Beneficiation process for low grade uranium ores

Abstract

The disclosure relates to a beneficiation process for low grade uranium ore, wherein the process comprises a primary beneficiation stage comprising: wet scrubbing the low grade uranium ore to separate the low grade ore into a fine fraction and a coarse fraction; screening the fine fraction according to a size separation parameter to provide an undersize fraction and an oversize fraction, wherein the uranium predominantly reports to the undersize fraction; and separating the undersize fraction to produce an intermediate uranium concentrate. The intermediate uranium concentrate may be further processed in a secondary beneficiation stage to produce a high grade uranium concentrate.

Claims

1. A beneficiation process for low grade uranium ore, wherein the process comprises: a primary beneficiation stage comprising: wet scrubbing the low grade uranium ore to separate the low grade ore into a fine fraction and a coarse fraction; screening the fine fraction according to a size separation parameter to provide an undersize fraction and an oversize fraction, wherein the uranium predominantly reports to the undersize fraction; and separating the undersize fraction to produce an intermediate uranium concentrate.

2. The process according to claim 1, wherein the low grade uranium ore is a calcrete hosted uranium ore.

3. The process according to claim 2, wherein the low grade uranium ore comprises carnotite [K.sub.2(UO.sub.2).sub.2(VO.sub.4).sub.2.3H.sub.2O].

4. The process according to claim 1, wherein the coarse fraction comprises particles having a minimum diameter or width greater than about 4-6 mm and the fine fraction comprises particles having a maximum diameter or width less than about 4-6 mm.

5. The process according to claim 1, wherein the size separation parameter is approximately 125 microns.

6. The process according to claim 5, wherein the undersize fraction contains uranium particles having a maximum diameter or width of less than 125 microns and the oversize fraction contains uranium particles having a minimum diameter or width of greater than 125 microns.

7. The process according to claim 1 further comprising a pre-screening step before the wet scrubbing step to separate liberated carnotite particles from the low grade uranium ore.

8. The process according to claim 7, wherein the pre-screening step comprises wet-screening.

9. The process according to claim 7, wherein the liberated carnotite particles have a maximum diameter or width of approximately 125 microns.

10. The process according to claim 9, wherein the liberated carnotite particles are combined with the undersize fraction to produce the intermediate uranium concentrate.

11. The process according to claim 1, wherein the intermediate concentrate contains at least about 75% of the uranium present in the low grade uranium ore.

12. The process according to claim 1, wherein the concentration of uranium in the intermediate concentrate is from about 3-times to about 10-times the concentration of uranium in the low grade uranium ore.

13. The process according to claim 1, wherein the mass of the intermediate concentrate is from about 10% to about 40% of the mass of the low grade uranium ore.

14. The process according to claim 13, wherein the mass of the intermediate concentrate is from about 15% to about 30% of the mass of the low grade uranium ore.

15. The process according to claim 1, further comprising processing the intermediate concentrate in a secondary beneficiation stage to produce a high grade concentrate having an increased concentration of uranium and reduced mass relative to the intermediate concentrate.

16. The process according to claim 15, wherein the secondary beneficiation stage comprises one or more concentration steps.

17. The process according to claim 16, wherein the or each concentration step is selected from the group consisting of de-sliming, gravity separation, flotation, reflux classification and magnetic separation.

18. The process according to claim 15, wherein the high grade concentrate contains at least about 70% of the uranium present in the low grade uranium ore.

19. The process according to claim 15, wherein the mass of the high grade concentrate is from about 0.1% to 10% of the mass of the low grade ore.

20. The process according to claim 15, wherein the concentration of uranium in the high grade concentrate is at least about 15-times the concentration of uranium in the low grade uranium ore.

21. The process according to claim 1, wherein the intermediate concentrate is further processed in a leaching circuit.

22. The process according to claim 15, wherein the high grade concentrate is further processed in a leaching circuit.

23. The process according to claim 21, wherein the leaching circuit comprises alkali leach treatment, acidic leach treatment, or a combination thereof in any order.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In order that the beneficiation process of the present invention may be more clearly understood, preferred embodiments will be described with reference to the processing of a low grade uranium ore as depicted in FIG. 1, which is a flowsheet exemplifying a presently preferred embodiment of the invention.

(2) While the following embodiment is particularly concerned with the physical beneficiation of a calcrete hosted uranium ore containing well-liberated carnotite [K.sub.2(UO.sub.2).sub.2(VO.sub.4).sub.2.3H.sub.2O], those skilled in the art will recognise that the general principles are equally applicable to a wide range of other low-grade mineral resources in which the mineral of value is well liberated and amenable to recovery in an intermediate concentrate and optionally further concentration to a high grade concentrate.

