Acid leaching of rare earth minerals
10273562 ยท 2019-04-30
Assignee
Inventors
Cpc classification
C22B3/08
CHEMISTRY; METALLURGY
Y02P10/20
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
Abstract
The invention provides hydrometallurgical processes for the recovery of rare earth values from ore, using simple crushing without beneficiation to produce an enriched and purified mixed rare earth concentrate. Ore is crushed to a relatively coarse particle size, and then treated with relatively small amounts of acid, at a relatively modest elevated temperature, to render the rare earth elements extractable in a subsequent water leach.
Claims
1. A process for extracting rare earth elements from an ore, comprising: crushing the ore to a coarse particle size of greater than 10 mesh, to provide a crushed ore; subjecting the crushed ore to an acid treatment, to provide an acid treated ore; subjecting the acid treated ore to a water leach, to produce a weakly acidic product leach solution; subjecting the weakly acidic product leach solution to oxidation and pH adjustment to precipitate an iron and thorium-containing precipitate from the solution; separating the weakly acidic product leach solution from the iron and thorium-containing precipitate, to provide a treated leach solution; and, adding sodium carbonate to the treated leach solution to precipitate a mixed carbonate rare earth product.
2. The process of claim 1, wherein the acid treatment is application of from about 50 to about 150 kg/t of H.sub.2SO.sub.4 at from about 100 C. to 300 C. for about 1 to 3 hours.
3. The process of claim 1, wherein the water leach is for at least 5, 10, 15, 20 or 24 hours.
4. The process of claim 1, wherein the acid treatment is carried out in a heated pug mill or a series of heated pug mills.
5. The process of claim 1, further comprising one or more steps of: ore/acid mixing, ore/acid heating, ore/acid drying, and/or ore/acid holding for a reaction time at a reaction temperature; so as to render additional rare earth elements soluble in a subsequent water leach step.
6. The process of claim 1, wherein the oxidation and pH adjustment is carried out with a MgCO.sub.3, MgO, NaOH, Na.sub.2CO.sub.3, NH.sub.3, NH.sub.4OH or NaHCO.sub.3.
7. The process of claim 1, further comprising re-leaching the mixed carbonate rare earth product with a re-leaching acid to produce a strong rare earth chloride solution.
8. The process of claim 7, wherein the re-leaching acid is HCl, HNO.sub.3 or H.sub.2SO.sub.4 at pH 1 or less.
9. The process of claim 7, further comprising increasing the pH of the strong rare earth chloride solution with a titrating base so as to precipitate thorium and other impurities, to produce a base-treated strong rare earth chloride solution.
10. The process of claim 9, wherein the titrating base is MgO, NaOH, Na.sub.2CO.sub.3, NH.sub.3, NH.sub.4OH or NaHCO.sub.3.
11. The process of claim 9, wherein rare earths are re-precipitated from the base-treated strong rare earth chloride solution with addition of a re-precipitation acid, to produce a high quality mixed rare earth acid precipitate.
12. The process of claim 11, wherein the re-precipitation acid is oxalic acid, and the mixed rare earth acid precipitate is an oxalate.
13. The process of claim 11, wherein the mixed rare earth acid precipitate is calcined.
14. The process of claim 13, wherein the calcining is carried out at at least 750 C., to produce a high quality mixed rare earth oxide product.
15. The process of claim 14, wherein the high quality mixed rare earth oxide product is re-leached with refinery re-leaching acid to produce a high strength rare earth solution.
16. The process of claim 15, wherein the high strength rare earth solution is treated by multi-stage solvent extraction for rare earth separation.
17. The process of claim 15, wherein the refinery re-leaching acid is HCl, HNO.sub.3 or H.sub.2SO.sub.4.
18. The process of claim 1, wherein the ore is crushed to a coarse particle size of greater than 6 mesh, to provide the crushed ore.
19. The process of claim 1, wherein the recovered rare earth elements comprise at least two of: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb and Lu.
20. The process of claim 19, wherein the overall recovery of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y or Er is at least about 70%.
