WO2021094647A1

WO2021094647A1 - Arrangement and method for recovering lithium hydroxide

Info

Publication number: WO2021094647A1
Application number: PCT/FI2019/050821
Authority: WO
Inventors: Marika Tiihonen; Sami KINNUNEN; Eero KOLEHMAINEN
Original assignee: Outotec (Finland) Oy
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2021-05-20
Also published as: CA3160982A1; BR112022009315A2; AU2019474270A1; KR20220098764A; EP4058612A1; CN112811445A; MX2022005783A; CN215439699U; EP4058612A4

Abstract

The present invention relates to an arrangement and a method for recovering lithium hydroxide from a fresh feed comprising a mineral raw material containing lithium or a raw material containing lithium carbonate, or a mixture of these raw mate- rials,combined with a recycled solution and/or slurry containing lithium, by pulping the feed in the presence of water and alkali metal carbonate,leaching the obtained slurry twice, first at an elevated temperature, and secondly in an aqueous solution containing alkali earth metal hydroxide, separating the thus obtained slurry into solids that may be discarded,and a solution containing lithium hydroxide,whereby lithium hydroxide mono hydrate can be recovered from the solution by crystallising, and finally separating the solution and/or slurry obtained during the crystallization from the process and recycling it to one or more previous step, including the pulp- ing step,and optionally the first leaching step.

Description

ARRANGEMENT AND METHOD FOR RECOVERING LITHIUM HYDROXIDE

FIELD OF THE INVENTION

The present invention relates to an arrangement and a method for re- covering lithium hydroxide from lithium-containing mineral and lithium carbonate.

BACKGROUND OF THE INVENTION

CN102115101 discloses a method for producing lithium carbonate from spodumene mineral by performing a sulfuric acid treatment in order to obtain lithi- um sulfate, followed by a step of preparing the lithium carbonate mother liquor, from which the carbonate product can be separated, and finally the lithium hydrox- ide is obtained from the mother liquor by adding lime to causticize said mother liq- uor. Also barium hydroxide is said to be useful as a causticizing hydroxide.

CN 100455512 C discloses a process for preparing lithium hydroxide monohydrate by adding sodium hydroxide to a lithium sulfate solution in order to obtain liquid lithium hydroxide, followed by cooling, filtering and separating the lith- ium hydroxide from the sodium sulfate, whereafter a series of recrystallization steps are performed to provide the pure lithium hydroxide monohydrate.

In CN 1214981 C a similar process is described, wherein the step of adding sodium hydroxide into the lithium sulfate solution is carried out, followed by cooling and separating to obtain the liquid lithium hydroxide. The lithium hydroxide solution is then concentrated and crystallized, whereby a coarse lithium hydroxide monohydrate product can be separated. In this publication the pure lithium hydrox- ide monohydrate is obtained by reacting the coarse product with barium hydroxide, followed by concentrating and crystallizing.

However, these processes all proceed via the lithium sulfate.

US 3343910 A describes a method for recovering lithium hydroxide from a mineral raw material (calcined spodumene concentrate), by decomposing the mineral using sodium carbonate at 200°C, leaching with calcium hydroxide at or near ambient temperature, and finally crystallizing the LiOH. It is further men- tioned that the usual practice for causticizing an isolated lithium carbonate is at about 85°C, or 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 may be removed in order to recycle the sodium car- bonate. Optionally, the lithium compound can be separated from the leaching re- action product, and the solution concentrated to the point of crystallization, where- after the mother liquor may be returned to the process. However, no specific route for recycling is mentioned. Without further purification and recycling, the method is not very effi- cient.

Thus, there is still a need for procedures, which allow the use of mineral raw materials, and that will utilize the recycled streams containing or forming lithi- um carbonate, that in known procedures will end up in the fractions that are dis- carded.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is thus to provide an arrangement and a method suitable for recovering lithium hydroxide from a feed comprising mineral raw material with high yield and high purity, typically of battery grade, without the need for multiple processing steps, including precipitation and purifica- tion steps, followed by further needs for solid-liquid separations.

Particularly, it is an object of the invention to provide an arrangement and a method for recovering lithium hydroxide using simple purification steps, and by optimising the recirculations.

Battery grade lithium hydroxide herein means lithium hydroxide mono- hydrate crystals having a purity of 56.5%, or higher of lithium hydroxide.

In addition, the process concept is sulphate and acid free, without the formation of undesired crystallized byproducts. The objects of the invention are achieved by an arrangement and a method which are characterized by what is stated in the independent claims. Preferred embodiments of the invention are dis- closed in the dependent claims. The present invention relates to an arrangement for recovering lithium hydroxide from a fresh feed comprising a mineral raw material containing lithium or a raw material containing lithium carbonate, or a mixture of these, combined with a recycled solution and/or slurry, which arrangement comprises

- a pulping unit 1 for pulping the feed in the presence of water and alkali metal carbonate, in order to form a first slurry containing lithium,

- a first leaching unit 2 for leaching said first slurry containing lithium, op- tionally combined with a recycled solution and/or slurry, at an elevated temperature, in order to form a second slurry containing lithium car- bonate, - a second leaching unit 3 for leaching said second slurry containing lithi- um carbonate, or a fraction thereof, in the presence of water and alkali earth metal hydroxide, in order to form a third slurry containing lithium hydroxide,

- a solid-liquid-separation unit 31 for separating said third slurry contain- ing lithium hydroxide into solids that may be discarded, and a solution containing lithium hydroxide, and

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

Said crystallization unit 4 is further connected to: one or more recycle lines 403,414,421,422 for carrying a solution and/or slurry from the crystallizing unit 4 to one or more upstream units including the pulping unit 1 , and optionally the first leaching unit 2.

According to an embodiment of the invention the arrangement compris- es also further necessary lines for carrying solutions, solids or slurries to their in- tended units.

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

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

- leaching the first slurry containing lithium, optionally combined with a recy- cled solution and/or slurry, in a first leaching step at an elevated tempera- ture for producing a second slurry containing lithium carbonate,

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

- separating the third slurry into solids that may be discarded, and a solution containing lithium hydroxide by solid-liquid separation,

- recovering lithium hydroxide monohydrate by crystallising from a solution containing lithium hydroxide, and

- separating the solution and/or slurry remaining after the crystallization from the process, and returning it as a recycled solution and/or slurry to one or more of the previous process steps including the pulping step, and optional- ly the first leaching step. Typically the mineral raw material containing lithium is selected from spodumene, petalite, lepidolite, micas or clays, or mixtures thereof, most suitably from spodumene.

According to an embodiment of the present invention the mineral raw material containing lithium is selected from a mineral which has undergone heat treatment, whereby a particularly preferred material is beta-spodumene.

