of the American Chemical Society Meeting, Anaheim, CA, March 12-17,1978; “Nitrogenous Air Pollutants”; Grosjean, D., Ed.; Ann Arbor Press: Ann Arbor, MI, 1979; p 189. (8) Atkinson, R.; Darnall, K. R.; Lloyd, A. C.; Winer, A. M.; Pitts, J. N., Jr. Adu. Photochem. 1979,11,375. (9) Hendry, D. G. “Chemical Kinetic Data Needs for Modeling the Lower Trooosuhere”: Reston. VA, May 15-17, 1978; NBS Spec. Publ. (V.S:) 1979, NO. 557,89. (10) Hendry, D. G.; Baldwin, A. C.; Barker, J. R.; Golden, D. M. “Comouter Modeline of Simulated Photochemical Smog”: EPA600/3-’78-059, June G78. (11) Kenlev. R. A.: DavenDort. . . J. E.: Hendrv, - . D. G. J . Phys. Chem. I
.
1978,82,-io95. (12) Hoshino, M.; Akimoto, H.; Okuda, M. Bull. Chem. Soc. Jpn. 1978,51,718. (13) Atkinson, R.; Darnall, K. R.; Pitts, J. N., Jr. J. Phys. Chem. 1978, 82,2759. (14) Perry, R. A.; Atkinson, R.; Pitts, J. N., Jr. J . Phys. Chem. 1977, 81, 1607. (15) Doyle, G. J.; Lloyd, A. C.; Darnall, K. R.; Winer, A. M.; Pitts, J. N., Jr. Enuiron. Sci. Technol. 1975,9,237. (16) Llovd. A. C.: Darnall. K. R.: Winer. A. M.: Pitts. J. N.. Jr. J. Phvs. ‘ Chem: 1976,80,789. ’ (17) Dovle. G. J.: Bekowies. P. J.: Winer. A. M.: Pitts, J. N., Jr. Enuiron.-Sci. Technol. 1977; 11,45. (18) Pitts, J. N., Jr.; Carter, W. P. L.; Harris, G. W.; Winer, A. M.; ,
1
Graham, R. A. “Studies of Trace Gases from Corona Discharge Ozonizers”; Final Report to Chemical Manufacturer Association (Agreement No. 79/80), June 1980.
(19) O’Brien, R. J., Portland State University, private communication, 1980. (20) Graham, R. A.; Johnston, H. S. J. Phys. Chem. 1978,82,254. (21) Morris, E. D., Jr.; Niki, H. J . Phys. Chem. 1974, 78, 1337. (22) Japar, S. M.; Niki, H. J. Phys. Chem. 1975,79,1629. (23) Pitts, J. N., Jr.; Darnall, K. R.; Winer, A. M.; McAfee, J. M. “Mechanisms of Photochemical Reactions in Urban Air, 11. Smog Chamber Studies”; EPA-600/3-77-0146b, Feb 1977. (24) Winer, A. M.; Graham, R. A.; Doyle, G. J.; Bekowies, P. J.; McAfee, J. M.; Pitts, J. N., Jr., Adu. Enuiron. Sci. Technol. 1980, 10.461. (25) Pate, C. T.;Atkinson, R.; Pitts, J. N., Jr. J. Enuiron. Sci. Health, Part A 1976,11,1. (26) Herron, J. T.;Huie, R. E. J . Phys. Chem. 1974,78,2085. (27) Huie, R. E.; Herron, J. T. Int. J . Chem. Kinet., Symp. 1975,1, 165. (28) Japar, S. M.; Wu, C. H.; Niki, H. J . Phys. Chem. 1974, 78, 2318. (29) Carter, W. P. L.; Lloyd, A. C.; Sprung, J. L.; Pitts, J. N., Jr. Znt. J. Chem. Kinet. 1979,11,45. (30) Platt, U.; Perner, D.; Winer, A. M.; Harris, G. W.; Pitts, J. N., Jr., Geophys. Res. Lett. 1980, 7,89.
Received for review November 3,1980. Accepted March 9,1981. This work was supported primarily by the National Science Foundation, Directorate for Applied Science and Research Applications, Grant PFR7801004.
