3 Application of Inorganic Sorbents in Actinide Separations Processes W A L L A C E W. SCHULZ Rockwell Hanford Operations, Richland, WA 99352
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JOHN W. KOENST Mound Facility, Monsanto Research Corporation, Miamisburg, OH 45342 DAVID R. T A L L A N T Sandia Laboratories, Albuquerque, NM 87185
Plant-scale applications of organic ion exchange resins, both anion and cation, in actinide recovery, separation, and purification processes are well established. Typical anion resin applications include tailend purification and concentration of plutonium and neptunium recovered by the Purex process and recovery and separation of Np and Pu from irradiated neptunium targets. (1) Cation exchange resins are used in Am recovery and purification processes and, also, in pressurized systems, to recover and purify kilogram amounts of Cm and Am. (2) For several good reasons - poor hydraulic behavior, unsatisfactory sorption kinetics, unavailability, in some cases, of commercial quantities, etc., - inorganic sorbents, in contrast to their organic counterparts, have not been used extensively in the backend of the nuclear fuel cycle. Also, such production-scale applications of inorganic exchangers as have been made have been concerned much more with sorption of particular fission products (e.g., Cs) than with separation or purification of actinides. This paper summarizes the present status of research which is currently underway at several U. S. Department o f Energy 237
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l a b o r a t o r i e s - Rockwell Hanford Operations, Mound F a c i l i t y , and Sandia L a b o r a t o r i e s , Albuquerque - t o explore the p r o p e r t i e s and c h a r a c t e r i s t i c s o f two i n o r g a n i c sorbents, bone char (a form o f calcium hydroxyapatite) and sodium t i t a n a t e [Na(Ti20sH)], i n decontaminating l i q u i d waste streams from a c t i n i d e s and i n s e p a r a t i n g americium and curium from l a n t h a n i d e s . Success i n t h i s research might l e a d t o a p o t e n t i a l breakthrough i n p l a n t s c a l e a p p l i c a t i o n o f i n o r g a n i c exchangers i n a c t i n i d e s e p a r a t i o n schemes. Sorbent: P r e p a r a t i o n - S o u r c e - P r o p e r t i e s Bone Char. Bone char, a form o f calcium hydroxyapatite [Caio(POi|)g(OH)2]» i s the commercial name given a n a t u r a l product 0-8412-0527-2/80/47-117-017$05.00/0 © 1980 A m e r i c a n C h e m i c a l Society Navratil and Schulz; Actinide Separations ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
ACTINIDE SEPARATIONS
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made from granulated cattlebone. In the United States t h i s m a t e r i a l i s c u r r e n t l y a v a i l a b l e i n granular form from S t a u f f e r Chemical Corporation at a cost of approximately $1.00/kg ( $ 0 . 5 0 / l b ) . The chemical composition of the commercial product along with some p e r t i n e n t p h y s i c a l p r o p e r t i e s i s l i s t e d i n Table I; the Ca/P weight r a t i o i n bone char i s 2.153 compared t o 2.156 i n pure calcium hydroxyapatite. A d d i t i o n a l information on some other p r o p e r t i e s of bone char i s given elsewhere. (_3) TABLE I
Downloaded by FUDAN UNIV on February 15, 2017 | http://pubs.acs.org Publication Date: April 16, 1980 | doi: 10.1021/bk-1980-0117.ch003
SELECTED PHYSICAL PROPERTIES OF BONE CHAR AND SODIUM TITANATE Property
Sodium T i t a n a t e
Bone Char 3
Bulk d e n s i t y (g/cm ) Surface area (m /g) Pore volume (cm /g) Average p a r t i c l e s i z e (mm) 3
(a) Composition:
0.35 200-U00
0.6Ul 110-120 0.25-0.30 1.1
2
0.25
7.0-8.5$ C; 214.3-25.0$ Ca; 0.k-0.6% Fe; 0.02-0.03$ A l ; 0.50-0.7$ Mg; ih.8-15.2$ P.