According to an alternative embodiment of the invention, as stated above, a recycled solution and/or slurry can be used, containing lithium carbonate. Preferably, said recycled solution and/or slurry is recycled from a downstream unit of the arrangement. Most suitable, said recycled solution and/or slurry is used in combination with fresh feed .

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

According to an embodiment of the present invention the first leaching solution is separated from the solids after the first leaching step and is returned as a recycled solution either to the pulping step or to the first leaching step, or a frac- tion to each.

According to an embodiment of the present invention a purifying step is carried out on the solution obtained from the solid/liquid separation step carried out after the second leaching.

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

Since a precipitate possibly forming already in the pre-concentration step would most likely be formed of, or at least contain, lithium carbonate, such a precipitate-containing slurry would be highly suitable for recycling to said steps.

Optionally, the bleed solution obtained from the crystallization step is pretreated prior to returning it to previous process steps, e.g. by carbonation, using CO₂ to form a carbonate precipitate.

When performing a first, optional, solid-liquid separation between the leaching steps, it is possible to recover the solution used in the first leaching step, containing any excess of the leaching chemical, i.e. the alkali metal carbonate, and recycle it. BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to Figures 1 , 2, 3, 4, 5 and 6, which all show general flow diagrams and arrangements of units of certain embod- iments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention, as presented schematically in Figure 1 , is an arrangement for recovering lithium hydroxide from a fresh feed, combined with a recycled solution and/or slurry containing lithium, the arrangement of this particular embodiment including a pulping unit 1 for pulping the feed in the pres- ence of water and alkali metal carbonate, leaching the obtained slurry, optionally combined with a 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 alkali earth metal hydroxide, whereafter the obtained slurry is separated in a solid-liquid- separation unit 31 into solids that may be discarded, and a solution containing lith- ium hydroxide, whereby the solution can be carried to a crystallization unit 4, for producing high purity lithium hydroxide. In the embodiment of Figure 1, the ar- rangement also includes recycle lines 421,422 for carrying a solution and/or slurry from the crystallization unit 4 to one or more upstream units, which in this embod- iment include the pulping unit 1 and optionally the first leaching unit 2. However, also other recycling options are available, as indicated in Figures 2 to 6 as well as in the claims.

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

The dotted lines in the drawings indicate that the units within these dot- ted lines can be combined in certain embodiments of the invention.

In the present invention, the feed containing lithium is typically selected from a fresh feed comprising a mineral raw material containing lithium or a raw material containing lithium carbonate, or a mixture of these raw materials, com- bined with a recycled solution and/or slurry containing lithium.

Preferably, the mineral raw material is selected from spodumene, pet- alite, lepidolite, micas or clays or mixtures thereof. This mineral raw material is preferably a lithium-containing mineral in calcined form, more preferably obtained by heat treating the raw material, most suitably by using a temperature of 900- 1200°C, particularly a temperature of 1000-1100°C. A particularly preferred mineral is spodumene, providing beta- spodumene in a calcination step.

In a preferred embodiment, said mineral raw material is used in combi- nation with a slurry containing said lithium carbonate, preferably recycled from a subsequent step of the method.

Thus, the present invention relates to an arrangement for recovering lithium hydroxide from a fresh feed comprising a mineral raw material containing lithium or a raw material containing lithium carbonate, or a mixture of these raw materials, combined with a recycled solution and/or slurry. The arrangement com- prises

- a first leaching unit 2 for leaching said first slurry containing lithium, op- tionally in combination with a recycled slurry or solution, at an elevated temperature, in order to form a second slurry containing lithium car- bonate,

- a second leaching unit 3 for leaching said second slurry containing lithi- um carbonate, or a fraction thereof, in the presence of water and an al- kali earth metal hydroxide, in order to form a third slurry containing lithi- um hydroxide,

- a solid-liquid-separation unit 31 for separating said third slurry contain- ing lithium hydroxide into solids that may be discarded, and a solution containing lithium hydroxide,

- a crystallising unit 4 for recovering lithium hydroxide monohydrate from a solution containing lithium hydroxide, o which further comprises one or more recycle lines

403,414,421 ,422 for carrying a solution and/or slurry from the crystallizing unit 4 to one or more upstream units including the pulping unit 1 and optionally the first leaching unit 2.

In an embodiment of the invention, the arrangement further comprises a calcination unit for heat treating the raw material intended to be carried to the pulp- ing unit 1 .

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

The first leaching unit 2 is preferably an autoclave. In an embodiment, the first leaching unit 2 is connected to the pulping unit 1 via a slurry line 102.

Both the pulping unit 1 and the first leaching unit 2 may include sepa- rate inlets for carrying recycled solution, e.g. from recycle lines 211 and 421 to the pulping unit 1 and from recycle lines 212 and 422, to the first leaching unit 2.

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

Preferably, a recycle line 211 ,212 leads from the first leaching unit 2, or from the liquid section of a solid-liquid separation unit 21, to a unit upstream from said first leaching unit 2. More preferably, said recycle line leads from the first leaching unit 2, or from the liquid section of a solid-liquid separation unit 21, either 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.

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 includes an inlet 303 for alkali earth metal hydroxide or an aqueous slurry thereof.

Optionally, the second leaching unit 3 may be connected to a slurrying unit 30 for mixing an alkali earth metal hydroxide into an aqueous slurry before carrying it via inlet 303 to the second leaching unit 3.

Further, the second leaching unit 3 is typically connected to the first leaching unit 2, or to 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 carried via slurry line 304 to the crystallization unit 4 (see e.g. Fig. 3).

In an embodiment of the invention (see Figs 4-6), a purification unit 32 is positioned between the solid-liquid separation unit 31 and the crystallization unit 4. This optional purification unit 32 is thus used in the purification of the solution separated from the third slurry. The optional purification unit 32 preferably includes one or more of ion exchange units and membrane separation units, more prefera- bly at least one or more ion exchange units, most preferably cation exchange units, 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 (see Fig. 5), where the purification unit 32 is an ion exchange unit, it is connected to a regeneration unit 33 for regenerating a purification resin. This regenerated resin can then be fed via a recycle line 332 back to the ion exchange unit 32. However, these purification and regeneration steps can also be carried out in a single unit 32 (see dotted line around units 32 and 33 of Fig. 5).

No such regeneration is required when the purification unit 32 is a membrane separation unit. However, in the case a membrane separation unit is used, the unit provides two streams, one being a purified solution, which can be carried directly to the crystallization unit 4, while the other is a recycle stream, which is suitable for carrying to the second leaching unit 3, for example via a recy- cle line 323 (see Fig. 6).

