7 th Response Submittal to the EPA Enclosure 1

1 April 1 2 , 2010 EPA Comment 4

- C

- 26 On page 12 of Borkowski et al. (2008), the americium

- borate species is represented as AmB(OH) 4 2+ , but on page 46, the neod ymium

- borate species are represented as N dB 4 O 7 + and Nd(B 4 O 7

) 2 - . DOE should address whether there is any basis for assuming the identi t y of the species (borate or tetraborate) that would form, and the anticipated effects the formation of such a species would have on ne o dymium solubility in GW B and ERDA

6 brines.
EPA Reference Borkowski, M., J.

- F. Lucchini, M.K. Richma nn, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. DOE Response The EPA has correctly pointed out that there is some ambiguity i n how borate species are represented in Borkowski et al

. , (2008). This is primarily due to the complexity of the borate chemistry and the lack of clarity in the open literature about the speciation of borate species at high pH. It is possible, however, b ased on experimental work completed after the CRA

- 2009 data cutoff, to answer EPA’s question. Borate is added to GWB and ERDA

- 6 brines as the tetraborate species. It has been recently confirmed by X

- Ray Diffraction (XRD) analysis that the tetraborate st ructure is retained in WIPP brine (see Figure 1). Some Extended X

- ray Absorption Fine Structure (EXAFS) experiments are also in progress to confirm the exact structure of the metal

- borate complexes. In this context, the correct speciation is the tetrabor ate complexes proposed on page 46 of Borkowski et al. (2008) :

Neodymium(III) + B 4 O 7 2

-  NdB 4 O 7 + Neodymium(III) + 2B 4 O 7 2

-  Nd(B 4 O 7 ) 2 - The DOE has also shown that tetraborate and boric acid behave similarly with respect to pKa and complexation strength (Section 4.4.4 in Borkowski et al., 2008) . Because of this, the exact structure of the borate species does not have a significant impact on the overall solubility and solubility trends that were measured in the WIPP

- relevant experiments performed

. DOE Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.7 th Response Submittal to the EPA Enclosure 1

2 April 1 2 , 2010 Figure 1. X

- ray diffraction (XRD) pattern of precipitated tetraborate at pH ~ 9

(top spectrum) . There is an excellent fit of the XRD pattern to the tetraborate reference pattern diffraction file (bottom spectrum) that confirms that the tetraborate not boric acid sp ecies is present . The broad peak at 26 o is a background interference peak; all other peaks are specific to the tetraborate species
.7 th Response Submittal to the EPA Enclosure 1

3 April 1 2 , 2010 EPA Comment 4

- C

- 27 DOE should address whether transformation of the initial NdOHCO 3 (s) in their experiments to Nd(OH) 3 (s) could have substantially changed the carbonate concentrations during the undersaturation experiments, including whether it was possible that the initial spike addition was relatively unimportant and the total carbonate at the end of the experiments cou ld have been completely controlled by dissolution of the neodymium hydroxy

- carbonate solid. DOE Response
In the WIPP

- relevant neodymium experiments described in Borkowski et al. (2008), very small amounts (3mg or less) of the mixed hydroxy

- carbonate solid w ere added to the carbonate

- containing brine experiments performed (see Table s 4

- 2 and 4

- 4 in Borkowski et al., 2008 ). The reason for adding a very small amount was to minimize its potential impact on the brine chemistry and solubility measurements being made. With this approach, 100% dissolution of the mixed hydroxy

- carbonate phase would lead to a total additional carbonate concentration of 2.5 x 10 - 4 M. This has a relatively small potential effect on experiments with the highest carbonate concentratio ns (25% for 1 mM and 2.5% for 10 mM), but would potentially have a significant impact on the lowest concentration (0.1 mM). In the experiments performed, based on visual inspection of the solids, it was estimated that less than 10% of the initial mixed hy droxy

