阅读说明：本技术 用于回收氢氧化锂的装置和方法 (Apparatus and method for recovering lithium hydroxide ) 是由 玛丽卡·提利洪 萨米·基努南 埃罗·寇罗麦内恩 于 2020-10-26 设计创作，主要内容包括：本发明涉及用于回收氢氧化锂的装置和方法,特别是涉及用于从与含有锂的再循环溶液和/或浆料组合的新鲜进料回收氢氧化锂的装置和方法,所述新鲜进料包含含有锂的矿物原材料或含有碳酸锂的原材料或这些原材料的混合物,在水和碱金属碳酸盐的存在下将进料制浆,浸出获得的浆料两次,首先在升高的温度下,并其次在含有碱土金属氢氧化物的水溶液中,将如此获得的浆料分离为可丢弃的固体和含有氢氧化锂的溶液,由此可通过结晶从溶液回收氢氧化锂一水合物,最后将在结晶过程中获得的溶液和/或浆料从该工艺分离,并将其再循环至包括制浆步骤和任选的第一浸出步骤的一个或多个先前步骤。(The present invention relates to an apparatus and a process for recovering lithium hydroxide, in particular to an apparatus and a process for recovering lithium hydroxide from fresh feed combined with a lithium containing recycle solution and/or slurry, the fresh feed comprises a lithium containing mineral raw material or a lithium carbonate containing raw material or a mixture of these raw materials, the feed is slurried in the presence of water and alkali metal carbonate, the resulting slurry is leached twice, first at elevated temperature, and secondly separating the slurry thus obtained into a discardable solid and a solution containing lithium hydroxide in an aqueous solution containing an alkaline earth metal hydroxide, whereby lithium hydroxide monohydrate can be recovered from the solution by crystallization, and finally the solution and/or slurry obtained during crystallization is separated from the process, and recycled to one or more of the previous steps including the pulping step and the optional first leaching step.)

1. Apparatus for recovering lithium hydroxide from fresh feed comprising lithium containing mineral raw material or lithium carbonate containing raw material or a mixture of these raw materials in combination with a lithium containing recycle solution and/or slurry, comprising

-a pulping unit (1) for pulping a feed in the presence of water and an alkali carbonate so as to form a first slurry comprising lithium,

-a first leaching unit (2) for leaching the first slurry containing lithium, optionally in combination with a recirculation solution and/or slurry, at an elevated temperature so as to form a second slurry containing lithium carbonate,

-a second leaching unit (3) for leaching the second slurry containing lithium carbonate, or a part thereof, in the presence of water and an alkaline earth metal hydroxide, so as to form a third slurry containing lithium hydroxide,

-a solid-liquid separation unit (31) for separating the third slurry comprising lithium hydroxide into a discardable solid and a solution comprising lithium hydroxide,

-a crystallization unit (4) for recovering lithium hydroxide monohydrate from a solution containing lithium hydroxide,

the plant also comprises one or more recycle lines (403, 414, 421,422) for conveying the solution and/or slurry from the crystallization unit (4) to one or more upstream units including the pulping unit (1) and the optional first leaching unit (2).

2. The apparatus according to claim 1, further comprising a calcination unit for heat treating the mineral raw material intended to be conveyed as at least a part of the feed to the pulping unit (1).

3. An apparatus according to claim 1, wherein the first leaching unit (2) is an autoclave.

4. An apparatus according to claim 1, wherein the first leaching unit (2) is connected with the pulping unit (1) by a slurry line (102).

5. An apparatus according to claim 1, wherein a solid-liquid separation unit (21) is arranged between the first leaching unit (2) and the second leaching unit (3), and an optional washing unit or washing section within the separation unit (21) is used to wash solids separated from liquid in the separation unit (21).

6. An apparatus according to claim 1 or 5, comprising a recirculation line (211, 212), which recirculation line (211, 212) leads from the first leaching unit (2) or from the liquid section of the solid-liquid separation unit (21) connected to the first leaching unit (2) to a unit upstream of the first leaching unit (2).

7. The plant according to claim 1 or 5, comprising a recirculation line (211, 212), which recirculation line (211, 212) leads from the first leaching unit (2) or from the liquid section of the solid-liquid separation unit (21) placed in connection with the first leaching unit (2) as line (211) to the pulping unit (1) or as line (212) to the first leaching unit (2), or as separate lines (211) and (212) to each unit.

8. An arrangement according to claim 1 or 5, comprising a recirculation line (211), which recirculation line (211) leads from the first leaching unit (2) or from the liquid section of the solid-liquid separation unit (21) connected to the first leaching unit (2) to the pulp making unit (1).

9. The plant according to claim 1, wherein the second leaching unit (3) is a tank reactor, preferably a stirred tank reactor.

10. The apparatus of claim 1, wherein the second leaching unit (3) comprises an inlet (303) for an alkaline earth metal hydroxide or an aqueous slurry thereof.

11. The apparatus according to claim 1, wherein the second leaching unit (3) is connected to a slurrying unit (30), the slurrying unit (30) being for mixing alkaline earth metal hydroxides into an aqueous slurry.

12. An apparatus according to claim 1 or 5, wherein the second leaching unit (3) is connected to the first leaching unit (2) or a downstream solid-liquid separation unit (21) by a slurry line (203).

13. An apparatus according to claim 1, wherein a solid-liquid separation unit (31) located downstream of the second leaching unit (3) is connected to a washing unit or comprises a washing section within the separation unit (31) for washing solids separated from liquid in the separation unit (31).

14. The apparatus according to claim 1, comprising a purification unit (32) connected to the solid-liquid separation unit (31) for purifying the solution obtained from the separation unit (31).

15. The apparatus according to claim 14, wherein the purification unit (32) comprises one or more of an ion exchange unit and a membrane separation unit, preferably at least one or more ion exchange units, more preferably a cation exchange unit, in particular containing a selective cation exchange resin.

16. The apparatus according to claim 14, wherein the purification unit (32) is an ion exchange unit or a series of two or more ion exchange units and is connected to the regeneration unit (33) or a series of two or more regeneration units (33) for regenerating the purification resin, wherein a line (332) is typically connected between the purification unit (32) and the regeneration unit (33) for returning the regenerated resin to the ion exchange unit.

17. The apparatus according to claim 14, wherein the purification unit (32) is a membrane separation unit which is connected to the crystallization unit (4) by supplying the crystallization unit (4) with a purification solution and to the second leaching unit (3) by means of a recycle line (323) for returning the recycle stream to the leaching step.

18. The apparatus according to claim 14, wherein the purification unit (32) is a combination of a membrane separation unit and an ion exchange unit, wherein the membrane separation unit has an outlet connected to an inlet of the ion exchange unit.

19. The device according to claim 1, comprising two or more crystallization units (4), preferably arranged sequentially.

20. The plant according to claim 1, 14 or 16, wherein the crystallization unit (4) or the downstream purification unit (32) or the downstream regeneration unit (33) is connected by a liquid line (304) to a solid-liquid separation unit (31) located downstream of the second leaching unit (3).

21. The apparatus according to claim 1, wherein a pre-concentration unit, preferably in the form of an evaporation unit, designed to provide a crystallization feed with an optimized concentration, precedes the crystallization unit (4).

22. The apparatus according to claim 1, comprising a solid-liquid separation unit (41) connected to the crystallization unit (4) for separating the crystals obtained in the crystallization unit (4) from the waste solution.

23. The plant according to claims 1 and 22, comprising a recirculation line (403), which recirculation line (403) is arranged between the crystallization unit (4) and/or the liquid section of the solid-liquid separation unit (41) connected to the crystallization unit (4) and the second leaching unit (3).

