METHOD FOR THE HIGH EFFICIENCY RECYCLING OF IRON PHOSPHATE BLACK POWDER SLAG

Abstract

This method recycles iron phosphate slag, which is produced as waste during lithium iron phosphate battery recycling processes that contain leaching or crushing for the sole extraction of lithium. This method extracts aluminum phosphate, iron phosphate, and lithium phosphate from the waste slag. The recycling process comprises these steps: (a) extraction of aluminum phosphate through addition of sodium hydroxide; (b) removal of carbon additives, graphite and other organic compounds through solvation of solely lithium, iron, and phosphate compounds through addition of sulfuric acid; (c) precipitation of iron phosphate by addition of hydrogen peroxide; (d) extraction of lithium phosphate from the mother liquor; (e) recycling of mother liquor into water and sodium sulfate. This process wastes few chemicals while still having a high reclamation efficiency in terms of purity and quantity. Furthermore, due to its relatively low costs, the profit margin of this process is very good.

Claims

1. A method for recycling iron phosphate slag, comprising the following sequential steps: (S1) extracting the aluminum phosphate in the iron phosphate slag by sequentially: a) mixing iron phosphate slag, sodium hydroxide, and water to solvate the aluminum present in the slag as sodium aluminum oxide; b) filtering the resulting solution from a) to remove the solid slag (the solid slag of which is characterized primarily by iron phosphate, lithium compounds, and carbon, and henceforth known as Soli-1) from the filtrate (the filtrate of which is characterized primarily by sodium aluminum oxide, and henceforth known as Solu-1); c) mixing Solu-1 and phosphoric acid to precipitate aluminum phosphate; d) filtering the resulting solution from c) to extract the aluminum phosphate from the filtrate (the filtrate of which is characterized primarily by phosphate compounds with very little lithium compounds, and henceforth known as Solu-2); (S2) removing carbon additives, graphite and other organic compounds by sequentially: e) mixing Soli-1, sulfuric acid, and water to solvate the lithium, iron, and phosphate compounds; f) filtering the resulting solution from e) to remove the solid carbon slag from the filtrate (the filtrate of which is characterized primarily by lithium sulfate, iron sulfate, and phosphoric acid, and henceforth known as Solu-3); (S3) extracting the iron phosphate by sequentially: g) mixing Solu-2, Solu-3, and hydrogen peroxide to precipitate iron phosphate; h) filtering the resulting solution of g) to obtain the impure iron phosphate from the filtrate (the filtrate of which is characterized primarily by lithium sulfate, and henceforth known as Solu-4); i) mixing the impure iron phosphate with a low concentration solution of phosphoric acid; j) filtering the resulting solution of i) to obtain the iron phosphate from the filtrate, the filtrate of which is added to Solu-4; k) washing the obtained iron phosphate of j) by mixing the iron phosphate with water and filtering the resulting solution to extract the wet iron phosphate; l) subjecting the wet iron phosphate to be sequentially dried in an air atmosphere, calcined at a high temperature, crushed, and sieved; (S4) extracting lithium phosphate from the mother liquor by sequentially: m) mixing Solu-4 and sodium hydroxide to precipitate unreacted slag waste; n) filtering the resulting solution of m) to remove the unreacted slag waste from the lithium sulfate solution; o) placing a lithium adsorbent into the resulting lithium sulfate solution of n) to extract lithium ions into or onto the adsorbent; p) taking the adsorbent out of the solution (the solution of which is characterized primarily by sulfate compounds, and henceforth known as Solu-5) and placing the adsorbent into a high concentration of sulfuric acid to solvate the lithium ions into lithium sulfate; q) mixing the resulting lithium sulfate solution of step p) with sodium phosphate to precipitate lithium phosphate; r) filtering the resulting solution of q) to obtain the lithium phosphate from the filtrate (the filtrate of which is characterized primarily by sodium sulfate, and henceforth known as Solu-6); s) drying the lithium phosphate in an air atmosphere; (S5) Recycling the mother liquor into water and sodium sulfate by sequentially: t) mixing Solu-5 and Solu-6 and feeding the resulting solution into a mechanical vapor recompression (henceforth known as MVR) system; u) centrifuging and drying any recovered solid materials from t) in an air atmosphere to extract sodium sulfate.

2. The method for recycling iron phosphate slag of claim 1, wherein, in step S1 (a), sodium hydroxide and water is mixed with the slag such that the resulting solution's pH is 8-10 and its liquid mass percentage content is 30-80%.

