7

th Response Submittal to the EPA Enclosure 1

1 April 12, 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 neodymium-borate species are represented as NdB4O7+

and Nd(B4O7)2

-

. DOE should address whether there is any basis for assuming the 

identity of the species (borate or tetraborate) that would form, and the anticipated effects 

the formation of such a species would have on neodymium solubility in GWB and ERDA6 brines.

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 EPA has correctly pointed out that there is some ambiguity in 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, based 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 structure 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 tetraborate complexes proposed on page 46 of 

Borkowski et al. (2008): 

Neodymium(III) + B4O7

2-  NdB4O7+

Neodymium(III) + 2B4O7

2-  Nd(B4O7)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 12, 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 species is present. The 

broad peak at 26ois a background interference peak; all other peaks 

are specific to the tetraborate species. 
7

th Response Submittal to the EPA Enclosure 1

3 April 12, 2010

EPA Comment 4-C-27

DOE should address whether transformation of the initial NdOHCO3(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 could 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 were added to the 

carbonate-containing brine experiments performed (see Tables 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 concentrations (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 hydroxy-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. Carlsbad, NM: Los Alamos National Laboratory.
7

th Response Submittal to the EPA Enclosure 1

4 April 12, 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 CO2, 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 CO2-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. Hydrolysereaktionen und 

Karbonatkomplexierung von Dreiwertigem Americium in Natürlichen Aquatischen 

System. Report RCM-02884, Institute für 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 pointing out that the proper reference for the solubility of Am3+ 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. Hydrolysereaktionen und 

Karbonatkomplexierung von Dreiwertigem Americium in Natürlichen Aquatischen 

System. Report RCM-02884, Institute für 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. 246
7

th Response Submittal to the EPA Enclosure 1

5 April 12, 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 undersaturation 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 data 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 observed 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\ACRSP 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 precipitation 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 12, 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 pCH+ 7 to 10. 
7

th Response Submittal to the EPA Enclosure 1

7 April 12, 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 Nd2(C03)2

2+ complex at 

pcH greater than 9. The analogous americium(III) species [Am2(C03)2

2+] is not included

in the FMT database. DOE should discuss whether the Am2(C03)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 Recommendations.” 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 Am2(CO3)2

2+ species in the FMT database at this time.

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

8 April 12, 2010

EPA Comment 4-C-31 

The formation 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-Water 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 

aluminum(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 Fe3+, Al3+ and Nd3+ 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 highphosphate system under conditions that relate to high-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 12, 2010

EPA Comment 4-C-32

On page 29 of Borkowski et al. (2008), it was stated that XRD analysis of NdOHCO3(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 undersaturation 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 

(NdOHCO3) was a match with the reference pattern diffraction file (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 controlling 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 longerterm 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 12, 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 WIPP 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 experiments that governed the research. The LANLCO 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 12, 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

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 DOE agrees that Figure 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 Borkowski (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

construct Figure 4-5 in Borkowski et al. (2008). 

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.

Borkowski, M. (2010). “Numerical values for graphs presented in the report LCO-ACP08, Rev.0 entitled “Actinide(III) solubility in WIPP brine: Data summary and 

recommendations.” LANL/ACRSP report LA-UR 10-00898. Reference # ACP-1002-

05-17-01. Carlsbad, NM: Los Alamos National Laboratory.