24. The plant according to claims 1 and 22, comprising one or more recirculation lines (421,422), which recirculation lines (421,422) are arranged between the crystallization unit (4) and/or a liquid section of the solid-liquid separation unit (41) connected to the crystallization unit (4) and one or more of the pulping unit (1) and the first leaching unit (2).

25. The apparatus according to claims 1 and 22, comprising a lithium precipitation unit (42) connected to the crystallization unit (4) or the solid-liquid separation unit (41) by a line (423).

26. An apparatus according to claim 25, wherein the lithium precipitation unit (42) comprises a feed inlet (424) for feeding carbon dioxide or alkali metal carbonate or a mixture of these to the unit (42).

27. An apparatus according to claim 25, wherein one or more recirculation lines (421,422) are arranged between the lithium precipitation unit (42) connected to the crystallization unit (4) or the solid-liquid separation unit (41) and one or more of the pulping unit (1) and the first leaching unit (2), whereby the slurry obtained in the lithium precipitation unit (42) is recirculated to one or both of said units (1, 2).

28. The apparatus according to claim 22, wherein the liquid section of the solid-liquid separation unit (41) is connected to the crystallization unit (4), optionally via a crystallization feed, via a recirculation line (414) for recirculating a part of the waste solution separated from the crystallization step back to the crystallization unit (4).

29. The apparatus according to claim 1, comprising a product purification unit (43), which product purification unit (43) is connected to the crystallization unit (4) and/or to a solid-liquid separation unit (41) connected to the crystallization unit (4), wherein the solid obtained in the crystallization step can be purified.

30. The apparatus according to claim 29, wherein the product purification unit (43) comprises a feed inlet (431) for supplying a washing solution to the product purification unit (43), the feed inlet (431) preferably being connected with a recirculation line, such as recirculation line (445).

31. The apparatus according to claim 29, comprising a solid-liquid separation unit (44) connected to and downstream of the product purification unit (43) for separating purified lithium hydroxide monohydrate crystals from the spent wash solution.

32. The plant according to claim 29 or 31, wherein the product purification unit (43) or a solid-liquid separation unit (44) connected to the product purification unit (43) and downstream of the product purification unit (43) is connected to the upstream purification unit (32) or to an optional regeneration unit (33) connected to the upstream purification unit (32) by means of a recirculation line (432).

33. The plant according to claim 29 or 31, wherein a solid-liquid separation unit (44) connected to the product purification unit (43) and downstream of the product purification unit (43) is connected to the crystallization unit (4) by means of a recirculation line (444).

34. The apparatus according to claim 29 or 31, wherein a solid-liquid separation unit (44) connected to the product purification unit (43) and downstream of the product purification unit (43) is connected to the product purification unit (43) by means of a recirculation line (445).

35. The device according to claim 1, comprising a combined product purification unit (41, 43, 44) for purifying crystals obtained from the waste solution in the crystallization unit (4) and separating the purified crystals from the waste wash solution.

36. The apparatus according to claim 35, wherein the combined product purification unit (41, 43, 44) is connected to the crystallization unit (4) by a recirculation line (414) for returning the waste solution separated from the crystallization step as a recirculation solution to the crystallization unit (4).

37. The apparatus according to claim 35, wherein the combined product purification unit (41, 43, 44) comprises a feed inlet (431) for feeding a washing solution to the unit (41, 43, 44).

38. The apparatus according to claim 35, wherein the combined product purification unit (41, 43, 44) is connected with an upstream purification unit (32) or with a separate regeneration unit (33) by means of a recirculation line (432).

39. The apparatus according to claim 35, wherein the combined product purification unit (41, 43, 44) is connected to the crystallization unit (4) by a recycle line (444).

40. The apparatus according to claim 35, wherein the solid section of a combined product purification unit (41, 43, 44) is connected to the liquid section of the same combined unit (41, 43, 44) by a recycle line (435).

41. The apparatus according to claim 1, comprising a drying unit (45), which drying unit (45) is connected to the crystallization unit (4) or to the solid section of the solid-liquid separation unit (41, 44) downstream of the crystallization unit (4) or to the solid section of the combined product purification and separation unit (41, 43, 44) downstream of the crystallization unit (4), in which drying unit (45) the obtained lithium hydroxide monohydrate crystals can be dried.

42. An apparatus according to claim 41, wherein the drying unit (45) comprises a product outlet (451) through which the final product is recoverable.

43. Process for recovering lithium hydroxide from fresh feed comprising lithium containing mineral raw material or lithium carbonate containing raw material or a mixture of these in combination with a lithium containing recycle solution and/or slurry, wherein the process comprises

-pulping a lithium containing feed in the presence of water and an alkali metal carbonate for producing a first lithium containing slurry,

-leaching the first slurry containing lithium, optionally in combination with a recirculation solution and/or slurry, at an elevated temperature in a first leaching step for producing a second slurry containing lithium carbonate,

-leaching the second slurry or a part thereof in an aqueous solution containing an alkaline earth metal hydroxide in a second leaching step for producing a third slurry containing lithium hydroxide,

-separating the third slurry by solid-liquid separation into a discardable solid and a solution containing lithium hydroxide,

recovering lithium hydroxide monohydrate by crystallization from a solution containing lithium hydroxide, and

-separating the solution and/or slurry obtained in the crystallization process from the process and returning it as recycled solution and/or slurry to one or more previous process steps comprising a pulping step and optionally a first leaching step.

44. The method as claimed in claim 43, wherein the mineral raw material used as at least part of the feed in the pulping step is a lithium containing mineral in calcined form, preferably obtained by heat treating the raw material, more preferably by using a temperature of 900-.

45. A process according to claim 43, wherein the mineral raw material used in the pulping step is selected from spodumene, petalite, lepidolite, mica or clay, or mixtures thereof, preferably spodumene, more preferably β -spodumene.

46. The process according to claim 43, wherein the lithium carbonate-containing raw material is a freshly added raw material or is recycled from a subsequent step of the process, preferably at least a part from the crystallization step.

47. A process according to claim 43, wherein at least a portion of the water and alkali metal carbonate that is passed to the pulping step is a recycled aqueous solution containing said alkali metal carbonate.

48. A process according to claim 43, wherein the alkali metal carbonate used in the pulping step is selected from sodium carbonate and potassium carbonate, preferably consisting at least in part of sodium carbonate.

49. A process as claimed in claim 43, in which the first leaching step is carried out at a temperature of 160 to 250 ℃, preferably at a temperature of 200 to 220 ℃.

50. A process according to claim 43, wherein the first leaching step is carried out at a pressure of 10 to 30 bar, preferably at a pressure of 15 to 25 bar.

51. A process as claimed in any one of claims 43 or 49 to 50, in which suitable conditions for the first leaching step are achieved using high pressure steam.

52. A process according to claim 43, wherein the solution is separated from the solids in a separate solid liquid separation step after the first leaching step and the solids are optionally sent to the second leaching step after washing the solids.

53. A method according to claim 43 wherein the solution is separated from the solids after the first leaching step and returned to one or more of the previous steps as a recycle solution.

54. A process as claimed in claim 43, in which the solution is separated from the solids after the first leaching step and returned to the pulping step or the first leaching step, or each step, as a portion of the recycle solution.

55. A process according to claim 54 wherein the solution is returned to the pulping step.

56. A method according to claim 43, wherein the alkaline earth metal hydroxide used in the second leaching step is selected from calcium hydroxide and barium hydroxide, preferably is calcium hydroxide.

57. A method according to claim 43, wherein the alkaline earth metal hydroxide used in the second leaching step is mixed with water or an aqueous solution before addition to the second leaching step.