3. The method for recycling iron phosphate slag of claim 1, wherein, whenever a filtering step is conducted, a machine or tool is used primarily to separate the solid material in a solution from the liquid portion or to separate the liquid portion of a solution from the solid material; this does not include embodiments wherein the machine or tool performs another primary function that benefits the final product.

4. The method for recycling iron phosphate slag of claim 1, wherein, whenever a filtering step is conducted, the step is replaced by two or more sequential filtering steps, whereby the filtrates from a preceding step are sequentially fed into a subsequent filtering step and, during these multiple steps, the residual solids from each step are collated while only the final filtrate is collected.

5. The method for recycling iron phosphate slag of claim 1, wherein each mixing step is performed at 30? C.-80? C. under rapid stirring for at least 1 min.

6. The method for recycling iron phosphate slag of claim 1, wherein, in step S1 (c), phosphoric acid is added to the sodium aluminum oxide solution to control the pH to 4.5-5.5.

7. The method for recycling iron phosphate slag of claim 1, wherein, in step S2 (e), sulfuric acid and water is mixed with the slag such that the resulting solution's pH is 3-4 and its liquid mass percentage content is 30-80%.

8. The method for recycling iron phosphate slag of claim 1, wherein, in step S3 (g), hydrogen peroxide is added to Solu-3 to control the pH to 3-4.

9. The method for recycling iron phosphate slag of claim 1, wherein, in step S3, an aging step is performed directly after (g) mixing Solu-2, Solu-3, and hydrogen peroxide to precipitate iron phosphate; this aging step of which may utilize a stirring, heating, or cooling step, or a combination of one or multiple stirring, heating and cooling steps, but the overall aging step takes no more than 5 hours to precipitate the iron phosphate.

10. The method for recycling iron phosphate slag of claim 1, wherein, in step S3 (i), the low concentration phosphoric acid has a concentration between 0.05M-0.3M and has an overall mass equal to 50%-200% of the impure iron phosphate's mass.

11. The method for recycling iron phosphate slag of claim 1, wherein, in step S3 (k), the iron phosphate washing with water step is either not performed, or is performed multiple times, whereby the resulting wet iron phosphate after a preceding washing step is fed into the subsequent step as the next step's iron phosphate.

12. The method for recycling iron phosphate slag of claim 1, wherein, in step S3, S4, and S5, during drying steps (l) (s) (u), the material is dried at 100? C.-200? ? C. for 1 to 24 hours.

13. The method for recycling iron phosphate slag of claim 1, wherein, in step S3 (l), the iron phosphate is calcined at 350-550? C. for 1 to 9 hours.

14. The method for recycling iron phosphate slag of claim 1, wherein, in step S3 (l), the crushing and sieving can be replaced by two or more sequential grinding or milling steps, whereby in each step, a machine or tool is used primarily to evenly or unevenly apply force to the iron phosphate such that the material either becomes smaller or has less or smaller clumps; this does not include embodiments wherein the machine or tool performs another primary function that benefits the final product.

15. The method for recycling iron phosphate slag of claim 1, wherein, in step S4 (m), sodium hydroxide is added to Solu-4 to control the pH to 7-8.

16. The method for recycling iron phosphate slag of claim 1, wherein, in step S4 (o), the lithium adsorbent is one or a combination of cellulose nanocrystal, lithium ion sieve, lithium manganese oxide, lithium titanium oxide, hydrogen titanium oxide, and hydrogen manganese oxide, wherein the mass of the lithium adsorbent is 2% to 20% of the mass of the lithium sulfate solution and the adsorption process takes 15 minutes to 5 hours.

17. The method for recycling iron phosphate slag of claim 1, wherein, in step S4 (p), the high concentration sulfuric acid has a concentration between 0.5M-3M and has an overall mass equal to 10%-100% of the adsorbent's mass, and the desorption process takes 15 minutes to 5 hours.

18. The method for recycling iron phosphate slag of claim 1, wherein, in step S4 (q), the sodium phosphate has a mass equal to 5%-50% of the adsorbent's mass.

19. The method for recycling iron phosphate slag of claim 1, wherein one of or a combination of Solu-2, the filtrate produced after filtering the low concentration phosphoric acid and iron phosphate solution in step S3, and Solu-5 is thrown away as waste or recycled directly in an MVR system and not later mixed with their respective solutions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a flow chart of the recycling method of the iron phosphate slag material in one embodiment.

