Solvent extraction process

Abstract

A process for extracting uranium from an acidic uranium, chloride, iron and sulphate containing solution, including the steps: a. contacting the solution with an organic phase containing a trialkylphosphine oxide to form a uranium loaded organic phase; b. scrubbing the uranium loaded organic phase to remove any impurities and form a scrubbed organic phase; c. stripping the scrubbed organic phase with an acidic sulphate solution to produce an aqueous uranium strip solution; and precipitating a uranium product from the aqueous uranium strip solution.

Claims

1. A process for extracting uranium from saline acidic uranium, chloride, iron (III) and sulphate containing solution having >5 g/L chloride, comprising: a. contacting the solution with an organic phase containing a trialkylphosphine oxide (TAPO) as an extractant to form a uranium loaded organic phase; b. scrubbing the uranium loaded organic phase with a scrubbing solution comprising a sulphuric acid based aqueous solution to remove any impurities and to form a scrubbed organic phase; c. stripping uranium from the scrubbed organic phase with a concentrated sulphate solution having a sulphate concentration greater than IM to produce an aqueous uranium strip solution; and d. precipitating a uranium product from the aqueous uranium strip solution.

2. The process of claim 1 wherein the trialkylphosphine oxide is a trioctylphosphine oxide.

3. The process of claim 1 wherein the organic phase includes a blend of at least two trialkylphosphine oxides.

4. The process of claim 1 wherein the organic phase additionally includes a substituted amine or its salt.

5. The process of claim 4 wherein the ratio of trialkylphosphine oxide to substituted amine or its salt is varied according to the level of impurities in the acidic uranium and chloride containing solution.

6. The process of claim 4 wherein the ratio of trialkylphosphine oxide to substituted amine or its salt is varied according to the salinity of the acidic uranium and chloride containing solution.

7. The process of claim 4 wherein at chloride concentrations above 5 g/l, the molar ratio of substituted amine or its salt to TAPO in the organic phase is a minimum of 90:10.

8. The process of claim 4 wherein at chloride concentrations above 10 g/l, the ratio of substituted amine or its salt to TAPO in the organic phase is at least 50:50.

9. The process of claim 1 wherein at chloride concentrations above 20 g/l, the organic phase contains no substituted amine or its salt.

10. The process of claim 1, where the sulfuric acid based aqueous solution has an acid concentration from 0.1 M-1.0 M.

11. The process of claim 1 wherein the scrubbed organic is stripped using an ammonium sulfate solution.

12. The process of claim 11, wherein the ammonium sulfate is solution has a concentration of up to saturation.

13. The process of claim 1 wherein the scrubbed organic is stripped using a sodium sulfate solution.

14. The process of claim 1 wherein the process is conducted at a temperature up to 50 C.

15. The process of claim 1 wherein the uranium product is an ammonium diuranate (ADU).

16. The process of claim 1 wherein the process is operated continuously.

17. A process for extracting uranium from an acidic saline uranium and iron (III) solution having >5 g/L chloride, comprising: a. contacting the solution with an organic phase containing a trialkylphosphine oxide as an extractant to form a uranium loaded organic phase; b. scrubbing the uranium loaded organic phase with a scrubbing solution comprising a sulphuric acid based aqueous solution to remove any impurities and to form a scrubbed organic phase; c. stripping uranium from the scrubbed organic phase with a concentrated sulphate solution to produce an aqueous uranium strip solution; and d. precipitating a uranium product from the aqueous uranium strip solution.

18. A process for extracting uranium from an acidic saline uranium and iron (III) containing solution comprising contacting the solution with an organic phase containing a trialkylphosphine oxide (TAPO) and a substituted amine or its salt as extractants, wherein the organic phase has a ratio of the TAPO to the substituted amine or substituted amine salt which is determined by the chloride concentration in the saline uranium containing solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Notwithstanding any other forms which may fall within the scope of the process set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a flowsheet illustrating a process embodiment. Note, we have used the term solvent in place of organic in this diagram.

