Sorption of nickel on kaolinite: Completing the parameters Cation exchange capacity of kaolinite Potentiometric titration of kaolinite

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1 Working Report 2-11 Sorption of nickel on kaolinite: Completing the parameters Cation exchange capacity of kaolinite Potentiometric titration of kaolinite Sorption of europium on kaolinite Esa Puukko Martti Hakanen February 2 POSIVA QV Mikonkatu 15 A, FIN-1 HELSINKI, FINLAND Tel Fax

2 Radiokemian laboratorio Kemian laitos PL 55 (A.I. Virtasen aukio 1) 14 HELSINGIN YLIOPISTO Tutkimussopimus Posiva 9674/98/MVS TOIMEKSIANTO SORPTION MEKANISTINEN MALLINNUS - KOKEELLINEN OSA NIKKELIN SORPTIO KAOLINIITTIIN: P ARAMETRIEN TA YDENT AMINEN KOLMENARVOISEN KATIONIN (X 3 +) SORPTIO KAOLINIITTIIN Posivan raportti NIKKELIN SORPTIO KAOLINIITTIIN: P ARAMETRIEN TA YDENT AMINEN KAOLINIITIN KA TIONINV AIHTOKAPASITEETTI KAOLINIITIN POTENTIOMETRINEN TITRAUS EUROPIUMIN SORPTIO KAOLINIITTIIN SORPTION OF NICKEL ON KAOLINITE: COMPLETING THE PARAMETERS CATION EXCHANGE CAPACITY OF KAOLINITE POTENTIOMETRIC TITRATION OF KAOLINITE SORPTION OF EUROPIUM ON KAOLINITE Helsingin yliopisto Kemian laitos Radiokemian laboratorio //~ ;5C.,.,A_#--<>._/~ Timo JaakkoMro;~~sori Esa Puukko Martti Hakanen

3 Working Report 2-11 Sorption of nickel on kaolinite: Completing the parameters Cation exchange capacity of kaolinite Potentiometric titration of kaolinite Sorption of europium on kaolinite Esa Puukko Martti Hakanen Laboratory of Radiochemistry University of Helsinki February 2 Working Reports contain information on work in progress or pending completion. The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva.

4 SORPTION OF NICKEL ON KAOLINITE: COMPLETING THE PARAMETERS CATION EXCHANGE CAPACITY OF KAOLINITE POTENTIOMETRIC TITRATION OF KAOLINITE SORPTION OF EUROPIUM ON KAOLINITE ABSTRACT The sorption of nickel on fracture minerals has been modelled using the surface complexation model (SCM), which describes the reaction as the formation of a complex between the sorbing species and the surface of the mineral. The kaolinite used in the experiments was a natural kaolinite, KGa-1 b, having Ti2 and F e2 3 as the main specified impurities. The kaolinite was washed with hydrochloric acid, which removed the iron content but not Ti2. The cation exchange capacity of kaolinite KGa-1 b was determined by the means of silver thiourea (AgTU) method. The sorption of cesium and sodium on kaolinite was also studied. The kaolinites used were the natural kaolinite, kaolinite washed with acid and kaolinite conditioned with Na +. The cation exchange capacity obtained by means of the AgTU method was the same as that determined by the sorption of Cs, 4 meq/1 g kaolinite. The sorption ofna on kaolinite was low. The results obtained for the potentiometric titration of kaolinite KGa-1 b can be used to calculate the surface protonation and deprotonation constants. The kaolinite washed with acid (HKGa) was titrated with HCl or NaOH. Europium is an element of the lantanide series and can be used to simulate the trivalent actinide elements (Pu, Am). The sorption of europium on the kaolinite washed with acid (HKGa) was studied in.1 M,.1 M and.1 M NaN 3 solutions. Keywords: sorption, cation exchange capacity, kaolinite, europium

5 NIKKELIN SORPTIO KAOLINIITTIIN: PARAMETRIEN TAYDENTAMINEN KAOLINIITIN KATIONINV AIHTOKAP ASITEETTI KAOLINIITIN POTENTIOMETRINEN TITRAUS EUROPIUMIN SORPTIO KAOLINIITTIIN TIIVISTELMA Nikkelin sorptiota rakomineraaleihin on mallinnettu pintakompleksaatiomallilla, joka esittaa sorption kompleksinmuodostusreaktiona sorboivan spesieksen ja mineraalin pinnan valilla. Sorptiokokeissa kaytetty kaoliniitti oli luonnon kaoliniittia KGa-1 b, joka sisalsi epapuhtauksina Ti 2 :a ja Fe 2 3 :a. Kaoliniitin puhdistus happopesulla poisti raudan mutta ei Ti 2 :a. Kaoliniitin KGa-1 b kationinvaihtokapasiteetti maaritettiin hopea-tioureamenetelmalla. Lisaksi tutkittiin Cs:n ja Na:n sorptiota kaoliniittiin. Kokeissa kaytettiin luonnon kaoliniittia, happopestya kaoliniittia ja Na-tasapainotettua kaoliniittia. Hopeatioureamenetelmalla saatu kationinvaihtokapasiteetti oli samansuuruinen cesiumin sorption avulla maaritetyn ioninvaihtokapasiteetin kanssa, 4 meq/1 g. Natriumin sorptio kaoliniittiin KGa-1 b oli vahaista. Kaoliniitin potentiometrisella titrauksella saatavia tuloksia voidaan kayttaa kaoliniitin protonoitumis- ja deprotonoitumisvakioiden laskemiseen. Happopestya kaoliniittia (HKGa) titrattiin HCl:lla tai NaOH:lla. Europium kuuluu lantanideihin ja silla voidaan simuloida kolmenarvoisia aktinideja (Pu, Am). Europiumin sorptiota kaoliniittiin (HKGa) tutkittiin.1 M,.1 M ja.1 M NaN 3 -liuoksissa. A vainsanat: sorptio, kationinvaihtokapasiteetti, kaoliniitti, europium