In a further embodiment of the invention (see Fig. 6), the arrangement of the invention can include both an ion exchange unit 32a and a membrane sepa- ration unit 32b, and thus also a regeneration unit 33. Due to the presence of the membrane separation unit 32b, a recycle stream can be provided, carrying a recy- cle stream via line 323 to the second leaching unit 3.

In said embodiment it is particularly preferred to position the ion ex- change unit 32a downstream from the membrane separation unit 32b.

In an embodiment of the invention, the arrangement includes two or more crystallization units 4, preferably being sequentially arranged.

Optionally, the crystallization unit(s) 4 can be preceded by a separate pre-concentration unit, preferably in the form of an evaporation unit, designed to provide a crystallization feed having an optimized concentration.

Typically, the arrangement 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 spent slurry.

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

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

Recycle line 403 is intended, among others, for carrying soluble alumin- ium back to the second leaching unit 3, after which it will form solid compounds that may be discarded. Recycle line 414, in turn, is intended for providing means of 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 crystalliza- tion mother liquor, which is a saturated solution that contains lithium hydroxide.

Preferred alternatives, however, include recycle lines 421 and 422, of which recycle line 421 is particularly preferred. These lines are intended for recy- cling and thus utilizing the lithium hydroxide that ends up in the mother liquor in the crystallization unit 4, while also preventing the build-up of other salts in the crystal- lization unit 4.

In an embodiment of the invention, the arrangement comprises a lithium precipitation unit 42 connected to the crystallization unit 4 or the solid-liquid sepa- ration unit 41 through a line 423.

One advantage of this precipitation unit 42 is that it provides means for reusing the solution recovered from the crystallization unit 4, which is a concen- trated solution of a strong base, carrying a remarkable concentration of hydroxide ions. This concentration of hydroxide ions is caused by the fact that lithium hydrox- ide crystallization can only be achieved from a saturated solution of lithium hydrox- ide, which is typically >12 % solutions, depending on selected temperature.

On the other hand, the leaching units 2,3 are lower alkalinity environ- ments, with the first leaching unit 2 forming a sodium carbonate milieu , and the second leaching unit 3 forming a milieu with a lower concentration lithium hydrox- ide solution; typically about 2-3,5 %. Hence, large amounts of strong base should be avoided in the leaching units 2,3.

As a consequence, neutralization of the major part of the hydroxide ions is needed. Carbonization provides suitable neutralization for the hydroxide ions, as described below by referring to reaction formula (4).

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

The precipitation reaction is, preferably not carried out completely, whereby the slurry recycled via the recycle lines 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 has been explained above. For example, there is no need to make a complete conversion of hydroxide to carbonate in the precipitation unit 42, since some carbonation will occur also in the pulping unit 1 or the first leaching unit 2.

According to an 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 422a. According to another embodiment, separate lines 421 and 421a as well as separate lines 422 and 422a are provided, and there is no requirement to com- bine these recycled slurries and/or solutions before leading them to the pulping unit 1 or first leaching unit 2, respectively.

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

Since the lithium hydroxide solution is a concentrated solution of a strong base, it provides a highly suitable solution to be used to control the pH in the first leaching unit 2, which control is necessary in order to maintain suitable leaching conditions. When this solution is brought into contact with the sodium carbonate solutions for example in the pulping step, some sparingly soluble lithium carbonate will simultaneously precipitate, as described below, by referring to reac- tion formula (3). This reaction provides lithium carbonate for further lithium hydrox- ide recovery and sodium hydroxide for pH control.

Thus, one specific feature of the present invention is that it provides the means for supplying lithium carbonate already in line 102, leading to the first leaching unit 2, instead of forming the lithium carbonate only in the first leaching unit 2.

In an embodiment of the invention, the arrangement includes a purifica- tion unit 43 connected to the crystallization unit 4, and/or to the solid-liquid separa- tion unit 41 , wherein the solids obtained in the crystallization step can be purified.

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

In an embodiment, the arrangement includes a solid-liquid separation unit 44 connected to and downstream from the purification unit 43, for separating the purified crystals of lithium hydroxide monohydrate from the spent washing so- lution.

Preferably, the purification unit 43, or a solid-liquid separation unit 44, connected to and downstream from the purification unit 43 is connected via a re- cycle line 432 to an upstream purification unit 32, or to a regeneration unit 33.

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

Even more preferably, a solid-liquid separation unit 44 connected to and downstream from the purification unit 43 is connected via a recycle line 445 to the purification unit 43. In another option, the arrangement of the invention comprises a com- bined purification unit 41 ,43,44 for purifying the crystals obtained in the crystalliza- tion unit 4 from the spent solution, and separating the purified crystals from the spent washing solution.

In this alternative option, the recycle line 414 connects the combined unit 41 ,43,44 to the crystallization unit. Likewise, the feed inlet 431 is connected to the combined purification unit 41,43,44. Further, a recycle line 432 may connect the combined purification unit 41,43,44 to an upstream purification unit 32, or to a separate regeneration unit 33, and a recycle line 444 may connect the combined purification unit 41,43,44 to the crystallization unit 4. Finally, a recycle line 445 may connect a solids section of the combined purification unit 41,43,44 to the liq- uid section of the same combined unit 41 ,43,44.

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

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

The present invention also includes a method for recovering lithium hy- droxide from a fresh feed comprising mineral raw material containing lithium, or a raw material containing lithium carbonate, or a mixture of these, combined with a recycled solution and/or slurry containing lithium.

The method of the invention comprises (by referring to the numbering used for the arrangement) pulping 1 the feed containing lithium in the presence of water and alkali metal carbonate for extracting the lithium from the feed and pro- ducing a first slurry containing lithium.

The alkali metal carbonate is preferably selected from sodium and po- tassium carbonate, most suitably being at least partly composed of sodium car- bonate. Typically, the alkali metal carbonate is present in excess.

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

The presence of alkali metal carbonate and process conditions result in the formation of lithium carbonate and analcime solids, which can be presented in the case of spodumene and sodium carbonate with the following formula (1 ).

2 LiAI(Si0₃)₂ + Na₂C0₃ = 2NaAI(Si0₃)₂ + Li₂C0₃ (1 ) The first leaching 2 of the first slurry containing lithium is typically per- formed 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°C, preferably at a temperature of 200 to 220°C. Likewise, the first leaching step is preferably carried out at a pressure of 10 to 30bar, preferably 15 to 25bar. Suitable conditions for this step are typically achieved using high-pressure steam.

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

An optional solid-liquid separation step 21 can be carried out, wherein the solution can be separated from the solids after the first leaching step 2, and the solids carried to the second leaching step 3.

