraction Data Cards No. 4-055c, 5-0550, 5-05~9.

1

1

12

PART II: RADIONUCLIDE CO-PRECIPITATION IN THE FAR FIELD

Introduction

As we have already pointed out in the previous sectio!"l, the co­precipitation/co-dissolutlon behaviour of the radior:uc::.ides in t~e far-field will be related to the major hydrogeoche~ical char.ges '~ the grounciwa:er.

Accord::.nc; to Eriksson [lj and Stur:-.:'!" a:1d P.:orga!"l [2], the J'!',a~or

geoc.hem:cal cha:1ges occ~rring as 10a:er perco:a:es fro~. the sc.:r!ace towards deep areas can be schema::zed by fig~re r:-1.

~ ,.. r • .. ~.

~ ... .J'" •• ~ •

v-..,~,.~: -.e -o:. .. Hi1 • ,,.-:..c: ... cn. o' :-:-.:.- C"' : 1·-.~o~s. 'co-.:1Fo} 'o~-,.~;

l .. r- c ,1"'1': ... • -:: ~ ~,. H , :.1 t 4! t-d sal t ~ _'r~€-"''H ... .;.a~r':'nr.; :.::.:...-"" ... ' ':•·( .. ar-.~ ,..f"!ta'S.E' {.',. c;.-c;;r. "l r.r: ~ :€,.

s.~:=::-:-. .:.·_c..J~ ... ~d~~~,. c1 ;',..Odo~..:t~

""D"" ~·i"\C.J"lZQr, llltoj@'ra t~ •to at ,.,e-,. 1 "~

=· ~ca~1::.,,.- cf ere jP.,~tt-r PrE-.·:·~at·.:,r, ~~ F'~~::•; • .,~ .. ., :. J

c. .. ~~Q: :'J. s ~ ,,t wE-a: "E>nru;: of :·a r·t,t Md tt:·" • 41 5: lub11lt_w- e-~ .. 11 ,l"'na

ColiC ~~~!t C02 ore metter o,.,,.,,. ,.,. ••' o••••t.~•• •••••••• 002 o ,.,..,tO ... ,o·3 ,,;2.,..,

Fiqure 11-1. Acquisition of solutes during infiltration.

,·

2

13

It is now well established [3) that ground\<later flows preferen­tially through fissures. It is logical to expect that th~ majo:­chemical processes will occur in these fissures and at the inter­face with t~e fracture filling minerals. Independently of the flo~ pattern, the geochemical changes will be related to the weather1ng of ~he bedrock. Hence, it is neces~ary to identify which are the possible fracture filling minerals and weather inc; products in granitic bedrock and the geochemical processes related with them. Muller [4] has made a compilation of the different types of minerals present in granite. In Table Il-l, we show the fracture­filling and secondary minerals for granite.

During the SKB site charactl!!rization program, investigations of low temperature fracturl!! fillings havli! been performed [Sa-b). Calcite, iron-oxides and clay minerals have beli!n found to cot·­respond to the latest geological I!!Vent. It has also bli!en observed that calcite is found in areas of recharge and discharge [3). Thli! dissolution-precipitation reactions of calcite and iron-oxides are known to proceed fast, even at low temperatures. The mean life of a calcite surface (monolayer) in seawater has been experimentally demonstrated to be one day [6,7]. Conseque~tly, calcite and iron­oxidli!s mobilization will play an important role in the g~oche~ica: cycle of radionuclides in the granite environment. There is a great dti!al of information about co-precip~tation liystems related to calcite dissolution-precipitation. M;.;ch less has bee:-: do:1e respect to iron hydrox1des. In the case o! goethite and limonite nrJch emphasis has been put in studying the adsorptbn prope:-ties of different ions on the iron hydroxide surface.

J. Morse [8) has done an excE:lent overvie..,. on the surface che­mistry of calcium carbonate rr.i:-:e:-als. Acco:-c.:.ng to his wo:-k and the experimt>ntal findings of different investigators it is pos­sible to find that there is a related sequence from adsorptio:-: to co-precipitation through surface precipltation. Adsorption and surface precipitation require the existence of a contiguous solid phase. However, in most of the cases the me-:han1sms of these three, prc~esses 're closli!ly related.