6 1 CONTENTS page 1 INTRODUCTION MATERIALS The kaolinite in sodium form (NaHKGa) The specific areas of the kaolinites The determination of the cation exchange capacity by means of the silver thiourea method METHODS Sorption experiments Adjustment of ph in solutions and ph measurement Radioassay of the radionuclides SORPTION OF CESIUM ON KAOLINITE Sorption of cesium on natural kaolinite KGa-1 b Sorption of cesium on kaolinite washed with acid Sorption of cesium on kaolinite conditioned with Na SORPTION OF SODIUM ON KAOLINITE EFFECT OF CESIUM ON THE SORPTION OF NICKEL ON KAOLINITE POTENTIOMETRIC TITRATION OF THE KAOLINITE SORPTION OF EUROPIUM ON KAOLINITE CONCLUSIONS REFERENCES... 28

7 2 page LIST OF APPENDICES APPENDIX 1: Sorption of cesium on natural kaolinite (KGa-1 b) as function of ph at initial Cs concentrations,.2 M and.1 M... 3 APPENDIX 2: Sorption of cesium on kao1inite washed with acid (HKGa) at initial Cs concentrations 9 X 1 o- 12 M, 1 X 1 o- 7 M, 1 X 1 o-s M and 1 X 1 o- 3 M APPENDIX 3: Sorption of cesium on kaolinite conditioned with Na + (NaHKGa) as function of Cs concentration at ph APPENDIX 4: Sorption of cesium on kaolinite conditioned with Na + (NaHKGa) as function of Cs concentration at ph APPENDIX 5: Sorption of cesium on kaolinite conditioned with Na+ (NaHKGa) as function ofcs concentration at ph 8 and ph APPENDIX 6: Sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditoned with Na + (NaHKGa) as function of Na concentration. Primary results APPENDIX 7: Sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditoned with Na + (NaHKGa) as function ofna concentration. Recalculated values APPENDIX 8: Sorption of nickel on kao1inite washed with acid (HKGa) in.1 M CsCl-solution APPENDIX 9-12: The results of acid-base titrations of kaolinite washed with acid (HKGa) APPENDIX 13: Sorption of europium on kao1inite washed with acid (HKGa) in.1 M,.1 M and.1 M NaN 3 solutions... 42

8 3 1 INTRODUCTION The sorption of nickel on fracture minerals has been modelled using the surface complexation model (SCM), which describes the reaction as the formation of a complex between the sorbing species and the surface of the mineral. The kaolinite used in the experiments was KGa-1 b a natural "well-crystallized " kaolinite obtained from Clay Mineral Society (USA); the main impurities specified for this kaolinite were Ti2 and Fe2 3. The kaolinite was washed with hydrochloric acid, which removed the iron content but not Ti2 (Lehikoinen et al., 1999). The sorption of nickel on kaolinite KGa-1b in.1 M NaN 3 solution and in the acid ph range of 3-5 was greater than predicted by the SCM. In this ph range nickel was not expected to form complexes with the kaolinite surface and so sorption by cation exchange was an alternative explanation (Lehikoinen et al., 1999). In the present study, the cation exchange capacity of kaolinite KGa-1 b was determined by the silver thio urea (AgTU) method (Chhabra, R., et al., 1975). The sorption of cesium and sodium on kaolinite was also studied in order to determine the ion exchange capacity of kaolinite KGa-1 b. The kaolinite washed with acid (HKGa) was titrated with HCl or NaOH. The results of the potentiometric titration of kaolinite KGa-1 b can be used to calculate the surface protonation and deprotonation constants. Europium is an element of the lantanide series. Because europium exists in valence state + 3 in water solutions, Eu can be used to simulate the trivalent actinide elements (Pu, Am). The sorption of europium on the kaolinite (HKGa) was studied in.1 M,.1 M and.1 M NaN 3 solutions.

9 4 2MATERIALS The kaolinites used in the experiments were natural kaolinite, natural kaolinite that had been washed with acid and kaolinite that had been washed with acid and conditioned with Na +. The kaolinite (KGa) was a natural "well-crystallized" kaolinite, KGa-1 b, obtained from Clay Mineral Society (USA); it was washed with hydrochloric acid to remove iron impurities (Puukko and Hakanen, 1998). After being washed with acid, the kaolinite (HKGa) was then conditioned with a NaN 3 solution to produce kaolinite in sodium form (NaHKGa). 2.1 The kaolinite in sodium form (NaHKGa) The kaolinite that had been washed with acid (HKGa) was mixed with 1 M NaN 3 solution for five hours, after which the kaolinite was sedimented on the bottom of the vessel over a period of 15 hours. The solution was sucked off and kaolinite was mixed with deionised water (MilliQ) for one hour. The kaolinite was allowed to settle for 15 hours. This washing with deionised water was done three times. After washing, the kaolinite was mixed with.1 M NaN 3 solution and allowed to settle for 24 hours. The solution was sucked off and the kaolinite was dried. 2.2 The specific areas of the kaolinites The specific areas of the natural kaolinite (KGa), kaolinite washed with acid (HKGa) and kaolinite conditioned with Na+ (NaHKGa) were determined at Tampere University of Technology (TUT) by the means of the BET/N2 method. The specific areas measured for the three kaolinites were almost the same (Table 1 ).

10 5 Table 1. Specific areas measured for the kaolinites by means of the BETIN2 method (TUT). The average of the values and standard deviation (1 a). Sample (preparation date) Specific area (m 2 /g) Value Average Standard deviation (1 cr) KGa t (natural kaolinite) HKGa 11. (3298) HKGa 11.5 (14798) NaHKGa 11.3 (8897) NaHKGa 9.8 (22698) NaHKGa 1.1 (27798) KGa: natural kaolinite KGa-1 b HKGa: KGa washed with acid NaHKGa: HKGa conditioned with Na + t Puukko and Hakanen, Determination of the cation exchange capacity by means of the silver thio urea method The cation exchange capacity (CEC) of soil has been determined by the means of silver thio urea method (Chhabra et al., 1975). The results were in accordance with those of the ammoniumacetate method, which has been used as the standard method (Schollenberger and Simon, 1945). The silver thio urea (AgTU) method is based on the equilibrium of sample with silver thio urea (Ag(S=C(NH2h)n=I-4) solution. The solution is buffered with ammonium acetate and the Ag-11 Om is used as a tracer. After separation of the solid and liquid phases, the gamma radiation of Ag-11 Om is radioassayed. The cation exchange capacity can be calculated from the absorbed amount of AgTU (Chhabra et al., 1975). In the literature (Langmuir, 1997) the cation exchange capacity reported for kaolinite is 3-15 meq/1 g. The cation exchange capacities of natural kaolinite KGa-1 b (KGa), kaolinite washed with acid (HKGa) and kaolinite conditioned with Na + (NaHKGa) were determined by means of the silver thio urea method. First a thio urea solution was prepared, buffered