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

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

In the second leaching step 3, the lithium-containing phase (here typi- cally the solids, or the entire second slurry) is leached 3 for a second time using a hydroxide reagent, i.e. an alkaline earth metal hydroxide, preferably in an aqueous solution of the hydroxide reagent, in order to form a third slurry containing lithium hydroxide. Subsequently, a separation of solids from the solution is carried out by solid-liquid separation 31. This separation 31 results in the formation of a solids fraction that may be discarded, and a solution containing lithium hydroxide.

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

In an embodiment of the invention, the alkali earth metal hydroxide used in the second leaching step 3 is mixed with water or an aqueous solution pri- or to addition to the second leaching step 3. The hydroxide reagent may, for ex- ample, be obtained from a separate slurrying step 30.

Preferably, at least a fraction of the solution separated from the solids in separation step 31 , containing among others lithium and sodium, is added to said second leaching step in the form of a recycled solution, preferably mixed with fresh alkali earth metal hydroxide prior to addition to the second leaching step, more preferably mixed with fresh alkali earth metal 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 result in the formation of lithium hydroxide, which can be presented in the case of analcime, lithium carbonate and calcium hydroxide with the following formula (2).

2NaAI(Si0₃)₂ + Li₂C0₃ + Ca(OH)₂= 2NaAI(Si0₃)₂ + CaC0₃ + 2LiOH (2)

All the lithium carbonate reacts in this second leaching step 3 in said conditions. This includes the lithium carbonate formed in the first leaching step 2, in reaction (1), i.e. in high pressure conditions, and the lithium carbonate precipi- tated in the below described reactions (3) and (4), as well as lithium carbonate added as the fresh feed.

After the two leaching steps 2,3 have been performed, the obtained third slurry containing lithium hydroxide is separated 31 into a solid phase and a solution. The solution contains at least the main part of the formed lithium hydrox- ide, whereby the solid phase may be discarded. The separation 31 can be done with any suitable solid-liquid separation method. For example, the third slurry can be routed to a thickener, from where the overflow can be routed directly to purifica- tion and the underflow can be filtered further in order to recover all lithium hydrox- ide present in the solution and separate it from solid impurities, or a simple filtering technique can be used. Typically, all solid-liquid separations described herein re- quire a supply of washing water for washing of the solids (as shown in Figures 3- 6). One reason for this optional solids-washing step is to displace a further fraction of the solution that is accompanying the solids as moisture. After washing, the spent washing water is typically returned to a preceding step of the method as a recycle solution. If the used washing water is recycled, this washing step will also provide the further benefit of recovery of useful reagents.

The solids obtained from this separation of the third slurry into solids and a solution are typically composed of unwanted residues, which can be dis- carded, e.g. as tailings.

According to an embodiment of the invention, the third slurry separated from the second leaching step 3 is purified 32 before carrying it to the crystalliza- tion step. This optional purification step is preferably based on purification of dis- solved ions and components, and more preferably includes ion exchange or a membrane separation steps, or both, most suitably by using a cation exchange resin, particularly a selective cation exchange resin.

Typically the purifying by ion exchange is performed by using cation ex- change resin, wherein the cation exchange group is for example iminodiacetic acid (IDA) or aminophosphonic acid (APA).

Selective cation exchange resins typically have a chelating functional group attached to the resin matrix. These chelating functional groups usually have a much higher selectivity towards multi-valent metal cations, such as heavy and alkaline earth metal cations, compared to the monovalent alkali metal cations (Li, Na, K). Suitable resin functionalities are, for example the above mentioned imino- diacetate and the aminophosphonate. These chelating resins can be used to purify the typical cationic impurities, such as calcium ions (Ca²⁺) from lithium hydroxide solutions.

In an embodiment, the step of purifying the solution obtained from the third slurry is carried out at least partly using a resin that has been regenerated in a separate regeneration step.

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

In a preferred embodiment, this regeneration is carried out using at least acidic solution for metal elution, preferably being hydrochloric acid (HCI), and an alkaline solution for neutralization, preferably being sodium hydroxide (NaOH) or an alkaline lithium hydroxide solution, more preferably a recycled solution con- taining lithium hydroxide. Further, water can be fed to the regeneration step. The regenerated resin can be fed back to the ion exchange.

These purification and regeneration steps can, however, also be com- bined, and carried out in the same purification unit.

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

The membrane separation can be carried out using a semi-permeable membrane, which separates ionic or other dissolved compounds from aqueous solutions. More precisely, the membrane separation can be used to fractionate the 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). A positive surface charge repels cations (with a stronger re- pelling action for multi-valent cations) and attracts anions, and vice versa. These phenomena will enable the purification of, for example, multi-valent metal cations, complexed species (such as aluminium hydroxide complexes), polymeric species (such as dissolved silica) and larger anions (e.g. sulfate and carbonate ions) from lithium hydroxide solutions. With the membrane separation, no regeneration is re- quired.

Since lithium hydroxide is a strong alkali having a high concentration of hydroxide ions, metals that are strongly complexed by hydroxide ions (such as aluminium ions, Al³⁺) cannot be purified by the above mentioned selective cation exchange resins. Therefore, these ions are purified using the herein described recirculations.

The selective cation exchange is preferably used in the polishing re- moval of multivalent metal cations that form sparingly soluble hydroxide com- pounds (typically calcium hydroxide). These metals (or metal cations) should be removed, or at least their concentrations should be reduced to very low levels in the solution to be carried to the crystallization, in order to prevent them from con- taminating the crystallized lithium hydroxide monohydrate product. The removal of these metals is not as efficient with membranes, and is thus preferably done by ion exchange, particularly with a selective cation exchange resin.

In case a membrane separation is carried out, either alone or combined with an ion exchange, a recycle stream is provided from the membrane separa- tion, which is suitable for carrying to the second leaching step 3.

In membrane separation, the retained ions and compounds will end up in a concentrated fraction, typically called the “retentate”, which can be returned to the second leaching step as a recycled fraction as described above. The other obtained fraction is the permeated liquid fraction, i.e. the “permeate”, which is fed to the crystallization, optionally via the ion exchange purification, if these purifica- tions are combined.

The fraction to which each ion and compound ends up in the membrane separation depends on their characteristics: for example their charge and size. This targeting of the retention can be done based on selection of the desired membrane type, based on surface charge and/or pore size.

For the charge, the targeted retained species would typically be multi- valent metal cations, for example: calcium ions (Ca²⁺), magnesium ions (Mg²⁺) vs. permeated (or zero to negatively retained) monovalent alkali metal cations, such as lithium ions (Li⁺) or sodium ions (Na⁺).

For the size, the retained species would typically be larger compounds, for example: polymeric species (such as dissolved silica), complexed ions (such as aluminium hydroxide complexes), and the largest types of anions (such as car- bonate,CC>3² , and sulfate, SO4^2'), whereas the smallest types of anions (such as hydroxide, OH ), are permeated (or: has zero or negative retention).