Hence, in our literature survey we have devoted our attention not only to radionuclide co-precipitation with calcite and iron hydroxide, but also to the investigations of radionuclide adsorp­tion on these solid phases where emphasis has been put in the surface coordination aspects.

Radionucfide Co-precipitation with C.lcite

As pointed out by Pingitorli! [9} the incorporation of trace ele­ml!!nts in calcite has an extensive impact in several areas of environmli!ntal chemist. 1 and geochemistry. The exp~rimental infor­mation collected in these areas can ~I!! summarized as follows.

----~·

\

. ;

\

14

'!.Uil• 11-1. *--ls f__. ia sr-!t.ea.

..u.nJ ~ Species 1'Jpe Specific r-La

SuJpbi ... Pyrite l'ract. fill. Fes2

Pyrrhotite l'ract. fill. l'eS( pyrr), l'e7S8

Qaicles Pyrolusite Second. •in. Hno2

.,.._idM Goethite Second. •in. FeOOH

Diaspore Second. 11in. AlOOH

llohelll i te Second. 11in. AlOOH

Gibtsite Second. 11in. Al(OH) 3

Limonite Second. min. l'eOOH nH2o FrliC t. fi 11.

Bali ... nuorite Second. min. Wz ·-

carllonat.ea Calcite l'ract. fill. eaco3

Sulpbllt.M Alunite Second. min. KA1 3(S04 )2(0H) 6

Jarosite Second. min. KFe3(S04)2(0H)b

Anhydrite Second. 11in. ease4

Gypsum Second. 11in. ease4 2112o l'ract. fi 11.

Soroa i J icatu Zo15ite l'ract. fill. CazA1 3(Si04)30H

Clinotoisite Fract. fi 11. ea2Al 3(Si04)30H

Epidote Second. min. ea21'eA1 2Csio4)30H l'ract. fill.

Piemontite FrliCt. fill. ea2CAl,Mn,Fe) 3(Si04)30H

l'llylla.ilicatM Kaolinite Second. •in. AlzSi 2o5(0H) 4 Fract. fill.

Smectite Second. •in. CaAll"SizzObo<OH>12

Clinochlore Second. ain. Hc"oAllbSizlo080(0H)blo Fract. fi 11.

Illite Second. llin. k2Al 10si 14o40 COHl 80

Sericite Second. 11in. KAlz(AlSi 3o10 )(0H,FJ 2 I

I 'beta.i U.cat.ea 0\alcedony Fract. fill. SiOz{chal) .

Opal FrliCt. fill. SiOz '.0.5H20(am)

/

---- ---- ...........

15

Dou~led charged ions with ionic radii leso; u.an calclurr (e.g. Mn2•, zn2•, Fe2•, ca2• and Co2•) can be extenslvely lncorporated into calcite precipitat~d at groundwater conditions. Spectroscopic techniques, X-Ray dlffraction and EPR measurements, have demonst­rated that these trace cations substitute ca2• in the lattice. Th~ calcium ion may occur in the caco3 lattice as hexacoordinateci (calclte), or ninefold-coordinated (aragonite). Cations larger than ca2•, like sr2•, Ba2•, Pb2• and Ra2• substitute also ca2• i~ the rombohedral calcite, even if t.heir p._.re carbonates, like strontianite or barite, bild up orthoromboedral structures. J. great number of studies have been carried out on the adsorption/ co-precipitation of Mg2+ with calcite (10,11,12,13). Bancroft et al., (10) studied the uptake of Ba2• by calcite. Also the sorption of Mn2• on calcite has been investigated by several authors [11,12.13]. McBride carried out an spectruscopic investigatlon o~ the Mn2• surface concentt·at ions by ESR ~13 1. He observed the formation of a new l'.nco3 phase at high Mn • surface concentra­tions. Also the uptake of Cu(Il) by calcite has been investigated [ 141. In this case the surface precipitated phase seer.; to cor­respor:d to malachite cu2( OH) 2co3 . The interact ion of Cd ( 11) ..,. i ~!". calcite surfaces has also been investigated by ~cBride [:5]. T~e