58. The process according to claim 43, wherein at least a part of the solution separated from solids in the solid-liquid separation of the third slurry is added to the second leaching step in the form of a recycled solution, preferably mixed with fresh alkaline earth hydroxide before being added to the second leaching step, more preferably mixed with fresh alkaline earth hydroxide in a separate slurrying step.

59. The process according to claim 43, wherein the solids obtained from the solid-liquid separation of the third slurry are washed, and preferably at least a portion of the spent wash solution is combined with the solution separated from the solids in said solid-liquid separation of the third slurry.

60. A method according to claim 43, wherein the second leaching step is carried out at a temperature of 10-100 ℃, preferably 20-60 ℃ and most suitably 20-40 ℃.

61. A method according to claim 43, wherein the second leaching step is carried out at atmospheric pressure.

62. The method according to claim 43, wherein a step of purifying the solution obtained from the third slurry is performed, which step comprises a purification based on purifying dissolved ions and components, preferably comprising ion exchange or membrane separation or both.

63. The method according to claim 43 or 62, wherein the step of purifying the solution obtained from the third slurry is performed by ion exchange, preferably by using a cation exchange resin, in particular a selective cation exchange resin.

64. A process according to claim 63, wherein the ion exchange is carried out at least partly using purified resin which has been regenerated in a separate regeneration step, typically the regenerated resin is returned to ion exchange.

65. The method according to claim 64, wherein the regeneration step is performed using a recycled solution from a subsequent process step, preferably a separated solution obtained from crystallization or from a subsequent washing step.

66. The process according to claim 43 or 62, wherein the step of purifying the solution obtained from the third slurry is performed by membrane separation, whereby the membrane separation produces a purified stream that is sent to the crystallization step and a recycle stream that is preferably sent to the second leaching step.

67. The method according to claim 43 or 62, wherein the step of purifying the solution obtained from the third slurry is performed by first performing a membrane separation and by sending the thus purified solution to an ion exchange step for further purification.

68. The method of claim 43, wherein the crystallization of lithium hydroxide monohydrate is carried out by heating a solution comprising lithium to a temperature of about the boiling point of the solution.

69. A process according to claim 43, wherein a pre-concentration step is carried out prior to crystallization of lithium hydroxide monohydrate, preferably as evaporation, for dispersing excess liquid from the lithium containing solution.

70. The process according to claim 43, wherein the crystallization of lithium hydroxide monohydrate is carried out in two or more crystallization units, preferably arranged sequentially.

71. A process according to claim 43, wherein the solution containing lithium hydroxide is mixed with one or more solutions recycled from subsequent steps of the process, or all of them are fed separately to the crystallisation step, before being sent to the crystallisation step.

72. A process according to claim 43, wherein at least a portion of the solution separated from the crystallisation step is returned to the second leaching step as a recycle solution.

73. A process according to claim 43, wherein at least a portion of the solution separated from the crystallization step is returned to one or both of the pulping step and the first leaching step as a recycle solution.

74. The process according to claim 43, wherein at least a portion of the solution separated from the crystallization step is sent to a lithium precipitation step, preferably carried out as carbonation, wherein the solution is reacted with either carbon dioxide or a mixture of alkali carbonate or both, preferably carbon dioxide or a mixture of carbon dioxide and alkali carbonate, to form a lithium carbonate slurry.

75. The method according to claim 74, wherein precipitation in the incomplete reaction is carried out as carbonation, whereby at least trace amounts of lithium hydroxide will still be present in the lithium carbonate slurry.

76. The process according to claim 74 or 75, wherein the slurry comprising lithium carbonate is recycled to one or both of the pulping step and the first leaching step, preferably to the pulping step.

77. The process according to claim 43, wherein a portion of the solution separated from the crystals obtained after the crystallization step is returned to the crystallization step as a recycle solution.

78. The process according to claim 43, wherein the solid containing lithium hydroxide monohydrate crystals obtained in the crystallization step is purified using a wash solution prior to recovery as product.

79. The process of claim 78, wherein the purified lithium hydroxide monohydrate crystals are separated from the wash solution, dried, and subsequently recovered.

80. The process according to claim 78, wherein the spent wash solution is separated from the purified lithium hydroxide monohydrate crystals and returned as a recycle solution to the crystal wash step or to the step of purifying the solution separated from the third slurry or to a regeneration step prior to said purification step or to the crystallization step, or a portion of the spent wash solution is returned to two or more of these steps.

81. The method of any one of steps 43 to 80, carried out using the apparatus of any one of claims 1 to 42.

Technical Field

The present invention relates to an apparatus and method for recovering lithium hydroxide from lithium containing minerals and lithium carbonate.

Background

CN102115101 discloses a process for producing lithium carbonate from spodumene mineral: by performing a sulfuric acid treatment in order to obtain lithium sulfate, followed by a step of preparing a lithium carbonate mother liquor, the carbonate product can be separated from the lithium carbonate mother liquor, and finally lithium hydroxide is obtained from this mother liquor by causticizing the mother liquor by adding lime. Barium hydroxide is also said to be useful as a causticizing hydroxide.

CN 100455512C discloses a process for the preparation of lithium hydroxide monohydrate: pure lithium hydroxide monohydrate is provided by adding sodium hydroxide to a lithium sulfate solution so as to obtain liquid lithium hydroxide, followed by cooling, filtration and separation of the lithium hydroxide from sodium sulfate, followed by a series of recrystallization steps.

A similar process is described in CN 1214981C, wherein a step of adding sodium hydroxide to a lithium sulfate solution is performed, followed by cooling and separation to obtain liquid lithium hydroxide. The lithium hydroxide solution is then concentrated and crystallized, whereby the crude lithium hydroxide monohydrate product can be isolated. In this publication pure lithium hydroxide monohydrate is obtained by reacting the crude product with barium hydroxide, followed by concentration and crystallization.

However, these processes are all carried out by means of lithium sulfate.

US 3343910 a describes a process for the recovery of lithium hydroxide from mineral raw materials (calcined spodumene concentrate): the minerals are decomposed at 200 ℃ by using sodium carbonate, leached with calcium hydroxide at or near ambient temperature, and finally LiOH is crystallized. It is also mentioned that the usual practice of causticising the separated lithium carbonate is at about 85 ℃, otherwise the results will be poor and uneconomical. US 334910 also describes that the hot mother liquor from the decomposition step containing unspent sodium carbonate can be removed in order to recycle the sodium carbonate. Optionally, the lithium compound can be separated from the leaching reaction product and the solution concentrated to the point of crystallization, after which the mother liquor can be returned to the process. However, no specific recirculation route is mentioned.

This process is not very efficient without further purification and recycling.

Thus, there remains a need for a process that allows the use of mineral feedstock and that will utilize a recycle stream containing or forming lithium carbonate that in known processes will end up in a discarded portion.

Disclosure of Invention

The object of the present invention is therefore to provide an apparatus and a process suitable for recovering lithium hydroxide from a feed comprising mineral raw materials in high yield and high purity (typically battery grade) without the need for multiple processing steps including precipitation and purification steps (followed by further solid-liquid separation).

In particular, it is an object of the present invention to provide an apparatus and a process for the recovery of lithium hydroxide using simple purification steps and by optimized recycling.

By cell grade lithium hydroxide herein is meant lithium hydroxide monohydrate crystals having a purity of 56.5% or more of lithium hydroxide.

In addition, the process concept is sulfate and acid free and does not form undesirable crystalline by-products. The object of the invention is achieved by means of a device and a method which are characterized by what is stated in the independent claims. Preferred embodiments of the invention are disclosed in the dependent claims.