Based on the above, it is particularly preferred to combine a membrane separation with an ion exchange, most suitably by first carrying out a membrane separation, and then an ion exchange for polishing removal of multivalent metal cations.

In the final steps of the method, crystals of lithium hydroxide monohy- drate are recovered by crystallising 4 from a lithium-containing solution, which has optionally been purified. The crystallizing is typically performed by heating the so- lution containing lithium to a temperature of approximately the boiling point of the solution, to evaporate the liquid, or by recrystallizing the monohydrate from a suit- able solvent.

Optionally, a pre-concentration can be carried out before the crystalliza- tion step, preferably as an evaporation.

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

The method of the invention enables production of pure lithium hydrox- ide monohydrate with excellent yield and purity in a continuous and simple pro- cess, typically providing battery grade lithium hydroxide monohydrate crystals, having a purity of 56.5% or higher of lithium hydroxide.

In another embodiment, the purified solution containing lithium hydrox- ide is mixed with one or more solutions recycled from subsequent steps of the method before being carried to the crystallization step 4, or these solutions can be fed separately to the crystallization 4.

Preferably, the crystallization step 4 is followed by a solid-liquid separa- tion step 41.

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

It is particularly preferred to recycle at least a fraction 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 solu- tion that contains a remarkable concentration of lithium hydroxide, which should be recovered. Further, it is a concentrated solution of a strong base. Hence, it pro- vides a highly suitable solution to be used to control the pH in the first leaching unit 2. Due to the recycling streams carried to the pulping step 1 and the first leaching step 2, the main one being the stream carried to the pulping step via recycle line 211, this pH control is necessary. When this lithium hydroxide solution is brought into contact with the sodium carbonate solutions for example in the pulping step, some sparingly soluble lithium carbonate will simultaneously precipitate, as pre- sented in the following formula (3):

LiOH(aq) + Na₂C0₃(aq) = Li₂C0₃(s) + NaOH (aq) (3)

This reaction provides lithium carbonate for further lithium hydroxide re- covery and sodium hydroxide for pH control.

Further, some impurities in the crystallization bleed solution (e.g. alu- minium and silicon) have a solubility that increases with increasing alkalinity (e.g. caused by increasing lithium hydroxide concentration), whereby these alkali- soluble impurities can be removed by returning them in solution to a step of lower alkalinity, such as the pulping or first leaching steps. In said lower alkalinity envi- ronment, these impurities form sparingly soluble compounds (e.g. aluminium hy- droxide), and can be discarded with the solids in separation step 31. Also car- bonate ions can be recovered and utilized in this manner.

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

The advantage of these recycling options is that the soluble impurities remaining in the liquids after crystallization (main impurities being sodium, potas- sium, aluminium and carbonate ions, as well as soluble silicon and silicates) can be circulated upstream, where they can be removed. Particularly in the leaching steps, these impurities form sparingly soluble compounds, which can be discarded as solids after the second leaching step. Without the herein mentioned recycling options, these impurities would be concentrated in the crystallization step, and contaminated in the product.

In another embodiment, a fraction 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 maintained in a continu- ous circulation, from which product crystals are continuously separated, and the advantage of recycling at least a fraction of the remaining mother liquid is that it increases the yield of the process.

In a further embodiment, at least a fraction of the solution separated from the crystallization step is carried to a lithium precipitation step 42, which pref- erably is carried out as a carbonation, wherein the solution is reacted with either carbon dioxide or an alkali metal carbonate, or both, preferably at least with car- bon dioxide, in order to form a lithium carbonate slurry, as presented in the follow- ing formula (4)

2LiOH + C0₂ = Li₂CO₃ + H2O (4)

This optional lithium precipitation step 42 has the advantage of reacting lithium hydroxide contained in the crystallization bleed solution into the corre- sponding carbonate, which is highly suitable for returning as a recycle solution to the pulping step 1 or the first leaching step 2 of the method.

Lithium hydroxide crystallization can only be achieved from a saturated solution of lithium hydroxide, which is typically >12 % solutions, depending on se- lected temperature. Thus, the solution recovered from the crystallization step pro- vides a concentrated solution of a strong base carrying a remarkable concentra- tion of hydroxide ions. On the other hand, the leaching steps (first and second) are lower alkalinity environments. The first leaching step is carried out in a sodium carbonate milieu, and the second leaching step is carried out on a lower concen- tration lithium hydroxide solution; typically about 2-3,5 %. Hence, there is very little need for a strong base in the leaching steps. As a consequence, neutralization of the major part of the hydroxide ions is needed, and carbonization provides such a suitable neutralization.

When using this optional precipitation step, the solution returned from the crystallization step 4 to the pulping step 1 and optionally the first leaching step 2 can be carried via this precipitation step, where, among others, lithium hydroxide is converted into lithium carbonate. The reaction can, however, be left incomplete, whereby at least a trace amount of lithium hydroxide will still be present in the lithi- um carbonate slurry to be recycled. As mentioned above, some conversion of the lithium hydroxide to the corresponding carbonate will occur also in the pulping step, whereby a complete carbonation in the precipitation step is unnecessary. However, also some carbonate is useful in these steps.

Regardless of whether the precipitation step is used or not, the solution and/or slurry returned from the crystallization step to the pulping step and optional- ly the first leaching step will thus contain some lithium hydroxide. This lithium hy- droxide will, however, typically be converted to the corresponding sparingly soluble carbonate in the pulping or first leaching step.

In an embodiment of the invention, the solids obtained in the crystalliza- tion step, containing crystals of lithium hydroxide monohydrate, are purified using a washing solution before recovery as the product. The purified crystals of lithium hydroxide monohydrate are preferably separated from the washing solution, are dried, and thereafter recovered.

The spent washing solution is, in turn, preferably separated from the pu- rified crystals of lithium hydroxide monohydrate, and is returned to the crystal washing step or to a step of regenerating a resin intended for being carried to the purification step, or to the crystallization step, or a fraction of the spent washing solution is returned to two or all three of these steps as a recycle solution.