11 (ph 7) with ammonium acetate (NH 4 Ac ). A AgN 3 solution containing Ag-11 Om was then added to the thio urea solution. The product was.1 M AgTU solution buffered with.1 M NH 4 Ac. After weighing, 1. g of kaolinite was placed into the plastic centrifugation tubes and the AgTU solution added. The tubes were shaken for 15 hours. After centrifugation (G= 1446), samples were taken from the liquid phase and the Ag-11m was radioassayed with a Na(I)-detector (Wallac 128 Ultragamma). The calculated cation exchange capacities are presented in Table 2. The uncertainty (error) of the result is calculated on the basis of the statistics of the radioassay ( 1 cr). Table 2. Cation exchange capacity of the natural kaolinite (KGa), the kaolinite washed with acid (HKGa) and the kaolinite conditioned with Na + (NaHKGa) determined by means of the silver thio urea method. Kaolinite Cation exchange capacity CEC (meq/1 g) (preparation date) Result Error (1 a) Average Error (lcr) KGa (natural kaolinite) HKGa (14798) NaHKGa (22698) kaolinite (Langmuir, 1997) 3-15 KGa: natural kaolinite KGa-1 b HKGa: kaolinite KGa washed with acid NaHKGa: kaolinite HKGa conditioned with Na + Determination of the CEC by means of the silver thio urea method gave similar values for the three kaolinites. The results were in agreement with the value reported in the literature (Langmuir, 1997).

12 7 3METHODS 3.1 Sorption experiments The sorption experiments were made as batch experiments following the procedure ASTM standard D First the mixtures of kaolinite and electrolyte solution were shaken for 15 hours, after which the solid phase (kaolinite) was separated by means of centrifugation (Sorvall RC-5B, G= 1446). All solutions were made with deionised water (Millipore MilliQ) using p.a. grade chemicals. The retardation factor Rd was calculated from the amount of radionuclide absorbed on kaolinite and the amount of radionuclide in the solution. R = amount of radionuclide (Bq) on kaolinite x volume of solution (ml) d amount of radionuclide (Bq) in solution mass of kaolinite (g) 3.2 Adjustment of ph in solutions and ph measurement The measurement of ph was done us1ng a Orion 92A ph-meter and a Ross combination electrode (type 81 2BN). The calibration solutions were Merck's Titrisol buffer solutions (ph 4 and ph 7). In the sorption experiments for nickel, the buffer solutions (Perrin and Dempsey, 1974) were similar to those used in the earlier experiments (Puukko and Hakanen, 1998). These buffer solutions covered the ph range of 4 to Radioassay of the radionuclides Radioassay of the radionuclides was performed according to the method given in the ASTM standard D The gamma radiation of Na-22, Ag-11m and Cs-134 was measured with a Wallac 148 Wizard gamma counter equipped with a 3" Nai(Tl) detector. Nickel Ni-63 was determined using liquid scintillation counting with a Wallac 1217 Rackbeta counter.

13 8 4 SORPTION OF CESIUM ON KAOLINITE The sorption of cesium on kaolinite was studied in order to investigate the cation exchange properties of the kaolinite. Cesium is an alkaline metal; it does not form complexes in NaN 3 solution, but it is in ionic form Cs +. The sorption experiments were performed with all three kaolinite forms: natural kaolinite, kaolinite washed with acid and kaolinite conditioned with Na+. The concentration ofkaolinite was 2 g/l. 4.1 Sorption of cesium on natural kaolinite KGa-lb Sorption of cesium on kaolinite KGa-1 b was studied as a function of ph in.1 M NaN 3 solution. The experiments were done as batch experiments. Kaolinite samples were brought to equilibrium with.1 M NaN 3 solution. The ph of the mixture was then adjusted with.1 M HN 3 or.1 M NaOH. The Cs-134 was added in a CsCl solution containing Cs so that the concentration of cesium was.2 M or.1 M. The mixtures were shaken for 15 hours, after which they were centrifuged. Cesium Cs-134 was determined from the solution and ph of the solution was measured. The results are presented in Appendix 1 and in Figure 1. 16~ ~ Cs + KGa-lb +.1 M NaN ~ g 8 -r- "C:l ~ D D D D D 2 -r- D I I. I D D I.. I D D o [Cs]=.2 M o [Cs]=.1 M Figure 1. Sorption of cesium on natural kaolinite KGa-1 b as a function of ph, with two starting concentrations of cesium (.2 M and.1 M). ph

14 9 When the starting concentration of Cs was.2 M, the sorption of cesium on kaolinite KGa-1 b increased from the acidic ph range to the alkaline ph range. When the initial concentration of Cs was.1 M, the sorption increased with ph in the ph range 3-5 and was constant in both neutral and alkaline conditions. The sorption capacities of Cs can be calculated from the RI values. When the initial Cs concentration was.2 M, the maximum Rd was 9 ml/g; thus the sorbed amount of Cs was 1.6 meq/1 g. The initial Cs concentration.1 M gave Rd= 4 ml/g; thus the sorbed amount of Cs was 3.5 meq/1 g. These experiments show that the natural kaolinite KGa-1 b has sorption capacity for Cs. The sorbed amount of Cs at.1 M concentration is about the same as the values obtained with the AgTU method (Table 1 ). 4.2 Sorption of cesium on kaolinite washed with acid The sorption of Cs on kaolinite washed with acid HKGa, was studied with four initial concentrations of Cs: 9 x 1-12 M, 1 x 1-7 M, 1 x 1-5 M and 1 x 1-3 M. The concentration of HKGa was 2 g/l in.1 M NaN 3 The batch experiments were made at ph 5, when the HKGa kaolinite was in equilibrium with.1 M NaN 3 solution. In the experiments there were two parallel samples for each initial concentration ofcs. The results are presented in Appendix 2 and in Figure 2.

