WO2020206567A1

WO2020206567A1 - Process for obtaining lithium carbonate from spodumene ore by sulphation with ferrous sulphate at high temperature

Info

Publication number: WO2020206567A1
Application number: PCT/CL2020/050038
Authority: WO
Inventors: Igor Wilkomirsky Fuica; Fernando Parada Luna
Original assignee: Universidad De Concepcion
Priority date: 2019-04-12
Filing date: 2020-04-09
Publication date: 2020-10-15
Also published as: CL2019000991A1

Abstract

A process for producing lithium carbonate or other lithium chemical products from spodumene ore concentrates, LiAl(SiO3)2, which comprises: (a) calcining the spodumene concentrate to transform it from its crystalline form α to the crystalline form; (b) dehydrating hydrated ferrous sulphate; (c) sulphation reaction of the spodumene with anhydrous ferrous sulphate; (d) cooling the sulphated calcines; (e) leaching the calcines; (f) thickening and filtering the pulp generated; (g) forming lithium and aluminium sulphate; (h) thickening and filtering the pulp; (i) precipitating and filtering the pulp; (j) precipitating the lithium carbonate; (k) thickening and filtering the pulp; and (l) drying and packaging the lithium carbonate precipitate.

Description

PROCESS TO OBTAIN LITHIUM CARBONATE FROM SPODUMEN MINERAL BY SULFATATION WITH FERROUS SULPHATE AT HIGH TEMPERATURE.

Technical Sector

The technology is oriented to the mining area, more particularly, it corresponds to a process to produce lithium carbonate or other lithium chemical products from concentrates of spodumene mineral, LiAI (Si03) 2.

Previous Technique

Lithium has become in just over a decade a central player in the technological change that is taking place around the world in the automotive industry, and since the new generation of these will be electric, it will require electrical storage batteries. large capacity.

Lithium is the ideal metal to make batteries of high charge density, because it has the highest standard potential positive oxidation among all elements, with 3.05 volts at 25 ^Q C and an electrochemical equivalent of 13.9 kcal / g. The use of lithium in rechargeable batteries increases at rates of 15 to 20% per year, already exceeding 52% of the total world lithium consumption in 2018. Other important uses of this metal are as carbonate, hydroxide, chloride and other compounds organic and inorganic, which represent the rest of world consumption.

Apart from lithium produced from salt flats, one of the main sources of obtaining lithium are lithium pyroxenes, such as the double pyroxene of lithium and aluminum called “spodumene” with the chemical formula LiAI (Si03) 2 or U2O. AI2O3 · 4S1O2, which has a lithium content of 3.73%. Other lithium minerals with commercial levels of lithium are lepidolite (K (Li, Al) 3 (Si, AI) 40io (F, OH) 2; petalite (LiAISUO-io) and others with lower lithium content such as hectorites and montmorillonites. Of all these minerals, the most important and currently most exploited is spodumene. This is always associated with pegmatites and is concentrated by differential flotation to obtain a concentrate with 2.5 to 3.2% lithium, which which is equivalent to 85% and 95% of spodumene, respectively. In the United States, one of the most important developments to produce lithium from spodumene was carried out by the company Foote Mineral Corp. at the beginning of the 1950s when, for strategic reasons, it began to exploit a spodumene ore in North Carolina The process developed is basically the same as that which has continued to be used elsewhere, with minor variations.

Spodumene occurs in nature in the monoclinic crystalline form that is virtually insoluble even in concentrated sulfuric acid, so it must be transformed to the crystalline state. tetragonal b which is soluble in acid, a reaction that occurs above 800 ^Q C.

The process employed in universal virtually form to treat spodumene to as detailed in DE 3622105 A the ®, consists of a first calcination step at 800-1 100 ^Q C, alone or in the presence of lime (CaO), limestone (CaCC> 3) and / or calcium sulfate (CaSC) to transform it from a crystalline form to a crystalline form b and neutralize part of the silica to form a calcium silicate. The calcined spodumene b is ground and then treated with concentrated sulfuric acid (96-98%) at 200-280 ^Q C in a reactor (furnace) stirred, thereby forming lithium sulfate and aluminum sulfate, which are then dissolved by leaching with water at 50 - 60 ° C for subsequent recovery.