21. The process of claim 19, wherein the overall recovery of Tm is at last about 65%.
22. The process of claim 19, wherein the overall recovery of Yb is at least about 60%.
23. The process of claim 19, wherein the overall recovery of Lu is at least about 50%.
24. The process of claim 1, wherein the recovered rare earth elements include: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb and Lu.
25. The process of claim 19, wherein the acid treatment and the water leach are carried out so as to minimize the addition of acid while obtaining the recovered rare earth elements.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
(4)
DETAILED DESCRIPTION OF THE INVENTION
(5) Characteristics of a simple direct leaching process are described herein for treatment of rare earth element ores. In select aspects, as described in more detail below, the process involves crushing, for example to approximately 6, 7, 8, 9 or 10 mesh particle size, application of 50-150, or approximately 100 kg/t of H.sub.2SO.sub.4 to the ore at 100 C.-300 C., for example approximately 200 C., for 1-3 hours, for example approximately 2 hours, followed by a water leach, for example for at least 5, 10, 15, 20 or 24 hours, to produce a weakly acidic product leach solution. The acid treatment operation may for example be carried out in a heated pug mill arrangement, a relatively small reactor with a screw conveyor pushing the acid treated material through the mill. The heated pub mill arrangement may for example include a plurality of successive heated pug mills, for example 2 or 3 heated pug mills. The screw or screws in the pug mill arrangement can be heated to heat the contents of the mill to the target temperature. Alternative steps, for example within the context of the pug mill arrangement may for example include steps of ore/acid mixing, heating in a dryer reactor, such as a Holoflite filter (a heated dryer in which the ore/acid material is pushed through horizontal tubes), holding or soaking in an insulated hopper to allow the acid further time to react at temperature with the ore and render additional rare earth elements soluble in the subsequent water leach.
(6) After oxidation and pH adjustment of the weakly acidic product solution with an alkali, such as MgO, NaOH, Na.sub.2CO.sub.3, NH.sub.3, NH.sub.4OH, NaHCO.sub.3 or MgCO.sub.3 slurry, to precipitate and separate the bulk of the iron and thorium from the solution, sodium carbonate is added to precipitate a mixed carbonate rare earth product. The mixed carbonate is then re-leached with acid, for example HCl, HNO.sub.3 or H.sub.2SO.sub.4 at pH 1 or less, to produce a strong rare earth chloride solution. The pH is again increased with alkali, such as MgO, NaOH, Na.sub.2CO.sub.3, NH.sub.3, NH.sub.4OH or NaHCO3, to reject small amounts of thorium and other impurities. The rare earths may be re-precipitated with oxalic acid addition to produce a high quality mixed rare earth oxalate for calcination. The oxalate precipitate may then be calcined, for example at 750 C., to produce a high quality mixed rare earth oxide product for refining. This product may be re-leached at a refinery with acid, such as HCl, HNO.sub.3 or H.sub.2SO.sub.4, to produce a high strength solution for rare earth separation by multi-stage solvent extraction processing.
(7) In an exemplary embodiment, an ore for treatment was sourced from the Foxtrot Deposit within the Port Hope Simpson REE District in Labrador, Canada (Srivastava et al, 2013). The direct treatment of Foxtrot ore was illustrated through a series of studies on acid treatment/water leaching, solution purification, RE precipitation, RE re-dissolution and purification to remove thorium and finally RE precipitation with oxalic acid and calcination to make a mixed REO. The general flowsheet for the treatment scheme is shown in
(8) The recovered rare earth elements may for example comprise at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or all of: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb and Lu. In selected embodiments, The overall recovery of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y or Er may for example be at least about 70%. The overall recovery of Tm may for example be at last about 65%. The overall recovery of Yb may for example be at least about 60%. The overall recovery of Lu may for example be at least about 50%.
(9) Acid Treatment and Water Leaching
(10)
(11) The impact of acid addition is illustrated in
(12) Embodiments were tested that illustrated the benefits of rabbling of the ore/acid mixture during the acid treatment test. This rabbling enhanced the contact between acid and ore and promoted higher extraction. Similarly the impact of stirring speed and time indicated that better extraction was promoted by faster stirring and longer times for water leaching.
