Purification of coal and fly ash by ionic liquids

Abstract

A method for recovering heavy metals and rare earth elements from fly ash, coal ash, and unrefined mineral ores containing rare earth metals using an ionic liquid and an organic acid to solubilize the metals. The solubilized components are removed from the ionic liquid by electrochemical deposition. The heavy metals and rare earth elements are deposited onto an electrode, and then purified via electrochemical processing.

Claims

1. A method to recover heavy metals and rare earth elements from coal and fly ash, comprising: mixing an ionic liquid with an organic acid; adding coal ash, fly ash, or a combination thereof to the ionic liquid and organic acid mixture to form a slurry, wherein the coal ash, fly ash, or combination thereof comprises metals and rare earth elements; stirring the slurry; depositing the metals onto an electrode using electrodeposition; and filtering the slurry to remove any solid material.

2. The method of claim 1, wherein the ionic liquid comprises one of the following structures: ##STR00001## where R is an alkyl group or a hydrogen or a halide and X is N or P.

3. The method of claim 1, wherein the ionic liquid comprises 1-methyl-3-ethyl-midazolium trifluoroacetate.

4. The method of claim 1, wherein the ionic liquid comprises tetrafluoroborate, proprionate, or butanate.

5. The method of claim 1, wherein the organic acid comprises acetic acid.

6. The method of claim 1, wherein the electrode comprises copper.

7. The method of claim 1, additionally comprising recovering the ionic liquid.

8. The method of claim 1, additionally comprising electrochemically treating the electrode to remove the metals.

9. The method of claim 1, wherein the radioactivity of the coal ash, fly ash, or combination thereof is reduced by 90% or greater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A-1E show embodiments of the structure of the ionic liquid. FIG. 1A shows a substituted imidazolium, where R is an alkyl group or a hydrogen or a halide. In FIG. 1B, X is N or P, and R is an alkyl group, hydrogen or a halide.

(2) FIG. 2 is a schematic of the process of the present invention.

(3) FIG. 3 shows the XRD pattern of the coal ash.

(4) FIG. 4 shows the XRD pattern of the separated magnetic material.

(5) FIG. 5 shows the XRD pattern of metals deposited onto the gold electrode from the ionic liquid after purification of the coal ash.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention provides a multi-step process of using an ionic liquid to purify and remove heavy metals and rare earth elements from mineral ores, fly ash and coal (bottom) ash. The types of ionic liquids are shown in FIGS. 1A-1E. Although only three anions are shown, a host of other anions that create hydrophobic ionic liquids are viable, including, but not limited to, tetrafluoroborate, proprionate, and butanate. Also not shown in FIGS. 1A-1E but also possible, is a pyridinium cation; however, these are susceptible to attack by an acid gas, as are the ammonium and phosphonium cations.

(7) FIG. 2 is a schematic of the process of the present invention. In step 1, the ash (usually stored as a wet slurry in large fields), is placed in a container with the ionic liquid.

(8) In step 2, the ore or fly ash in the ionic liquid is agitated by a mechanical stirring process, and an organic acid is added to the ionic liquid.

(9) In step 3, the ionic liquid with the solubilized rare earth elements and heavy metals are electrochemically purified by using electrodeposition to deposit the metals onto an electrode. Both electrodes could be made of copper or some other conductive material. The main by-product of this reaction is the organic acid, which could be re-used in step 2 of this process.

(10) In step 4, the purified ionic liquid is strained to remove the leftover solid material (mostly silica), while the electrode coated with the heavy metals is removed and then electrochemically treated to remove the metal components deposited out of the ash.

(11) In step 5, the ionic liquid is heated to 100 C. to remove much of the water, then the ionic liquid is ready to re-start the process at step 1.

(12) The following example was performed to determine if removal of the radioactive and heavy metal contaminants could be removed by this process. For the ionic liquid, 10 grams of 1-methyl-3-ethyl-midazolium trifluoroacetate was used, and 10% acetic acid was added. 5 grams of coal ash was added to the ionic liquid/acetic acid solution. The slurry of coal ash in the ionic liquid/acid solution was stirred and heated for 1 hour at 80 C. The solid material was filtered from the ionic liquid/acid solution and washed with water resulting in remaining silicate ash and magnetic iron compounds. A gold foil electrode was used, and the metals electrodeposited out of the ionic liquid coal ash wash onto the electrode.

(13) Tests showed that prior to the ionic liquid treatment, the coal ash exhibited radioactivity in the amount of 70 mS/hour. Post treatment measurement showed only 5 mS/h, or over a 90% reduction in the radioactivity.

(14) FIG. 3 shows the x-ray diffraction results of the coal ash before and after purification with the ionic liquid/acid mixture. Table 1 shows the peak list for the initial fly ashthe composition was nearly a 50/50 blend of silicon oxide and iron oxides with some cerium oxide. Table 2 shows the peak list for the ash after purificationthe composition is over 99% silicon oxide, with most of the iron oxides and cerium oxide removed. FIG. 4 shows the x-ray diffraction pattern of the separated magnetic material. Analysis of the separated magnetic components indicated mostly Fe.sub.2O.sub.3 and Fe.sub.3O.sub.4. Table 3 shows the peak identifications for the separated magnetic components. FIG. 5 shows the x-ray diffraction pattern of the material electroplated onto the gold electrode. In FIG. 5, the main peaks of gold are shown with stars, while the other peaks are identified as iron as well as several other lanthanides and actinides. Table 4 lists the peaks and the elements associated with them. The elements identified include thorium, samarium, europium, ytterbium, and iron.