- carbonate phase was converted to the hydroxide phase.
DOE Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carls bad , NM: Los Alamos National Laboratory.7 th Response Submittal to the EPA Enclosure 1

4 April 1 2 , 2010 EPA Comment 4

- C

- 28 Figure 3

- 4 of Borkowski et al. (2008) show the solution concentrations of americium (III) as a function of pcH in the absence and presence of CO 2 , and the data are attributed to Kim et al. (1984). However, examination of this reference show that the reported solubility experiments were carried out in a CO 2 - free system. DOE should confirm that the data source is Bernkopf and Kim (1984) or otherwise clarify the data source. DOE should also clarify whether other references to Kim et al. (1984), for example in the final paragraphs of page 37 should in fact be Bernkopf and Kim (1984).
EPA References Bernkopf and Kim (1984)

- Bernkopf, M, and J. I . Kim. 1984. Hydrolysereaktione n und Karbonatkomp lexierung von Dreiwertigem Americium in Nat ü rlichen Aquatischen System. Report RCM

- 02884, Institute f ü r Radiochemie, Tech. Univ. Munich. Kim et al. (1984)

- Kim J.I, M. Bernkopf, Ch. Lierse, and F. Koppold. 1984. Hydrolysis reactions of Am(III) and Pu(VI) ions in near

- neutral solutions, in: Geochemical Behavior of Disposed Radioactive Waste, Eds.: GS. Barney, J.D. Navratill, W.W. Schultz; ACS Symp. Ser., No. 246, Washington, DC.: American Chemical Society 115

- 134. DOE Response The EPA is correct in pointin g out that the proper reference for the solubility of Am 3+ in carbonate

- containing systems is Berhkopf and Kim (1984), not Kim et al., (1984) as indicated in Borkowski et al., 2008. This Berhkopf and Kim reference is the correct reference for Figure 3

- 4. This reference is also the correct reference when Am

- carbonate species are discussed on page 37 (section 4.4.1) and all of Sections 3.2.3 and 4.4.1.
DOE References Bernkopf and Kim (1984)

- Bernkopf, M, and J. I . Kim. 1984. Hydrolysereaktione n und Karbona tkomplexierung von Dreiwertigem Americium in Nat ü rlichen Aquatischen System. Report RCM

- 02884, Institute f ü r Radiochemie, Tech. Univ. Munich. Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. Kim et al. (1984)

- Kim J.I, M. Bernkopf, Ch. Lierse, and F. Koppold. 1984. Hydrolysis reactions of Am(III) and Pu(VI) ions in near

- neutral solutions , in: Geochemical Behavior of Disposed Radioactive Waste, Eds.: GS. Barney, J.D. Navratill, W.W. Schultz; ACS Symp. Ser., No. 2467 th Response Submittal to the EPA Enclosure 1

5 April 1 2 , 2010 EPA Comment 4

- C

- 29 Figure 4

- 7 of Borkowski et al. (2008) shows the neodymium concentration as a function of time in the unde rsaturation experiments with GWB and carbonate. The data in this figure show that neodymium concentrations increased rapidly after the start of the experiments, then gradually decreased over time toward the final concentrations in the experiments. These da ta indicate that in the GWB experiments with carbonate, the steady

- state concentration was approached from oversaturation in the "undersaturation" experiments as well as in the oversaturation experiments. DOE should address whether this phenomenon was obse rved in the ERDA

- 6 and 5 M NaCI undersaturation experiments with carbonate.
EPA Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRS P Report. Carlsbad , NM: Los Alamos National Laboratory. DOE Response An “overshoot” of the neodymium concentration, where the concentration of neodymium initially exceeded the solubility of neodymium, was also observed in the ERDA

- 6 experiments (See Figure 1). In the 5 M NaCl experiments, early

- time data was not collected so an overshoot could have existed but there are no data to support this. The reason for this overshoot is that the dissolution of the unstable phase is faster than the rate of precipita tion for the solubility