In this form of treatment, the reaction stage of spodumene b with concentrated sulfuric acid at 200 - 280 ° C is difficult and complicated, and occurs in the form of a semi-plastic paste with the appearance of pasty cement and with generation of gases with SO2 , SO3 and gaseous sulfuric acid, which requires agitated reactors such as mixer or deck ovens, with control and neutralization of the exhaust gases. Generally, from 50 to 200% excess of acid is used with respect to the stocheometric, since part of it evaporates, which must be captured and neutralized. The hot sulfuric acid sulphation stage is the most complex of the process and represents a major technical and operational challenge. The semi dry paste discharging the reactor is cooled directly in the leach tanks, maintaining the temperature of leaching 50 - 60 ^Q C. The overall reaction which occurs with sulfuric acid in the sulfation step is:

2AIL¡ (S¡0 ₃ ) ₂ + 4H ₂ S0 ₄ = LÍ ₂ S0 ₄ + AI ₂ (S0 ₄ ) ₃ + 4Si0 ₂ + 4H ₂ 0 (i)

When using, for example, 100% excess acid with respect to the stocheometric with a weight ratio of spodumene / acid = 1 / 1.4, when the sulphated mass is leached, it generates a solution of high acidity due to the excess acid used in sulphation, with over 120 g / L of free acid, which must then be neutralized, generating a large amount of hydrated calcium sulfate CaSC> 4 2H2O. The leached pulp containing the lithium in solution as sulfate can then be treated in different ways depending on the desired lithium product.

The calcination stage of spodumene to transform it from its crystalline form c to b is generally carried out in rotary reactors (furnaces), since they have higher thermal efficiency than others. However, alternatives to this have been proposed using fluidized bed, as in the European patent WO201 148040A1, "Method and equipment for processing spodumene" ® in which

0 DE 3622105 A1, (07.01. 1988), P. Broedemann, G. Krueger and R. Heng, "Process for minning lithium carbonate".

⁽⁾ W0201 1 148040 Al, (01 .12.201 1), LL Metsarinta, "Method and equipment to process spodumene" using mineral or fine concentrate of spodumene (under 0.5 mm) it is transformed to its crystalline form b by heating it in a fluidized bed at 800 - 1000 ^° C. There is no information on the subsequent treatment of calcine.

Another more recent patent (Fl 126509B)

it describes a rotary kiln two sections in which the first fine spodumene is heated (from 0.02 to 1 mm in size) to 600 to 700 ^Q C and in the second part is heated to 1000 C. No details ^Q on the subsequent treatment of calcine.

If lime (CaO) or limestone (CaC03) is added in the calcination stage, in addition to transforming the spodumene oc to form b, it allows removing part of the silica from the spodumene as dicalcium silicate and liberating lithium as oxide (U2O):

2LiAI (S¡0 ₃ ) ₂ + 4CaO (s) = Li ₂ 0 _(s) + 4CaSi0 _{3 (s)} + Al ₂ 0 _{3 (s)}

For the calcination stage of spodumene, even though most commercial operations do not use additives or only limestone (CaCC> 3), different combinations of additives have been used or proposed, as well as different reagents in the chemical stage and in the following leaching.

