WO2000034538A1

WO2000034538A1 - Selective extraction of an actinide

Info

Publication number: WO2000034538A1
Application number: PCT/AU1999/001088
Authority: WO
Inventors: Peter Van Hoof; Peter James Martin; Robert Eibl
Original assignee: Incatec Pty Ltd
Priority date: 1998-12-07
Filing date: 1999-12-07
Publication date: 2000-06-15
Also published as: AUPP755498A0

Abstract

A process is provided for separating uranium ions from other metal ions by contacting an aqueous solution containing uranium and other metal ions with a polymeric material prepared using at least one monomer selected from diallylamine, α, w - bis (dialkyl aminoalkanes) and triallylamine.

Description

SELECTIVE EXTRACTION OF AN ACTINIDE FIELD OF THE INVENTION

This invention relates to a method for the selective extraction of an actinide, in particular uranium. BACKGROUND OF THE INVENTION

Uranium is widely distributed and is more abundant than Ag, Hg, Cd, or Bi.

However, it has few economic ores, the main one being uraninite, an oxide of approximate composition UO₂. The other major ores are USiO₄. Typically finely divided ore is leached under oxidising conditions to give uranyl nitrate solutions. Uranium may be recovered from nitric acid solutions by

1. Extraction of uranyl nitrate into diethylether or isobutylmethylketone; a salt such as NH₄ ⁺, Ca²⁺ or Al³ nitrate is added as a "salting out" agent to increase the extraction ratio to technically useable values. If tributylphosphate in kerosene is used, no salting out agent is necessary. 2. Removal from organic solvent by washing with dilute HNO₃.

3. Recovery of U₃O₈ or UO₃ by precipitation with ammonia. The uranium trioxide may then be reduced with hydrogen to the dioxide or yellow cake.

Uranium may also be recovered by in situ mining. In this operation a leaching solution (lixiviate), formed by adding gaseous carbon dioxide and oxygen to groundwater, is injected into a uranium ore-bearing rock through a series of injection wells. As the lixiviate moves through the aquifer contacting the ore, the oxygen reacts and oxidises the uranium to the +6 valence state. The dicarbonate ion [UO₂(CO₃)₂]^"1. The uranium-rich lixiviate flows through the formation to a recovery well where it is pumped to the surface by submersible pumps and transported through a piping system to a surface recovery plant. At the recovery plant, the uranium is removed from the fluid by ion exchange. The barren fluid is then re-fortified with carbon dioxide and oxygen and re-injected to extract additional uranium.

As the uranium-rich lixiviate enters the recovery facility, booster pumps pressurise the fluid to 100 to 130 psig. The lixiviate is then routed through the ion exchange columns and dissolved uranium in the lixiviate is chemically adsorbed on to ion exchange resins. In the recovery plant the resin first passes over vibrating screens with wash water to remove entrained sand particles and any other debris. The resin is then fed into downflow elution vessels for uranium recovery and resin regeneration. In the elution vessel, the resin is contacted with an eluate containing about 90 g/1 sodium chloride and 20 g/1 sodium carbonate (soda ash), which regenerates the resin.

The eluate containing the high concentration of uranium is treated with sulphuric acid, ammonia and hydrogen peroxide to begin the precipitation process. Sulphuric acid is added to break down the uranyl carbonate complex, which liberates carbon dioxide and frees uranyl ions. The acidic, uranium-rich fluid is pumped to agitated tanks where hydrogen peroxide is added (0.2 kg H₂O₂/kg U₃O₈) in a continuous circuit to form a uranyl peroxide compound. Ammonia is then added to raise the pH to a level where the uranyl peroxide becomes insoluble and initiates the digestion and precipitation process.

The U-O system is extremely complex. The main oxides are orange-yellow UO₃, black U₃O₈, and brown UO₂. UO₃ is made by heating the hydrous oxide, mainly UO₂(OH)₂, obtained by adding NH₄OH to UO₂ ²⁺ solutions.

The most common uranium salt is the yellow uranyl nitrate which may have 2, 3 or 6 molecules of water depending on whether it is crystallised from fuming, concentrated or dilute nitric acid. Green tetravalent uranium and yellow uranyl ion (UO²⁺⁺) are the only species that are stable in solution.

In this invention reference to uranium ions includes uranyl ions. Commercially it is important for uranium ions to be isolated from other metal ions both in mining operations and also in waste water clean up procedures.

The use of ion-exchange resins for the removal of metal ions from aqueous solutions is commercially wide spread, especially in water softening applications and for the removal of toxic products from effluents. Other areas of importance are in the processing of radioactive wastes, the purification of rare earth metals and the analysis of geological samples.