The invention relates to an apparatus for recovering lithium hydroxide from a fresh feed comprising a lithium containing mineral raw material or a lithium carbonate containing raw material or a mixture of these in combination with a recycled solution and/or slurry, comprising

A pulping unit 1 for pulping a feed in the presence of water and an alkali carbonate to form a first slurry comprising lithium,

a first leaching unit 2 for leaching the first lithium containing slurry, optionally in combination with a recirculation solution and/or slurry, at an elevated temperature so as to form a second slurry containing lithium carbonate,

a second leaching unit 3 for leaching the second slurry containing lithium carbonate, or a portion thereof, in the presence of water and an alkaline earth metal hydroxide, so as to form a third slurry containing lithium hydroxide,

a solid-liquid separation unit 31 for separating the third slurry comprising lithium hydroxide into a discardable solid and a solution comprising lithium hydroxide, and

a crystallization unit 4 for recovering lithium hydroxide monohydrate from the lithium-containing solution.

The crystallization unit 4 is also connected to:

one or more recycle lines 403, 414, 421,422 for conveying the solution and/or slurry from the crystallization unit 4 to one or more upstream units including the pulping unit 1 and the optional first leaching unit 2.

According to an embodiment of the invention, the apparatus further comprises additional necessary lines for transporting the solution, solids or slurry to their intended units.

The invention also relates to a process for recovering lithium hydroxide from fresh feed combined with recycled solution and/or slurry, said fresh feed comprising a lithium containing mineral raw material or a lithium carbonate containing raw material or a mixture of these. The method comprises the following steps

-pulping a feed in the presence of water and an alkali metal carbonate for producing a first slurry comprising lithium,

-leaching the first slurry containing lithium, optionally in combination with a recirculation solution and/or slurry, at an elevated temperature in a first leaching step for producing a second slurry containing lithium carbonate,

-leaching the second slurry or a part thereof in an aqueous solution containing an alkaline earth metal hydroxide in a second leaching step for producing a third slurry containing lithium hydroxide,

-separating the third slurry by solid-liquid separation into a discardable solid and a solution containing lithium hydroxide,

recovering lithium hydroxide monohydrate by crystallization from a solution containing lithium hydroxide, and

-separating the solution and/or slurry remaining after crystallization from the process and returning it as recycled solution and/or slurry to one or more previous process steps comprising a pulping step and optionally a first leaching step.

Typically, the lithium containing mineral raw material is selected from spodumene, petalite, lepidolite, mica or clay, or mixtures thereof, most suitably from spodumene.

According to an embodiment of the invention, the lithium containing mineral raw material is selected from minerals that have undergone a heat treatment, whereby a particularly preferred material is β -spodumene.

As noted above, according to alternative embodiments of the present invention, a recycled solution and/or slurry containing lithium carbonate may be used. Preferably, the recirculating solution and/or slurry is recirculated from a unit downstream of the apparatus. Most suitably, the recycle solution and/or slurry is used in combination with fresh feed.

According to an embodiment of the invention, the first leaching solution is separated from the solids after the first leaching step, whereby only the solids are transported to the second leaching step.

According to an embodiment of the invention, the first leaching solution is separated from the solids after the first leaching step and returned to the pulping step or the first leaching step as a recycle solution, or a part of each step.

According to an embodiment of the invention, the solution obtained from the solid/liquid separation step carried out after the second leaching is subjected to a purification step.

According to an embodiment of the present invention, the solution and/or slurry (also referred to as drained solution) obtained from the crystallization step or from the optional pre-concentration step, preferably performed as an evaporation step, is recovered and returned to one or more previous process steps including the pulping step, and possibly also to the first leaching step, the second leaching step and/or to the crystallization step.

Since the precipitate that may have been formed in the pre-concentration step will most likely be formed from or at least contain lithium carbonate, such a slurry containing precipitate will be highly suitable for recycling to the step.

Optionally, before returning it to the previous process step, for example by using CO₂The effluent solution from the crystallization step is pretreated by carbonation to form a carbonate precipitate.

When an optional first solid-liquid separation is performed between the leaching steps, the solution used in the first leaching step (containing any excess leaching chemicals, i.e. alkali metal carbonates) can be recovered and recycled.

Drawings

The invention will be described in more detail in the following by way of preferred embodiments with reference to figures 1,2, 3, 4, 5 and 6, which all show general flow charts and unit configurations of some embodiments of the invention.

Detailed Description

As schematically presented in fig. 1, an embodiment of the invention is an apparatus for recovering lithium hydroxide from fresh feed combined with a recycled solution and/or slurry containing lithium, the apparatus of this particular embodiment comprising a pulping unit 1 for pulping the feed in the presence of water and an alkali metal carbonate, leaching the obtained slurry optionally in combination with the recycled slurry or solution in a first leaching unit 2, followed by leaching in a second leaching unit 3 in the presence of water and an alkaline earth metal hydroxide, after which the obtained slurry is separated in a solid-liquid separation unit 31 into a discardable solid and a solution containing lithium hydroxide, whereby the solution can be transported to a crystallization unit 4 for producing high purity lithium hydroxide. In the embodiment of fig. 1, the apparatus further comprises recycle lines 421,422 for conveying the solution and/or slurry from the crystallization unit 4 to one or more upstream units, which in this embodiment comprise a pulping unit 1 and optionally a first leaching unit 2. However, as indicated in fig. 2 to 6 and in the claims, other recycling options are also available.

Further embodiments of the invention are illustrated in fig. 2 to 6. These specific embodiments are described in more detail below.

The dashed lines in the figures represent elements that may be combined within the dashed lines in some embodiments of the invention.

In the present invention, the lithium containing feed is typically selected from fresh feeds comprising lithium containing mineral raw materials or lithium carbonate containing raw materials or mixtures of these raw materials in combination with a lithium containing recycle solution and/or slurry.

Preferably, the mineral raw material is selected from spodumene, petalite, lepidolite, mica or clay, or mixtures thereof. Such a mineral raw material is preferably a lithium-containing mineral in calcined form, more preferably obtained by heat treatment of the raw material, most suitably by using a temperature of 900-.

A particularly preferred mineral is spodumene, which provides β -spodumene during the calcination step.

In a preferred embodiment, the mineral raw material is used in combination with a slurry containing the lithium carbonate, preferably a slurry recycled from a subsequent step of the process.

The present invention therefore relates to an apparatus for recovering lithium hydroxide from fresh feed combined with recycled solution and/or slurry, said fresh feed comprising a lithium containing mineral raw material or a lithium carbonate containing raw material or a mixture of these raw materials. The device comprises

A pulping unit 1 for pulping a feed in the presence of water and an alkali carbonate to form a first slurry comprising lithium,

a first leaching unit 2 for leaching the first slurry containing lithium, optionally in combination with a recycled slurry or solution, at an elevated temperature so as to form a second slurry containing lithium carbonate,

a second leaching unit 3 for leaching the second slurry containing lithium carbonate, or a portion thereof, in the presence of water and an alkaline earth metal hydroxide, so as to form a third slurry containing lithium hydroxide,

a solid-liquid separation unit 31 for separating the third slurry comprising lithium hydroxide into a discardable solid and a solution comprising lithium hydroxide,

a crystallization unit 4 for recovering lithium hydroxide monohydrate from a solution containing lithium hydroxide,

the plant also comprises one or more recirculation lines 403, 414, 421,422 for conveying the solution and/or slurry from the crystallization unit 4 to one or more upstream units comprising the pulping unit 1 and the optional first leaching unit 2.

In an embodiment of the invention, the apparatus further comprises a calcination unit for heat treating the raw material intended to be transported to the pulping unit 1.

The pulping unit 1 preferably contains a feed inlet 101 for supplying lithium containing raw material to the unit 1.

The first leaching unit 2 is preferably an autoclave.