Calcination can also be done with calcium sulfate (anhydrite, CaSC> 4). At high temperatures, various solid-state reactions can occur between spodumene and anhydrite to form lithium sulfate and other compounds such as single, double, and triple oxides. Thermodynamically, only the formation reaction of anorthite (CaÓ-Al203-2Si02 or CaAl2SÍ2C> 3) is possible, which has a small equilibrium constant (4.54) at 1200 ^Q C, so that under 1 100 ^Q C this reaction hardly occurs, while, the formation of lithium oxide by the reaction with CaO or limestone spodumene occurs above 600 C. ^Q

In the "chemical" stage in which spodumene is transformed into a soluble form of lithium (sulfate or oxide), as indicated above, concentrated sulfuric acid is used at high temperature, but other alternatives have been proposed such as that described in US Patent 2,972,517 < ⁴ > which describes the use of SO2 and / or SO3 to treat fine spodumene mineral b (under 0.1 mm) in a fluidized bed reactor using air and SO2 or SO3 at 650-800 ^Q C. The process, although it was relatively efficient, particularly when using SO3, was not applied commercially due to the difficulty of having an external source of SO3 generation (which came from a sulfuric acid plant), and because the use of a reactor fluidized bed resulted in

< ³ > FI126509B, (01.13.2017), O. Sirén and PA Transkanen, “Process for the preparation of beta-alpha spodumene-containing materials”.

⁽⁴⁾ US. 2,972,517, (21.02.1 961), JU Mc Ewan, "Method of producing lithium sulphate from alpha and beta spodumene." a low conversion efficiency of SO3 to sulfate, with less than 20%, with a large amount of these unreacted gases in the reactor exit gas, which had to be neutralized.

Another option is described in patent US 3,017,243 A ⁽⁵⁾ which also ore fines spodumene is I treated in a fluidized bed with a mixture of SO3, H2O and air to 335-450 ^Q C to form U2SO4 and Na2SÜ4, followed by the leaching of calcine with water, purification of the solution and crystallization of lithium sulfate. As in the previous patent, the conversion efficiency of SO3 to lithium sulfate did not exceed 20% and the reactor exit gas contained sulfuric acid vapor that corroded the gas cleaning equipment due to the presence of SO3 and water vapor.

Alternatively, in the patent US 2,801,153 A < ⁶ > the calcine of spodumene b is treated with ammonium sulfate (NH4) 2SC> 4 at 150 - 330 ^Q C. The process is not clarified in its foundation since above 380 ^Q C ammonium sulfate decomposes generating ammonium bisulfate, (NH4 HSO4) and ammonia (NH3) (to be recovered), and above 360 ^Q C ammonium bisulfate decomposes to ammonia, SO2 and water vapor, which they had to be treated. The calcine was leached with an ammonia solution. Lithium extraction is not reported.

A different option is represented by the alkaline digestion with sodium hydroxide (NaOH), as mentioned in the Chinese patent CN 104003428 A ⁽⁷⁾ where the spodumene is treated with a concentrated solution of sodium hydroxide in a plug flow type reactor. from 0.5 to 5 has from 90 to 250 ^Q C and pressure to dissolve about 95% of the spodumene. Treatment of the solution is complex due to the formation of sodium silicate and sodium aluminate. A similar process was patented by Palmer et al. (EP1994191 A2) < ⁸ > where NaOH or KOH is used for the same purpose.

Table 1 contains a summary of the studies and commercial operations for the treatment of spodumene, as well as the reagents and conditions used. It is observed that, independent of the additive added in the calcination stage and in the chemical treatment stage, the lithium extraction in the leaching stage fluctuates between 85 to 90% and that of all the reagents used in the chemical stage (extraction), H2SO4 appears as the most recurrent.

⁽⁵⁾ US. 3,017,243 A, (16.01. 1962), M. Archembault, U. Me Ewan and CA Oliver, "Method of producing lithium sulphate from spodumene".

⁽⁶⁾ US 2,801, 153 A, (07/30/1957), TE Dwyer, "Recovery of lithium from spodumene ores".

⁽⁷⁾ CN 10,4003,428 A, (18.1 1 .2015), Y. Kuan et al., "Method of producing lithium hydroxide by dissolving spodumen in a pipeline reactor".

< ⁸ > EP 9941 91 -2, (26.1 1 .2008) DA Palmer, LM Anovitz and BB Blencoe, "Lithium extraction process". Currently, all commercial plants that produce lithium carbonate and hydroxide from spodumene use calcination as the first stage followed by hot sulfuric acid sulphation and then water leaching of the sulphated acidic pulp.

