Nov. 12, 1974 R. H. MOORE 3,848,048 RECOVERY OF FISSION-PRODUCED TECHNETIUM, PALLADIUM, RHODIUM AND RUTHENIUM Filed July 12. 1973 cr, in "O EZ CLE 3 a. J I £T "O LLS GL O -J < Q United States Patent Office P„lented 2 3,848,048 Technetium and the platinum group metals, ruthenium, RECOVERY OF FISSION-PRODUCED TECH- rhodium and palladium, are produced in fairly high yield NETIUM, PALLADIUM, RHODIUM AND in nuclear reactors. Technetium is nonexistent in nature RUTHENIUM and may have properties of value which warrant its re- Raymond H. Moore, Richland, Wash., assignor to the 5 covery. The platinum metals are of high intrinsic value United States of America as represented by the United and should be recovered to supplement waning natural States Atomic Energy Commission resources. Filed July 12,1973, Ser. No. 378,471 The projected annual availability of technetinm and the Int. CI. COlg 55/00, 57/00 platinum group metals is given in Table I below: i U.S. CI. 423—22 5 Claims 10 TABLE I Annual Availability of Fission Product Pd, Eh, Ru and Te In (10') ABSTRACT OF THE DISCLOSURE Troy oz./yr." The fission-produced technetium and the platinum Pd Eh Eu To metals, palladium, rhodium and ruthenium, are recovered ic 1970 0.77 0.51 2.3 0.93 from an aqueous acidic fuel reprocessing waste solution 1975 _ 22-23 1S-14 61-67 25-27 1980- ... 55-75 30^12 145-201 57-70 and separated from each other by contacting the waste 1985. 115-170 6<t-95 302-450 119-178 solution sequentially with a series of beds of carbon, each 1990 214-328 110-176 524-801 201-311 bed having adsorbed thereon a different chelating agent a The ranges given reflect the differences obtained from the difieren specific for the metals to be recovered, whereby the metal types of reactors. ions are selectively chelated and removed from the waste 20 solution. Technetium is present in fission product wastes as "Tc. Palladium is present as stable isotopes containing about 15.7 atom percent 107Pd of long half-life but low energy CONTRACTURAL ORIGIN OF THE INVENTION (—04 mev.). This low energy radiationo together with the 25 biological inertness of palladium suggest this material can The invention described herein was made in the course be utilized without regard to the presence of 107Pd. of, or under, a contract with the United States Atomic En- Stable 103Rh is produced in fairly high yield (2.9% from ergy Commission. 235U and 5.6% from 239Pu). All other isotopes produced BACKGROUND OF THE INVENTION have half-lives of a few seconds to a maximum of 36 30 hours and rapidly decay away. However, three isotopes This invention relates to a method for the recovery and are produced by («, 2n) and {n, 3n) reactions with 103Rh separation of some platinum metals and technetium from which have appreciable half-lives and energetic beta and aqueous solutions. More specifically, this invention relates gamma emissions. These are 102Rh (/'A =206 days), and to a method for the recovery and separation of fission- 102 Rh (fi/2=2.9 years), and ^Rh (fi/->=3.3 years). The produced palladium, technetium, rhodium and ruthenium 35 latter forms via a rather improbable route and can prob- from aqueous acidic fuel reprocessing waste solutions. ably be neglected. Before reactor-produced rhodium can Fission products which result from the irradiation of be utilized in normal channels of commerce, it will have nuclear reactor fuels are generally considered as harmful to be stored for a sufficient period to permit decay of radioactive wastes which require storage in an insoluble these isotopes to inconsequential levels of activity (e.g. form for centuries. Some of these wastes contain metals 40 30-50 years). (rhodium, palladium, and ruthenium) which, when con- The stable isotopes of ruthenium are accompanied by sidered in the context of an ever increasing demand for radioactive isotopes of which 106Ru (/Vi = 1.0 year) is the these metals and their finite and diminishing reserves, be- only one with a half-life long enough to cause a problem. come potential resources. As with rhodium, ruthenium must also be stored to per- The recent decisions by U.S. automobile manufacturers 45 mit decay of 106Ru (e.g. for 30 years). to use platinum-metals-based catalyst systems will mark- edly increase the demand for these metals. Although pre- SUMMARY OF THE INVENTION vious systems for air pollution control have been platinum based, there is some indication that other platinum metals A process has been developed by which fission-pro- may be used in conjunction with platinum. Palladium has 50 duced technetium and the platinum group metals, pal- found general use as an electrical contact metal and as a ladium, rhodium and ruthenium can be recovered from catalyst for various chemical manufacture and purifica- the