In one embodiment, the first leaching unit 2 is connected to the pulping unit 1 by a pulp line 102.

Both the pulping unit 1 and the first leaching unit 2 may comprise separate inlets for conveying the recirculation solution, e.g. from recirculation lines 211 and 421 to the pulping unit 1 and from recirculation lines 212 and 422 to the first leaching unit 2.

In one embodiment, a solid-liquid separation unit 21 is arranged between the first leaching unit 2 and the second leaching unit 3.

Preferably, the recycle lines 211, 212 lead from the first leaching unit 2 or from the liquid section of the solid-liquid separation unit 21 to units upstream of said first leaching unit 2. More preferably, the recycle line leads from the first leaching unit 2 or from the liquid section of the solid-liquid separation unit 21 to the pulping unit 1 as line 211 or to the first leaching unit 2 as line 212, or to each unit as separate lines 211 and 212.

In an embodiment of the invention, the second leaching unit 3 is a tank reactor, preferably a stirred tank reactor.

Preferably, the second leaching unit 3 comprises an inlet 303 for alkaline earth metal hydroxide or an aqueous slurry thereof.

Optionally, a second leaching unit 3 may be connected to the slurrying unit 30 for mixing the alkaline earth hydroxide into an aqueous slurry before it is transported to the second leaching unit 3 through the inlet 303.

In addition, the second leaching unit 3 is typically connected to the first leaching unit 2 or a downstream solid-liquid separation unit 21 via a slurry line 203.

Typically, the solution or slurry obtained from the liquid section of the solid liquid separation unit 31 is transported to the crystallization unit 4 via a slurry line 304 (see e.g. fig. 3).

In an embodiment of the present invention (see fig. 4-6), the purification unit 32 is located between the solid-liquid separation unit 31 and the crystallization unit 4. This optional purification unit 32 is therefore used in the purification of the solution separated from the third slurry. The optional purification unit 32 preferably comprises one or more of an ion exchange unit and a membrane separation unit, more preferably at least one or more ion exchange units, most preferably a cation exchange unit (particularly containing a selective cation exchange resin). Thus, one option is to use a series of two or more ion exchange units, and possibly also a series of two or more regeneration units 33.

In a preferred embodiment in which the purification unit 32 is an ion exchange unit (see fig. 5), the purification unit 32 is connected to a regeneration unit 33 for regenerating the purified resin. This regenerated resin may then be fed back to the ion exchange unit 32 via recycle line 332. However, it is also possible to perform these purification and regeneration steps in a single unit 32 (see dashed lines around units 32 and 33 of fig. 5).

Such regeneration is not required when the purification unit 32 is a membrane separation unit. However, in case a membrane separation unit is used, this unit provides two streams, one being a purified solution that may be directly sent to the crystallization unit 4 and the other being a recycle stream suitable for sending to the second leaching unit 3, e.g. through recycle line 323 (see fig. 6).

In a further embodiment of the invention (see fig. 6), the apparatus of the invention may comprise an ion exchange unit 32a and a membrane separation unit 32b, and thus also a regeneration unit 33. Due to the presence of the membrane separation unit 32b, a recycle stream may be provided, carrying the recycle stream to the second leaching unit 3 via line 323.

In the embodiment, it is particularly preferable to dispose the ion exchange unit 32a downstream of the membrane separation unit 32 b.

In an embodiment of the invention, the apparatus comprises two or more crystallization units 4, which are preferably arranged sequentially.

Optionally, a separate pre-concentration unit, preferably in the form of an evaporation unit, may be designed to provide the crystallization feed with an optimized concentration before the crystallization unit(s) 4.

Typically, the apparatus comprises a solid-liquid separation unit 41 connected to the crystallization unit 4 for separating the crystals obtained in the crystallization unit 4 from the waste slurry.

In addition, as indicated above, one or more recycle lines 403, 414, 421,422 are arranged between the liquid section of the crystallisation unit 4 and/or the solid-liquid separation unit 41 and the upstream unit.

These recirculation lines may include a recirculation line 403 arranged between the liquid section of the crystallization unit 4 or the solid-liquid separation unit 41 and the second leaching unit 3, a recirculation line 414 arranged between the liquid section of the crystallization unit 4 or the solid-liquid separation unit 41 and the inlet of the crystallization unit 4, a recirculation line 421 arranged between the liquid section of the crystallization unit 4 or the solid-liquid separation unit 41 and the pulping unit 1, and a recirculation line 422 arranged between the liquid section of the crystallization unit 4 or the solid-liquid separation unit 41 and the first leaching unit 2.

Where the recycle line 403 is intended for carrying the soluble aluminium back to the second leaching unit 3, after which it will form a solid compound that can be discarded. The recirculation line 414 is in turn intended to provide means for reusing in the crystallization as quickly as possible the solution and/or slurry separated from the crystals obtained in the crystallization unit 4, i.e. the crystallization mother liquor, which is a saturated solution containing lithium hydroxide.

However, preferred alternatives include recycle lines 421 and 422, with recycle line 421 being particularly preferred. These lines are intended for recycling and therefore use of the lithium hydroxide eventually present in the mother liquor in the crystallization unit 4, while also preventing the accumulation of other salts in the crystallization unit 4.

In an embodiment of the invention, the apparatus comprises a lithium precipitation unit 42 connected to the crystallization unit 4 or the solid-liquid separation unit 41 via line 423.

One advantage of this precipitation unit 42 is that it provides a means for reusing the solution recovered from the crystallization unit 4, which is a strong alkaline solution carrying a large concentration of hydroxide ions. This concentration of hydroxide ions is caused by the fact that: lithium hydroxide crystallization can be achieved only from a saturated solution of lithium hydroxide (which is typically > 12% solution depending on the temperature selected).

In another aspect, the leaching units 2, 3 are lower alkalinity environments, with the first leaching unit 2 forming a sodium carbonate environment and the second leaching unit 3 forming an environment with a lower concentration of lithium hydroxide solution, typically about 2-3.5%. Therefore, large amounts of strong alkali should be avoided in the leaching units 2, 3.

As a result, most of the hydroxide ions need to be neutralized. Carbonation provides suitable neutralization of the hydroxide ions as described below with reference to equation (4).

Preferably, lithium precipitation unit 42 includes a feed inlet 424 for supplying carbon dioxide and optionally alkali metal carbonate to unit 42.

The precipitation reaction is preferably not completely carried out, whereby the slurry recycled through the recycle line 421a and/or 422a contains both lithium carbonate and lithium hydroxide. The advantage of using such a slurry containing both lithium carbonate and lithium hydroxide is explained above. For example, there is no need to completely convert the hydroxide to carbonate in the precipitation unit 42, since some carbonation will also occur in the pulping unit 1 or the first leaching unit 2.

According to one embodiment, the recycle lines 421 and/or 422 may be connected to this precipitation unit 42, instead of being connected directly to the crystallization unit 4 or the liquid section of the solid-liquid separation unit 41 as recycle lines 421a and/or 422 a.

According to another embodiment, separate lines 421 and 421a and separate lines 422 and 422a are provided and there is no need to combine these recycled pulps and/or solutions before they are led to the pulping unit 1 or the first leaching unit 2, respectively.

It is particularly preferred to pass the recirculation line 421 through the precipitation unit 42, since carbonation will also take place in the pulping unit 1 to which the recirculation line 421 will lead.

Since the lithium hydroxide solution is a concentrated solution of a strong base, it provides a highly suitable solution for controlling the pH in the first leaching unit 2, which is necessary in order to maintain suitable leaching conditions. When such a solution is brought into contact with a sodium carbonate solution, for example in a pulping step, some lithium carbonate, which is hardly soluble, will precipitate at the same time by referring to reaction formula (3) as described below. This reaction provides lithium carbonate for further lithium hydroxide recovery and sodium hydroxide for pH control.