(15) The above data provide proof that this approach of using an ionic liquid/acid treatment can achieve the following: reducing the radioactivity of coal ash by over 90%; almost completely removing the iron from the coal ash (and thus providing iron for use in other applications); and significantly removing rare earth elements from the coal ash, which can then be removed from the ionic liquid via electrodeposition.

(16) An alternative to the process would be to vary the type of ionic liquid. For instance, many rare earth ores are phosphate based rocks. If an ionic liquid using hexafluorophosphate is used, and the acid used is HF, then the results of the processing could also be used to remanufacture the ionic liquid as it is being used by fluorination of the resulting phosphate by-products.

(17) Moreover, if the cost of using an ionic liquid is too high, this process could be adaptable to other solvent systems, such as ethylene glycol or poly-ethylene glycol.

(18) TABLE-US-00001 TABLE 1 Reflections for the initial fly ash. Note that it is nearly a 50/50 blend of silicon oxide and iron oxides, with some cerium oxide. Int. 2-theta Height 1 (cps No. (deg) d (ang.) (cps) deg) Phase name 1 16.42 5.394 (11 129 (13) 34 (4) Maghemite-Q, syn(1, 1, 2), Cerium Oxide(0, 0, 2) 2 20.77 4.273 (4) 167 (15) 39 (4) Quartz alpha, alpha-Si O2(1, 0, 0), Maghemite-Q, 3 25.39 3.505 (5) 48 (8) 47 (10) Maghemite-Q, syn(2, 1, 2) 4 26.515 3.3589 (7) 922 (35) 291 (8) Quartz alpha, alpha-Si O2(0, 1, 1), Cerium Oxide(1, 1, 2) 5 30.18 2.959 (4) 87 (11) 118 (11) Maghemite-Q, syn(2, 1, 5) 6 33.120 2.7027 (7 233 (18) 67 (4) Maghemite-Q, syn(3, 0, 2), Cerium Oxide(0, 0, 4) 7 35.245 2.5443 (1 115 (12) 169 (7) Quartz alpha, alpha-Si O2(1, 1, 0), Maghemite-Q, 8 35.554 2.5230 (1 255 (18) 85 (7) Maghemite-Q, syn(3, 1, 3) 9 40.83 2.2081 (1 141 (14) 35 (4) Maghemite-Q, syn(3, 0, 7), Cerium Oxide(2, 1, 3) 10 42.52 2.1245 (1 37 (7) 12 (2) Quartz alpha, alpha-Si O2(2, 0, 0), Maghemite-Q, syn(3, 1, 7) 11 43.44 2.081 (4) 36 (7) 23 (11) Maghemite-Q, syn(4, 0, 0) 12 50.02 1.8221 (9 102 (12) 55 (4) Quartz alpha, alpha-Si O2(1, 1, 2), Maghemite-Q, 13 53.89 1.700 (2) 67 (9) 95 (14) Quartz alpha, alpha-Si O2(0, 2, 2), Maghemite-Q, 14 57.22 1.6085 (1 74 (10) 92 (16) Quartz alpha, alpha-Si O2(2, 1, 0), Maghemite-Q, 15 59.72 1.547 (3) 47 (8) 25 (11) Quartz alpha, alpha-Si O2(1, 2, 1), Maghemite-Q, syn(4, 2, 9) 16 60.54 1.5281 (7 90 (11) 39 (8) Maghemite-Q, syn(5, 1, 6), Cerium Oxide(4, 0, 4) 17 63.00 1.4743 (1 75 (10) 141 (14) Quartz alpha, alpha-Si O2(1, 1, 3), Maghemite-Q, 18 67.84 1.3803 (4 41 (7) 27 (4) Quartz alpha, alpha-Si O2(1, 2, 2), Maghemite-Q, 19 90.13 1.0881 (1 24 (6) 62 (12) Quartz alpha, alpha-Si O2(1, 3, 2)

