Separation of rare earth elements from other elements

Abstract

A process for separating rare earth elements (REE) from Ca, Mg and other non-REE elements comprises raising the pH of an acidic aqueous solution of REE to pH 8 to pH 11; adding nano- or micro (NoM) particles having a silica or titanium oxide surface; agitating the suspension for 6 h to 48 h to provide for adherent crystallization of REE hydroxide on the particles; separating the particles from the solution; releasing REE by treatment with aqueous acid to form an aqueous solution of REE salt; separating them from the aqueous solution of REE salt formed. The acidic aqueous solution comprising REE is preferably provided by leaching of an REE mineral with aqueous acid; adding a base to bring the pH to from pH 4.0 to pH 6.5; separating precipitated non-REE hydroxide from the solution.

Claims

1. A process for separation of rare earth elements (REE) from calcium and magnesium, characterized in that the process comprises the following steps: a) providing an acidic aqueous solution of REE, calcium and magnesium; b) adding a base to bring the pH of the solution to a pH in the range of pH 8 to pH 11, to form REE hydroxide; c) adding nano- or micro- particles selected from silica particles, titanium oxide particles and particles covered by a layer of silica to the solution to provide a particle suspension; d) agitating the particle suspension for a time period of from 6 h to 48 h, to provide for adherent crystallization of REE hydroxide on the particles; e) separating the particles loaded with REE hydroxide from the aqueous solution; f) releasing REE from the particles by treatment with aqueous acid to form an aqueous solution of REE salt; g) separating the non-loaded particles from the aqueous solution of REE salt; with the proviso that step c) can precede step b).

2. The process of claim 1, wherein the process is carried out at ambient temperature.

3. The process of claim 1, wherein particles covered with silica are iron(III) oxide particles.

4. The process of claim 1, wherein particles loaded with REE hydroxide are separated from the aqueous solution by filtration, decantation, centrifugation or by magnetic means.

5. The process of claim 1, wherein the base is selected from ammonia, sodium hydroxide, potassium hydroxide.

6. The process of claim 5, wherein the base is provided in form of an aqueous solution.

7. The process of claim 1, wherein the thickness of the silica layer is 10 m or more.

8. The process of claim 1, wherein non-loaded particles are separated in step g) from the aqueous solution of REE salt by filtration, decantation, centrifugation or by magnetic means.

9. The process of claim 1, wherein treatment with aqueous acid is carried out at pH 2 or lower.

10. The process of claim 1, wherein the aqueous acid is selected from the group consisting of nitric acid, hydrochloric acid, hydrobromic acid.

11. The process of claim 1, wherein the acidic aqueous solution of REE, calcium and magnesium of step a) is provided by: i) leaching a mineral comprising REE with aqueous acid at pH 2 or lower to form an acidic solution comprising REE, magnesium, calcium, iron(III); ii) adding a base to bring the pH of the leaching solution to a pH of from 4.0 to 6.5; iii) separating precipitated iron(III) hydroxide by means of filtration, decantation or centrifugation so as to obtain said aqueous solution of REE, calcium and magnesium of step a).

12. The process of claim 11, wherein the base of step ii) is selected from ammonia, sodium hydroxide, potassium hydroxide.

13. The process of claim 1, wherein REE is selected from the group consisting of lanthanum, dysprosium, neodymium.

14. The process of claim 1, wherein the particles have a diameter of 5 nm to 100 m.

15. The process of claim 1, wherein pH of the aqueous solution provided in step a) is continuously monitored.

16. The process of claim 11, wherein pH of the acid solution provided in step i) is continuously monitored.

17. The process of claim 1, wherein the base is provided in form of an aqueous solution thereof.

18. The process of claim 11, wherein the base of step ii) is provided in form of an aqueous solution thereof.

19. The process of claim 1, wherein step (b) comprises adding a base to bring the pH of the solution to a pH in the range of pH 9 to pH 10.