Effect of Peroxyacetyl Nitrate on the Initiation of Photochemical Smog William P. L. Carter,’ Arthur M. Winer, and James N. Pitts, Jr. Statewide Air Pollution Research Center, University of California, Riverside, California 92521
Propene-NO, mixtures ( 4 . 5 ppm each) were irradiated in air in a 5800-L evacuable environmental chamber under simulated atmospheric conditions a t 300 K with 0 to 4 . 2 6 ppm added peroxyacetyl nitrate (PAN). A 5-7-min period elapsed between final reactant (NO and NOz) injection and the beginning of the irradiation, during which time -50% of the injected PAN was cdnsumed, and some oxidation of the initial NO and propene occurred. Upon irradiation, enhanced initial rates of 0 3 formation and hydrocarbon consumption were observed, the maximum 0 3 yield increased, and the time to reach ozone maximum decreased. These observations are attributed in part to the reactions of the radicals formed in the dark reaction of PAN with NO, and to a lesser extent t o the production of NO, from the added PAN. Our results indicate that, if PAN is carried over from the previous air pollution episodes, it will enhance photochemical smog formation on subsequent days.
Introduction Peroxyacetyl nitrate (PAN), an important component of photochemical smog, is toxic to man and plants as well as being a strong lachrymator ( 1 , Z ) . The mechanism of its formation is reasonably well understood; it results from the NO,-air photooxidation of acetaldehyde (3-5) and other organics ( 5 , 6 )present in polluted atmospheres. Specifically it is formed from the reaction of NO2 with peroxyacetyl radicals formed in hydrocarbon-NO, photooxidations.
0
0
II
CH,C-00.
+ NO,
I1
CHIC-OONO,
--c
Sink processes for PAN in the atmosphere are less well understood. Smog-chamber studies (7,8)have shown that, once formed under simulated atmospheric conditions, PAN can be relatively stable, and, if NO levels remain low, it is not 0013-936X/81/0915-0831$01.25/0
consumed even upon continued irradiation. In the presence of NO, PAN is known to decompose via reaction 2 followed by reaction 3. 0 0 CH,C--OONO, I1 -t CH,C--OO* II + NO,
(2)
0
0 I1 + NO --.cCH,C--O* II +NO, CH,COO.
( 31
Although some loss of PAN, which can be attributed to reaction with NO emissions, has been observed during the night by kilometer pathlength FT-IR spectroscopy, the same study has shown that significant amounts of PAN can persist throughout the night (9). This suggests that in multiday photochemical air pollution episodes, or during stagnant atmospheric conditions, PAN formed on the previous day may persist during the night and possibly have an impact on photochemical smog formation on the following day. The possibility of ozone enhancement by residual PAN has been examined theoretically by Hendry and co-workers (10, 11). They predicted from model calculations that initially present PAN will significantly enhance the rate of photochemical smog formation due to radicals formed from its thermal decomposition (reactions 2 and 3). However, as far as we are aware, these predictions have not been experimentally tested. Consequently, we performed smog-chamber irradiations of half-ppm levels of propene and NO, in air with varying amounts of added PAN and report here the results of this study.
Experimental Section The experimental facilities and methods employed in the environmental-chamber experiments in this study have been discussed in detail elsewhere (7,12,13)and are only briefly described here. Irradiations were carried out in the 5800-L SAPRC evacuable, thermostated, Teflon-coated environ-
@ 1981 American Chemical Society
Volume 15, Number 7, July 1981 831
mental chamber which is equipped with quartz windows and is interfaced to a 25-kW solar simulator (13).Absolute light intensity within the chamber was determined periodically by using NO2 actinometry ( 1 4 ) .Relative spectral distributions were obtained with a double monochromator-photomultiplier system located a t the far end of the chamber facing the solar simulator. Temperature was monitored with thermocouples, and relative humidity with a Brady array. Methods and reliabilities for monitoring reactants and products are described in detail elsewhere (7,13).Ozone, NO, NO2 and NO, were monitored by chemiluminescence methods, and CO, organics, and PAN by gas chromatography. Known interferences by PAN and organic nitrates on chemiluminescence NO, analyzers (15) were corrected for by subtracting the chromatographically determined PAN and organic nitrate concentrations from the NO2 readings. Before each experiment, the chamber was evacuated to a t least lod5torr, pumped overnight, and then filled with purified matrix air (16) a t -60% relative humidity. The reactant injection procedure depended on whether added PAN was used in the run. In the control experiment, the propene, NO, and NO2 were all added a t approximately the same time and allowed to mix for 30 min before the irradiation. In the added PAN runs, the propene and the PAN (synthesized as described previously (17 ) )were added -30-40 rnin before the irradiation and then rapidly mixed in the chamber by turning on mixing fans for a t least 2 min. (Experience has shown that the fans completely mix gases in the chamber in less than that time.) At 5-7 min before the irradiation, the NO2 and the NO were added (in that order) and the fans again were turned on for a t least 2 min. This procedure was employed t o minimize the extent of the known dark reaction between NO and PAN (11,lB-20) prior to the irradiation (reactions 2 and 3).