(13) A number of illustrative embodiments were exemplified with 1 kg charges to acid treatment, to confirm extractions and produce a larger volume of water leach solution for processing. The material is coarse (6 mesh) and dry in appearance both before and after the acid treatment. Leach results are shown in Table 1.
(14) TABLE-US-00001 TABLE 1 Bulk Acid Treatment and Water Leach Results. Conditions: Acid Treatment at 6 mesh, 200 C., 2 hours and 24 h Water Leach at 90 C. with 600 rpm mixing intensity. Feed PLS Residue Extraction Element Units Assay (mg/L, %, g/t) % La g/t 1720 144 392 76.7 Ce 3720 321 805 78.1 Pr 437 39.7 90.8 79.6 Nd 1610 148 330 80.0 Sm 297 27.9 63.8 79.6 Eu 15.5 1.51 3.6 79.1 Gd 244 22.6 56.1 78.4 Tb 37.3 3.59 8.5 79.2 Dy 223 20.8 54.6 77.5 Ho 43.7 4.09 11.7 76.0 Y 1090 107 288 77.0 Er 122 11.2 36 73.8 Tm 17.2 1.49 5.8 69.9 Yb 111 8.56 41.8 64.9 Lu 15.8 1.02 7.3 55.9 Sc 25 0.07 25 4.7 Th 109 9.35 34.6 70.4 U 22.4 1.2 13.5 44.4 Si % 31.32 288 32.44 0.8 Al 3.99 212 3.97 4.6 Fe 7.83 496 7.69 5.5 Mg 0.12 43.5 0.07 36.7 Ca 1.45 642 0.96 40.0 Na 2.13 47 2.14 2.6 K 3.36 384 3.44 9.2 Ti 0.27 4.6 0.28 1.5 P 0.01 5 0.02 33.5 Mn 0.23 82.3 0.19 27.6
(15) The average extraction was 78% for the series LaEr. The extractions of TmLu were lower. The radioactive elements Th and U were extracted but the major gangue elements (Si, Al, Fe, Na, K) were weakly extracted. Some Mg, Ca, Ti, P, Mn were also extracted.
(16) Impurity Removal by Oxidation and Precipitation
(17) The initial removal of impurities was illustrated by pH adjustment and oxidation (for Fe removal). Three alkalis were exemplified, including MgO, MgCO.sub.3 and Na.sub.2CO.sub.3. For each example, the removal of impurities appeared to be maximized with minimum rare earth loss due to co-precipitation. All three alkalis were successful. Magnesium carbonate (MgCO.sub.3) was selected for a bulk impurity removal test. A volume of 13 L of water leach solution was prepared and heated to 75 C. and treated with 0.5 g/L of H.sub.2O.sub.2 to raise the ORP to +600 mV (vs Ag/AgCl). The pH was then adjusted to 3.75 with a 15% solid slurry of MgCO.sub.3 and held for 1 h. The impurity precipitates were filtered and washed. The results are summarized in Table 2. More than 90% of the iron was eliminated along with 88.4% of the thorium. There was also significant rejection of Si, Al, Ti and P. The losses of REEs ranged from 0.74 to 3.6% from La to Lu. Note that the final precipitate was analyzed at 0.018% Mg indicating a high efficiency of MgCO.sub.3 use.