20. The process of claim 1, wherein the agitating of (d) is done for 12 h to 36 h.

Description

DESCRIPTION OF PREFERRED EMBODIMENTS

(1) Materials and Methods

(2) Imaging and measurements were performed with a Hitachi TM-1000 tabletop Scanning Electron Microscope with an Oxford Instruments plc. Beryllium-window Energy Dispersive X-ray Spectroscopy detector. Imaging was done using a backscattering electron detector with the preset charge-up reduction mode and standard issue Hitachi software was used to control the instrument. The accelerating voltage was preset at 15 kV. Not less than 5 independent measurements were made at magnifications 500, 1000 and 5000. The data obtained in the form of wt % in heavy element (silicon and metal) content were compared and averaged. Complexometric titration of lanthanides (Dy.sup.3+, Nd.sup.3+, La.sup.3+). Titration was carried out in mother liquor over IDA bonded silica covered Fe.sub.3O.sub.4 nanoparticles. Stock solutions containing 0.0215 M Dy(NO.sub.3).sub.3, 0.0125 M Nd(NO.sub.3).sub.3 and 0.022 M La(NO.sub.3).sub.3 were prepared. To 50 mg of Fe.sub.3O.sub.4SiO.sub.2 NPs, a calculated amount of lanthanide salt solution (corresponding to the number of moles of IDA grafted on the surface) was added. NaNO.sub.3 1 M was added up to a final concentration of 0.1 M in a total volume of 20 mL, which was completed with distilled water. The mixtures were then sonicated in order to disperse the nanoparticles in the solution and they stayed in static sorption conditions for different times (2, 8, 24 and 48 hours). After the corresponding time, the mixtures were poured into centrifuge tubes, centrifuged at 10.000 rpm for 10 minutes and washed once with distilled water (20 mL). Both the first and the washing solutions were collected in an Erlenmeyer and the solid sorbent was dried under N.sub.2 (g) at room temperature. The collected solutions were titrated with Trilon B 5 mM using xylenol orange as indicator. Trilon B complexates metals in a 1:1 ratio, therefore the amount of lanthanides adsorbed to the surface of the Fe.sub.3O.sub.4SiO.sub.2 NPs could be calculated by subtraction, since the initial amount is known and the remaining amount in solution is determined by titration. The titrations were repeated in triplicate for control of reproducibility.

Example 1. Recovery of Neodymium from an Aqueous Solution by Means of 80-100 nm SiO.SUB.2 .Nanoparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(3) SiO.sub.2 nanoparticles of a diameter of about 80-100 nm were synthesized according to Stber [12]. In order to maintain ionic strength the particles (50 mg) were contacted with 6.5 mL of a 0.025 M solution of Nd(NO.sub.3).sub.3.Math.6H.sub.2O (CAS No: 16454-60-7, Sigma Aldrich, ref. 289175) and 2 mL of 1M NaNO.sub.3 (CAS No: 7631-99-4, Sigma Aldrich, ref. 221341). Volume was filled up to 20 mL with miliQ water and pH was adjusted to pH 9 by dropwise addition of 5% aqueous NH.sub.4OH (CAS No: 1334-21-6, Sigma Aldrich, ref. 09857). The resulting mixture was orbitally shaken for 24 h. The particles loaded with Nd(OH).sub.3 were separated by centrifugation and dried under nitrogen. The amount of REE remaining in the solution was determined by complexometric titration with EDTA (CAS No. 6381-92-6). EDTA forms complexes with REE in a 1:1 ratio and therefore, by titrating the remaining amount in the solution, the uptake of REE by the particles can be determined by subtraction between the initial amount and the remaining in solution. This analysis revealed an uptake capacity of 443 mg Nd.sup.3+/g SiO.sub.2 nanoparticles, corresponding to a recovery of 93%.

Example 2. Recovery of Neodymium from an Aqueous Solution by Means of 80-100 nm SiO.SUB.2 .Nanoparticles; pH Adjusted to pH 8.0 with Aqueous Ammonia

(4) Particles and procedure as in Example 1 but pH adjusted to pH 8. The loaded particles were checked by energy-dispersive X-ray spectroscopy (EDS) analysis, repeating the analysis at least 5 times on different random points for all samples, revealing an uptake capacity of 332 mg Nd.sup.3+/g SiO.sub.2.

Example 3. Recovery of Neodymium from an Aqueous Solution by Means of 80-100 nm SiO.SUB.2 .Nanoparticles; pH Adjusted to pH 8.0 with Aqueous Ammonia

(5) Particles and procedure as in Example 1 but pH adjusted to pH 10. The loaded particles were checked by EDS (five scans), revealing an uptake capacity of 947 mg Nd.sup.3+/g SiO.sub.2.

Example 4. Recovery of Lanthanum, Dysprosium and Neodymium from an Aqueous Solution by Means of 80-100 nm Functionalised SiO.SUB.2 .Nanoparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(6) The surface of SiO.sub.2 nanoparticles of Example 1 was functionalised with iminodiacetic acid derivate organosilane [13]. The functionalised nanoparticles (100 mg) were contacted with 12.5 mL of a 0.025 M lanthanide trinitrate hexahydrate solution comprising equimolar amounts of lanthanum, dysprosium and neodymium. Particle loading and separation was performed as in Example 1. EDS analysis (five scans) showed an average adherence of 280 mg for Nd.sup.3+, 400 mg for Dy.sup.3+ and 607 mg for La.sup.+ per g SiO.sub.2 nanoparticles respectively.