Results The initial concentrations, run conditions, and selected results in the control propene-NO,-air irradiation and the propene-NO,-air runs with added PAN are shown in Table I. Plots of concentration-time profiles for PAN, 0 3 , and propene are shown in Figures 1-3. The following observations can be made from these data. During the 5-8-min period between the injection of NO, to the propene t PAN mixture and the beginning of the irradiation, consumption of PAN, NO, and propene occurs, along with formation of NO2 and acetaldehyde (the latter being a known NO,-air photooxidation product of propene ( 5 , 7 , B ) ) This . indicates the occurrence of dark reactions in the propene-PAN-NO, system. 0.25
;i 0 . 2 0 n
I
I
Table I. Experimental Conditions and Selected Results for Propene-PAN-NO, -Air Smog-Chamber Irradiations EC-317 (control) EC-320 EC-318 EC-319
run no.
av temp ("C)
30.7
30.5
30.2
30.5
av humidity ( % RH)
59
65
60
65
light intensity, k l a (min-')
0.53
0.55
0.53
dilution rate (%/h)
1.56
1.57
1.55
0.55 1.57
concn injected (ppm)
-
PAN
-0.06
-0.13
-0.26
NO
0.26
0.26
0.26
0.26
NO2
0.26
0.26
0.26
propene
0.49
0.55
0.54
0.26 0.55
0.49
0.53 0.04
0.07
0.50 0.15
concn at start of irradiation (ppm) propene
-
PAN
0.51
NO
0.26
0.22
0.17
0.10
NO2 acetaldehyde
0.28
0.29 0.009
0.33
e
0.43 0.028
0.8
2.3
5.4
9.8
4.1
5.6
7.5
initial
03
-
formation ratef(ppb min-')
initial propene loss rate8 (ppb min-I) time, O3 max (min)
1390
max 0
3 (ppm) 6-h PAN (ppm) 6-h acetaldehyde (ppm)
330
300
7.4 255
L0.613 0.642
0.689 0.755
0.130 0.142
0.153 0.207
0.089 0.077
0.065 0.051
a kj = rate of NO?photolysis, obtained from correlations between average measured solar simulator power and results of NO2 actinometry experiments ( 12) done around the time of these runs. Calculated on the basis of measured levels of the butyl nitrate Impurity in the PAN sample used, and measured PANlbutyl nitrate ratios for that sample. Calculated from 1.5 mL each of NO and NO? injected into 5774-L chamber. Background acetaldehyde levels of -2 ppb subtracted. * Data not available. Initial 0 3 formatlon rate = A(ozone)/A(time) for the first 15 min of the irradiation. 8 Initial propene loss rate = A(propene)/A(time)for the first 15 min of the irradiation.
As predicted by Hendry and Kenley (10,1 1 ) , it is seen from Figures 1-3 that the addition of PAN does indeed result in a significant increase in the rates of O3 formation, particularly in the early stages of the irradiation. For example, in the first 60 rnin 0.1 ppm of 0 3 was formed in the control experiment, whereas 0.4 ppm was formed in the run with 0.26 ppm of added PAN. The addition of PAN also increases the maximum O3 yield and results in the O3 maximum occurring more 0.8
1
,
I
OZONE
n
PAN
"
0.6
z 0
tU
2
0.4
e W z
9
0 u
0.2
0.00 -60
1 0
60
120
180
T I M E Crnln)
240
300
360
0.0 -60
P 0
' 60
120
180
240
300
360
T I M E Crnln)
Flgure 2. Observed ozone concentrations as a function of irradiation Figure 1. Observed PAN concentrations as a function of irradiationtime: (A) EC-317 (control run); (8)EC-318 (-0.13 ppm added PAN): (0) time: (A) EC-317 (control run); (8)EC-318 (-0.13 ppm added PAN); (0) EC-319 (-0.26 ppm added PAN): (0)EC-320 (-0.06 ppm added EC-319 ( ~ 0 . 2 6ppm added PAN): (0)EC-320 (-0.06 ppm added PAN). PAN).