aqueous acidic fuel reprocessing waste solutions and, tion processes. Rhodium, likewise, has been used with in general, separated from each other. other metals as a catalyst in various chemical manufac- In the method of this invention for recovering palla- ture processes and in electrical contacts. Increasingly large 55 dium, technetium and rhodium and ruthenium values from amounts of ruthenium have also been used in the electrical an aqueous acid solution and separating them from each and chemical industries during recent years. other by contacting an aqueous acid feed solution con- Any of the fission products which result from the radia- taining these and other fission product values with a first tion of uranium and plutonium in nuclear reactors may be bed of carbon, said first bed having adsorbed thereon a an important source of elements in the future. These ele- go chelating agent which is specific for palladium, whereby ments may exist as stable elements such as those found in the palladium in the feed solution is chelated and is re- nature, e.g., barium, lanthanum, praseodymium and neo- tained on the first bed, contacting the feed solution with dymium, or they may be some of the highly radioactive, a second bed of carbon, said second bed having adsorbed unique and potentially useful fission products such as thereon a chelating agent which is specific for technetium, strontium-90, americium and cerium. Others of these iso- 55 whereby the technetium is chelated and is retained on the topes may include some of the platinum metals such as second bed, and contacting the feed solution with a third palladium, rhodium and ruthenium in addition to tech- bed of carbon, said third bed having adsorbed thereon a netium for which there is no known natural supply. While chelating agent specific for rhodium and ruthenium, the demand for some of these elements is increasing, the whereby the rhodium and ruthenium are chelated and are natural reserves for these elements are shrinking. The re- 70 retained on the third bed, whereby the values are recov- covery of some of these fission product elements may be ered from the acid feed solution and separated from an important natural resource in the years to come. each other. 11 848 3,840,365 It is therefore one object of the invention to provide a in loss of fission product values. The carbon bed material method for recovering palladium, technetium, rhodium may be any activated charcoal. If the sorbate is used in and ruthenium values from an aqueous acid solution. a fixed bed, granular carbon may be used; however, if It is another object of the invention to provide a method a batch contact is preferred, the carbon may be crushed for recovering palladium, technetium, rhodium and ra- 5 and screened to a size range of 16 to 48 mesh or smaller, thenium values from an aqueous acid nuclear fuel reproc- Although a number of chelating agents are satisfactory essing waste solution. for the recovery of palladium, dimethylglyoxime (DMG) Finally, it is the object of the invention to provide a is specific for the chelation of palladium from an aqueous method for recovering palladium, technetium, rhodium acid media and is therefore preferred. Acetylacetone and and ruthenium values from an aqueous acid nuclear fuel 10 some of the dithiols are satisfactory for the chelation of reprocessing waste solution and separating the palladium, technetium, such as diacetyltoluene-3,4-dithiol, and dia- technetium, and rhodium and ruthenium values from each cetyl dithiol (which is preferred). A number of agents other. will chelate both rhodium and ruthenium, such as 8- BRIEF DESCRIPTION OF THE DRAWING mercaptoquinoline or 8-hydroxyquinoline, although the 15 most preferred agent is phenyl thiourea. The drawing is a simplified flow diagram of the method Although it is possible to elute the chelated elements of the invention. from the carbon sorbate beds, it is easier and faster to DESCRIPTION OF THE PREFERRED EMBODIMENT recover ths fission products from the carbon sorbate beds by calcining the bed in a closed system and leaching the These and other objects of the invention may be met by contacting the aqueous nitric acid feed solution containing values to be recovered from the resulting ash. The re- the palladium, technetium, rhodium and ruthenium and covered values may then be readily purified and prepared other fission product values with a first bed of carbon, for commercial use or, in the case of rhodium and said first bed having adsorbed thereon 20 to 25 w/o ruthenium, encapsulated and sent to storage for the re- (weight percent) dimethylglyoxime (hereinafter referred quired period of time to permit proper decay of their to as DMG) whereby the palladium contained in the feed radioactivity.