Example 5. Recovery of Dysprosium from an Aqueous Solution by Means of 80-100 nm SiO.SUB.2 .Nanoparticles; pH Adjusted to pH 9.5 with Aqueous Sodium Hydroxide

(7) Particles and procedure as in Example 1 except of adjustment of pH by 1 M aqueous NaOH, final pH 9.5. Nanoparticles (25 mg) were contacted with 3.1 mL of 0.02 M Dy(NO.sub.3).sub.3.Math.6H.sub.2O (CAS No: 100641-13-2. Sigma Aldrich, ref. 289175). EDS analysis (five scans) showed an average adherence of 1804 mg Dy.sup.3+/g SiO.sub.2.

Example 6. Recovery of Dysprosium from an Aqueous Solution by Means of 80-100 nm SiO.SUB.2 .Nanoparticles; pH Adjusted to pH 9.5 with Aqueous Potassium Hydroxide

(8) Particles and procedure as in Example 5, except for adjusting pH with 1M aqueous KOH to a final value of pH 9.5. EDS analysis (five scans) showed an average Dy adherence 826 mg Dy.sup.3+/g SiO.sub.2.

Example 7. Recovery of Neodymium from an Aqueous Solution by Means of 100 nm Silica Covered Fe.SUB.3.O.SUB.4 .Nanoparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(9) Core-shell magnetic silica covered nanoparticles of about 100 nm in size comprising a silica layer of about 25 nm in thickness were synthesized by the Stber method. The nanoparticles (15 mg) were contacted with 1.7 mL of 0.025 M aqueous Nd(NO.sub.3).sub.3.Math.6H.sub.2O according to the procedure of Example 1. Complexometric titration showed an uptake of 861 mg Nd.sup.3+/g, corresponding to a recovery of 97%. EDS analysis indicated an average adherence of about 64%, i.e. 830 mg per g SiO.sub.2, which is in good agreement with the titration results, meaning that EDS provides reliable information about relative weight percentage and is a local surface analysis.

Example 8. Recovery of Neodymium from an Aqueous Solution by Means of 100 nm Surface Functionalised Silica Covered Fe.SUB.3.O.SUB.4 .Nanoparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(10) The surface of core-shell magnetic silica covered nanoparticles of Example 7 was functionalized with the iminodiacetic acid organosilane derivate of Example 4. Nanoparticles (25 mg) were contacted with 3.2 mL of a 0.025M solution of Nd(NO.sub.3).sub.3.Math.6H.sub.2O following the procedure of Example 1. Complexometric titration showed an uptake of 446 mg Nd.sup.3+/g, which corresponds to a 96% of the initial amount introduced.

Example 9. Recovery of Dysprosium from an Aqueous Solution by Means of 100 nm Surface Functionalised Silica Covered Fe.SUB.3.O.SUB.4 .Nanoparticles; pH Adjusted to pH 9.5 with Aqueous NaOH

(11) Core-shell magnetic silica covered nanoparticles of Example 7 were used, and the procedure of Example 5 followed. EDS analysis showed an average (five scans) adherence of 733 mg Dy.sup.3+ per g SiO.sub.2.

Example 10. Recovery of Dysprosium from an Aqueous Solution by Means of 100 nm Surface Functionalised Silica Covered Fe.SUB.3.O.SUB.4 .Nanoparticles; pH Adjusted to pH 9.5 with Aqueous KOH

(12) The core-shell magnetic silica covered nanoparticles of Example 7 were used, and the procedure of Example 6 followed. EDS analysis showed an average (five scans) adherence of 898 mg Dy.sup.3+ per g SiO.sub.2.

Example 11. Recovery of Neodymium from an Aqueous Solution by Means of 0.5-10 m Silica Microparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(13) SiO.sub.2 particles (100 mg) of 0.5-10 m in diameter (CAS No: 14808-60-7, Sigma Aldrich, ref. S5631) were contacted with 12.5 mL of aqueous 0.025 M Nd(NO.sub.3).sub.3 according to the procedure of Example 1. The loaded particles were checked by EDS analysis as in Example 2, revealing an average degree of adherence of about 700 mg Nd.sup.3+ per g SiO.sub.2.