uptake patterns are very similar to those of Mn2•. Korn:cKer et al. I 161 studied the adsorption of co2 .. on carbonate r:ir:era~ surfaces, no evidence for the fo~a~ion of a differentlated CoCO~ phase was observed. Finally, fo:orse and co~o~orkers have dedicated much effort to the study o! the ir:terac~ !.on of actinides ...-: tr. calcite sutfaces. A:n(lll) [17]. 7h:IV) llB]. NpO~ [191, P;,jo; 12:] and uo~· [211 adsorb sign:!icar:t:y or: ca:cite. Nevertheless, there ls a co:npetlt!or. from car.cor.ate cor".plexa:::on 1n the aqueous phase, partic~larly for U(Vl). Fror" all these data a genera: mecha~~stic pattern car. be found for the transition fro::-. adsorption to co­precip;tatio~. ~~is is sche~~tized in F:g;.lre ::•2.

Site adsorp.

Mxca1_xco3(monolayer)

+ surface prec:pitation

co2· 3

+ 3-dim. lattice

+t homogeneous dist. equil.

Fiqure II-2. A tentative -chanism for ion-adsorplion/co-preci­pit.ation transi lion in calcite.

/

3

DIG.II 0'

TaACI -TAl-ION

U'TAKI

1 DAY

16

I '

..

TtN(

Figure II-3. Schematic time-dependence of radionuclide uptake by calcite. ( 1) Langmuir type adsorption = surf ace t.om­plexation; ( 2) Freundlich type adsorption • surf ace precipitation; (3) Co-Precipitation; (4) Equilibrium.

According to this model the kinetics o! rad.:.on·.;clide t.:ptai!.e by calcite could be visua!ized as in Fig~re :I-3.

Radionuclide Co-precipitation with Iron-Oxides

There is practically no ir.!ormation availaole about co-precip:ta­tion of trace metals "''lth iron-l':ydroxides/oxides. Much experlmer.­ta 1 and theoretical work has been devoted to the st-.•dy of t~e

metal adsorption on goethite-hematite surfaces. Nevertheless, Benjamin and Leckie [22], studied in a very comprehensive ~ork t~e adsorption ot trace metals (Cd, Cu. Zn a:.d Pb) on a:ncrpho~s

goethite. They observed that at low adsor;>t ion der.s it y the data could be described by a Langmuir isotherm. At larger adsorption density, the metal uptake fitted to a Freundlich behaviour (see Figure II-3). During their kineLlC experiments they also observed that the initial adsorption was fast, followed by a much slower uptake. This last step was related by the authors to a possible solid-state diffusion. This behaviour is perfectly in concordance with the previously proposed kinetic model for trace metal uptake by calcite.

The adsorption of actinides on different ferric oxy/hydroxides has been extensively studied. There is quantitative infor:nation !or uo~• [23], Pu4• and ;>uo; [24] and Np(V) [25]. In all these st\;iies

/

/

s

17

the triple layer model (TLM) [26,27,28] for surface site bo~ding has been applied and intrinsic surface binding cor.star.ts for dlfferent actinlde specie• have been obtained.

Conclusions

This study on the large literature available on trace metal upta~e by calcite and iron indicates that:

Trace metal and radionuclide uptake by naturally occurring minerals is extensive. The solubility of trace metals in r.atural waters cannot be only mvdelled from thea ir.d~v.:.d-.;a:

thermodynamic properties. Also the redox properties of radior.u­clides are drastical1y affected by their interaction with naturally occurring solid sur!aces [20].

There is a sequential transition, ADSORPTION ~ SURFACE ?~EC:?:­TATION ~ CO-PRECIPI'I'AT:ON. This has been demonstrated by spectroscopic met~ods in the case of calcite and adsorpt :c:-. data indicate a similar behaviour for ircn hydro/oxides.