- controlling phases. So it is a phenomenon that is often, but not always, observed in undersaturation experiments that start from a position of disequilibrium.7 th Response Submittal to the EPA Enclosure 1

6 April 1 2 , 2010 Figure 1
. Early

- time profile of neodymium concentration as a function of time in

ERDA

- 6 experiments performed. An “overshoot” in concentration profiles was observed in all experiments at pC H+ 7 to 10.7 th Response Submittal to the EPA Enclosure 1

7 April 1 2 , 2010 EPA Comment 4

- C

- 30 On page 46 of Borkowski et al. (2008), it is stated that the addition of carbonate to modeling calculations performed with Geochemists Workbench led to a slight increase in the neodymium concentration because of the formation of the Nd 2 (C0 3 ) 2 2+ complex at pcH greater than 9. The analogous americium(III) species [Am 2 (C0 3 ) 2 2+ ] is not included in the FMT database. DOE should discuss whether the Am 2 (C0 3 ) 2 2+ species should be included in the FMT database.
EPA Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Re commendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. DOE Response The calculations mentioned on page 46 of Borkowski et al. (2008) were performed as an exercise to qualitatively establish the potential impact of carbonate on the solubility of neodymium in the 5 M NaCl simplified brine system investigated. This carbonate species is not expected to be important in the more complex simulated WIPP brine systems where other species are predominant. In this context there is no significant justification to include the Am 2 (CO 3 ) 2 2+ species in the FMT database at this time.
DOE Re ference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.7 th Response Submittal to the EPA Enclosure 1

8 April 1 2 , 2010 EPA Comment 4

- C

- 31 The fo rmation of significant actinide(III)

- borate species appears to be previously unreported. DOE should investigate whether there are any literature data, for example related to dissolution of borosilicate glasses containing + III actinides, that would support or contradict the formation of such species. A publication that might be considered, among others, is Rai et al. (1992).
EPA Reference Rai et al. (1992)

- Rai, D., A.R Felmy, RW. Fulton, and J.L. Ryan. 1992. Aqueous Chemistry of Nd in Borosilicate Glass

- W ater Systems. Radiochimica Acta. 58/59: 9

- 16. DOE Response There are two literature reports of metal borate complexes that are relevant to the experimental work performed for WIPP. Bousher (1995) and Byrne and Thomson (1997) report an iron(III)

- borate complex (log K = 5.5). Bousher (1995) also reported an alumi num(III)

- borate complex (Log K = 4.5). These formation constants are qualitatively consistent with the estimated formation constant for the Nd

- borate system (log K ~ 3.5) that is reported in Borkowski et al. (2008) when the complexation tendencies of the Fe 3+ , Al 3+ and Nd 3+ are compared. The Rai et al. (1992) paper referenced in the EPA comment does not contain any information that is pertinent to the question raised. This publication pertains to a high

phosphate system under conditions that relate to h igh

- level waste glass dissolution and the authors did not provide any information on the borate that may have been present in their system and did not discuss the issue of borate explicitly.
DOE References Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory.
Bousher , A. 1995. “Unidentate Complexes Involving Borate.” J. Coord. Chem. 34 : 1

- 11. Byrne, R.H. and S.W. Thompson. 1997. “Ferric Borate Formation in Aqueous Solution.” J. Soln. Chem. 26 : 729

- 734. Rai, D., A.R Felmy, RW. Fulton, and J.L. Ryan. 1992. Aqueous Chemistry of Nd in Borosilicate Glass

- Water Systems. Radiochimica Acta. 58 /59: 9

- 16.7 th Response Submittal to the EPA Enclosure 1

9 April 1 2 , 2010 EPA Comment 4

- C

- 32 On page 29 of Borkowski et al. (2008), it was stated that XRD analysis of NdOHCO 3 (s) synthesized for the purpose of the experiments confirmed the "predominance" of a neodymium mixed hydroxy