Sodium T i t a n a t e , Niobate, and Z i r c o n a t e . Preparation and p r o p e r t i e s of the inorganic c a t i o n exchangers Na(Ti20 H), Na(Nb 0 H), and N a ( Z r 0 H ) have been i n t e n s i v e l y studied by R. G. Dosch and h i s colleagues at Sandia L a b o r a t o r i e s . (j^,_5) These ion exchange m a t e r i a l s are synthesized v i a the h y d r o l y t i c r e a c t i o n of NaOH and water with the metal alkoxides T i ( 0 C H ) i , Nb(0C2H )5, and ZriOC^Hg)^ as i l l u s t r a t e d f o r preparation of sodium t i t a n a t e (Eqn l ) . 5
2
6
2
5
3
7
+
5
NaOH(methanol + 2 T i ( 0 C H ) i 3
7
+
+ UH 0 2
- N a ( T i 0 H ) + 8C H 0H ( l ) 2
5
3
7
Titanium isopropoxide and NaOH are reacted i n a molar r a t i o of 2:1, r e s p e c t i v e l y , with the t i t a n i u m isopropoxide added t o the NaOH-methanol s o l u t i o n with s t i r r i n g . Subsequently, h y d r o l y s i s i s done by pouring the mixture i n t o an acetone-water mixture c o n t a i n i n g 8.5 vol$ water; one l i t e r of the acetone-water mixture i s r e q u i r e d f o r each mole of t i t a n i u m . The hydrolyzed m a t e r i a l i s coarse and can be e a s i l y and r a p i d l y vacuum f i l t e r e d through a 50 micrometer f r i t . A f t e r drying at ambient temperature under vacuum, d r i e d t i t a n a t e powder i s then screened with the m a t e r i a l which passes a Number ho U. S. Standard sieve and i s r e t a i n e d on a Number ikO U. S. Standard sieve being the desired fraction. Some p r o p e r t i e s of sodium t i t a n a t e powder are l i s t e d i n Table I. Sodium z i r c o n a t e and sodium niobate exchangers have been prepared only i n small l a b o r a t o r y - s c a l e batches and t h e i r p r o p e r t i e s have been f a r l e s s w e l l c h a r a c t e r i z e d than those of
Navratil and Schulz; Actinide Separations ACS Symposium Series; American Chemical Society: Washington, DC, 1980.
3.
SCHULZ E T AL.
Inorganic
sodium t i t a n a t e . Kilogram q u a n t i t i e s o f -UO+lUO mesh sodium t i t a n a t e powder, s y n t h e s i z e d according t o Equation 1, have been prepared by Cerac, Inc., Milwaukee, Wisconsin. A l s o , a cooperative research program between Rockwell Hanford Operations and Sandia L a b o r a t o r i e s i s underway t o develop p e l l e t - f o r m s o f t i t a n a t e with b e t t e r h y d r a u l i c p r o p e r t i e s than the powder. Two such forms c u r r e n t l y being t e s t e d are 1.6 mm diameter c y l i n d e r s prepared by room temperature e x t r u s i o n of water-wet powder and t i t a n a t e - l o a d e d m a c r o r e t i c u l a r anion exchange r e s i n s . E q u i l i b r a t i o n o f sodium t i t a n a t e , sodium n i o b a t e , and sodium z i r c o n a t e with d i l u t e HNO3 s o l u t i o n s converts them t o the r e s p e c t i v e hydrogen forms H ( T i 0 H ) , H(Nb 0 H), and H ( Z r 0 H ) . (Vacuum d r i e d , -^0+lUO mesh hydrogen form exchangers were used i n some of the work reported here.) T i t a n a t e , z i r c o n a t e , and niobate exchangers e x h i b i t v a r y i n g s t a b i l i t i e s toward HNO3 s o l u t i o n s . The t i t a n a t e sorbent i s s t a b l e i n