It is therefore a particular feature of the present invention that it provides means for having supplied lithium carbonate in line 102 which leads to the first leaching unit 2, rather than only forming lithium carbonate in the first leaching unit 2.

In an embodiment of the invention, the apparatus comprises a purification unit 43 connected to the crystallization unit 4 and/or to the solid-liquid separation unit 41, wherein the solid obtained in the crystallization step can be purified.

Preferably, the purification unit 43 comprises a feed inlet 431 for feeding the washing solution into the purification unit 43.

In one embodiment, the apparatus comprises a solid-liquid separation unit 44 connected to and downstream of the purification unit 43 for separating purified lithium hydroxide monohydrate crystals from the spent wash solution.

Preferably, the purification unit 43 or the solid-liquid separation unit 44 connected to the purification unit 43 and downstream of the purification unit 43 is connected to the upstream purification unit 32 or the regeneration unit 33 by a recycle line 432.

More preferably, the solid-liquid separation unit 44 connected to the purification unit 43 and downstream of the purification unit 43 is connected to the crystallization unit 4 through a recycle line 444.

Even more preferably, the solid-liquid separation unit 44 connected to the purification unit 43 and downstream of the purification unit 43 is connected to the purification unit 43 by means of a recirculation line 445.

In another option, the apparatus of the invention comprises a combined purification unit 41, 43, 44 for purifying the crystals obtained from the waste solution in the crystallization unit 4 and separating the purified crystals from the waste washing solution.

In this alternative, a recycle line 414 connects the combination units 41, 43, 44 with the crystallization unit. Likewise, the feed inlet 431 is connected to the combined purification units 41, 43, 44. In addition, recycle line 432 may connect the combined purification unit 41, 43, 44 with the upstream purification unit 32 or with the separate regeneration unit 33, and recycle line 444 may connect the combined purification unit 41, 43, 44 with the crystallization unit 4. Finally, the recycle line 445 may connect the solid section of a combined purification unit 41, 43, 44 with the liquid section of the same combined unit 41, 43, 44.

In an embodiment of the invention, the apparatus comprises a drying unit 45, which drying unit 45 is connected to the crystallization unit 4 or to the solids section of the solid-liquid separation unit 41, 44 downstream of the crystallization unit 4, wherein the obtained lithium hydroxide monohydrate crystals can be dried.

Preferably, the drying unit 45 comprises a product outlet 451 through which the final battery grade product can be recovered.

The invention also comprises a process for recovering lithium hydroxide from fresh feed comprising lithium containing mineral raw material or lithium carbonate containing raw material or a mixture of these in combination with a lithium containing recycle solution and/or slurry.

The process of the invention comprises (with reference to the numbers used for the plant) pulping 1a feed containing lithium in the presence of water and an alkali metal carbonate for extracting lithium from the feed and producing a first slurry containing lithium.

The alkali metal carbonate is preferably selected from sodium carbonate and potassium carbonate, most suitably at least partially consisting of sodium carbonate. Typically, the alkali metal carbonate is present in excess.

After pulping, the first slurry containing lithium, optionally in combination with a recycled slurry or solution, is leached 2 at an elevated temperature for a first time for producing a second slurry containing lithium carbonate.

The presence of alkali metal carbonates and process conditions lead to the formation of lithium carbonate and analcime solids, which in the case of spodumene and sodium carbonate can be represented by the following formula (1).

2 LiAl(SiO₃)₂+Na₂CO₃＝2NaAl(SiO₃)₂+Li₂CO₃ (1)

The first leaching 2 of the first slurry containing lithium is typically carried out in a suitable autoclave or series of autoclaves.

In an embodiment of the invention, the first leaching step is carried out at a temperature of 160 to 250 ℃, preferably at a temperature of 200 to 220 ℃. Also, the first leaching step is carried out at a pressure of 10 to 30 bar, preferably 15 to 25 bar. Suitable conditions for this step are typically achieved using high pressure steam.

Preferably, at least a portion of the water and alkali metal carbonate conveyed to the pulping step is obtained from a recycled aqueous solution containing said alkali metal carbonate and optionally lithium carbonate.

An optional solid liquid separation step 21 may be performed, wherein the solution may be separated from the solids after the first leaching step 2 and the solids are sent to the second leaching step 3.

In one embodiment, the solution separated from the solids in optional separation step 21 is returned to one or more of the previous steps as a recycle solution.

Preferably, the solution is returned to the pulping step or the first leaching step, or a portion of each step. More preferably, the solution is returned to the pulping step.

In a second leaching step 3, the lithium-containing phase (here typically a solid or the entire second slurry) is leached 3 using a hydroxide reagent, i.e. an alkaline earth metal hydroxide (preferably in an aqueous solution of the hydroxide reagent), so as to form a third slurry containing lithium hydroxide. Subsequently, the solid and liquid are separated by solid-liquid separation 31. This separation 31 results in the formation of a disposable solid and a solution containing lithium hydroxide.

The alkaline earth metal hydroxide used in the second leaching step 3 is preferably selected from calcium hydroxide and barium hydroxide, more preferably calcium hydroxide, optionally prepared by reaction of calcium oxide (CaO) in aqueous solution.

In an embodiment of the invention, the alkaline earth hydroxide used in the second leaching step 3 is mixed with water or an aqueous solution before being added to the second leaching step 3. The hydroxide reagent may be obtained, for example, from a separate slurrying step 30.

Preferably, at least a part of the solution separated from the solids in the separation step 31 (containing in particular lithium and sodium) is added to the second leaching step in the form of a recycled solution, preferably mixed with fresh alkaline earth hydroxide before being added to the second leaching step, more preferably mixed with fresh alkaline earth hydroxide in a separate slurrying step 30.

The second leaching step 3 is typically carried out at a temperature of 10-100 c, preferably 20-60 c and most suitably 20-40 c. Typically, the second leaching step 3 is carried out at atmospheric pressure.

The presence of alkaline earth metal hydroxide and process conditions lead to the formation of lithium hydroxide, which in the case of analcime, lithium carbonate and calcium hydroxide can be represented by the following formula (2).

2NaAl(SiO₃)₂+Li₂CO₃+Ca(OH)₂＝2NaAl(SiO₃)₂+CaCO₃+2LiOH (2)

All lithium carbonate is reacted in this second leaching step 3 under the conditions described. This includes lithium carbonate formed in the first leaching step 2 according to reaction (1), i.e. under high pressure conditions, and lithium carbonate precipitated in reactions (3) and (4) described below, as well as lithium carbonate added as fresh feed.

After the two leaching steps 2, 3 have been carried out, the obtained third slurry containing lithium hydroxide is separated 31 into a solid phase and a solution. The solution contains at least a major part of the lithium hydroxide formed, whereby the solid phase can be discarded. Separation 31 may be accomplished using any suitable solid-liquid separation method. For example, the third slurry may be sent to a thickener from which the overflow may be sent directly to purification and the underflow may be further filtered to recover all lithium hydroxide present in the solution and separate it from solid impurities, or a simple filtration technique may be used. Typically, all solid-liquid separations described herein require the supply of wash water for washing the solids (as shown in fig. 3-6). One reason for this optional solids washing step is to displace another portion of the solution that accompanies the solids as moisture. After washing, the spent wash water is typically returned to the previous step of the process as a recycle solution. This washing step will also provide the additional benefit of recovering usable reagents if the used wash water is recycled.

The solids obtained from this separation of the third slurry into solids and solution typically consist of unwanted residues that can be discarded as tailings.