It is particularly preferred to return at least a fraction of this spent wash- ing solution (or crystallization mother liquid) to the regeneration step, since the solution is relatively pure and contains un crystallized lithium hydroxide, which should be reused, particularly in a step upstream from the crystallization, or in the crystallization. Thus, the regeneration 33 is an option for the recycling. REFERENCE NUMBERS

The reference numbers according to an embodiment of the present in- vention, as used in Figures 1 to 6, are shown below (some of these units and lines being optional):

1 pulping unit

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

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

2 first leaching unit

203 slurry line for carrying a 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 recycle line from separation unit 21 to first leaching unit 2

3 second leaching unit

30 slurrying unit for mixing an alkali earth metal hydroxide into an aqueous slurry

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

304 liquid line for carrying a third slurry from the second leaching unit 3, or from the separation unit 31, either di- rectly to the crystallization unit 4, or to the purification unit 32 or the optional regeneration unit 33 solid-liquid separation unit

313 recycle line for carrying a solution obtained from the sep- aration unit 31 to the second leaching unit 3, or to the op- tional slurrying unit 30 purification unit downstream from the S/L separation unit 31 , and upstream from the crystallization unit 4

323 recycle line for carrying a recycle stream from the purifi- cation unit 32 to the second leaching unit 3 regeneration unit

332 recycle line for carrying a regenerated stream from the regeneration unit 33 to the purification unit 32 crystallizing unit

403 recycle line from crystallizing unit 4, or the separation unit 41 , to the second leaching unit 3 solid-liquid separation unit

414 recycle line from a downstream point of the crystallization unit 4, or from the separation unit 41 , back to the crystal- lizing unit 4 lithium precipitation unit

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

421a recycle line from the crystallization unit 4, via the precipi- tation unit 42, to the pulping unit 1

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

422a recycle line from the crystallization unit 4, via the precipi- tation unit 42, to the first leaching unit 2

423 slurry line for carrying a reacted slurry from the crystalli- zation unit 4, or the separation unit 41 , to the lithium pre- cipitation unit 42

424 feed inlet for supplying carbon dioxide or an alkali metal carbonate to the precipitation unit 42 purification or washing unit 431 feed inlet for supplying washing solution to the purifica- tion or washing unit 43

432 recycle line for carrying spent washing solution to the up- stream purification unit 32, or to an optional regeneration unit 33

44 solid-liquid separation unit

444 recycle line for carrying spent solution from purification unit 43 or the separation unit 44 to the crystallization unit 4

445 recycle line for carrying spent solution from purification unit 43 or the separation unit 44 to 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 obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The inven- tion and its embodiments are not limited to the examples described above but may vary within the scope of the claims.

EXAMPLES EXAMPLE 1

A batch test for leaching and recycling was carried out by adding solid lithium carbonate to a beta-spodumene slurry, and treating the obtained mixture in an autoclave leaching step, followed by a second leaching step, as follows:

A 700g batch of calcined beta-spodumene material with a 3.0% Li con- tent, 178g of sodium carbonate and an additional 7g of solid lithium carbonate were mixed with water to form a slurry having a total volume of 2.8 liters. The slur- ry was added to a 1-gal autoclave and treated for two hours at 220°C. The auto- clave contents were allowed to cool and then the slurry was filtered. A 225.93g portion of the pressure leach cake and 25g of calcium oxide were slurried with 0.63I of deionized water and mixed to make up a slurry of total volume 0.75I. The slurry was treated for 1h at ambient temperature and finally solids and a liquid were separated by filtration, and the cake was washed with water. The contents of both the solids and the solution were analyzed. The solids residue contained 0.16% Li and the solution had a Li content of 6.7g/l. The contents of the solution are specified in the following Table 1. The lithium recovery/yield to the solution was excellent, at around 93%, whereby recycling of this solution to an early step of the process is highly benefi- cial.

It was also clear based on these results that a further purification step, e.g. by ion exchange, can be included in the procedure, particularly to remove im- purity metals, such as calcium.

Table 1. Solution intended for product LiOH · H₂0 crystallization

IΌ co

Claims

1. An arrangement for recovering lithium hydroxide from a fresh feed comprising a mineral raw material containing lithium or a raw material containing lithium car- bonate, or a mixture of these raw materials, combined with a recycled solution and/or slurry containing lithium, which arrangement comprises

- a pulping unit (1 ) for pulping the feed in the presence of water and alkali metal carbonate, in order to form a first slurry containing lithium,

- a first leaching unit (2) for leaching said first slurry containing lithium, op- tionally combined with a recycled solution and/or slurry, at an elevated temperature, in order to form a second slurry containing lithium car- bonate,

- a second leaching unit (3) for leaching said second slurry containing lith- ium carbonate, or a fraction thereof, in the presence of water and alkali earth metal hydroxide, in order to form a third slurry containing lithium hydroxide,

- a solid-liquid-separation unit (31) for separating said third slurry contain- ing lithium hydroxide into solids that may be discarded, and a solution containing lithium hydroxide,

- a crystallising unit (4) for recovering lithium hydroxide monohydrate from a solution containing lithium hydroxide, o which further comprises one or more recycle lines

(403,414,421 ,422) for carrying a solution and/or slurry from the crystallization unit (4) to one or more upstream units including the pulping unit (1 ) and optionally the first leaching unit (2).

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

3. The arrangement according to any preceding claim, wherein the first leaching unit (2) is an autoclave.

4. The arrangement according to any preceding claim, wherein the first leaching unit (2) is connected to the pulping unit (1 ) via a slurry line (102).

5. The arrangement according to any preceding claim, wherein a solid-liquid sepa- ration unit (21) is arranged between the first leaching unit (2) and the second leaching unit (3), and optionally a washing unit, or a washing section within the separation unit (21), for washing the solids separated from the liquid in the separa- tion unit (21).

6. The arrangement according to any of claims 1 to 5, which includes a recycle line (211 ,212) leading from the first leaching unit (2), or from the liquid section of a sol- id-liquid separation unit (21) connected to said first leaching unit (2), to a unit up- stream from said first leaching unit (2).

7. The arrangement according to any of claims 1 to 5, which includes a recycle line (211 ,212) leading from the first leaching unit (2), or from the liquid section of a sol- id-liquid separation unit (21) placed in connection with said first leaching unit (2), either as line (211) to the pulping unit (1) or as line (212) to the first leaching unit (2), or a separate line (211 ) and (212) to each.

8. The arrangement according to any of claims 1 to 5, which includes a recycle line (211) leading from the first leaching unit (2), or from the liquid section of a solid- liquid separation unit (21) connected to said first leaching unit (2), to the pulping unit (1).

9. The arrangement according to any preceding claim, wherein the second leach- ing unit (3) is a tank reactor, preferably a stirred tank reactor.

10. The arrangement according to any preceding claim, wherein the second leach- ing unit (3) includes an inlet (303) for alkali earth metal hydroxide or an aqueous slurry thereof.

11. The arrangement according to any of claims 1 to 9, wherein the second leach- ing unit (3) is connected to a slurrying unit (30) for mixing an alkali earth metal hy- droxide into an aqueous slurry.

12. The arrangement according to any preceding claim, wherein the second leach- ing unit (3) is connected to the first leaching unit (2), or to a downstream solid- liquid separation unit (21), via a slurry line (203).