(3) FIG. 2 is a graph showing the concentrations of various elements loaded onto a TOPO containing solvent at varying chloride concentrations.

(4) FIG. 3 is a graph showing the concentrations of various elements loaded onto organic solvent containing TOPO or a blend of TOPO and tertiary amine at varying chloride concentrations.

(5) FIG. 4 is a graph illustrating the % removal of elements from a loaded solvent during the scrub and strip stages.

(6) FIG. 5 is a graph showing the extraction of uranium (mg/L) versus chloride concentration (g/L) in the PLS for different ratios of TAPO to tertiary amine.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(7) Referring firstly to FIG. 1, a flow sheet, 10, illustrates a first embodiment of the disclosed solvent extraction process. Pregnant leach solution (PLS), 12, which contains dissolved uranium and impurities comprising dissolved chloride and iron, is contacted with an organic phase (solvent) containing TOPO or TOPO/Alamine, 14, in an extraction stage 16. The loaded solvent, 18, is then passed to a scrubbing stage, 20, where a sulfate based scrub solution, 22 such as sulfuric acid, is contacted with the loaded solvent 18 and substantially removes chloride and iron ions therefrom. It is thought that the impurity ions are less strongly extracted/solvated than uranium by the organic phase and therefore can be removed with moderate aqueous conditions as compared to uranium. The spent scrub solution, 24, is recycled to the PLS stream, 12. The scrubbed solvent, 26, then passes to a stripping stage, 28, where it is contacted with a strip liquor, 30, comprising an ammonium sulfate solution.

(8) Uranium loads into the strip liquor and the loaded strip liquor, 32, is transferred to the uranium precipitation stage, 34. Precipitation occurs by an increase in pH of the aqueous strip solution by addition of ammonia to achieve a pH of 7 and a uranium product, 36, comprising ammonium diuranate is produced. The stripped solvent, 38, is subjected to a conventional solvent treatment step, 40, in which the solvent is washed to remove entrained sulphates (from residual strip liquor) and the acidity of the solvent is adjusted (i.e. it is re-protonated if a tertiary amine is present) and the treated barren solvent is returned to the extraction stage, 16.

(9) Referring now to FIG. 2, a graph shows the results of a solvent extraction process of the first aspect of the disclosure conducted on a uranium containing PLS which also contains various impurities. The concentrations of uranium, iron, chloride, zirconium and silicon loaded onto a TOPO containing solvent are plotted against varying chloride concentrations. Also shown for comparison are the respective loadings using a conventional tertiary amine extraction process (Site at 3.5 g/L Cl). The conventional process was conducted using a PLS having a chloride concentration of 3.5 g/L and an extractant comprising a tertiary amine (Alamine 336) dissolved in a conventional solvent extraction diluent (i.e. Shellsol kerosene). The results are shown in the bottom left hand corner of the graph where the concentrations of uranium, iron, chloride, zirconium and silicon loaded onto the solvent are represented by the bars from left to right, respectively. The remaining groups of bars show the loadings of the elements from a PLS having chloride concentrations of (from left to right) 3, 10, 25, 50 and 100 g/L, when contacted with 0.2 M TOPO (Cyanex 921) in kerosene at an aqueous to organic ratio of 10:1.

(10) The results demonstrate that U extraction occurred with 0.2M TOPO over the range tested (3 to 100 g/L). A similar level of uranium extraction from a PLS containing 25 gpl Cl was achieved using TOPO as compared to the conventional process at a chloride concentration of 3.5 gpl. Peak performance occurred between 25 to 50 g/L chloride. It is also evident from a comparison of the results at increasing chloride concentration that there is a relationship between Cl concentration and uranium uptake and selectivity when TOPO is used as the extractant: uranium selectivity decreased with increasing chloride concentration.