15 <> Cs + HKGa +.1 M NaN3 35- <>. 3 D ~ D :::::. 25 g. ~ 2-15 <> <> El 8 [J 1. 5 <>Test 1 o Test 2 l.e-12 l.e-1 1.E-8 1.E-6 1.E-4 1.E-2 l.e+oo Initial concentration of Cs (M) Figure 2. Sorption of cesium on kaolinite washed with acid HKGa at ph 5. The initial concentrations ofcs were 9 x 1-12 M, 1 x 1-7 M, 1 x 1-5 Mja 1 x 1-3 M The sorption of cesium on HKGa kaolinite in.1 M NaN 3 decreased as the initial concentration ofcs increased. The ph of the HKGa and.1 M NaN 3 has normally been about ph 5. In these experiments the ph dropped from 5 to 4, when the initial concentration of Cs was 1 x 1-3 M (Appendix 2). The sorption of Cs on -Al-OH or -Si-OH site produces H+ ions in the solution, which causes the ph to fall. Figure 3 presents the amount of absorbed Cs as a function ofthe concentration ofcs. A curve is fitted to the measured values. The amount of absorbed Cs increased with increasing concentration of Cs. The greatest experimental concentration of Cs, 1 x 1 o- 3 M, represented a concentration range at which the amount of absorbed Cs no longer changed with the initial concentration of Cs. Using the equation of the fitted curve, two values of the absorbed amount of Cs were calculated for the concentrations 6 X 1 o- 4 M and 8 X 1 o- 4 M. A regression line was fitted to these three points. The line represents the maximum level of absorbed Cs. At this level the log (Cs) was 1.95 and the amount of Cs was 1.1 meq/1 g. The CEC for AgTU of the kaolinite washed with acid HKGa was about 3. 7 meq/1 g (ph 4-5).

16 11 O.OT ~ Amount of Cs absorbed on HKGa ~ -2. ]...:.::.zo 1-4. ~ u "' "' Q) "' ~ ) Measured values o Calculated values """T""-----r----~---,---~ , r-----r O.OE+OO 2.E-4 4.E-4 6.E-4 8.E-4 l.oe-3 1.2E-3 Initial concentration of Cs (M) Figure 3. Amount of absorbed Cs (mmol/g kaol.) as a function of the concentration of Cs. The initial concentrations of Cs were 9 X 1 o-l2 M, 1 X 1 o- 7 M, 1 X 1 o- 5 M, 1 X 1 (! 3 M and the concentrations for the calculated amounts of Cs were 6 x 1 o- 4 M and 8 x 1 o- 4 M 4.3 Sorption of cesium on kaolinite conditioned with N a+ The isotherms of sorption for Cs on kaolinite conditioned with Na + in.1 M NaN3 solution were determined at three ph's: ph 3, ph 6 and ph 8-1. The ph of the kaolinite and.1 M NaN3 solution was adjusted with HN3 (ph 3) or NaOH (ph 8-1). The value of ph 6 represented the situation at which no acid or base was added to the mixture of kaolinite and.1 M NaN3. Table 3 shows the concentrations of Cs together with the ph values of the experiment at which the starting ph was ph 6. Increasing the concentration of Cs caused the ph of the solution to decrease. This phenomenon was the same as observed in the sorption experiments with KGa-1 b, the natural kaolinite. The results of the sorption experiments are shown in Appendices 3-5 and in Figures 4-6.

17 12 Table 3. Sorption of cesium on kaolinite conditioned with Na +. The initial concentrations of Cs and the ph values of the solutions at the end of experiment. Initial concentration of Cs (M) Average ph of solutions at the end of experiment t 9x x1 o xl o-) xl o xl o x1 o t The starting ph was ph 6 3~ ~ Cs + NaHKGa +.1 M NaN3 ph3 1 5 B o Test 1 o Test 2 o+-~~~~~~~~--~~~~~~~~o~~~b~~r~~~tnrl l.e-12 l.e-1 l.e-8 l.e-6 l.e-4 l.e-2 l.e+oo Initial concentration of Cs (M) Figure 4. Sorption of cesium on kaolinite conditioned with Na + as a function of the initial concentration of Cs at ph 3.

18 Cs + NaHKGa +.1 M NaN3 ph6 1 : 8 :g "Ci :: 6. B D 4 D 2 o Test 1 o Test 2 +--T-r,TT,n.. ~.. r---,-r~rn~~~~~nn--~~~~ --~~n~~~~-r~mm~ l.e-12 l.e-1 l.e-8 1.E-6 1.E-4 l.e-2 l.e+oo Initial concentration of Cs (M) Figure 5. Sorption of cesium on kaolinite conditioned with Na + as a function of the initial concentration of Cs at ph a "@ ;::: "Ci :: Cs + NaHKga +.1 M NaN3 ph 8 and ph oph 8 5.,., OpH1 l.e-12 l.e-1 l.e-8 l.e-6 l.e-4 l.e-2 l.e+oo Initial concentration of Cs (M) Figure 6. Sorption of cesium on kaolinite conditioned with Na + as a function of the initial concentration of Cs at ph 8 and 1.

19 14 The sorption of cesium on NaHKGa was similar (Figures 4 and 6) at both the acidic ph range (ph 3) and the alkaline ph range (ph 8-1). The maximum Rd was the same order of magnitude at the acidic and alkaline ph range. At the ph of kaolinite and NaN 3 (ph 6), the maximum sorption of Cs was greater than in the acidic or alkaline ph range. Also at ph 6, the ~ values of the same initial concentration of Cs varied more in the 1 o-il - 1 o- 5 M concentration range than in the acidic (Figure 4) or in the alkaline ph range (Figure 6). When the initial concentration of Cs reached the value 1 x 1 o- 4 M, the sorption of Cs decreased at all phs. Figures 7-9 present the amount of Cs that was absorbed as a function of the concentration of Cs. The sorption of Cs increased until a level was reached at which the increasing concentration of Cs did not affect to the amount of Cs that was absorbed. This level was used to calculate the maximum amount of Cs absorbed on kaolinite NaHKGa and thus the capacity of sorption for Cs on NaHKGa. The results are shown in Table 4. Table 4. Sorption capacity of cesium for NaHKGa, kaolinite conditioned with Na +. NaHKGa Sorption capacity ph meq/ 1 g kaol Average 3.9±.7