Ion exchange on a laboratory scale has played a major role in the isolation and identification of the trans-uranium elements and of many of the fission products. Separation of plutonium (as the complexed-nitrate anion) from uranium and fission products has been accomplished on a pilot scale at Chalk River, Canada. This process is discussed by Wells and Pepper (in Flagg, "Chemical Processing of Reactor

Fuels", pp. 323-324, Academic, New York, 1961). The selectivity and concentrating power of ion-exchange materials find use in the management of waste streams from nuclear-fuel reprocessing, and in the purification of water supplies used in nuclear plants or inadvertently contaminated by radioactive streams. Such systems are reviewed in Swope (in Nachod and Schubert, op.cit., Chap. 17). Recently more selective chelating resins have become commercially available.

For example, Dowex 21KXLT ("Dowex" is a registered trademark) is a relatively new product. However, these resins are only marginally selective for uranium metal ion and require complex procedures to affect practical separations in commercial situations.

The main advantage this ion exchange resin relates to faster kinetics apparently attributed to a narrower particle size distribution of the resin (575 μm ± 50μm).

However, this resin still suffers from lack of selectivity with common traveller metals such as Fe, Ni and Cu. Furthermore, relatively long contact times with the ion exchange resin are required. These resins are also not stable in the presence of strong oxidising agents. Ion exchange resins may be operated at a fixed bed or packed. In this fixed bed set up the solute undergoing adsorption is removed continuously from the carrier fluid and accumulated in the solid phase. Ion exchange resins can also be operated in counter current sorption operations.

It is an object of the present invention to provide an improved process for separating uranium ions from other metal ions. SUMMARY OF THE INVENTION

This invention provides in one form a process of separating uranium ions from other metal ions by contacting an aqueous solution containing uranium and other metal ions with a polymeric material prepared using at least one monomer selected from diallylamine, , w - bis (dialkyl aminoalkanes) and triallylamine. Preferably the monomer is diallylamine. Preferably the polymeric material is in the form of a bead, granule or powder. Preferably the polymeric material is crosslinked.

In an alternative form this invention provides a process of separating uranium ions from other metal ions by contacting the aqueous solution containing uranium and other metal ions with polymeric beads, granules or powders prepared using at least one monomer selected from diallylamine, a , w - bis (dialkyl aminoalkanes) and triallylamine wherein the beads, granules or powder are mobile relative to each other. DETAILED DESCRIPTION OF THE INVENTION

The polymeric materials used in the present invention are only ionised at low pH. Hence they are chelating resins and so do not absorb monovalent or alkaline earth ions. Furthermore, surprisingly, they have been found to have a very high selectivity and capacity for uranium over other multivalent ions that are commonly associated with uranium in the mining and processing industries. They are also very easily and cheaply produced as they are synthesised directly from simple monomers.

Diallylamine (as its acid salt) has been polymerised previously either by itself, (to give a linear polymer, (G. B. Butler, A. Crawshaw and M. L. Milles; J. Amer. Chem. Soc, 80, 3615 (1958) or as a copolymer to form crosslinked resins, U.S. Pat. No. 3,957,699. Many methods of producing diallylamine polymers are known, including radiation polymerisation and a number of free radical methods. One of the most useful ways we have found to obtain a crosslinked resins is by the titanous chloride/hydrogen peroxide or ferrous sulphate/hydrogen peroxide redox-initiated polymerisation of diallylamine hydrochloride containing 5-40 mole % of 1 ,6-bis(diallylamino)hexane dihydrochloride monomer. Although a crosslinking monomer is usually required to get a mechanically durable resin, even uncrosslinked water-soluble forms of resin can be used to complex uranium ions in relatively concentrated uranium solutions (above about 300ppm) as the metal complex forms an insoluble heavy precipitate in such cases. In preferred embodiments the resin is in the form of beads, granules or slurried powder.

We have found that when the resin or polymer is in the form of a bead, granule or powder that improved rates of uptake are achieved. The leachate solution containing the uranium ions is pumped into the top of resin filled columns and allowed to permeate through the resin bed. The uranium ions are absorbed by the resin beads. However, we found that in a solution containing uranium ions that also contained sodium chloride the resins of the present invention were poisoned to a certain extent. While these resins were not performing optimally they were still performing better than conventional ion-exchange resins in a similar situation. When the resin material of this invention is used as a conventional packed ion- exchange column we have found that improved performance occurred. However, we have also found that the ability to absorb uranium ions was greatly improved by continuously stirring the resin in the leachate solution.

The crosslinked resins described above used in accordance with the present invention will selectively remove uranium ions from dilute solutions containing other metal ions. Surprisingly, these solutions may be acidic, neutral or basic. Thus the method of this invention is extremely versatile and useful for the recovery of uranium for commercial recovery analytical purposes, or for removing uranium from waste water streams. The invention will be further described by reference to preferred embodiments described in the following examples.