According to an embodiment of the invention, the third slurry separated from the second leaching step 3 is purified 32 before it is sent to the crystallization step. This optional purification step is preferably based on the purification of dissolved ions and components and more preferably comprises an ion exchange or membrane separation step or both, most suitably by using a cation exchange resin, especially a selective cation exchange resin.

Typically, purification by ion exchange is carried out by using a cation exchange resin, wherein the cation exchange group is, for example, iminodiacetic acid (IDA) or aminophosphonic acid (APA).

Selective cation exchange resins typically have chelating functional groups attached to the resin matrix. These chelating functional groups generally have much higher selectivity for polyvalent metal cations (e.g., heavy metal cations and alkaline earth metal cations) than monovalent alkali metal cations (Li, Na, K). Suitable resin functional groups are, for example, the iminodiacetates and aminophosphonates mentioned above. These chelating resins can be used to purify typical cationic impurities such as calcium ions (Ca) from lithium hydroxide solutions²⁺)。

In one embodiment, the step of purifying the solution obtained from the third slurry is performed at least partially using resin regenerated in a separate regeneration step.

Preferably, the regeneration step is carried out using a recycled solution from a subsequent process step, more preferably an isolated solution (optionally in purified form) obtained during crystallization.

In a preferred embodiment, this regeneration is carried out using at least an acidic solution, preferably hydrochloric acid (HCl), for metal elution and an alkaline solution, preferably sodium hydroxide (NaOH) or an alkaline lithium hydroxide solution, more preferably a recycled solution containing lithium hydroxide, for neutralization. In addition, water may be supplied to the regeneration step. The regenerated resin may be fed back to the ion exchange.

However, it is also possible to combine these purification and regeneration steps and to carry out them in the same purification unit.

According to another option, the purification step may be performed in a unit 32 comprising a series of two or more ion exchange units. Also, a series of two or more regeneration units 33 may be used.

Membrane separation may be performed using a semi-permeable membrane that separates ionic or other dissolved compounds from aqueous solutions. More specifically, membrane separation may be used to fractionate dissolved ions and compounds by their size (depending on the pore size of the membrane material) and/or their charge (depending on the surface charge of the membrane material). Positive surface charges repel cations (more strongly repelling multivalent cations) and attract anions, and vice versa. These phenomena will enable purification of, for example, polyvalent metal cations, complexing species (e.g., aluminum hydroxide complexes), polymeric species (e.g., dissolved silica), and larger anions (e.g., sulfate and carbonate ions) from lithium hydroxide solutions. Membrane separation is used and regeneration is not required.

Since lithium hydroxide is a strong base having a high hydroxide ion concentration, a metal strongly complexed by hydroxide ions (for example, aluminum ion Al) cannot be purified by the above-mentioned selective cation exchange resin³⁺). Thus, these ions are purified using the recycle described herein.

Selective cation exchange is preferably used in the polishing removal (polising removal) of multivalent metal cations that form poorly soluble hydroxide compounds, typically calcium hydroxide. In the solution to be subjected to crystallization, these metals (or metal cations) should be removed, or at least their concentration should be reduced to a very low level in order to prevent them from contaminating the crystallized lithium hydroxide monohydrate product. The use of membranes for the removal of these metals is not efficient and is therefore preferably accomplished by ion exchange, particularly with selective cation exchange resins.

In case a membrane separation is performed, alone or in combination with ion exchange, a recycle stream is provided from the membrane separation, which is suitable to be sent to the second leaching step 3.

In membrane separation, the retained ions and compounds will eventually become a concentrated fraction (fraction), typically referred to as the "retentate", which can be returned to the second leaching step as a recycle fraction as described above. The other fraction obtained is the permeate liquid fraction, i.e. "permeate", which is optionally fed to the crystallization by ion exchange purification if these purifications are combined.

The final fraction of each ion and compound in the membrane separation depends on their properties: such as their charge and size. The goal of such retention may be accomplished based on the selection of the desired film type (based on surface charge and/or pore size).

For charge, the target retention species will typically be a polyvalent metal cation such as calcium ion (Ca)²⁺) Magnesium ion (Mg)²⁺) Monovalent alkali metal cations such as lithium ion (Li) with respect to penetration (or zero to negative retention)⁺) Or sodium ion (Na)⁺)。

With respect to size, the retention species will typically be larger compounds such as polymeric species (e.g., dissolved silica), complex ions (e.g., aluminum hydroxide complex), and the largest type of anion (e.g., carbonate CO)₃ ^2-And sulfate radical SO₄ ^2-) However, the smallest type of anion (e.g. hydroxide OH)^-) Is osmotic (or has zero or negative retention).

Based on the above, it is particularly preferred to combine membrane separation with ion exchange, most suitably first to perform membrane separation and then ion exchange for polishing to remove polyvalent metal cations.

In the final step of the process, lithium hydroxide monohydrate crystals are recovered by crystallization 4 from the optionally purified lithium-containing solution. Crystallization is typically carried out by heating a lithium-containing solution to a temperature around the boiling point of the solution to evaporate the liquid or by recrystallizing the monohydrate from a suitable solvent.

Optionally, pre-concentration may be performed prior to the crystallization step, preferably as evaporation.

In an embodiment of the invention, two or more crystallization units are used, which are preferably arranged sequentially.

The process of the present invention enables the production of pure lithium hydroxide monohydrate with excellent yield and purity using a continuous and simple process, typically providing battery grade lithium hydroxide monohydrate crystals with a lithium hydroxide purity of 56.5% or greater.

In another embodiment, the purified lithium hydroxide-containing solution is mixed with one or more solutions recycled from subsequent steps of the process before crystallization step 4 is performed, or these solutions may be fed separately to crystallization 4.

Preferably, the solid-liquid separation step 41 follows the crystallization step 4.

The effluent solution obtained when crystallizing 4 lithium hydroxide monohydrate can be recovered and recycled to one or more of the preceding process steps, including pulping step 1 and optionally the first leaching step, the second leaching step 3 and/or back to crystallization step 4.

It is particularly preferred to recycle at least a part of the solution separated from the crystallization step to at least the pulping step 1 and the first leaching step 2.

The solution separated from the crystallization step is a saturated solution containing a large concentration of lithium hydroxide that should be recovered. In addition, it is a concentrated solution of a strong base. It thus provides a highly suitable solution to be used for controlling the pH in the first leaching unit 2. Such pH control is necessary due to the recycle streams sent to the pulping step 1 and the first leaching step 2, the main one being the stream sent to the pulping step through the recycle line 211. For example, when such a lithium hydroxide solution is brought into contact with a sodium carbonate solution in a pulping step, as represented by the following formula (3), some lithium carbonate which is hardly soluble will precipitate simultaneously:

LiOH(aq)+Na₂CO₃(aq)＝Li₂CO₃(s)+NaOH(aq) (3)

this reaction provides lithium carbonate for further lithium hydroxide recovery and sodium hydroxide for pH control.

Furthermore, some impurities (e.g., aluminum and silicon) in the crystallization effluent solution have a solubility that increases with increasing basicity (e.g., caused by increasing the lithium hydroxide concentration), and thus can be removed by returning these alkali-soluble impurities in the solution to a step with lower basicity, such as the pulping step or the first leaching step. In the lower alkalinity environment, these impurities form poorly soluble compounds (e.g., aluminum hydroxide) and can be discarded with the solids in the separation step 31. Carbonate ions can also be recovered and utilized in this manner.

In an embodiment of the invention, a portion of the solution separated from the crystallization step is returned to the second leaching step as recycled solution.

An advantage of these recycling options is that the soluble impurities (the main impurities being sodium, potassium, aluminium and carbonate ions, and soluble silicon and silicates) remaining in the liquid after crystallization can be recycled upstream from which they can be removed. In particular in the leaching step, these impurities form poorly soluble compounds which can be discarded as solids after the second leaching step. Without the recycle option mentioned herein, these impurities would concentrate in the crystallization step and contaminate the product.