20 15.~ ~ ph 3: Amount ofcs absorbed on NaHKGa (mmollg) _ -4.. E 5 u.2 ~ Ol) D oqo D ~--~ r---r---r---r----t O.OE+OO 2.E-3 4.E-3 6.E-3 [Cs] (M) 8.E-3 1.E-2 1.2E-2 a ~ ph 6: Amount of Cs absorbed on NaHKGa (mmollg) _ -4. E 5 u rli -6. ~ Ol).2-8. ( :> o ~ r---r---r---r---r O.OE+OO 2.E-3 4.E-3 6.E-3 [Cs] (M) 8.E-3 I.OE-2 1.2E-2 b.~ ~ ph 8-1: Amount ofcs absorbed on NaHKGa (mmollg) a ' b. ] u rli -6. ~ Ol) ""T"""--""T""" t O.OE+OO 2.E-3 4.E-3 6.E-3 [Cs] (M) 8.E-3 1.E-2 1.2E-2 Figure 7. Amount of cesium (mmol/g kaol.) absorbed on NaHKGa kaolinite as a function of the concentration of Cs at three ph values ph 3 (a), ph 6 (b) and ph 8-1 (c). c

21 16 The sorption capacity of Cs for kaolinite conditioned with Na + is same at acidic and at alkaline ph ranges. At an almost neutral ph range (ph 6), the capacity was less than at ph 3 or ph 8-1. However the average sorption capacity at the three ph's, 3.9 ±.7 meq/1 g was the same as the CEC determined by means of the AgTU method, which was 4.3 ±.8 meq/1 g.

22 17 5 SORPTION OF SODIUM ON KAOLINITE The sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditioned with Na + (NaHKGa) was studied as function of the concentration of Na. The concentration of kaolinite was 2 g/l. The batch experiments were made by mixing NaN 3 solution containing Na-22 as the tracer with the kaolinite for a period of 15 hours. After centrifugation, the Na-22 content of the solution was determined. The sorption of sodium on kaolinite was so small that the results were not reliable. The Na on kaolinite was thus desorbed with CsCl. On the basis of experiences with the sorption of Cs on kaolinite, the desorbing solution chosen was.1 M CsCl. The sodium sorbed on kaolinite was desorbed by mixing the kaolinite with.1 M CsCl for a period of 15 hours. After centrifugation, the Na-22 content of the solution was determined. The desorbing procedure was repeated, but no Na-22 was detected in the second solution. 3~ ~. N a + kaolinites g HKGa and NaHKGa I. 8.5 OHKGa ONaHKGa +-~.~.~.~~.~--~~~~~~~~~~--~~~~--~~~~ l.oe-4 l.oe-3 l.oe-2 l.oe-1 l.oe+oo l.oe+ol Concentration ofna (M) Figure 8. Sorption of sodium on kaolinite washed with acid (HKGa) and on kaolinite conditioned with Na + (NaHKGa) as function of the concentration of Na. The data were calculated from the results of desorption with CsCI.

23 18 The sorption of sodium on kaolinite was low even at the low concentration of Na (1 x 1 o- 3 M), and it decreased as the concentration of Na increased. When the kaolinite and the NaN3 solution containing Na-22 were separated, a small amount of NaN3 remained in the kaolinite. The desorption solutions contained also this residue and the desorbed sodium. If the RI values of.1 M and 1 M describe the amount of Na residue, and if this value is subtracted from the other Rd values, the corrected results for the sorption of Na on kaolinite can be calculated. Figure 9 presents the recalculated values for the sorption ofna on kaolinite. 2~ ~ Na + kaolinites HKGa and NaHKGa B D D ohkga ONaHKGa ~.~--~.~.~~.~~ ~.~~~.. ~.~.~ ~~.~.~.~~.~. l.oe-4 l.oe-3 l.oe-2 l.oe- 1 Concentration ofna (M) Figure 9. Sorption of sodium on kaolinite washed with acid (HKGa) and on kaolinite conditioned with Na + (NaHKGa) as function of the concentration of Na. The data were calculated from the results of desorption with CsCI. The results obtained for the kaolinite washed with acid were similar to those obtained for the kaolinite conditioned with Na +. The sorption of sodium on kaolinite was small even in 1 xl- 4 M NaN3. The concentration of sorbed Na corresponding to the ~.4 ml/g was.4 meq/1 g ofkaolinite.

24 19 6 EFFECT OF CESIUM ON THE SORPTION OF NICKEL ON KAOLINITE The sorption of nickel on kaolinite in.1 M NaN 3 and in the acidic ph range was greater than predicted by the model (Lehikoinen et al., 1999). The effect of cesium on the sorption of nickel was studied by bringing the kaolinite to equilibrium with CsCl solution and then adding the Ni-63 tracer. The batch experiments were made in ph buffered (ph 3-9).1 M NaN 3 solutions. The kaolinite washed with acid was mixed with solution containing.1 M NaN 3 and.1 M CsCl. The tracer Ni-63 was in the acidic solution and so the spike solution was dried on a teflon plate. Adding of the Ni-63 tracer in this way did not change the ph of the solution. The kaolinite and solution were mixed for a period of 15 hours and then centrifuged. The ph of each solution was measured and the Ni-63 determined. The results are shown in Appendix 8 and Figure 1. l.e+6- l.e+5 ;. = ,. Ni + HKGa + NaN3 I.E+4 ~. ~. a :;' I.E+3 ~ l.e+2 ~. l.e+1 ~ o.1 M NaN3 o.1 M NaN3 6.1 M CsCI (+.1 M NaN3) 1.E+OO +---r---r--~~---r---r---.,.--"t"""--r----r-~ ro-~---,~ Figure 1. Sorption of nickel on kaolinite washed with acid (HKGa) in.1 M NaN M CsCI as function of ph (buffered solutions). ph

25 2 Figure 1 also presents data on the sorption of Ni in.1 M NaN3. At the acidic ph range (ph < 6), cesium fills the sites of sorption and the sorption of nickel is thus small. At the alkaline ph range, there is no difference in sorption between the NaN3 and CsCl solutions. This finding shows that at the acidic ph range nickel is sorbed by the cation exchange when sites for this are available. At the alkaline ph range, nickel forms complexes with the surface of kaolinite.