[0043] FIG. 2 is a table for various physical and chemical properties of the iron phosphate extracted according to an embodiment of the present invention (Embodiment 1).

[0044] FIG. 3 is an X-ray diffraction (XRD) pattern of the iron phosphate extracted according to an embodiment of the present invention (Embodiment 1).

DETAILED DESCRIPTION OF EMBODIMENTS

[0045] In order to promote the understanding of the present disclosure, the disclosure will be described below in detail, with reference to the preferred embodiment. It should be understood that the embodiment is merely illustrative, and is not intended to limit the scope of the present disclosure. Any changes, modifications and replacements made by those skilled in the art without departing from the spirit of the disclosure should fall within the scope of the disclosure defined by the appended claims.

[0046] The instruments used in the following embodiments include: a sanding machine (model SX-200, manufactured by Wuxi Xiguang Powder Technology Co., LTD); a spray dryer (model LP-12, manufactured by Shanghai Gaoling Technology Development Co., LTD); a tube box furnace (model OTL1200-11, manufactured by Anhui Hefei Hengli Electronic Equipment Company); an air box furnace (model HXL004-12, manufactured by Anhui Hefei Hengli Electronic Equipment Company).

Embodiment 1

[0047] Iron phosphate slag was obtained from Weijin recycling technology limited. [0048] (S1) 200 g of iron phosphate slag, 100 mL of 1M sodium hydroxide, and 500 mL of deionized water were mixed at 40? C. for 30 min under rapid stirring. The solution was then press filtered. Phosphoric acid was mixed with the resulting sodium aluminum oxide solution at 40? C. for 30 min under rapid stirring until the solution's pH was ?5.2 to precipitate aluminum phosphate. The solution was then press filtered to extract the aluminum phosphate from the filtrate. [0049] (S2) The solid that was obtained after the first filtration in S1 was mixed with 100 mL of 1M sulfuric acid and 500 ml of water at 40? C. for 30 min under rapid stirring. The solution was press filtered and the solid slag obtained was collected as waste. [0050] (S3) The filtrate resulting from S2, the resulting filtrate from S1, and 100 mL of 1M hydrogen peroxide were mixed at 40? C. for 45 min under rapid stirring until the solution's pH was 1.3?1.7. The resulting solution was aged at 60? C. for 1 hour and then press filtered (Solu-4). The impure iron phosphate and 200 ml of 0.1M phosphoric acid were mixed at 40? C. for 20 min under rapid stirring. The solution was then filtered, and the filtrate was added to Solu-4. The resulting iron phosphate and 200 mL of deionized water were mixed at 40? ? C. for 20 min under rapid stirring. The solution was then filtered. The iron phosphate was washed with water twice more in this fashion. The iron phosphate was dried at 110? C. in an air atmosphere for 3 hours before it was calcined at a high temperature of 450? C. for 3 hours. Finally, the iron phosphate was crushed and fed through a 200 um sieve. [0051] (S4) Solu-4 and 100 mL of 1M sodium hydroxide were mixed at 40? C. for 15 min under rapid stirring until the solution's pH was 7.5. The solution was press filtered, and the resulting solid slag was collected from the filtrate (Solu-5). 75 g of hydrogen titanium oxide was put into Solu-5 for 2 hours. The adsorbent was then taken out of Solu-5 and placed into 80 mL of 2M sulfuric acid for 2 hours. The adsorbent was then taken out. 15 g of sodium phosphate was mixed into the resulting lithium sulfate solution at 40? C. for 15 min under rapid stirring. The solution was then filtered to extract the lithium phosphate from the filtrate (Solu-6). Finally, the lithium phosphate was dried at 110? C. in an air atmosphere for 3 hours. [0052] (S5) Solu-5 and Solu-6 were mixed at 40? ? C. for 10 min under rapid stirring and fed into a MVR system. The remaining solid material was centrifuged and dried at 110? C. in an air atmosphere for 3 hours.

[0053] At the end of the process, 100.5 g of iron phosphate (99.5% in purity), 11 g of aluminum phosphate (99.0% purity), 2.16 g of lithium phosphate, and 38.7 g of sodium sulfate (95% purity) were extracted. The iron phosphate product was analyzed with various techniques, including X-ray diffraction spectroscopy, which all indicated overall high purity.

[0054] As shown in the example, this method is capable of retrieving significant amounts of aluminum and lithium from the iron phosphate slag. Furthermore, yield of iron phosphate is both higher than prior art and is more pure. In particular, it contains less aluminum.