Processes and systems for preparing lithium hydroxide
There are provided processes for preparing lithium hydroxide. The processes comprise submitting an aqueous composition comprising lithium sulfate and/or lithium bisulfate to a first electromembrane process that comprises a two-compartment membrane process under suitable conditions for conversion of the lithium sulfate and/or lithium bisulfate to lithium hydroxide, and obtaining a first lithium-reduced aqueous stream and a first lithium hydroxide-enriched aqueous stream; and submitting the first lithium-reduced aqueous stream to a second electromembrane process that comprises a three-compartment membrane process under suitable conditions to prepare at least a further portion of lithium hydroxide and obtaining a second lithium-reduced aqueous stream and a second lithium-hydroxide enriched aqueous stream. There are also provided systems for preparing lithium hydroxide.
1. A process for preparing lithium hydroxide, said process comprising:
submitting, in a first electrochemical cell that comprises a two-compartment membrane cell, an aqueous composition comprising lithium sulfate and/or lithium bisulfate to a first electromembrane process that comprises a two-compartment membrane process for conversion of said lithium sulfate and/or lithium bisulfate to lithium hydroxide, and obtaining a first lithium-reduced aqueous stream and a first lithium hydroxide-enriched aqueous stream;
monitoring conversion of said lithium sulfate and/or lithium bisulfate into lithium hydroxide such that when consumption of said lithium sulfate and/or lithium bisulfate reaches 30 to 50 weight %, conveying said first lithium-reduced aqueous stream from an anolyte compartment of said first electrochemical cell to a central compartment of a second electrochemical cell that comprises a three-compartment membrane cell; and
submitting said first lithium-reduced aqueous stream to a second electromembrane process that comprises a three-compartment membrane process to prepare at least a further portion of lithium hydroxide and obtaining a second lithium-reduced aqueous stream, sulfuric acid and a second lithium-hydroxide enriched aqueous stream.
2. The process of claim 1 , wherein said first electromembrane process comprises a two-compartment monopolar or bipolar membrane electrolysis process.
3. The process of claim 2 , wherein in said two-compartment monopolar or bipolar membrane electrolysis process, current density is maintained at a value of from 3 kA/m 2 to 5 kA/m 2 .
4. The process of claim 2 , wherein said two-compartment monopolar or bipolar membrane electrolysis process is carried out in said first electrochemical cell comprising said anolyte compartment separated from a catholyte compartment by a cation exchange membrane.
5. The process of claim 4 , wherein said cation exchange membrane comprises a perfluorinate sulfonic acid.
6. The process of claim 4 , wherein during said two-compartment monopolar or bipolar membrane electrolysis process, said aqueous stream comprising lithium sulfate and/or lithium bisulfate is introduced into said anolyte compartment, said first lithium-reduced aqueous stream is removed from said anolyte compartment and said first lithium hydroxide-enriched aqueous stream is removed from said catholyte compartment.
7. The process of claim 6 , wherein during said two-compartment monopolar or bipolar membrane electrolysis process, conversion of said lithium sulfate and/or lithium bisulfate to lithium hydroxide is carried out as long as hydroxide current efficiency is no longer maintained and when hydroxide current efficiency decreases, said two-compartment monopolar or bipolar membrane electrolysis process is stopped.
8. The process of claim 6 , wherein during said two-compartment monopolar or bipolar membrane electrolysis process, conversion of said lithium sulfate and/or lithium bisulfate to lithium hydroxide proceeds until pH in said anolyte compartment is a value of from 0.4 to 1.0.
9. The process of claim 8 , wherein in said catholyte compartment of said two-compartment monopolar or bipolar membrane electrolysis process, lithium hydroxide is maintained at a concentration of 2 M to 4 M.
10. The process of claim 6 , wherein during said two-compartment monopolar or bipolar membrane electrolysis process, said aqueous stream comprising lithium sulfate and/or lithium bisulfate is introduced into said anolyte compartment at a temperature of 20 ° C. to 100 ° C.
11. The process of claim 6 , wherein in said two-compartment monopolar or bipolar membrane electrolysis process, current density is maintained at a value of from 0.5 kA/m 2 to 6 kA/m 2 .
12. The process of claim 11 , wherein in said two-compartment monopolar or bipolar membrane electrolysis process, voltage is maintained at a value of 3 V to 8 V.
13. The process of claim 12 , wherein said first electrochemical cell has an overall cell size of 200 m 2 to 2000 m 2 .
14. The process of claim 6 wherein said process further comprises recycling at least a portion of said second lithium-reduced aqueous stream to said first electromembrane process.
15. The process of claim 14 , wherein said second lithium-reduced aqueous stream is recycled to said first electrochemical cell when the pH in said central compartment of said second electrochemical cell reaches a value of 2 to 12.
16. The process of claim 15 , wherein said second lithium-reduced aqueous stream is recycled to said first electrochemical cell in order to maintain pH of the first lithium-reduced aqueous stream above a value of 0.4 to 1.2.
17. The process of claim 14 , wherein said second lithium-reduced aqueous stream is recycled to said first electrochemical cell when the pH in said central compartment of said second electrochemical cell reaches a value of 8 to 10.
18. The process of claim 17 , wherein said second lithium-reduced aqueous stream is recycled to said first electrochemical cell in order to maintain pH of the first lithium-reduced aqueous stream above a value of 0.6.
19. The process of claim 14 , wherein said second lithium-reduced aqueous stream is recycled to said first electrochemical cell in order to maintain pH of the first lithium-reduced aqueous stream above a value of 0.4 to 1.2.
20. The process of claim 6 , wherein during said two-compartment monopolar or bipolar membrane electrolysis process, conversion of said lithium sulfate and/or lithium bisulfate to lithium hydroxide proceeds until pH in said anolyte compartment drops to a value of from 0.5 to 0.8.
21. The process of claim 1 , wherein said process further comprises recycling at least a portion of said second lithium-reduced aqueous stream to said first electromembrane process.