On the other hand, the extraction of lithium does not show a significant variation if limestone (or lime) is added or not in the calcination stage. However, the presence of CaO fixes part of the spodumene silica as insoluble calcium silicate, since silica in the presence of sulfuric acid at high temperature forms a gel in the leaching stage that can be infiltrable and, in addition, part of this can react with the lithium oxide formed.

Table 1. Extraction of lithium from spodumene concentrates. Summary of business operations and laboratory and pilot studies.

Calcination Chemical treatment Leaching Extraction

In the current form of calcination-sulfation treatment with acid-leaching it is possible to extract a significant part of the lithium, with the rest remaining in the silicate in partially reacted form, as calcium silicate-alumina coated particle cores, and probably, as lithium silicates due to the high temperature reaction between lithium oxide and silica.

Based on these antecedents, it is necessary to develop new, more efficient processes that allow the production of lithium carbonate or other lithium chemical products from concentrate or spodumene ore and avoid the use of hot concentrated sulfuric acid. as is the industrial technology currently used. Brief description of the figures

Figure 1: Process diagram for producing lithium carbonate from spodumene concentrates using separate calcination and sulphation steps.

Figure 2: Thermodynamic diagram of phase stability of the Fe - S - O system at 800 ^Q C.

Figure 3: Standard free energy reaction diagram.

Figure 4: Diagram of standard free energy decomposition of ferrous sulfates (FeSC> 4), lithium (U2SO4) and aluminum (Al2 (S04) 3).

Figure 5: One-stage calcination-sulfation reactor.

Figure 6: Ferrous sulfate sulfation-decomposition double concentric reactor.

Figure 7: Detail of the double concentric reactor, where in (a) the cross section of both reactors is shown and in (b) the detail of the internal reactor.

Disclosure of the Invention

The present technology corresponds to a process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2. In this process, the calcination stages of the spodumene and the sulphation of the spodumene b are carried out separately and sequentially, coupled and at high temperature, or together, using ferrous sulfate (FeSÜ4) or ferrous sulfate (FeSÜ4) in the sulphation stage instead of sulfuric acid. ferric sulfate (Fe2 (SC> 4) 3), which when thermally decomposed above 600 ^Q C generates SO3 and SO2 in situ within the mass of reactant material, effectively and completely sulphating the spodumene b, and thus forming lithium sulfate ( U2SO4) and aluminum sulfate (Al2 (SC> 4) 3) in the absence of a liquid phase, such as sulfuric acid.

By employing separate calcination and sulphation stages, the calcination stage of spodumene a to form b is carried out in a rotary reactor and part of the hot gases leaving the calcination reactor are used to dehydrate the hydrated ferrous sulphate, which is the commercial compound generally used in industry for its low cost and wide availability. If a single reactor is used, the calcination and sulfation stages occur simultaneously. In this case, the reactor is heated externally to keep the reacting gases inside.

Regardless of whether separate calcination and sulphation stages are used, or simultaneously in the same reactor, the sulphated spodumene calcine is cooled and then leached with water, and with part of the mother liquor (generated in the precipitation of lithium carbonate). Aluminum is then precipitated as insoluble alumina (AI2O3) and transforms lithium sulfate into lithium hydroxide (LiOH) in solution, using milk of lime (Ca (OFl2). The solution containing lithium as hydroxide can be treated as different forms, depending on the desired lithium end product. If the end product is lithium carbonate, the The solution is treated with soda ash (Na2CC> 3) to precipitate lithium carbonate (U2CO3).

For a better understanding of this invention, a detailed description of it will now be made with reference to Figures 1 to 7.