26 21 7 POTENTIOMETRIC TITRATION OF THE KAOLINITE The kaolinite was titrated in order to produce data from which the protonation and deprotonation constants of the kaolinite could be calculated. The potentiometric titrations of the kaolinite washed with acid (HKGa) were carried out at ionic strength I=.1 M of the background electrolyte NaN 3. The acid (HCl) and base (NaOH) solutions used were made from Merck Titrisol solutions. Separate titrations were made for the acidic and alkaline ph ranges. The titration of the kaolinite was continous, starting from the ph of the mixture of kaolinite and.1 M NaN 3. Nitrogen gas was bubbled through the titration vessel so that C 2 would be excluded. The measurement of ph was done with an Orion 92A ph meter and a Ross 812 combination electrode. The system was calibrated with Merck Titrisol buffer solutions ph 4, ph 7 and ph 1 each day before the ph measurements were made. The condition of the electrode was checked regularly according the instructions of the manufacturer. The acid or base was added using the Schott Titronic 97 dosing unit. According to the definition ph= -logah where ah is the activity of H+ ion The activity ofh+ where YH is the activity coefficient of H+ and [H+] is the concentration of H+ The YH can be calculated using the Davies equation 2.[j log y H = -.5 * z H * r: -.3 *I 1+vl where I is the ionic strength and ZH is the charge I=-* 1 2 c.* z. 2 2 l l where Ci is the concentration of component i and Zi is the charge The equation of ph can be written ph = - log y H * [H+] The measured ph values were converted to concentrations of H+ using these equations.

27 22 Blank titrations,.1 M NaN 3 without kaolinite, were made and these values were subtracted from the titration values for the kaolinite-nan 3 mixtures. The results are in Appendices Examples of the titration curves are given in Figures 11 and E-3 Kaolinite HKGa +.1 M HCl in.1 NaN3 9.E-4 S.E-4 7.E-4 ~ 6.E-4 + S.E-4 2:. 4.E-4 3.E-4 2.E-4 1.E-4 () O.E+OO O.OE+OO 2.E-5 4.E-5 6.E-5 8.E-5 1.E-4 1.2E-4 1.4E-4 1.6E-4 HCl (mol) Figure 11. Titration ofkaolinite HKGa with HC! in.1 M NaN 3.,_._, l.e+oo , Kaolinite HKGa +.1 M NaOH in.1 M NaN3 l.e- 1 1.E-2 l.e-3 1.E l.e-5 2:. 1.E-6 1.E-7 1.E-8 1.E-9 l.e r-r--""'t""~-~"""t"-r--.,...~-,--"""t""---,r--,--~-, ,r--,--~--1 O.OE+OO 2.E-5 4.E-5 6.E-5 8.E-5 l.oe-4 1.2E-4 1.4E-4 1.6E-4 1.8E-4 2.E-4 NaOH (mol) Figure 12. Titration of kaolinite HKGa with NaOH in.1 M NaN 3.

28 23 8 SORPTION OF EUROPIUM ON KAOLINITE Europium is an element belonging to the lanthanide series of the Periodic System. Europium has valence state of 3+ and so in sorption experiments, Eu can be used to simulate the elements ofthe actinide series, americium for instance. The isotope Eu-152 is a gamma emitter and it can easily be assayed from the samples. The kaolinite used in the experiments was HKGa, kaolinite washed with acid. The concentration of HKGa was 2 g/l and the batch experiments were made at three ionic strengths:.1 M,.1 M and.1 M NaN3. The work was done in a glove box filled and purged with argon. The concentration of oxygen was measured to be below 1 ppm; thus C 2 had a negligible effect on the experiments. The ph of the kaolinite NaN3 mixtures was adjusted with HN3 or NaOH (Merck Titrisol). The tracer Eu-152 was dried on plastic sheets put into the centrifugation tubes containing the kaolinite NaN3 mixtures. The addition of Eu-152 therefore did not change the ph of the mixtures. After 18 hours of mixing, the ph was measured with a Ross 812 combination electrode and an Orion 92A ph meter. The tubes were then transferred from the glove box to the centrifuge. After centrifugation, samples were taken from the solutions and assayed by an Nal detector (Wallac 128 Ultrogamma). The results are presented in Appendices and in Figures

29 24 6.~ ~ Eu + HKGa +.1 M NaN e g e ph Figure 13. Sorption of europium on the kaolinite washed with acid (HKGa) in.1 M NaN Eu + HKGa +.1 M NaN3 <> <> <> <> <> ~ ]_ 4. ~ 3. 1)..9 C> Figure 14. Sorption of europium on the kaolinite washed with acid (HKGa) in.1 M NaN3. ph

30 25 6.~ ~ Eu + HKGa +.1 M NaN3 5.. B ~ g 4.. ~ 3. 1).9 2. ID ph Figure 15. Sorption of europium on the kaolinite washed with acid (HKGa) in.1 M NaN 3. At the acidic ph range, the sorption of europium on kaolinite was greater in the.1 M and.1 M NaN 3 solutions than in the.1 M NaN 3 solution. At the two lower ionic strengths, the sorption seems to have a maximum around ph 5-6; the sorption then decreases in the alkaline ph range. In the.1 M NaN 3 solution the sorption of Eu on kaolinite was small at the acidic ph range; this is because the Na + ions take up the ion exchange sites. The sorption increases towards the alkaline ph range (ph 8-9), where Eu is sorbed by the surface complexation mechanism.

31 26 9 CONCLUSIONS The ion exchange properties of kaolinite were studied by using the silver thio urea (AgTU) method to determine the cation exchange capacity and by measuring the sorption of cesium or sodium on kaolinite. The results of these two methods are summarized in Table 5. Table 5. Sorption capacity of the kaolinite determined by silver thio urea (AgTU) method and by sorption of cesium. Kaolinite Sorption capacity (meq/1 g) AgTU Cs KGa 3.7 ± (ph 4-5) HKGa (14798) 3.75 ± (ph 4-5) 4.5 (ph 3) NaHKGa 4.3 ± (ph 6) (22698) kaolinite t 4.1 (ph8-1) 3.9±.7 (average) 3-15 KGa: natural kaoliniitti KGa-1 b HKGa: kaolinite KGa washed with acid NaHKGa: kaolinite HKGa conditioned with Na + t Langmuir, 1997 The results obtained with the silver thio urea method differ not between the three kaolinites: the natural kaolinite, the kaolinite washed with acid and the kaolinite conditioned with Na+. Thus the processing ofkaolinite did not change the ion exchange properties of the kaolinite. The cation exchange capacity was about 4 meq/1 OOg. The sorption capacity determined by the sorption of cesium on kaolinite washed with acid was lower than that detected by means of the AgTU method. However, the sorption capacities of Cs for natural kaolinite and kaolinite conditioned with Na + equalled the values obtained with the AgTU method. The results for Cs sorption showed a slight effect of ph on the sorption capacity, but the ph depedency mentioned in the literature was not discovered.