'!'here is a need for theororetical and experimental develop!':'.er.<; in order to include and quantify the water-particle interface processes in the general radionuclide speciation model. Empir:­cal scavenging parameters like Kd are of very limited validity. Intrinsic surface bir.dir.g constants are by de!inition no~­

conditional and consequently the only ones applicable to the modelling of radionuclide mobility in grour.d~ater enviro~~ents. This approach has been successful:i.y tested by Ba:.istrien., M·..lrray and coworkers [ 29] in order to model trace me-:.al spec.:.a­tion in sea water.

References

1. ERIKSON, E., in "Principles and applications of hydrochemist­ry", ed. Chapman and Hall, London 1985.

2. STUMM, w.; MORGAN, J., in "Aquatic Chemistry", John Wiley and Sons. New York 1981.

3. SMELLIE, J., LARSSON, N., WIKBERG, P., CARLSSON, L •• "Hydro­chemical investigations in crystalline bedrock in relation to existing hydraulic ccnditions: Experience from the SKB test­sites in Sweden". SKBF/KBS, Technical Report TR 85-11, November 1985.

18

4. MULLER, A.B., NEA Compilation of Che~ical Thermody~~~:c Data for Minerals Associated with Granite, RWM-5, OECD, l'tuc:ear Energy Agency, Paris.

Sa. TULLBORG, E-L., LARSSON, s-A., "Fissure flllir.gs fro~ Finnsjon and Studsvik, Sweden. Identification, chemlstry and d3ting". SKBF /KBS Tech.Jical Report TR 82-20, Stockholm 1982.

Sb. TULLBORG, E-L., LARSSON, s-1.., "Fissure fillings from GldeA, Central Sweden", SKBF/KBS, Technical Report TR 83-74, Stock­holm 1983.

6. BERNER, R., MO~JE, J.: Am. J. Sci., 274, 108 (1974).

7. MUCCI, A., MORSE, W.: Geochirn. Cosmochim. Acta, 48, 8:5 (1984).

8. MORSE, J.: Mar. Chern., 20, 91 (1986).

9. PINGITORE, N., in "Geochemical Processes at Mineral S:..r­f aces", ed. Hayes and Davis, ACS Sy:r.p. Ser. 32 3, Ar... C!':e~.

Soc., Washington DC, 1986.

10. BA~:CROFT, M. , BROWN, J. , FYFE, W. : Chen:. Geol. 19, 13.­(1977).

11. BOISCHCT, P., DURROUX, M., SY:.VES':'RE, G.: Ar:n. Inst. l'ta::. Recherche Argon., Anr.. Argon. A., 1, 307 (1950).

12. LEEPER, G.W.: Ann. Rev. Plant. Physiol .• 3, 1 (1952).

13. McBR:DE, H.: Soil Sci. Soc. Am. J., 43, 693 (1979).

14. FRANKLIN, M.L., MCRSE, J.W.: Ocea~. Sci. Er.gn., 7, 147 (1982).

15. McBR!DE, M.: Soil Sci. Soc. Am. J., 44, 26 (1980).

l&. KORNICKER, W.A., MORSE, J.W., DAMASCENO, R.N.: Chem. Geol., 53. 229 ( 1985) .

17. S~~BAG, P.M., MORSE, J.W.: Geochim. Cosmochim. Acta 46, 241 (1982).

18. SHANBAG, P.H., MOPSE, J.W.: unpublished data.

19. KEENEY-KENNICUTT, W.L., MORSE, J.W.: Mar. Cherr.., 15, 133 (1984).

20. KEENEY-KENNICUTT, W.L., MORSE, J.W.: Geochim. Cosmochim. Acta 49, 2577 (1985i.

2J. MORSE, J.W., SHANBAG, P.M., SAITO, A., CHOPPIN, G.R.: Che~.

Geol., 42, 85 (1984).

19

22. BENJAMIN, H. , LECKIE, J. : J. Coll. Inter. Sc. , 79 ( 1), 209 {1981).

23. HSI, C., LANGMt:IR, D.: Geochim. Cosmochirr.. Acta 49, 193: { 1985).

24. SANC~IEZ, A., HURRAY, J., SIBLEY, T.: Geochim. Cosmochim. Ac:a 49, 2297 {1985).

2~. GIRVIN, D.C., AMES, L.L., McGARRAH, J.E.: Paclfic Northwest

Laboratory: Richlar.d W.A., November 1984, PNL-SAAA-11229.