Example 1 - Preparation of a polymeric material derived from diallylamine: 1.1 Preparation of Crosslinker I

1,6 hexanediamine (116.2g (lmole)) was added to 300mls of 40% sodium hydroxide solution. 3 bromo-1-propene (254. Ig (2.05 mole)) was then slowly added to the above mixture over 5 hours at 20°C with stirring. This mixture was then stirred for a further 48 hours at 20°C. After this further stirring the mixture was allowed to separate, to form a non-aqueous layer and was washed twice with water. The product was designated Crosslinker . 1.2 Preparation of Crosslinker II, HI, IV and V

The 1,6 hexanediamine of 1.1 was replaced on a mole for mole basis with the following materials to produce the crosslinker in parenthesis:-

1,2 propanediamine (Crosslinker II) 1,8 octanediamine (Crosslinker III) 1,9 nonanediamine (Crosslinker IN)

1,4 butanediamine (Crosslinker N) The 3 bromo-1-propene was also able to be substituted with 3-chloro-l-propene to produce similar results. 1.3 Preparation of Diallylamine Polymeric Material

Diallylamine (971.6g) was added over 5 hours to a five litre flask containing 3000 ml of 35.5% hydrochloric acid. The mixture was maintained at 20°C and Crosslinker I (50g) was added. 1ml of a 60% Iron III chloride solution was then added and stirred into the solution.

2ml of hydrogen peroxide solution (30%), was added likewise. The solution slowly thickened and the additions of iron-chloride and hydrogen peroxide were repeated 8 - 10 times until the mixture formed a solid polymeric lump. Water was added and the solid polymeric material was subsequently washed with water to a neutral pH.

In place of hydrochloric acid, sulfuric acid (50%), phosphoric acid (89%), boric acid and 1,2,4 benzenetricarboxylic acid salts of diallylamine were able to be used. The 60% iron-Ill chloride solution was able to be substituted with either 50% ferrous sulfate solution or 30% titanium III chloride solution.

The 30% hydrogen peroxide solution was able to be replaced with either potassium or sodium peroxodisulfate solution or potassium chlorate solution to produce similar results. Example 2 - Evaluation of the Polymeric Material From Example 1 in Selectively Separating Uranium Ions:

Polymeric material from Example 1 (lg) was stirred into lOOmls of a 200ppm solution of uranium nitrate with various other metals at pH 3, 4, 5, 6, 7 for 3 - 4 hours. The other metal salts were iron (IΙI)-chloride, nickel-chloride copper sulfate, cobalt- nitrate, calcium-sulfate, mercuric chloride, tin chloride and silver nitrate. The solution was then filtered and the solution analysed by atomic absorption (AA). Removal of the uranium (100%) was confirmed. The polymeric material was then ashed and after dissolving the ash in aqua regia analysed by AA spectroscopy. Only uranium was detected in the ashed material. None of the other metals was absorbed by the polymeric material. The same results were achieved when repeated at the other pH values. Example 3

Polymeric material from Example 1 (lg) was stirred into lOOmls of a lOOppm solution containing calcium, cadmium and arsenic ions as well as the uranium ions at pH8. In this Example the uranium was introduced via its sodium salt. After 8 hours the polymeric material was filtered, washed, ashed and dissolved in aqua regia and the solution measured with a AA spectrometer. It showed only the presence of the uranium. The filtrate showed no presence of uranium. Example 4 -

This example shows the selective absorption of uranium to the polymeric material in the presence of a combination of metal ions as set out below. U²⁺ lOOOppm Fe²⁺ 60ppm Cu²⁺ 80ppm Ni²⁺ 50ppm Co²⁺ 60ppm

To an aliquot of 100ml of the above solution at pH4, lg of the polymeric material from Example 1 was added and the mixture stirred for 3 -4 hours. After filtering the solution was measured for uranium and the other metals using AA The uranium was totally removed while the concentrations of the other metals remained the same.

Since modifications within the spirit and scope of the invention may be readily effected by persons skilled in the art, it is to be understood that the invention is not limited to the particular embodiment described, by way of example, hereinabove.

Claims

Claims:

1. A process for separating uranium ions from other metal ions by contacting an aqueous solution containing uranium and other metal ions with a polymeric material prepared using at least one monomer selected from diallylamine, α, w - bis (dialkyl aminoalkanes) and triallylamine.

2. A process according to Claim 1 wherein the monomer is diallylamine.

3. A process according to Claim 1 or Claim 2 wherein the polymeric material is in the form of a bead, granule or powder.

4. A process according to Claim 3 wherein the polymeric material is crosslinked.

5. A process according to Claim 3 wherein the beads, granules or powder are mobile relative to each other.