32 27 The sorption capacity determined for kaolinite was small and does not explain the sorption behaviour of nickel in the acidic ph range at low ionic strength. The sorption of sodium on kaolinite KGa-1 b was small. However, when the ionic strength changes from.1 M to.1 M NaN3, nickel is not sorbed on kaolinite in the acidic ph range. In the case of cesium, a.1 M CsCl solution acted like.1 M NaN3. The results obtained for the titration of kaolinite are preliminary and still need to be fitted with the FITEQL program. Once this has been done, the results can be evaluated. More work should be done to gather additional data for statistical evaluation. The composition of the kaolinite-nan3 mixture should also be determined, especially at the acidic or alkaline ph range.

33 28 REFERENCES ASTM D (Reapproved 199): Standard Test Method for Distribution Ratios by the Short-Term Batch Method ASTM D : Standard Practices for the Measurement of Radioactivity Chhabra, R., Pleysier, J., Cremers, A. 1975, The measurement of the cation exhange capasity and exhangeable cations in soils: A new method, Proceedings of the International Clay Conference, Langmuir, D Aqueous Environmental Geochemistry, Prentice-Hall, Lehikoinen, J., Olin, M., Puukko, E., and Hakanen, M Application of surface complexation modelling: Adsorption of nickel on KGa-1 b kaolinite, working report POSIV A Perrin D. D. and Dempsey, B Buffers for ph and metal ion control, Chapman and Hall, London. Puukko E. and Hakanen M Surface complexation modelling: Experiments on sorption of nickel on quartz, goethite and kaolinite and preliminary tests on sorption of thorium on quartz, report POSIV A Puukko E. and Hakanen M Characterisation of kaolinite and the sorption of nickel on kaolinite, working report POSIV A Schollenberger, C.J. and Simon, R.H Determination of exchange capacity and exchangeable bases in soil - ammonium acetate method, Soil. Sci. Vol 59, 1.

34 29 LIST OF APPENDICES APPENDIX 1: APPENDIX2: APPENDIX3: APPENDIX4: APPENDIX5: APPENDIX6: APPENDIX 7: APPENDIX 8: APPENDIX 9-12: Sorption of cesium on natural kaolinite (KGa-1 b) as function of ph at initial Cs concentrations,.2 M and.1 M. Sorption of cesium on kaolinite washed with acid (HKGa) at initial Cs concentrations 9 X 1 o- 12 M, 1 X 1 o- 7 M, 1 X 1 o- 5 M and 1 x 1-3 M. Sorption of cesium on kaolinite conditioned with Na+ (NaHKGa) as function of Cs concentration at ph 3. Sorption of cesium on kaolinite conditoned with Na + (NaHKGa) as function of Cs concentration at ph 6. Sorption of cesium on kaolinite conditoned with Na+ (NaHKGa) as function ofcs concentration at ph 8 and ph 1. Sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditoned with Na + (NaHKGa) as function of Na concentration. Primary results. Sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditoned with Na+ (NaHKGa) as function of Na concentration. Recalculated values. Sorption of nickel on kaolinite washed with acid (HKGa) in.1 M CsCl-solution. The results of acid-base titrations ofkaolinite HKga APPENDIX 13: Sorption of europium on kaolinite washed with acid in.1 M,.1 M and.1 M NaN 3 solutions.

35 3 APPENDIX 1 Table 6. Sorption of cesium on natural kaolinite (KGa-1 b) as function of ph at initial Cs concentrations,.2 M and.1 M The amount ofkaolinite was 2 g/l. The errors of sorption S % and Rd (1 er) are due to the statistics of the radioassay. [Cs]=.2 M Kaolinite NaN3 pht S% Error Rd Error mass (g) volume (ml) (ml/g) (ml/g) Cs]=.1 M Kaolinite NaN3 pht S% Error Rd Error mass (g) volume (ml) (ml/g) (ml/g) t ph at the end of the experiment

36 31 APPENDIX2 Table 7. Sorption of cesium on kaolinite washed with acid (HKGa) at initial Cs concentrations 9 X 1 o- 12 M, 1 X 1 o- 7 M, 1 X 1 o- 5 M and 1 X 1 o- 3 M The amount of kaolinite (batch 3298) was 2 g/l and the specific area 11 m 2 /g. The errors of sorption S% and Rd (1 a) are due to the statistics of the radioassay. Experiment 1 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) (ml/g) (ml/g) x X x 1 o x 1 o x 1 o x 1 o x 1 o x 1 o-j Experiment 2 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) (mllg) (mllg) X x x 1 o x 1 o x 1 o x 1 o-) x 1 o-j x 1 o t ph at the end of the experiment

37 32 APPENDIX3 Table 8. Sorption of cesium on kaolinite conditioned with Na + (NaHKGa) as function of the Cs concentration at ph 3. The amount of kaolinite NaHKGa (batch 22698) was 2 g/l and the specific area (9. 83 ±. 4) m 2 /g. The errors of sorption S % and Rd ( 1 a) are due to the statistics of the radioassay. ph 3 Test 1 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) (ml/g) (ml/g) X x X x 1 o x 1 o x 1 o X x 1 o X lx ph 3 Test 2 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) {ml/g) (ml/g) x x x 1 o-' x Io-' x 1 o x 1 o X x 1 o x 1 o--' lx t ph at the end of the experiment

38 33 APPENDIX4 Table 9. Sorption of cesium on kaolinite conditioned with Na + (NaHKGa) as function of the Cs concentration at ph 6. The amount of kaolinite NaHKGa (batch 88697) was 2 g/l and the specific area ( 11.2 ±.14) m 2 /g. The errors of sorption S % and Rd ( 1 a) are due to the statistics of the radioassay. ph 6 Test 1 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) (mvg) (mvg) , X x x 1 o x 1 o x 1 o x 1 o X x 1 o x 1 o x ph 6 Test 2 Kaolinite NaN3 ph t [Cs] S% Error Rd Error mass (g) volume (ml) (M) (mug) (mug) X X x 1 o-' X 1-/ x 1 o x 1 o X x 1 o x 1 o-j x t ph at the end of the experiment