Example 12. Recovery of Neodymium from an Aqueous Solution by Means of 44 m Silica Microparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(14) SiO.sub.2 particles (44 m/325 mesh in size, 100 mg; CAS No. 60676-86-0, Sigma Aldrich ref. 342890), were contacted with 12.5 mL of aqueous 0.025 M Nd(NO.sub.3).sub.3.Math.6H.sub.2O while following the procedure of Example 1. Analysis of the loaded particles according to the method of Example 2 revealed an average adherence of about 1089 mg Nd.sup.3+ per g SiO.sub.2.

Example 13. Recovery of Neodymium from an Aqueous Solution by Means of 10 nm Titanium Oxide Nanoparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(15) TiO.sub.2 nanoparticles of 10 nm diameter were custom synthesized via a hydrothermal process [14]. The nanoparticles (40 mg) were contacted with 6.2 mL of aqueous 0.025 M Nd(NO.sub.3).sub.3.Math.6H.sub.2O solution following the procedure of Example 1. The loaded particles were analysed by EDS as in Example 2, revealing an adherence of 48 mg Nd.sup.3+ per g TiO.sub.2.

Example 14. Recovery of Neodymium from an Aqueous Solution by Means of 10 nm Titanium Oxide Nanoparticles; pH Adjusted to pH 10.0 with Aqueous Ammonia

(16) TiO.sub.2 nanoparticles of Example 13 (100 mg) were contacted with 6.2 mL of aqueous 0.025 M Nd(NO.sub.3).sub.3.Math.6H.sub.2O and the pH adjusted to pH 10. The loaded particles were analysed by the method of Example 2, revealing an adherence 286 mg Nd.sup.3+ per g TiO.sub.2.

Example 15. Recovery of Neodymium from an Aqueous Solution by Means of 20 nm Titanium Oxide Nanoparticles; pH Adjusted to pH 9.0 with Aqueous Ammonia

(17) The procedure of Example 13 was followed. TiO.sub.2 nanoparticles (20 nm, 100 mg; CAS No: 13463-67-7, Sigma Aldrich, ref. 718467) were contacted with 12.5 mL of aqueous 0.025 M Nd(NO.sub.3).sub.3.Math.6H.sub.2O. EDS analysis of the loaded particles showed an average adherence of 78 mg Nd.sup.3+ per g TiO.sub.2.

Example 16. EDS Analysis

(18) The results of EDS analysis for the investigated samples are shown in Table 1.

REFERENCES

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(20) TABLE-US-00001 TABLE 1 Results of EDS analysis % Al (from the Sample % Fe % Si % Ti % Nd % La % Dy % K sample holder) SiO.sub.2 custom 53.9 38.4 7.8 NPs, Nd, pH = 8 (NH.sub.4OH) SiO.sub.2 custom 62.6 37.4 NPs, Nd, pH = 9 (NH.sub.4OH) SiO.sub.2 custom 33.2 66.8 NPs, Nd, pH = 10 (NH.sub.4OH) SiO.sub.2-L3 62.3 37.4 custom NPs, Nd, pH = 9 (NH.sub.4OH) SiO.sub.2-L3 44.1 55.9 custom NPs, Dy, pH = 9 (NH.sub.4OH) SiO.sub.2-L3 53.8 46.2 custom NPs, La, pH = 9 (NH.sub.4OH) SiO.sub.2 custom 12.6 87.4 NPs, Dy, pH = 9.5 (NaOH) SiO.sub.2 custom 35.5 63.4 0.6 NPs, Dy, pH = 9.5 (KOH) Fe.sub.2O.sub.3SiO.sub.2 36.5 21.1 42.4 NPs, La, pH = 9 (NH.sub.4OH) Fe.sub.2O.sub.3SiO.sub.2 15.6 16.8 63.7 4.1 NPs, Nd, pH = 9 (NH.sub.4OH) Fe.sub.2O.sub.3SiO.sub.2 23.9 14.9 61.1 NPs, Dy, pH = 9.5 (NaOH) Fe.sub.2O.sub.3SiO.sub.2 17.4 16.5 65.8 0.3 NPs, Dy, pH = 9.5 (KOH) SiO.sub.2 42.2 57.8 microsize, Nd, pH = 9 SiO.sub.2 ~325 31 69 mesh, Nd, pH = 9 (NH.sub.4OH) TiO.sub.2 10 nm 86.1 7.4 6.5 NPs pH = 9 (NH.sub.4OH) TiO.sub.2 10 nm 55.5 32.3 12.2 NPs pH = 10 (NH.sub.4OH) TiO.sub.2 20 nm 88.5 11.5 NPs pH = 9 (NH.sub.4OH)