832 Environmental Science & Technology
HONO
0.6
PROPENE a v
z
0.4
0
l-H
2
0.3
I-
w z
0. I
0.0 -60
0
60
120
180
240
300
360
TIME Cmln)
Flgure 3. Observed propene concentrations as a function of irradtation time: (A)EC-317 (control run): (8)EC-318 (-0.13 ppm added PAN); (0)EC-319 (-0.26 ppm added PAN); (0)EC-320 (-0.06 ppm added
PAN).
than 2 h earlier in the 0.26 ppm added PAN run relative to the control experiment. Although the final PAN levels were higher in the added PAN runs, the amount of PAN actually formed (final - initial) in the irradiation decreased as the amount of added PAN increased. Further, the maximum yield of the propene photooxidation product, acetaldehyde, was independent of the amount of added PAN, but the final (6-h) levels of this product decreased as the added PAN increased. Discussion
The dark reactions observed after the NO, injection are a result of the known rapid reaction between PAN and NO (11, 18, 20) which consists of reactions 2 and 3 followed, in the propene-NO,-air system, by the following reactions:
0
It
CH,.+ CO,
CH,C-O.CHy
OH
+ CH3CH=CH2
+
OH
+ NO
(12)
HONO is expected t o have a photolytic half-life of -8 min under the conditions of these photolyses ( 2 1 ) .Based on the initial NO, NO2, and propene concentrations and the rate constants for the reaction of OH with NO (22),NO2 (22),and propene (23),an estimated 15-20% of the radicals formed in the PAN dark decomposition would be “stored” as HONO to be released during t h e photolysis. The significadtly earlier occurrence of O3 formation observed in added PAN runs is due to the fact that, in addition to causing higher levels of radicals, which initiate the 03forming reactions, the addition of PAN causes lower NO/N02 ratios to prevail a t the beginning of the photolysis, due to the preirradiation dark reactions. Since the formation of 0 3 cannot occur to a significant extent until initially present NO is consumed, runs with lower initial NO levels will have 0 3 formation occurring earlier even if radical levels are the same. The higher ultimate O3 yields in the runs with added PAN can be attributed in part to higher NO, levels introduced by PAN decomposition and in part t o the higher N02/NO ratios caused by the dark reactions. The contribution of the NO, produced by the reaction of initially present PAN to the final O3 yields was indicated by modeling calculations by Hendry and Kenley (II),who predicted higher O3 yields when PAN was added to mixtures containing no initial NO. However, ozone formation is ultimately caused by the conversion of NO to NO2 by peroxy radicals formed in the hydrocarbon oxidation reactions. This manifests itself as either NO disappearahce or O3 formation (in the presence of excess NO or 03,respectively (I)).Thus, the total amount of NO and NO2 conversion occurring during a hydrocarbon-NO, -air irradiation can be estimated by the change in the quantity [Os] - [NO], i.e., A([O3] - [NO]),whichwas0.87,0.84,0.85,and0.84inthe zero, low, middle, and high added PAN runs, respectively. It can be seen that this quantity does not change significantly with the amount of added PAN. This suggests that the higher O3 yields in these experiments can be attributed primarily to the lower NO levels resulting from the dark reaction with added PAN, rather than the addition of PAN increasing the total amount of NO to NO2 conversion during irradiation.
M
+ O2 --* CH300.
--
+ NO CH30. + NO2 CH30. + O2 H 0 2 + HCHO HO2 + NO OH + NO2 OH + NO ZHONO M OH + NO2 -+H N 0 3
CH300.
(41
+ hu
202,2NO ___+
(5) (6)
(7) (8) (9)
(10)
CH3CHO
+ HCHO + 2N02 + OH
(11)
(The detailed reactions in the OH-propene-NO, system are given elsewhere (5).)These reactions account for the observed conversion of NO t o NO2 and the oxidation of propene prior to irradiation. The more rapid rates of propene consumption observed in the added PAN runs after the irradiation begins are due to the excess radical initiation resulting from both the thermal decomposition of the remaining PAN, as predicted by Hendry and Kenley ( 1 0 , I I ) (reactions 1-8),and from the photolysis of HONO formed via reactions during the period of the dark NO-PAN reaction.