The spodumene concentrate 1, normally of a grade higher than 90% of spodumene and with a particle size under 100 ASTM mesh (-0.1 5 mm), is fed to a calcination reactor 2, such as a rotary kiln or other appropriate conventional heated directly with oil or other fuel 3 in conventional way. This calciner is operated at temperature between 600 to 300 ^Q C 1, preferably 900 to 1 200 ^Q C to transform the spodumene from monoclinic crystalline form its tetragonal crystalline form aa b. The reaction that occurs is as follows:

LiAI (Si0 ₃ ) _{2 (a)> 800 C} > L¡AI (S¡0 ₃ ) _{2 (p)} (ii)

The reaction time of the material (spodumene) 62 in the calcination reactor 2 ranges from 0.5-6 h, preferably between 2 to 4 h. The spodumene calcine b 5 discharges hot from the calciner 2 through a conventional gas seal system 19 such as a rotary star valve into a sulfation reactor 22.

Part or all of the combustion exhaust gases 4 from reactor 2 are taken 6 to a conventional gas cleaning system 7 such as one or more cyclones. The separated powder 18 is discharged through a conventional gas seal system 17 such as a rotary star valve and is joined in a common duct 20 with the calcine 5 from the calcination reactor to feed the sulfation reactor 22.

The clean hot gases 8 coming from the cleaning system 7 are taken to a conventional dehydration reactor 9 such as a rotary kiln, which is fed with commercial hydrated iron sulfate (ferrous sulfate) 10, which normally contains 7 molecules of water. hydration as FeSÜ4 7H2O. It is also possible to use ferric sulfate Fe2 (SÜ4) 3, but its cost is considerably higher than ferrous sulfate.

In the reactor or dehydration furnace 9, the thermal decomposition of the hydrated sulfates to their respective anhydrous sulfates 63 occurs according to the following general reactions:

FeS0 ₄ nH ₂ 0 = FeS0 ₄ + nH ₂ 0

(iii) Fe2 (SÜ4) 3 nhteO = Fe2 (SÜ4) 3 + nhteO

(iv) Where "n" represents the number of molecules of water of hydration of sulfates and can vary from n = 1 to n = 7, normally being 7.

These dehydration reactions are endothermic, that is, they consume heat which comes from hot gases 8. The dehydration temperature of FeSC hteO and Fe2 (S04) 3-nH20 (or with any number of water molecules) is 200 350 ^Q C, preferably between 220-260 ^Q C and a retention time in the reactor 9 0.25 to 4 h, preferably between 1 - 2 h.

The inlet temperature of the hot gas 8 is controlled by the addition of cold air 72 by a conventional duct 73 to prevent the ferrous sulfate (or ferric sulfate) or their sulfates Anhydrous 63 within the reactor 9 exceed 350 ^Q C , temperature above which begins a slight decomposition of both ferrous and ferric sulfate.

The hot gases 11 coming from the reactor 9 are cleaned in a conventional gas cleaning system 12 such as one or more cyclones and the clean gas 13 is sent to the atmosphere since it is essentially air and water vapor, and the collected dust 14 it can be returned to reactor 9 along with feed 10.

Anhydrous ferrous sulfate 15 (FeSÜ4) (or anhydrous ferric sulfate (Fe2 (SÜ4) 3)) discharges from reactor 9 through a conventional gas seal 16 such as a rotary star valve, and ferrous (or ferric) sulfate together with the calcine 5 and powders 18 from the calcination reactor 2, they are fed through a common pipeline 20 towards a sulfation reactor 22 such as a rotary kiln or other, provided with a conventional gas shut-off 32, in which they occur now the thermal decomposition reactions of ferrous (or ferric) sulfate above 600 ^Q C, according to the following reactions in the absence of oxygen:

3FeSÜ4 = Fe304 + 2S03 + S02 (v)

2FeSÜ4 = Fe203 + S03 + S02 (vi)

Fe2 (S04) 3 = Fe2Ü3 + 3SÜ3 (vii)

The formation of ferric oxide or hematite (Fe2Ü3) or ferrous oxide - ferric or magnetite (Fe3Ü4) depends on the oxygen potential within the reactor 22. For example, 800 ^Q C to form magnetite Fe3Ü4 requires a partial pressure of oxygen at 10 ⁹ atmospheres. Above this value, hematite, Fe2Ü3, is formed, as observed in Figure 2.