(11) Referring now to FIG. 3, this graph compares the selectivity for uranium when the PLS is contacted with kerosene containing either TOPO or a TOPO/tertiary amine blend. The middle group of bars shows (from left to right, respectively) the concentrations of uranium, iron, chloride, zirconium and silicon loaded onto the solvent when the PLS (containing 25 g/L chloride) is contacted with TOPO/tertiary amine blend (0.1 M Alamine 336 and 0.2M Cyanex 921). The group of bars to the right thereof shows the equivalent results when extraction is performed using TOPO alone. It is evident that the level of selectivity for uranium over iron and chloride is significantly lower using a TOPO/Tertiary amine blend than using TOPO alone at that particular chloride concentration. Consequently, stripping of TOPO is expected to be simplified compared to the TOPO/tertiary amine blend.

(12) The results suggest that at relatively lower chloride concentrations, uranium extraction is favoured using a solvent predominantly, or solely, comprising tertiary amine whereas at higher concentrations extraction of, and selectivity for, uranium is favoured using a solvent predominantly, or solely, comprising TOPO.

(13) At intermediate chloride concentrations (such as from approximately 5 to 20 g/L chloride) optimum extraction and selectivity is achieved by increasing the ratio of TOPO/tertiary amine with increasing chloride concentration.

(14) Referring now to FIG. 4, this graph illustrates the percentage of elements removed from the loaded solvent during the subsequent scrub and strip steps. Working from left to right, are the results from the scrub step, and the cumulative results from the three strip stages respectively.

(15) The key for dealing with decreased selectivity relies on effective scrubbing which may be achieved with dilute sulphuric acid in one or more stages. In FIG. 4, the scrub step was conducted using a 1.0M H.sub.2SO.sub.4 solution and comprised one stage. In a single contact the iron was reduced by 97.8% and the chloride was reduced by 90.4%. If a second counter current scrubbing stage is introduced (not illustrated) the total separation was found to be 99.9% for the iron and 98.4% for the chloride. A third counter current scrubbing stage separated iron and chloride levels even further, resulting in effectively 100% separation.

(16) Stripping of uranium was accomplished in three stages using a concentrated ammonium sulphate solution (3.5 M (NH.sub.4)SO.sub.4) at controlled pH of 2 where the uranium level in the organic was removed to a level below the detectable limit (<1 mg/L) of the employed analytical method. Standard ammonium diuranate (ADU) product was precipitated from the resulting strip liquor by addition of concentrated aqueous ammonia (25 wt %) to increase the strip liquor pH to 7 at a controlled temperature of 35 C.

(17) FIG. 5 demonstrates the various uranium extraction amounts achieved by varying the ratio of tertiary amine to TAPO in the organic phase for different salinities of PLS. For each salinity of 5, 7.5, 10, 12.5, 15, 17.5, and 20 g/L chloride, the ratio of tertiary amine to TOPO was varied from (going left to right) 100% amine to 100% TOPO. The graph suggests that at chloride concentrations of around 5 g/l, uranium extraction is maximised by using 100% tertiary amine in the organic phase. At chloride concentrations above 5 g/l and up to about 20 g/l, good uranium extractions can be achieved with an amine/TAPO ratio of at least 90:10 and preferably at least 70:30. As the chloride concentration in the PLS increases, the optimal amine/TAPO ratio decreases. For chloride concentrations greater than 7.5 g/l, the optimal ratio is 30:70. Above 20 gpl, 100% TAPO (ie, no amine) may be used.

EXAMPLES

(18) Non-limiting Examples of the solvent extraction process will now be described.

Comparative Example 1

(19) Acidic, uranium containing PLS having a chloride concentration of 3.5 g/L was contacted with a solvent comprising 0.13 M Alamine 336 in kerosene. Extraction was conducted over 4 stages at 70% efficiency per stage at an aqueous/organic (A:O) ratio of 8, a solvent loading of 49.7% of the maximum load (typically 40 to 70%) and a temperature of 45 C. The overall uranium extraction was 97.6%.