Conclusions
The prediction (IO, 11)that the initial presence of PAN will enhance rates of 0 3 production and hydrocarbon oxidation in model photochemical smog systems has been experimentally verified. This enhancement in reactivity results from the decomposition of PAN in the presence of NO and is due both to the fact that these reactions form radicals which initiate the transformations occurring in photochemical smog and to the fact that these reactions convert NO to NO2, which allows earlier formation of 0 3 and higher levels to be attained. It should be noted that this enhancement will result even if all of the PAN reacts with NO emitted a t nighttime, since the NO conversion does not require sunlight, and a t least some of the radicals formed with be “stored” as nitrous acid, to be released when the photolysis begins a t sunrise. These results could have important implications regarding multiday photochemical pollution episodes where significant buildup of PAN is observed ( 9 , 2 4 ) .Under such conditions, carry-over of PAN may be a significant factor in promoting ozone formation on subsequent days and may, in part, contribute to the progressively higher 0 3 levels often observed during such episodes ( 9 , 2 4 ) . Acknowledgment
We gratefully acknowledge the assistance of W. Long, F. Burleson, G. Vogelaar, S. Aschmann, and L. Willis in conVolume 15, Number 7, July 1981 833
ducting these experiments, and discussions with R. Atkinson.
Literature Cited (1) Leighton, P. A. “The Photochemistry of Air Pollution”; Academic Press: New York, 1961. (2) Stephens, E. R. Adu. Enuiron. Sci. Technol. 1969, I , 119. (3) Altshuller, A. P.; Bufalini, J. J. Enuiron. Sci. Technol. 1971,5, 39. (4) Cox, R. A.; Derwent, R. G.; Holt, P. M.; Kerr, J. A. J. Chem. Soc., Faraday Trans. I 1976,72,2061. (5) Carter, W. P. L.; Lloyd, A. C.; Sprung, J. L.; Pitts, J. N., Jr. Int. J. Chem. Kinet. 1979,II, 45. (6) Atkinson, R.; Carter, W. P. L.; Darnall, K. R.; Winer, A. M.; Pitts, J. N., Jr. Int. J . Chem. Kinet. 1980,12,779. (7) Pitts, J. N., Jr.; Darnall, K. R.; Carter, W. P. L.; Winer, A. M.; Atkinson, R. “Mechanisms of Photochemical Reactions in Urban Air”; Final Report; EPA-600/3-79-110,Nov 1979. (8) Akimoto, H.; Bandow, H.; Sakamaki, F.; Inoue, G.; Hoshino, M.; Okuda, M. Enuiron. Sci. Technol. 1980,14,172. (9) Tuazon, E. C.; Winer, A. M.; Graham, R. A.; Pitts, J. N., Jr. “Atmospheric Measurements of Trace Pollutants by Kilometer Pathlength Fourier Transform Infrared Spectroscopy”; Final Report, EPA Grant No. R-804546, Oct 1980. (10) Hendry, D. G.; Kenley, R. A. “The Role of Peroxyacetyl Nitrate (PAN) in Smog Formation”, given at the 173rd National Meeting of the American Chemical Society, New Orleans, LA, March 20-25, 1977. (11) Hendry, D. G.; Kenley, R. A. In “Nitrogenous Air Pollutants: Chemical and Biological Implications”; Grosjean, D., Ed.; Ann Arbor Science Publishers: Ann Arbor, MI, 1979; p 137.
(12) Pitts, J. N., Jr.; Darnall, K. R.; Winer, A. M.; McAfee, J. M.