(3) A low grade uranium ore 110 may be obtained by conventional mining methods 100 or continuous mining methods 106. Conventional mining 100 typically includes generating a stockpile 102 then crushing the stockpile in a primary crushing step 104 to produce the low grade uranium ore 110. In some cases, a secondary crushing step 108 may be performed after the primary crushing step 104. In particularly preferred embodiments the present invention is directed to the beneficiation and concentration of a low-grade uranium ore that typically has a U.sub.3O.sub.8 content of about 80-150 ppm in which the uranium-bearing mineral (carnotite) occurs as discrete, well-liberated grains with a particle size typically less than 125 m. The processing of such a low-grade uranium ore by conventional agitated tank or conventional heap leaching would be sub-economic because of the high leach reagent consumption as a consequence of the high mass of calcrete gangue mineralisation.

(4) A pre-screening step 112 may be performed on the low grade uranium ore 110 to separate out already liberated carnotite particles 114. Typically, the pre-screening 112 step may involve wet-screening to separate particles having a maximum diameter or width of about 125 microns, which is the typical size of discrete well liberated grains of carnotite.

(5) The remainder of the low grade ore 110 is then subjected to a low intensity wet scrubbing step 120 to separate the low grade ore 110 into a fine fraction 122 characterised by smaller particles and a coarse fraction 124 characterised by larger particles. The intensity of the wet scrubbing step 120 may be selected and varied to suit specific conditions and criteria. Suitable equipment for performing the low intensity scrubbing include industrial screens, scrubbers, trommels.

(6) The fine fraction 122 is typically comprised of particles having a maximum diameter or width of about 4-6 mm and the coarse fraction 124 is typically comprised of particles having a minimum diameter or width of about 4-6 mm. The fine fraction 122 contains a greater concentration (% weight, or % volume, or ppm) of uranium relative to the coarse fraction 124. Typically the coarse fraction (>4-6 mm) is substantially uranium free and may be discarded as waste 130. Alternatively, a radiometric sorting step 132 may be performed on the coarse fraction 124. If radioactivity is detected the coarse fraction 124 may be subjected to a further size reduction step 134 to separate a further fraction having a maximum diameter or width of about 4-6 mm, which may be combined with the fine fraction 122.

(7) The fine fraction 122 is subjected to an additional screening step 125 and wet scrubbing 130 at a suitable size whereby the bulk (eg, >80%) of the uranium (carnotite) mineralisation reports to the undersize fraction 127. For a typical low-grade uranium ore 110, approximately 80% of the carnotite reports to the <125 m fraction and constitutes about 10%-40%, typically about 15%-30%, more typically about 20% of the mass of the original mass of low-grade ore 110. The oversized fraction 126 may be discarded.

(8) The undersize fraction 127 may be refined in a desliming step 162 and waste 160 material separated to produce an intermediate concentrate 128. The liberated carnotite particles 114 may be incorporated into the intermediate concentrate to increase the overall uranium concentration in the intermediate concentrate 128. By this means an intermediate concentrate 128 that typically contains 400-750 ppm U.sub.3O.sub.8 may be obtained.

(9) In view of the substantially increased concentration of uranium and reduced mass of the intermediate concentrate 128 relative the low grade ore, in some embodiments the intermediate concentrate 128 may be fed directly to a downstream leaching circuit 145. Alternatively, the intermediate concentrate 128 may be subjected to a secondary beneficiation upgrade processing step 136 to produce a high grade uranium concentrate 138 having an increased concentration of uranium. Waste 140 may be discarded.

(10) The incorporation of a secondary beneficiation stage in the physical beneficiation process may provide additional advantages. Thus, treating the intermediate concentrate 128 with one or more additional beneficiation steps, such as de-sliming, magnetic separation, gravity separation (eg, spiral, falcon, MGS), reflux classification, or flotation, may yield a final high grade concentrate 138 containing in excess of 2500 ppm U.sub.3O.sub.8, with an overall uranium recovery of at least about 70% relative to the low grade ore 110. Additionally, the overall mass of high grade concentrate 138 fed to the leach circuit 144,145 may be reduced to about 20% or less relative to the mass of the initial low grade ore 110.

(11) A particular benefit of this embodiment of the invention is that the high grade concentrate 138 may be offered for sale 142 and the uranium extracted at another site. Alternatively, the high grade concentrate may be subjected to an acid or alkaline leaching circuit 144, 146 in a standard extraction leach plant. Due to the substantially reduced mass and increased concentration of uranium in the high grade concentrate 138, the size and complexity of the leach plant may be significantly reduced relative to conventional leaching of the low grade ore 110, or in processes that do not form the intermediate concentrate 128. In addition, the volume of water, acid and base required may be substantially reduced, all of which improve the potential commercial viability of the inventive process.

(12) The uranium residue of the leaching circuit 144, 146 may be separated by solid/liquid separation 148 to separate the valuable uranium product which may then be processed in a refinery 152. The waste tailings 150 may be discarded.

(13) It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

(14) Throughout this specification, unless the context requires otherwise, the word comprise, or variations such as comprises or comprising, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.