13. The arrangement according to any preceding claim, wherein the solid-liquid separation unit (31), positioned downstream from the second leaching unit (3), is connected to a washing unit, or includes a washing section within the separation unit (31), for washing the solids separated from the liquid in the separation unit (31).

14. The arrangement according to any preceding claim, which includes a purifica- tion unit (32) connected to the solid-liquid-separation unit (31), for purifying the solution obtained from said separation unit (31).

15. The arrangement according to claim 14, wherein the purification unit (32) in- cludes one or more of ion exchange units and membrane separation units, prefer- ably at least one or more ion exchange units, more preferably cation exchange units, particularly containing a selective cation exchange resin.

16. The arrangement 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 a regeneration unit (33), or a series of two or more regeneration units (33), for regenerating a purification resin, and wherein a line (332) is typically connected between the purification unit (32) and the regeneration unit (33), for returning re- generated resin back to the ion exchange unit.

17. The arrangement according to claim 14, wherein the purification unit (32) is a membrane separation unit, which is connected both to the crystallization unit (4), by feeding the crystallization unit (4) with purified solution, and to the second leaching unit (3), via recycle line (323), for returning a recycle stream to the leach- ing step.

18. The arrangement 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 that is connected to an inlet of the ion ex- change unit.

19. The arrangement according to any preceding claim, which includes two or more crystallization units (4), preferably being sequentially arranged.

20. The arrangement according to any preceding claim, wherein the crystallization unit (4), or a downstream purification unit (32) or a downstream regeneration unit (33), is connected to the solid-liquid separation unit (31) positioned downstream from the second leaching unit (3) via liquid line (304).

21 . The arrangement according to any preceding claim, wherein the crystallization unit (4) is preceded by pre-concentration unit, preferably in the form of an evapora- tion unit, designed to provide a crystallization feed having an optimized concentra- tion.

22. The arrangement according to any preceding claim, which comprises solid- liquid separation unit (41 ) connected to the crystallization unit (4) for separating the crystals obtained in the crystallization unit (4) from the spent solution.

23. The arrangement according to any preceding claim, which comprises a recycle line (403) arranged between the crystallizing 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 arrangement according to any preceding claim, which comprises one or more recycle lines (421 ,422), arranged between the crystallization unit (4), and/or the liquid section of the solid-liquid separation unit (41 ) connected to the crystalli- zation unit (4), and one or more of the pulping unit (1) and the first leaching unit (2).

25. The arrangement according to any preceding claim, which comprises a lithium precipitation unit (42) connected to the crystallization unit (4) or the solid-liquid separation unit (41) through a line (423).

26. The arrangement according to claim 25, wherein the lithium precipitation unit (42) includes a feed inlet (424) for feeding carbon dioxide or an alkali metal car- bonate, or a mixture of these, to the unit (42).

27. The arrangement according to claim 24, wherein the one or more recycle lines (421 ,422) are arranged between a 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 recycled to one or both of said units (1 ,2).

28. The arrangement according to any of claims 22 to 23, wherein the liquid sec- tion of the solid-liquid separation unit (41 ) is connected to the crystallization unit (4), optionally via the crystallization feed, via recycle line (414), for recycling a frac- tion of the spent solution separated from the crystallization step back to the crys- tallization unit (4).

29. The arrangement according to any preceding claim, which includes a product purification unit (43) connected to the crystallization unit (4), and/or to a solid-liquid separation unit (41) connected to the crystallization unit (4), wherein the solids ob- tained in the crystallization step can be purified.

30. The arrangement according to claim 29, wherein the product purification unit (43) includes a feed inlet (431) for feeding a washing solution into the product puri- fication unit (43), preferably being connected to a recycle line, such as recycle line (445).

31. The arrangement according to claim 29 or 30, which includes a solid-liquid separation unit (44) connected to and downstream from the product purification unit (43), for separating the purified crystals of lithium hydroxide monohydrate from the spent washing solution.

32. The arrangement according to any of claims 29 to 31 , wherein the product pu- rification unit (43), or a solid-liquid separation unit (44) connected to and down- stream from the product purification unit (43) is connected via a recycle line (432) to the upstream purification unit (32) or to an optional regeneration unit (33) con- nected to said upstream purification unit (32).

33. The arrangement according to any of claims 29 to 31, wherein a solid-liquid separation unit (44) connected to and downstream from the product purification unit (43) is connected via a recycle line (444) to the crystallization unit (4).

34. The arrangement according to any of claims 29 to 31, wherein a solid-liquid separation unit (44) connected to and downstream from the product purification unit (43) is connected via a recycle line (445) to the product purification unit (43).

35. The arrangement according to any of claims 1 to 19, which comprises a com- bined product purification unit (41,43,44) for purifying the crystals obtained in the crystallization unit (4) from the spent solution, and separating the purified crystals from the spent washing solution.

36. The arrangement according to claim 35, wherein the combined product purifi- cation unit (41,43,44) is connected to the crystallization unit (4) via recycle line (414), for returning the spent solution separated from the crystallization step back to the crystallization unit (4) as a recycled solution.

37. The arrangement according to claim 35, wherein the combined product purifi- cation unit (41 ,43,44) includes a feed inlet (431 ) for feeding a washing solution into the unit (41,43,44).

38. The arrangement according to claim 35, wherein the combined product purifi- cation unit (41,43,44) is connected via a recycle line (432) to the upstream purifi- cation unit (32), or to a separate regeneration unit (33).

39. The arrangement according to claim 35, wherein the combined product purifi- cation unit (41 ,43,44) is connected via a recycle line (444) to the crystallization unit (4).

40. The arrangement according to claim 35, wherein a solids section of the com- bined product purification unit (41,43,44) is connected via a recycle line (435) to the liquid section of the same combined unit (41,43,44).

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

42. The arrangement according to claim 41 , wherein the drying unit (45) includes a product outlet (451) through which the final product can be recovered.

43. A method for recovering lithium hydroxide from a fresh feed comprising miner- al raw material containing lithium, or a raw material containing lithium carbonate or a mixture of these, combined with a recycled solution and/or slurry containing lithi- um, wherein the method comprises

- pulping the feed containing lithium in the presence of water and alkali metal carbonate for producing a first slurry containing lithium, - leaching the first slurry containing lithium, optionally combined with a recy- cled solution and/or slurry, in a first leaching step at an elevated tempera- ture for producing a second slurry containing lithium carbonate,

- separating the third slurry into solids that may be discarded, and a solution containing lithium hydroxide, by solid-liquid separation,

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

44. The method according to claim 43, wherein the mineral raw material used as at least a part of the feed in the pulping step is a lithium-containing mineral in cal- cined form, preferably obtained by heat treating the raw material, more preferably by using a temperature of 900-1200°C, most suitably a temperature of 1000- 1100°C.