(18) TABLE-US-00002 TABLE 2 Impurity Removal Results. Conditions: pH 3.75 with MgCO.sub.3 addition for 1 h at 75 C. PLS Product Solution Precipitate PPT Element Units Assay (mg/L, %, g/t) % La g/t 141 145 643 0.74 Ce 314 324 1960 1.01 Pr 39.4 40.2 286 1.19 Nd 147 152 1120 1.23 Sm 27.8 28.9 254 1.46 Eu 1.5 1.54 13.2 1.43 Gd 21.9 22.5 210 1.55 Tb 3.55 3.55 37.6 1.76 Dy 20.7 20.9 224 1.78 Ho 4.08 4.1 45.4 1.84 Y 104 106 875 1.38 Er 11.1 11.1 156 2.32 Tm 1.51 1.49 26.7 2.94 Yb 8.51 8.34 185 3.61 Lu 1.01 0.99 21.8 3.58 Sc 0.07 0.07 25 36.95 Th 9.43 1.07 4810 88.41 U 1.21 1.15 36.5 5.09 Si % 279 202 5.10 29.89 Al 201 99.1 6.35 51.82 Fe 619 48.5 30.78 91.48 Mg 35.7 1690 0.018 0.02 Ca 602 649 0.021 0.06 Na 28 30 0.015 0.83 K 238 259 0.017 0.11 Ti 5.68 0.07 0.336 98.78 P 5 5 0.083 21.39 Mn 76.2 80.8 0.008 0.16
Bulk Rare Earth Precipitation
(19) The purified solution was treated with soda ash solution (Na.sub.2CO.sub.3) to precipitate the REEs into a mixed carbonate product for further purification. A pH target of 7.25 at ambient temperature was set. The results are shown in Table 3. The precipitation of REEs approaches 100%. The co-precipitation of Th, U, Fe, Al is similarly very high. The mixed REE carbonate precipitate may be further refined by a re-leach, oxalate precipitation and calcination method to form a mixed REO for refining. The overall recovery of REEs from ore to mixed carbonate precipitate has been calculated and summarized in Table 4.
(20) TABLE-US-00003 TABLE 3 REE Precipitation Results. Conditions: pH 7.25 with Na.sub.2CO.sub.3 addition for 3 h at 25 C. Feed Solution Product Solution Precipitate PPT Element Assay (mg/L, %, g/t) % La g/t 134 0.24 57700 99.8 Ce 315 0.39 129000 99.9 Pr 36.3 0.06 15600 99.8 Nd 136 0.18 58800 99.9 Sm 26.1 0.05 11000 99.8 Eu 1.39 0.03 584 97.6 Gd 23 0.04 10900 99.8 Tb 3.62 0.03 1640 99.1 Dy 20.8 0.05 9270 99.7 Ho 4.08 0.02 1800 99.5 Y 107 0.3 42100 99.7 Er 11.1 0.04 4880 99.6 Tm 1.46 0.04 636 97.1 Yb 7.92 0.03 3470 99.6 Lu 0.93 0.03 409 96.6 Sc 0.07 0.07 40 54.5 Th 0.85 0.04 422 95.7 U 1.07 0.13 467 88.4 Al 83.6 0.5 3.67 99.4 Fe 39.3 0.2 1.81 99.5 Mg 1550 1560 0.505 0.7 Ca 616 583 1.95 6.6 Na 191 1050 0.125 0.3 K 298 289 0.3 2.2 P 5 5 0.003 1.2 Mn 77.4 68.8 0.131 3.9
(21) TABLE-US-00004 TABLE 4 Overall Recovery (%) of Rare Earth Elements from Foxtrot Ore to Mixed Carbonate Precipitate. La Ce Pr Nd Sm Eu Gd Tb Dy Ho Y Er Tm Yb Lu 75.9 77.3 78.9 79.3 78.9 78.4 77.6 78.4 76.7 75.3 76.3 73.1 69.2 64.3 55.4
Mixed Carbonate Re-Leach, Thorium Removal, REE Oxalate Precipitation and Calcination
(22) The mixed carbonate product was re-leached with 37% HCl solution at pH 1 for 1 hour at 80 C. The chloride leach solution was then treated with 15% slurry of MgO in deionized water to pH 3.8 at 50 C. for 1 h to reprecipitate re-leached thorium. The re-leach process was virtually 100% effective in re-dissolving the REEs. The re-leach residue and the thorium removal residue would be returned to the water leach process to minimize any REE loss. The low-thorium solution was then treated with oxalic acid to selectively precipitate the REEs. The rare earth oxalate was then calcined at 750 C. for 4 h to produce a final mixed rare earth product. The assay of the rare earth oxalate and the calcined rare earth oxalate are shown below, in Table 5.