- carbonate phase. DOE should discuss whether any XRD peaks consistent with Nd(OH) 3 (cr) or other possible solid phases were observed in the XRD pattern, i.e., whether it is possible that the solids synthesized for the experiments contained a mixture of phases. If the solids in the unde rsaturation experiments could have been a mixture of phases, DOE should address the expected impact on the solubility results.
EPA Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. DOE Response
The X

- Ray Diffraction ( XRD ) analysis of the mixed hydroxy carbonate phase (NdOHCO 3 ) was a match with the reference pattern diffraction f ile (PDF # 01

- 070

- 2054 ) for this phase. It is not, however, possible to completely exclude the presence of small amounts (~5%) of the hydroxide and carbonate phases used in the synthesis of this mixed phase with this type of analysis. The initial presence of small amounts of the hydroxide and carbonate phase, should this have been the case, will not have an impact on the final results of these neodymium experiments since the results obtained were consistent with neodymium hydroxide as the solubility contro lling phase

– a result that was essentially independent of the starting phase present. It is not possible, however, to preclude some initial effects on the concentration of neodymium prior to the achievement of the longer

term steady state concentrations

– but this does not impact the overall conclusions of the study.7 th Response Submittal to the EPA Enclosure 1

10 April 1 2 , 2010 EPA Comment 4

- C

- 33 On page 35 of Borkowski et al. (2008), it was stated that neodymium solubility was studied in 5 M NaCI at 10 - 2 M total carbonate concentration. DOE should explain why this carbonate concentration was not listed in the test matrices (Tables 4

- 2 or 4

- 4).
EPA Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in W IPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. DOE Response
Tables 4

- 2 and 4

- 4 in Borkowski et al. (2008) pertained to the initial experimental matrices developed for the planned e xperiments that governed the research. The LANL

CO WIPP Quality Assurance program permits the option of making modifications to these matrices and this is documented in the pertinent scientific notebook. In this case, the experiments to investigate the 0 .01 M carbonate case were added through this process since it became clear to the investigator that this was needed to address their scientific questions.
DOE Reference Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations.” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad, NM: Los Alamos National Laboratory.7 th Response Submittal to the EPA Enclosure 1

11 April 1 2 , 2010 EPA Comment 4

- C

- 34 Because the data in Figure 4

- 5 (neodymium(III) solubility in 5 M NaCl in the presence of carbonate) were obtained over different time periods and had different initial carbonate concentrations, it is difficult to interpret these data. DOE should provide a table showing whether the experiments were from undersaturation or oversaturation, the initial pcH and carbonate concentration, experiment duration at time of sampling, sample pcH and neodymium concentrations for the data in this figure.
EPA Reference

Bo rkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. DOE Response The DOE agrees that Figu re 4

- 5 is difficult to interpret from the graph alone. It was difficult to make the details of the data points in this Figure clear because there is significant overlap in many of these data points. The data used to plot this Figure are given in Borkowsk i (2010). The specifics for the data in the 5 M NaCl undersaturation experiments are given in Table 9 and those for the oversaturation experiments are given in Table 10 ( Borkowski , 2010). These two data sets include all the information needed to construc t Figure 4

- 5 in Borkowski et al. (2008).
DOE Reference s Borkowski, M., J.

- F. Lucchini, M.K. Richmann, and D.T. Reed. 2008. “ Actinide (III) Solubility in WIPP Brine: Data Summary and Recommendations. ” LCO

- ACP

- 08, LANL \ ACRSP Report. Carlsbad , NM: Los Alamos National Laboratory. Borkowski, M. (2010). “Numerical values for graphs presented in the report LCO

- ACP

08, Rev.0 entitled “Actinide(III) solubility in WIPP brine: Data summary and recommendations.” LANL/ACRSP report LA

- UR 10

- 00898. Reference # ACP

- 10 02

- 05

- 17

- 01. Carlsbad, NM: Los Alamos National Laboratory

.