Cyclic process for the preparation of barium sulphate and lithium metal phosphate compounds
View Patent ↗A cyclic process for the preparation of barium sulphate and lithium-iron phosphate comprising (i) preparing an aqueous solution containing lithium and sulphate ions and (ii) adding solid barium hydroxide at a temperature of more than 50° C., wherein the barium hydroxide is added over a period of less than 15 minutes. Also, barium sulphate obtainable by the process according to the invention.
1. A cyclic process for the preparation of barium sulphate and lithium transition-metal phosphates, comprising:
(i) preparing an aqueous solution containing lithium and sulphate ions; and
(ii) adding solid barium hydroxide at a temperature of more than 50° C.,
wherein the barium hydroxide is added over a period of less than 15 minutes forming barium sulfate and lithium hydroxide in the solution.
2. The process of claim 1 , carried out in the absence of seed crystals.
3. The process of claim 2 , wherein the solid barium hydroxide is added in less than 5 minutes.
4. The process of claim 3 , wherein the solution is stirred during and after the addition of solid barium hydroxide.
5. The process of claim 4 , wherein the resultant barium sulphate is separated from the solution.
6. The process of claim 5 , wherein the lithium hydroxide-containing solution is mixed with an acid solution containing phosphoric acid and at least one transition-metal sulphate.
7. The process of claim 1 , wherein the aqueous solution containing lithium and sulphate ions from step i) is pretreated before carrying out step ii) by adding lithium hydroxide and setting a pH of more than 10 and wherein the resultant precipitate is separated.
8. The process of claim 7 , wherein the separated precipitate is used as starting material for the preparation of lithium-metal phosphates.
9. The process of claim 8 , wherein the separated precipitate is converted into easily soluble lithium hydrogen phosphate by acidification.
10. The process of claim 7 , wherein the pretreated solution containing lithium sulphate is passed to a concentration phase by reverse osmosis.
11. The process of claim 10 , wherein before the reverse osmosis the pretreated solution containing lithium sulphate is neutralized by the addition of sulphuric acid, or slightly acidified to a pH between 7 and 2.
12. Barium sulphate, obtained by the process of claim 1 , with an average particle size in the range from 0.5 to 1 μm.
13. Barium sulphate according to claim 12 , having a monomodal particle distribution with a D 50 value of 0.6 μm.
14. Barium sulphate according to claim 13 , wherein it is chloride- and/or sulphide-free.
15. Barium sulphate according to claim 13 , wherein it is alkali-free.
16. Barium sulphate according to claim 12 , having a brightness of greater than 95.