(23) TABLE-US-00005 TABLE 5 Chemical Analysis of the Rare Earth Oxalate and Rare Earth Calcine Products RE RE RE Oxalate Calcine Calcine ICP ICP XRF Element Assay (%, g/t) La g/t 58900 110000 125000 Ce g/t 135000 250000 284000 Pr g/t 16000 29500 32300 Nd g/t 64900 119000 131000 Sm g/t 10800 19900 18900 Eu g/t 573 1060 Gd g/t 10200 18300 Tb g/t 1570 2820 Dy g/t 8850 16100 Ho g/t 1730 3180 Y g/t 39500 75600 78900 Er g/t 4670 8560 Tm g/t 590 1070 Yb g/t 2910 5350 Lu g/t 348 629 Sc g/t <50 <50 Th g/t 3.6 6.5 <100 U g/t 21.1 48.5 Si g/t <5 Al g/t 146 <2000 <100 Fe g/t 9 744 Mg g/t 201 316 60 Ca g/t 1480 <2000 2600 Na g/t <400 <1000 K g/t <2000 <2000 700 Ti g/t <30 <40 <100 P g/t <30 <3000 <40 Mn g/t <9 64 <100 Zn g/t 804 1490 F % 0.15 C.sub.tot % 0.02
(24) The final weight of the calcine was less than 10 g. This made it difficult to accurately analyse the final product. Both ICP and XRF analytical techniques were used and gave some variation in the individual rare earth values. The results illustrate a variety of characteristics: 1. The calcine is generally very low in contamination and mostly consists of rare earth oxides. 2. The thorium content of the precipitate was 3.6 g/t and the calcine was reported at 6.5 g/t Th by ICP. This is an exceptionally low value for a rare earth oxide. 3. The uranium content of the calcine is <50 g/t. 4. The aluminum and iron values are suitably low at 146 and 9 g/t in the precipitate. The iron in the calcine was analyzed by ICP at 744 g/t. 5. Minor amounts of alkali, alkaline earth and base metals are present. 6. The F content at 0.15% may be minimized by more selective oxalate precipitation. 7. The total carbon content was very low at 0.02% indicating that the calcination was complete.
(25) Although various embodiments of the invention are disclosed herein, many adaptations and modifications may be made within the scope of the invention in accordance with the common general knowledge of those skilled in this art. Such modifications include the substitution of known equivalents for any aspect of the invention in order to achieve the same result in substantially the same way. Numeric ranges are inclusive of the numbers defining the range. The word comprising is used herein as an open-ended term, substantially equivalent to the phrase including, but not limited to, and the word comprises has a corresponding meaning. As used herein, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a thing includes more than one such thing. Citation of references herein is not an admission that such references are prior art to the present invention. Any priority document(s) and all publications, including but not limited to patents and patent applications, cited in this specification are incorporated herein by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein and as though fully set forth herein. The invention includes all embodiments and variations substantially as hereinbefore described and with reference to the examples and drawings.
REFERENCES
(26) Srivastava, R. M., Gauthier, J., Cox, J., Krutzelmann, H. (2013), Technical Report on the Foxtrot Project in Labrador, Newfoundland and Labrador Canada (Report NI 43-101), Toronto, ON. Srivastava, R. M., & Gauthier, J. (2012). Search Minerals Inc. Technical Report on the Foxtrot Project in Labrador, Newfoundland and Labrador Canada. (Report NI 43-101). Toronto, ON: Roscoe Postle Associates Inc. Dreisinger, D. B., Clucas, J. D., Verbaan, N., Grammatikopoulos, T., Aghamirian, M., Forstner, C., The Processing of REE's from Search Minerals Foxtrot Resource, Proceedings of Rare Earths 2012, Eds, J. R. Goode, G. Moldoveanu, M. S. Reyat, CIM Metsoc (Montreal), 81-94.