45. The method according to claim 43 or 44, wherein the mineral raw material used in the pulping step is selected from spodumene, petalite, lepidolite, micas or clays or mixtures thereof, preferably spodumene, more preferably beta- spodumene.

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

47. The method according to any of claims 43 to 46, wherein at least a fraction of the water and alkali metal carbonate carried to the pulping step is a recycled aqueous solution containing said alkali metal carbonate.

48. The method according to any of claims 43 to 47, wherein the alkali metal car- bonate used in the pulping step is selected from sodium and potassium carbonate, preferably being at least partly composed of sodium carbonate.

49. The method according to any of claims 43 to 48, wherein the first leaching step is carried out at a temperature of 160 to 250°C, preferably at a temperature of 200 to 220°C.

50. The method according to any of claims 43 to 49, wherein the first leaching step is carried out at a pressure of 10 to 30bar, preferably 15 to 25bar.

51. The method according to any of claims 43 to 50, wherein suitable conditions are achieved for the first leaching step using high-pressure steam.

52. The method according to any of claims 43 to 51, wherein the solution is sepa- rated from the solids after the first leaching step in a separate solid-liquid separa- tion step, and the solids are carried to the second leaching step, optionally after washing the solids.

53. The method according to any of claims 43 to 52, wherein the solution is sepa- rated from the solids after the first leaching step, and the solution is returned to one or more of the preceding steps as a recycled solution.

54. The method according to any of claims 43 to 53, wherein the solution is sepa- rated from the solids after the first leaching step, and the solution is returned as a recycled solution either to the pulping step or to the first leaching step, or a fraction to each.

55. The method according to claim 54, wherein the solution is returned to the pulp- ing step.

56. The method according to any of claims 43 to 55, wherein the alkali earth metal hydroxide used in the second leaching step is selected from calcium and barium hydroxide, preferably being calcium hydroxide.

57. The method according to any of claims 43 to 56, wherein the alkali earth metal hydroxide used in the second leaching step is mixed with water or an aqueous solution prior to addition to the second leaching step.

58. The method according to any of claims 43 to 57, wherein at least a fraction of the solution separated from the solids in the solid-liquid separation of the third slur- ry is added to said second leaching step in the form of a recycled solution, prefer- ably mixed with fresh alkali earth metal hydroxide prior to addition to the second leaching step, more preferably mixed with fresh alkali earth metal hydroxide in a separate slurrying step.

59. The method according to any of claims 43 to 58, wherein the solids obtained from the solid-liquid separation of the third slurry are washed, and preferably at least a fraction of the spent washing solution is combined with the solution sepa- rated from the solids in said solid-liquid separation of the third slurry.

60. The method according to any of claims 43 to 59, wherein the second leaching step is carried out at a temperature of 10-100°C, preferably 20-60°C, and most suitably 20-40°C.

61. The method according to any of claims 43 to 60, wherein the second leaching step is carried out at atmospheric pressure.

62. The method according to any of claims 43 to 61, wherein a step of purifying the solution obtained from the third slurry is carried out, which step includes a puri- fication based on the purification of dissolved ions and components, preferably an ion exchange or a membrane separation, or both.

63. The method according to any of claims 43 to 62, wherein the step of purifying the solution obtained from the third slurry is carried out by an ion exchange, pref- erably carried out by using a cation exchange resin, particularly a selective cation exchange resin.

64. The method according to claim 63, wherein the ion exchange is carried out at least partly using a purification resin that has been regenerated in a separate re- generation step, which regenerated resin typically is returned to the ion exchange.

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

66. The method according to any one of claim 43 to 62, wherein the step of purify- ing the solution obtained from the third slurry is carried out by membrane separa- tion, whereby the membrane separation yields a purified stream, which is carried to the crystallization step, and a recycle stream, which preferably is carried to the second leaching step.

67. The method according to any one of claims 43 to 62, wherein the step of puri- fying the solution obtained from the third slurry is carried out by first performing a membrane separation, and by carrying the thus purified solution to an ion ex- change step, for further purification.

68. The method according to any of claims 43 to 67, wherein the crystallising of the lithium hydroxide monohydrate is performed by heating the solution containing lithium to a temperature of approximately the boiling point of the solution.

69. The method according to any of claims 43 to 68, wherein the crystallising of the lithium hydroxide monohydrate is preceded by a pre-concentration step, pref- erably carried out as an evaporation, for dispensing of excess liquid from the solu- tion containing lithium.

70. The method according to any of claims 43 to 69, wherein the crystallising of the lithium hydroxide monohydrate is performed in two or more crystallization units, preferably being sequentially arranged.

71. The method according to any of claims 43 to 70, wherein the solution contain- ing lithium hydroxide is mixed with one or more solutions recycled from subse- quent steps of the method before being carried to the crystallization step, or they are all fed separately to the crystallization step.

72. The method according to any one of claims 43 to 71, wherein at least a frac- tion of the solution separated from the crystallization step is returned to the second leaching step as a recycled solution.

73. The method according to any one of claims 43 to 71, wherein at least a frac- tion of the solution separated from the crystallization step is returned to one or both of the pulping and first leaching steps as a recycled solution.

74. The method according to any one of claims 43 to 71, wherein at least a frac- tion of the solution separated from the crystallization step is carried to a lithium precipitation step, which preferably is carried out as a carbonation, wherein the solution is reacted with either carbon dioxide or an alkali metal carbonate, or a mixture of these, preferably being carbon dioxide or a mixture of carbon dioxide and alkali metal carbonate, in order to form a lithium carbonate slurry.

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

76. The method according to claim 74 or 75, wherein the slurry comprising lithium carbonate is recycled to one or both of the pulping and first leaching steps, prefer- ably to the pulping step.

77. The method according to any one of claims 43 to 76, wherein a fraction of the solution separated from the obtained crystals after the crystallization step is re- turned to the crystallization step as a recycled solution.

78. The method according to any of claims 43 to 77, wherein the solids obtained in the crystallization step, containing crystals of lithium hydroxide monohydrate, are purified using a washing solution before recovery as the product.

79. The method according to claim 78, wherein the purified crystals of lithium hy- droxide monohydrate are separated from the washing solution, are dried, and thereafter recovered.

80. The method according to claim 78, wherein the spent washing solution is sep- arated from the purified crystals of lithium hydroxide monohydrate, and is returned as a recycled solution to the crystal washing step or to a step of purifying the solu- tion separated from the third slurry or to a regeneration step preceding said purifi- cation step, or to the crystallization step, or a fraction of the spent washing solution is returned to two or more of these steps.

81. The method according to any of steps 43 to 80, which is carried out using the arrangement of any of claim 1 to 42.