In another embodiment, a portion of the solution separated from the crystallization step is returned to the crystallization step as a recycle solution. In a typical crystallization process, the crystallization slurry is kept in continuous circulation, from which product crystals are continuously separated, and at least a portion of the remaining mother liquor is recycled with the advantage that it increases the yield of the process.

In a further embodiment, at least a portion of the solution separated from the crystallization step is sent to a lithium precipitation step 42, the lithium precipitation step 42 preferably being carried out as carbonation, wherein the solution is reacted with either or both of carbon dioxide or an alkali metal carbonate, preferably at least with carbon dioxide, to form a lithium carbonate slurry, as represented in formula (4) below

2LiOH+CO₂＝Li₂CO₃+H₂O (4)

This optional lithium precipitation step 42 has the advantage of reacting the lithium hydroxide contained in the crystallization effluent solution into the corresponding carbonate, which is highly suitable for being returned as a recycle solution to the pulping step 1 or the first leaching step 2 of the process.

Lithium hydroxide crystallization can be achieved only from a saturated solution of lithium hydroxide (which is typically > 12% solution depending on the temperature selected). Thus, the solution recovered from the crystallization step provides a strong alkaline solution carrying a large concentration of hydroxide ions. In another aspect, the leaching steps (first and second) are lower alkalinity environments. The first leaching step is performed in a sodium carbonate environment and the second leaching step is performed on a lower concentration lithium hydroxide solution (typically about 2-3.5%). Therefore, there is very little need for strong alkali in the leaching step. As a result, it is desirable to neutralize a large portion of the hydroxide ions, and carbonation provides such a combination.

When this optional precipitation step is used, the solution returned from the crystallization step 4 to the pulping step 1 and the optional first leaching step 2, wherein the lithium hydroxide is converted to lithium carbonate, may be transported through this precipitation step. However, the reaction may not be complete, whereby at least trace amounts of lithium hydroxide will still be present in the lithium carbonate slurry to be recycled. As mentioned above, some conversion of lithium hydroxide to the corresponding carbonate will also occur in the pulping step, whereby complete carbonation in the precipitation step is not necessary. However, some carbonates are also useful in these steps.

The solution and/or slurry returned from the crystallization step to the pulping step and the optional first leaching step will therefore contain some lithium hydroxide, whether or not a precipitation step is used. However, such lithium hydroxide will typically be converted to the corresponding sparingly soluble carbonate in the pulping or first leaching step.

In an embodiment of the invention, the solid obtained in the crystallization step (containing lithium hydroxide monohydrate crystals) is purified using a washing solution before being recovered as product.

The purified lithium hydroxide monohydrate crystals are preferably separated from the washing solution, dried and subsequently recovered.

Conversely, it is preferred that the spent wash solution is separated from the purified lithium hydroxide monohydrate crystals and returned to the crystal washing step or to the step of regenerating the resin for transport to the purification step, or to the crystallization step, or that a portion of the spent wash solution is returned to two or all three of these steps as a recycle solution.

It is particularly preferred to return at least a portion of this spent wash solution (or crystallization mother liquor) to the regeneration step, since this solution is relatively pure and contains uncrystallized lithium hydroxide which should be reused, particularly in the upstream step of crystallization or in crystallization. Therefore, regeneration 33 is the recycling option.

Reference numerals

The following shows reference numerals according to embodiments of the invention as used in figures 1 to 6 (some of these devices and lines are optional):

1 pulping unit

101 for supplying fresh feed to the feed inlet of the pulping unit 1

102 slurry line for conveying the first slurry from the pulping unit 1 to the first leaching unit 2

2 first leaching unit

203 slurry line for conveying the second slurry from the first leaching unit 2 to the second leaching unit 3

21 solid-liquid separation unit

211 recycle line from separation unit 21 to pulping unit 1

212 recirculation line from the separation unit 21 to the first leaching unit 2

3 second leaching unit

30 pulping unit for mixing alkaline earth metal hydroxides into an aqueous slurry

303 for supplying alkaline earth metal hydroxide or an aqueous solution thereof to the inlet of the second leaching unit 3

304 liquid line for carrying the third slurry directly from the second leaching unit 3 or from the separation unit 31 to the crystallization unit 4 or to the purification unit 32 or optionally the regeneration unit 33

31 solid-liquid separation unit

313 recycle line for conveying the solution obtained from the separation unit 31 to the second leaching unit 3 or to the optional slurrying unit 30

Purification unit downstream of 32S/L separation unit 31 and upstream of crystallization unit 4

323 recycle line for conveying the recycle stream from the purification unit 32 to the second leaching unit 3

33 regeneration unit

332 recycle line for conveying the regeneration stream from the regeneration unit 33 to the purification unit 32

4 crystallization unit

403 recirculation line from the crystallisation unit 4 or the separation unit 41 to the second leaching unit 3

41 solid-liquid separation unit

414 from a point downstream of the crystallization unit 4 or from the separation unit 41 back to the crystallization unit 4

42 lithium precipitation unit

421 from the crystallization unit 4 to the recirculation line of the pulping unit 1, optionally via a separation unit 41 or a precipitation unit 42

421a from crystallization unit 4 through precipitation unit 42 to the recirculation line of pulping unit 1

422 from the crystallisation unit 4 to the first leaching unit 2, optionally via the separation unit 41 or the precipitation unit 42

422a recirculation line from the crystallisation unit 4 through the precipitation unit 42 to the first leaching unit 2

423 slurry line for conveying the reaction slurry from the crystallization unit 4 or the separation unit 41 to the lithium precipitation unit 42

424 feed inlet for supplying carbon dioxide or alkali carbonate to the precipitation unit 42

43 purification or washing unit

431 for supplying a washing solution to the feed inlet of the purification or washing unit 43

432 recycle line for transporting spent wash solution to upstream purification unit 32 or to optional regeneration unit 33

44 solid-liquid separation unit

444 recirculation line for conveying the waste solution from the purification unit 43 or the separation unit 44 to the crystallization unit 4

445 for conveying the waste solution from the purification unit 43 or the separation unit 44 to the recycle line of the purification or washing unit 43

45 drying unit

451 product outlet for crystallized and optionally purified and dried lithium hydroxide monohydrate

It will be apparent to those skilled in the art that: as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

Examples

Example 1

Batch tests of leaching and recycling were performed by adding solid lithium carbonate to the β -spodumene slurry and treating the resulting mixture in an autoclave leaching step, followed by a second leaching step, as follows:

a 700g batch of calcined β -spodumene material having a Li content of 3.0%, 178g of sodium carbonate and a further 7g of solid lithium carbonate was mixed with water to form a slurry having a total volume of 2.8 litres. The slurry was added to a 1 gallon autoclave and treated at 220 ℃ for two hours. The autoclave contents were allowed to cool and the slurry was then filtered. A portion of 225.93g of the pressure leached filter cake and 25g of calcium oxide were slurried with 0.63l of deionized water and mixed to form a total volume of 0.75l of slurry. The slurry was treated at ambient temperature for 1h and finally the solids and liquids were separated by filtration and the filter cake was washed with water. The contents of the solid and solution were analyzed. The solid residue contained 0.16% Li and the solution had a Li content of 6.7 g/l. The contents of the solution are detailed in table 1 below.

The lithium recovery/yield of the solution is excellent, about 93%, whereby recycling this solution to the early steps of the process is highly beneficial.

Based on these results it is also clear that further purification steps, for example by ion exchange, can be included in the process, in particular for removing impurity metals such as calcium.