2&. DAVIS, J., JAMES, R., LECXIE, J.: J_ Coll. Inte. Sc., c3(3),

480 ( 1978).

27. DAVIS, J., LECXIE, J.: J. Coll. Int. Sci., &7(1), 90 (:978).

28. DAVIS, J., LECXIE, J.: J. Coll. Int. Sci., 74(1), 32 (!988).

29. BALISTR1ER;, L.S., M~RRAY, J.: Am. J. Sci., 2Bl. 788 (:9e:).

Ust of SKB reports

Annual Reports 1977-78 TR 121 KBS Technical Reports 1 - 120. Summar~es S1oc~no1m. May 1979

1979 TR 79-28 The KBS Annual Report 1979. KBS Tecnn•cal Reports 79·01 - 79·27 &ummar~es Stockholm. Marct'l1980

1980 TR 8()-26 The KBS Annual Report 1980. KBS Tecnn•ca: R~po•ts 80·01 - 80·25 Summaroes Stocknolm March 1981

1981 TR81-17 The KBS Annual Report 1981. KBS Tec"~n•ca• Repo•ts 81·01 - 8 T ·16 Summaroes S1oc11no1m. Apnl 1982

1982 TR 82-28 The KBS Annual Report 1982. KBS Technoca; Reports 82·01 - 82·27 Summar~es. Stockholm. July 1983.

1983 TR 83-77 The KBS Annual Report 1983. KBS Tecnmcal Rep;:,rts 83·01- 83-76 Summar~es. Stockholm. June 1984

1984 TR85-01 Annual Research and Development Report 1984 Including Summanes of Technical Reports Issued dunng 1984. (Techn1ca1 Reports 84-01- 84·19) StockhOlm June 1985.

1985 TR85·20 Annual Research and DevP.Iopment Report 1985 Including Sum manes of Technical Repons Issued dunng 1965 (Techn•cal ~eports85-01·85-19J Stockholm May 1986.

1986

TR86·31

SKB Annual Report 1986 lncludmg Summar~es of Technocal Reporls Issued dunn~ ~986 Stockholm. May 1987

Technical Reports

1987

TR 87.01 Radar measurements perlormed at the Klipperb study site Seje Carls ten. Olle Olsson, Stefan Sehlstedt. Leif Stenber(l S>Nedish Geological Co. Uppsala/Luld February 1987

TR87.Q2 Fuel rod 007/815 from Ringhals 2 PWR: Source material for corrosion/leach tests In groundwater Fuel rod/pellet characterization program part one Roy Forsy1h. Editor Studs11ok Energoteknok AB. NykOp•ng March 1987

TR 87·03 Calculations on HYOROCOIN level1 using the GWHRT flow model Case 1 Transient flow of water from a

borehole penetrating a confined aquifer

Case 3 Saturated·unsaturated flow through a layered sequence of sedimentary rocks

Case: 4 Transient thermal convection In a saturated medium

Roger Thunvik. Royallnstotu:e of Technolulfy. S!ockholm March 1987

TR87.Q4 Calculations on HYOROCOIN level 2, case 1 using the GWHRT flow model Thermal convection and conduction around a field heat transfer experiment Roger Thunvik Royal Institute of Technology, Stockl".olm March 1987

TR87.Q5 Applications of stochastic models to solute transport in fractured rocks Lynn W Gelhar Massachusetts Institute of Technology January 1987

TR 87-06 Some properties of a channeling mod81 of fracture flow V W 'Tsang. C F isang 1 Neretn,eks Royal Institute of iechnolo~;y. Stockholm December 1986

TR 87-07 Deep groundwater chemistry Peter Wtkberg. Kann Axelsen. Falke Fredlund Royallnst,tute of Technology. Stockholm June 19~7

TR 87-08 An approach for evaluati~g ~he general and localized corrosion of carton steel containers for nuclear waste disposal GP March. KJ 'Taylor. SM Sharland. PW Tasker Harwell Laboratory. Oxtordshire June 1987