Example 1

(20) Acidic, uranium containing PLS having a chloride concentration of 25 g/L was contacted with a blend of 0.1M Alamine 336 and 0.2M TOPO in a kerosene solvent. Extraction was conducted over 4 stages at 70% efficiency per stage at an aqueous/organic (A:O) ratio of 8, a solvent loading of 27.7% of the maximum load and a temperature of 20 C. The overall uranium extraction was 98%. Accordingly, uranium extraction is approximately the same as in Comparative Example 1 despite the significantly higher chloride level and lower temperature, which ordinarily would be expected to have an adverse effect on reaction kinetics and therefore extent of extraction.

(21) Representative concentrations of the elements extracted in Example 1 are illustrated in FIG. 2 which shows the high levels of co-extracted impurities, mainly iron and chloride.

(22) It is noted that the solvent loading in Example 1 (27.7%) is lower than that of Comparative Example 1 (49.7%). This indicates that the available extraction sites in Example 1 exceeded the quantity of uranium able to be extracted. This suggests that the extractant concentration could be reduced, which would thereby increase the percentage of maximum uranium loading and lower the extraction of impurities while still resulting in acceptable uranium extraction.

(23) The loaded solvent was subsequently subjected to scrubbing with 1.0M H.sub.2SO.sub.4 solution. In a single contact the iron was reduced by 97.8% and the chloride was reduced by 90.4%.

(24) Stripping of uranium was accomplished in three consecutive stages using a concentrated ammonium sulphate solution (3.5 M (NH.sub.4)SO.sub.4) at controlled pH of 2 where the uranium level in the organic was removed to a level below the detectable limit (<1 mg/L). Standard ammonium diuranate (ADU) product was then precipitated from the resulting strip liquor by addition of concentrated aqueous ammonia (25 wt %) to increase the strip liquor pH to 7 at a controlled temperature of 35 C.

Example 2

(25) Acidic, uranium containing PLS having a chloride concentration of 25 g/L was contacted with 0.2M TOPO in a kerosene solvent. Extraction was conducted over 4 stages at 70% efficiency per stage at an aqueous/organic (A:O) ratio of 8, a solvent loading of 29.6% of the maximum load and a temperature of 20 C. The overall uranium extraction was 97.6%. Again, uranium extraction is approximately the same as in Comparative Example 1 despite the significantly higher chloride level and lower temperature.

(26) Representative concentrations of the elements extracted in Example 2 are illustrated in FIGS. 2 and 3 which show the high levels of co-extracted impurities, mainly iron and chloride. However, the quantities of coextracted iron and chloride were significantly lower at the particular chloride concentration when the solvent comprised TOPO alone.

(27) Again, compared to Comparative Example 1, the lower solvent loading of this Example indicates that the extractant concentration could be reduced. This would lower the extraction of impurities and still result in acceptable uranium extraction.

(28) The loaded solvent was subsequently subjected to scrubbing with 1.0M H.sub.2SO.sub.4 solution. In a single contact the iron was reduced by 97.8% and the chloride was reduced by 90.4%.

(29) Stripping of uranium was accomplished in three consecutive stages using a concentrated ammonium sulphate solution (3.5 M (NH.sub.4)SO.sub.4) at controlled pH of 2 where the uranium level in the organic was removed to a level below the detectable limit (<1 mg/L). Standard ammonium diuranate (ADU) product was then precipitated from the resulting strip liquor by addition of concentrated aqueous ammonia (25 wt %) to increase the strip liquor pH to 7 at a controlled temperature of 35 C.

(30) Advantages of the disclosed solvent extraction process include: The process enables exceptional uranium recovery levels from a high salinity PLS, particularly one containing both high levels of chloride and iron. The process is able to not only successfully extract uranium from ore or ore concentrate, but can also effectively recover the extracted uranium from the solvent in order to produce a final product. To date, such a process has not existed in either solvent extraction or ion exchange technologies. The process potentially enables the processing of PLS having substantial variation in composition (particularly salinity) with minimal variation in the physical process units and resultant flow sheet. The process may also be successfully operated over a reasonable temperature range.

(31) Whilst a number of process embodiments have been described, it should be appreciated that the process may be embodied in many other forms.

(32) In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word comprise and variations such as comprises or comprising are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.