| CPC C01B 25/375 (2013.01) [B01J 20/06 (2013.01); C01B 25/303 (2013.01); C01B 25/36 (2013.01); C22B 7/04 (2013.01); C22B 21/0023 (2013.01); C22B 21/04 (2013.01); C22B 26/12 (2013.01); H01M 10/54 (2013.01)] | 19 Claims |
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1. 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.
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