TR 87.00 Piping and erosion phenomena in soft clay gels Roland Pusch. Mtkael Erlstrom. Lennan Borgesson Swedish Geologtcal Co. Lund May 1987

TR 87-10 Outline of models of water and gas flow through smectite clay buffers Ro:and Pusch. Harald Hokmark. Lennan Borgesson Swedtsh Geolog:cal Co. Lund June 1987

TR 87-11 Modelling of crustal rock mechanics for radioactive waste storage In Fennoscandia-Problem definition Ove Stephans son University of Lulei May 1987

TR 87-12 Study of groundwater colloids ar.r.t their ability to transport radionuclides Kare r,us ·and Peter Wtkberg•• ·1nst1tute for Surface Chemtstry Stockholm

• • Royal Institute of 'Technology. lno~gantc Chemtstry Stockholm

March 1987

TR 87·13 Shallow reflection seismic investigation of fracture zon~s In the Finns;' area method evaluation irtne Dahi·J~ •sen Jonas Ltndg•en Un,verstty of Uppsa!a. Department o! GeocP'lys,cs June 1987

·rR 87-14 Combined interpretation of geophysical. geological, hydrological and radar investiga· lions in the boreholes ST1 and ST2 at the Saltsjotunnel Jan-Enk A:"ldersson Per Andersson Se1e Carlsten La•s Falk Olle Olsson Allan Strahle Swed,sh Geologtcat Co. Uppsala 1987·06·30

TR 87-15 Geochemical interpretation of groundwaters from Finnsjon, Sweden Jgnas' Putgdomenech 1

Ktrk Nordstrom2 1Royal Jnstttute of 'Technology StockhoJrr, 2U S Geologtcal Survey. Menlo Park. Cat:lornta August 23. 1987

TR 87-16 Corrosion tests on spent PWR fuel in synthetic groundwater q S Forsyth' and L 0 Werme< 1 StudSVIk Energttekntk AB. NykOptng s,.eCie'1 <The S""eCI,sP'l Nuclear Fuel and Waste Management Co :SKBt Stockholm Sweden Stockholm. September 1987

TR 87-17 The July - September 1986 Skovde aftershock sequence Conny HolmQvtst Rutger Wahlstrom Se,smologtcal Department. Uppsala Untverstty August 1987

TR 87-18 Calculation of gas migration in fractured rock Roger T,unvtk' and Carol Braester= 'Royallnst,tute c• Technology Stockholm Swe'Jen <1srae11nstttute ot Tec,nology Hatfa. Israel September 1987

TR 87-~9 Calculation of gas migration in fractured rock - a continuum approach Caroi Braester· and Roger Thunv1k: 'Israel Institute of Technology Ha1fa. Israel 2Royal lnst1tute of Technolo~;y Stockholm. Sweden September 1987

TR 87-20 Stabiiity fields of smectites and illites as a function of temperature and chemical composition '\' Tardy. J Ouplay anc1 8 Fritz Centre de Sed1mentolog1e et de Geoch1rr.1e de Ia Surface (CNRSI tnst1tut de Geo1og1e Un1vers1te Louis Pasteur (ULP) 1 rue Bless1g. F-67084 Strasbourg. France April1987

TR 87-21 Hydrochemical investigations in crystalline bedrock in relation to exesting hydraulic conditions: Klippe•·as test-site, Smaland, Southern Sweden John Smellie· N1ls-Ake Larsson' Peter W1kberg~ lgnas1 l'u1gc1omenech" Eva-Lena Tullborg' 'Swed1sch Geolog1ca1 Company. Uppsala 2Swed1sch Geo10g1cal Company, Goteborg 3Royallnstitute of Technology Stockholm 4 Btudsv1k Energi(ekn~~, AB. Nykop~ng September 1987

TR 87-22 Radionuclide sorption on granitic drill core material Trygve E Eriksen and 81rg,tta Locklund The Royal lnst,tute of Technology Department of Nuclear Chem1stry Stockholm November 1987

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