“Mechanisms of Photochemical Reactions in Urban Air”; Chamber Studies, Final Report, EPA-600/3-77-014b,Feb 1977;Vol. 11. (13) Winer, A. M.; Graham, R. A.; Doyle, G. J.; Bekowies, P. J.; McAfee, J. M.; Pitts, J. N., Jr. Adu. Enuiron. Sci. Technol. 1980, I O , 461. (14) Holmes, J. R.; O’Brien, R. J.; Crabtree, J. H.; Hecht, T. A.; Seinfeld, J. H. Enuiron. Sci. Technol. 1973, 7, 519. (15) Winer, A. M.; Peters, J. W.; Smith, J. P.; Pitts, J. N., Jr. Enuiron. Sci. Technol. 1974.8, 1118. (16) Doyle, G. J.; Bekowies, P. J.; Winer, A. M.; Pitts, J. N., Jr. Enuiron. Sci. Technol. 1977, 11,45. (17) Stephens, E. R.; Burleson, F. R.; Cardiff, E. A. J . Air Pollut. Control Assoc. 1965,15, 87. (18) Pate, C. T.: Atkinson. R.: Pitts. J. N.. Jr. J . Enuiron. Sci. Health. Part A 1976,11,19. (19) Cox, R. A.; Roffey, M. J. Enuiron. Sci. Technol. 1977,II, 900. (20) Hendry, D. G.; Kenley, R. A. J . Am. Chem. SOC.1977, 99, 3198. (21) Stockwell, W. R.; Calvert, J. G. J . Photochem. 1978,8,193. (22) Hampson, R. F., Jr. “Chemical Kinetic and Photochemical Data Sheets for Atmospheric Reactions”; US.DOT Report No. FAAEE-80-17, April 1980. (23) Atkinson, R.; Darnall, K. R.; Lloyd, A. C.; Winer, A. M.; Pitts, J. N., Jr. Adu. Photochem. 1979, I ! , 375. (24) Tuazon, E. C.; Winer, A. M.; Graham, R. A.; Pitts, J. N., Jr. Adu. Enuiron. Sci. Technol. 1980,10, 259. Received for reuiew November 10, 1980. Accepted March 16,1981. This work was supported by US.Enuironmental Protection Agency Grant No. R-800649.
Redox Behavior, Complexing, and Adsorption of Hexavalent Actinides by Humic Acid and Selected Clays Kenneth Nash, Sherman Fried, Arnold M. Friedman, and James C. Sullivan‘ Chemistry Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439
T h e sediments smectite and illite clay strongly adsorb Np(V1) from deoxygenated artificial seawater solution. In addition the former reduces the Np(V1) to Np(V). Humic acid strongly adsorbs U(VI), Np(VI), and Pu(V1) from aqueous bicarbonate-carbonate media. T h e humic acid reduces Np(V1) to Np(V), and Pu(V1) to Pu(IV), but does not reduce U(V1). Detailed spectrophotometric evidence for the complex-forming reactions is presented.
Introduction In the biosphere many organic and inorganic entities function as reducing agents. They include living organisms, nonliving organic matter, and reducing clays and minerals. T h e effect of such materials is t o facilitate or inhibit movement and concentration of trace-metal nutrients in soils and sediments. These materials may also be of great significance in the solubilization or concentration of trace-metal pollutants. Areas of t h e mid-Pacific Ocean which have low tectonic activity (i.e., midplate, midgyre regions) have been proposed as potential disposal grounds for high-level radioactive waste. T h e disposal plan involves boring holes -50 m deep in the seabed sediment, emplacing the waste canister, and backfilling the hole with the same sediment. As the waste canister deteriorates, leached radionuclides would have t o migrate horizontally and vertically through the sediment to reach the water column. T h e interactions of radionuclides with these 834
Environmental Science 8 Technology
clays are thus quite important in determining the mobility of radioactive wastes in the seabed. With respect to the problems of potential movement of radionuclides away from a nuclear waste repository, oxidizing or reducing agents may determine the tendency of metal ions to migrate away from the repository. For example, the transuranium elements are among the longest-lived products of reactor operations and hence represent one of the greatest long-term problems of nuclear activities. These metals exist in aqueous solution in multiple oxidation states which have widely varying tendencies to migrate through soil and porous rocks. T h e oxidation state can make a difference of a factor of as much as 250 in the rate of migration of the species through geologic media ( I ) . In the present work we have investigated the redox behavior, the complexing, and the absorption of hexavalent actinide ions (UOz2+, PuOz2+, Np0z2+) with selected clays and with a humic acid.
Experimental Section Stock solutions of z37Np022+and 24zPuOi’+ were prepared initially by fuming with HC104 and were periodically treated with ozone t o remove traces of lower oxidation states which grew into the solution due to radiolysis caused by the a decay of the actinides. Preparation of the U0z2+ stock has been described previously (2). Reagent-grade NaHC03, Na2CO3, and triply distilled water were used for solution preparation. Adjustment of p H was
0013-936X/81/0915-0834$01.25/0
@ 1981 American Chemical Society