39 34 APPENDIX5 Table 1. Sorption of cesium on kaolinite conditioned with Na + (NaHKGa) as function of the Cs concentration at ph 8 and ph 1. The amount of kaolinite NaHKGa (batch 22698) was 2 g/l and the specific area (9.83 ±.4) m 2 /g. The errors of sorption S% and Rd (1 cr) are due to the statistics of the radioassay. ph 1 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) (mllg) (ml/g) X x x 1 o X x 1 o x 1 o X X X x 1 o x 1 o X ph8 Kaolinite NaN3 pht [Cs] S% Error Rd Error mass (g) volume (ml) (M) (mllg) (mllg) X x x 1 o X x 1 o x 1 o-) X X X x 1 o X X t ph at the end of the experiment

40 35 APPENDIX6 Table 11. Sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditioned with Na + (NaHKGa) as function of the Na concentration. Primary results. The errors of sorption S% and Rd (1 a) are due to the statistics of the radioassay. NaKGa Kaolinite NaN3 pht [Na] S% Error Rd Error mass (g) volume (ml) (M) (mvg) (mvg) HKGa Kaolinite NaN3 pht [Na] S% Error Rd Error mass (g) volume (ml) (M) (mvg) (mvg) t ph at the end of the experiment

41 36 APPENDIX7 Table 12. Sorption of sodium on kaolinite washed with acid (HKGa) and kaolinite conditioned with Na + (NaHKGa) as function of the Na concentration. Recalculated values. The errors of sorption S% and Rd (1 a) are due to the statistics of the radioassay. NaKGa Kaolinite NaN3 pht [Na] Rd Error mass (g) volume (ml) (M) (mug) (mug) HKGa Kaolinite NaN3 pht [Na] Rd Error mass (g) volume (ml) (M) (mug) (mug) t ph at the end of the experiment

42 37 APPENDIX8 Table 13. Sorption of nickel on kaolinite washed with acid (HKGa) in.1 M CsCI solution. The errors of sorption S % and Rd (1 a) are due to the statistics of the radioassay. Kaolinite NaN3 pht Ni Error Rd Error mass (g) volume (ml) S% (ml/g) (ml/g) t ph at the end of the experiment

43 38 APPENDIX9 Table 14. Titration of kaolinite HKGa (kaolinite washed with acid) with.1 M HCI in.1 M NaN 3. The concentration of kaolinite was 1 g/l. Total volume HCl added [H+] measured [H+] added ml mol M M O.OOE+OO 3.99E E E E-5 9.3E E E E E E E E-5 1.6E E E-5 1.9E E E E E E E E E E E E-5 3.8E E E E E E E E E E E E E E E E E E E-4 7.9E E E-4 8.4E E E-4 8.9E E-5 5.7E E E E E E E-4 1.4E E E-4 1.9E E E E E E E E E E E E E E-4 8.1E E E-4 8.3E E E-4 8.6E E E E E E E E-3 Kaolinite HKGa (batch 14798) mass: 1.33 g specific area: 11.4 ±.2 m 2 /g

44 39 APPENDIX 1 Table 15. Test 1: Titration of kaolinite HKGa (kaolinite washed with acid) with.1 M NaOH in.1 M NaN 3. The concentration ofkaolinite was 1 g/l. Total volume NaOH added [H+] measured [H+] added ml mol M M 1.62 O.OOE+OO 2.2E-5 2.2E E E-6 1.1E E E E E E-9 4.3E E E E E E E E E-11 Kaolinite HKGa (batch 14798) mass: 1.44 g specific area: 11.4 ±.2 m 2 /g

45 4 APPENDIX 11 Table 16. Test 2: Titration of kaolinite HKGa (kaolinite washed with acid) with.1 M NaOH in.1 M NaN 3. The concentration of kaolinite was 1 g/l. Total volume NaOH added [H+] measured [H+] added ml mol M M 1.28 O.OOE+OO 3.72E E E E E E E E-5 7.8E Kaolinite HKGa (batch 14798) mass: 1.12 g specific area: 11.4 ±.2 m 2 I g

46 41 APPENDIX 12 Table 17. Test 3: Titration of kaolinite HKGa (kaolinite washed with acid) with.1 M NaOH in.1 M NaN 3. The concentration of kaolinite was 1 g/l. Tot. vol. NaOH [H+] (M) [H+] (M) Tot. vol. NaOH fh+l (M) fh+] (M) ml mol meas. added ml mol meas. added 1.31 O.OOE+OO 4.22E E E E E E E-5 5.2E E E E E-6 3.5E E E E E E E E E-5 2.E E E E-5 5.2E E E E E E E E E E E E E E E E E E E E E E E E E E-4 1.8E E E E E E E-1 3.4E E E E E-4 8.8E E E E E E-4 8.5E E E E E E E-1 3.6E E E E E E E E E E E E E E E E E-4 5.8E E E E-5 3.7E E-4 5.4E E E-5 1.4E E E-4 5.5E E E E E E E E E E E E E E E-5 7.7E E E E E E E E E-4 4.4E E E E E E E E E E E E E E E E E E E-1 2.1E E E E E-4 3.3E-1 2.4E E E E E E E E E E E-4 3.2E E E E E E E E E E E E E E E E-7 1.8E E E E E E-7 1.2E E E E E E E E E E E-5 1.6E E E-4 2.4E E E E E E E-1 1.6E E E-8 8.E E E E E-5 3.7E E E E E E E E E E E E E-8 6.8E E-4 2.6E E E E E E E E E-5 1.6E E E E E E E E E E E E E E E E E E-5 5.4E E E-4 1.8E-1 1.3E E-5 4.6E-9 5.1E-13 Kaolinite HKGa (batch 14798) mass: 1.15 g specific area: 11.4 ±.2 m 2 /g

47 I Table 18. The sorption of europium on kaolinite washed with acid (HKGa) in.1 M,.1 M and.1 MNaN 3 solutions. The errors (1 o:j are due to statistics of the radioassay M NaN3.1 MNaN3.1 MNaN3 mass ph Rd Error mass ph Rd Error mass ph Rd (g) (ml/g) (ml/g) (g) (ml/g) (ml/g) (g) (ml/g) Kaolinite HKGa (9198) specific area: 1.9 ±.4 m 2 /g Error (ml/g) ~ N > ~ ~ ~ ~ ~ ~ >< ~ w