A method for recycling iron phosphate slag, comprising the following sequential steps:
- (S1) extracting aluminum phosphate in the iron phosphate slag by sequentially:
- a) mixing iron phosphate slag, sodium hydroxide, and water to solvate aluminum present in the iron phosphate slag as sodium aluminum oxide and produce a solid slag;
- b) filtering the resulting solution of a) to remove the solid slag in the solution wherein the solid slag comprises iron phosphate, lithium compounds, and carbon and is designated Soli-1, from the resulting filtrate wherein the filtrate comprises sodium aluminum oxide and is designated Solu-1;
- c) mixing Solu-1 and phosphoric acid to precipitate aluminum phosphate;
- d) filtering the resulting solution of c) to extract the aluminum phosphate in the solution and produce a filtrate, wherein the filtrate comprises phosphate compounds and lithium compounds, and is designated Solu-2;
- (S2) removing carbon additives, graphite and other organic compounds by sequentially:
- e) mixing Soli-1, sulfuric acid, and water to produce a solution with lithium, iron, and phosphate compounds and precipitate solid carbon slag;
- f) filtering the resulting solution of e) to remove the solid carbon slag and produce a filtrate, wherein the filtrate comprises lithium sulfate, iron sulfate, and phosphoric acid, and is designated Solu-3;
- (S3) extracting 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 extract impure iron phosphate and produce a filtrate, wherein the filtrate comprises lithium sulfate, and is designated Solu-4;
- i) mixing the impure iron phosphate with a low concentration solution of phosphoric acid;
- j) filtering the resulting solution of i) to extract iron phosphate and produce a filtrate, the filtrate of which is added to Solu-4;
- k) optionally washing the extracted iron phosphate of j) by mixing the iron phosphate with water and filtering the resulting solution to extract less impure iron phosphate;
- l) Subjecting the iron phosphate of j or the less impure iron phosphate k), if washed, to sequential drying in an air atmosphere, high-temperature calcination, and then either crushing and sieving, or alternatively grinding and milling;
- (S4) extracting lithium phosphate from Solu-4 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 and produce a 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, wherein the solution comprises sulfate compounds and is designated 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 p) with sodium phosphate to precipitate lithium phosphate;
- r) filtering the resulting solution of q) to obtain lithium phosphate and produce a filtrate, wherein the filtrate comprises sodium sulfate, and is designated Solu-6;
- s) drying the lithium phosphate in an air atmosphere;
- (S5) Recycling Solu-5 and Solu-6 into water and sodium sulfate by sequentially:
- t) mixing Solu-5 and Solu-6 and feeding the resulting solution into a mechanical vapor recompression (MVR) system;
- u) centrifuging and drying any recovered solid materials from t) in an air atmosphere to extract sodium sulfate.