(19) TABLE-US-00002 TABLE 2 Reflections for fly ash after purification. Note that the sample is over 99% silicon oxide, with most of the iron oxides and cerium oxide removed. 2-theta Height Int. 1 (cps No. (deg) d (ang.) (cps) deg) Phase name 1 16.513 (14) 5.364 (5) 134 (13) 31 (2) Coesite(1, 1, 1) 2 26.0 (2) 3.42 (3) 124 (13) 812 (695) Coesite(1, 1, 1), 3 26.654 (2) 3.3417 (3) 1745 (48) 435 (14) Coesite(1, 1, 2) 4 30.75 (12) 2.905 (11) 127 (13) 1424 (963) Coesite(0, 4, 0), Magnetite, 5 33.22 (2) 2.6949 (16) 201 (16) 67 (8) Coesite(0, 4, 1) 6 35.69 (2) 2.5137 (13) 213 (17) 288 (10) Magnetite, syn(3, 1, 1) 7 40.86 (2) 2.2069 (12) 163 (15) 41 (4) Coesite(3, 1, 1) 8 42.36 (3) 2.1319 (12) 42 (7) 44 (5) Coesite(2, 2, 3), Magnetite, 9 50.02 (3) 1.8219 (11) 122 (13) 54 (5) Coesite(2, 4, 3) 10 57.56 (2) 1.5999 (5) 55 (9) 24 (3) Coesite(4, 2, 1) 11 60.74 (3) 1.5235 (6) 87 (11) 32 (4) Coesite(2, 4, 2) 12 62.92 (8) 1.4759 (16) 50 (8) 116 (15) Coesite(0, 8, 1), Magnetite, 13 68.06 (6) 1.3765 (10) 63 (9) 40 (3) Coesite(3, 1, 5) 14 75.4 (2) 1.260 (3) 21 (5) 26 (13) Coesite(4, 2, 5), Magnetite,

(20) TABLE-US-00003 TABLE 3 Reflections of the separated magnetic material. 2-theta Height Int. 1 (cps No. (deg) d (ang.) (cps) deg) Phase name 1 30.25 (2) 2.952 (2) 284 (31) 134 (8) iron diiron(III) oxide, magnetite HP, syn(2, 2, 0) 2 33.303 (6) 2.6882 (5) 226 (27) 73 (3) Hematite, syn(1, 0, 4) 3 35.570 (10) 2.5219 (7) 1130 (61) 573 (8) iron diiron(III) oxide, magnetite HP, syn(3, 1, 1), Hematite, syn(1, 1, 0) 4 43.23 (5) 2.091 (2) 155 (23) 106 (7) iron diiron(III) oxide, magnetite HP, syn(4, 0, 0), Hematite, syn(2, 0, 2) 5 49.83 (17) 1.828 (6) 23 (9) 33 (5) Hematite, syn(0, 2, 4) 6 54.06 (10) 1.695 (3) 53 (13) 51 (12) iron diiron(III) oxide, magnetite HP, syn(4, 2, 2), Hematite, syn(1, 1, 6) 7 57.109 (10) 1.6115 (3) 185 (25) 139 (6) iron diiron(III) oxide, magnetite HP, syn(5, 1, 1), Hematite, syn(1, 2, 2) 8 62.77 (4) 1.4791 (9) 244 (29) 310 (14) iron diiron(III) oxide, magnetite HP, syn(4, 4, 0), Hematite, syn(2, 1, 4) 9 71.9 (14) 1.31 (2) 20 (8) 156 (65) iron diiron(III) oxide, magnetite HP, syn(5, 3, 1), Hematite, syn(1, 2, 5)

(21) TABLE-US-00004 TABLE 4 Reflections of elements removed from the coal ash and electroplated out from the ionic liquid/acid solution. Int. 2-theta 1 (cps No. (deg) d (ang.) Height (cps) deg) Phase name 1 28.69 (14) 3.109 (15) 22.3 (19) 29 (4) beta-Th(1, 1, 0) 2 34.57 (15) 2.593 (11) 22.0 (19) 41 (14) Ytterbium(1, 0, 0) 4 38.3813 (12) 2.34337 (7) 3064 (23) 754 (7) Gold(1, 1, 1) 7 42.6501 (12) 2.11818 (6) 5239 (30) 960 (8) Samarium(1, 0, 1) 8 42.9458 (18) 2.10428 (8) 1238 (14) 223 (8) Samarium(0, 0, 2) 10 44.6377 (2) 2.028372 (10) 178453 (172) 36270 (25) Gold(2, 0, 0), alpha-Fe(1, 1, 0) 14 64.814 (3) 1.43730 (6) 2029 (18) 641 (4) Gold(2, 2, 0), Europium(2, 2, 0), alpha-Fe(2, 0, 0) 16 72.8 (6) 1.299 (9) 10.4 (13) 30 (6) Ytterbium(1, 0, 3), Samarium(1, 1, 2) 19 77.793 (3) 1.22675 (4) 2561 (21) 1141 (6) Gold(3, 1, 1), europium(3, 1, 1), Samarium(2, 0, 0) 20 81.91 (4) 1.1751 (4) 86 (4) 39 (2) Gold(2, 2, 2) 21 82.3 (14) 1.171 (16) 2.4 (6) 5 (4) Europium(2, 2, 2), alpha-Fe(2, 1, 1) 22 86.27 (2) 1.1267 (2) 71 (3) 21 (2) Ytterbium(2, 0, 2)

(22) The above descriptions are those of the preferred embodiments of the invention. Various modifications and variations are possible in light of the above teachings without departing from the spirit and broader aspects of the invention. It is therefore to be understood that the claimed invention may be practiced otherwise than as specifically described. Any references to claim elements in the singular, for example, using the articles a, an, the, or said, is not to be construed as limiting the element to the singular.