If a higher proportion of SO3 is required, which is a powerful sulphating agent, oxygen 21, oxygen enriched air or air can be added through an additional conventional duct 70. In this case, the reactions that occur are the following:

2FeSÜ4 + 0.502 = Fe2Ü3 + 2SO3 (viii)

3FeSÜ4 + 0.502 = Fe3Ü4 + 3SO3 (ix) 3Fe2 (S0 ₄ ) ₃ = 2Fe ₃ 0 ₄ + 9S0 ₃ + 0.502 (x)

The S0 ₃ and SO2 generated by the decomposition of ferrous (or ferric) sulfate react with spodumene b in reactor 22 to form the respective lithium and aluminum sulfates, hematite (or magnetite) and silica according to the following reactions:

2LiAI (Si0 ₃ ) 2 + 4S0 ₃ = U2SO4 + AI ₂ (S04) ₃ + 4Si0 ₂ (xi) 2LiAI (Si0 ₃ ) ₂ + 4S0 ₂ + 20 ₂ = LÍ2SO4 + AI2 (S0 ₄ ) ₃ + 4Si0 ₂ (xii )

These reactions have negative values of their standard free energies up to approximately 450 ^Q C, that is, they occur spontaneously according to the thermodynamic convention as observed in Figure 3.

In reactor 22, both the thermal decomposition reactions of ferrous and ferric sulfates (v), (vi), (vii), (viii), (ix) and (x) as well as the sulphation of spodumene with S0 ₃ and SO2 (xi) and (xii), occur simultaneously. The gaseous atmosphere 60 inside the reactor 22 is essentially S0 ₃ and SO2, while in the material bed 61, the spodumene continuously reacts with these gases according to the following global reactions with anhydrous ferrous sulfate:

2LiAI (Si0 ₃ ) 2 + 4FeS04 + O2 = Li S04 + AI ₂ (S04) ₃ + 2Fe ₂ 0 ₃ + 4S¡0 ₂ (xiii)

3LiAI (Si0 ₃ ) 2 + 6FeS04 + O2 = 1, 5 U2SO4 + 1, 5 AI (SC> 4) ₃ + 2 Fe ₃ 0 ₄ + 6SÍO2 (xiv)

These global reactions are also plotted in Figure 3 and also have negative values of the standard free energies of reaction. Reaction (xiii) has an inversion temperature of 1095 ^Q C, while reaction (xiv) occurs with a strong thermodynamic gradient (Figure 3).

Both the reactions (xi) and (xii) and the global ones (xiii) and (xiv) are exothermic, that is, they generate heat. Reactions (xiii) and (xiv) as well as (viii) and (ix) are carried out at temperatures between 400 to 1200 ^Q C, preferably between 700 to 900 ^Q C in order to have a kinetic fast, and time reaction time between 0.5-6 h, preferably between 2-4 h.

In Figure 4 the value of the standard free energy of decomposition of ferrous sulfate (FeSC), lithium (U2SO4) and aluminum (Al2 (S0 ₄ ) ₃ ) is observed, where it can be seen that ferrous sulfate decomposes completely above 620 ^Q C and aluminum over 950 ^Q C, while lithium is stable even above 1500 ^Q C, however, it melts at 859 ^Q C and boils at 1377 ^Q C in such a way that reactions (xi), (xii), (xiii) and (xiv) are performed under 850 C to avoid sintering ^Q bed 61 within the reactor 22.

If the global reactions (xiii) and (xiv) require external heat to reach their reaction temperature of 400 to 1000 ^Q C, part of the hot gases 65 coming from the calcination reactor of spodumene 2 are cleaned in a cleaning train of conventional gases such as one or more cyclones 66 and gas Clean 68 is taken to an external heating chamber 69 of reactor 22, where additional heat can be added by conventional burners 23 for oil or other fuel. The gases 24 can be vented to the atmosphere, as well as any excess flue gases 64. Collected powders 67 can be added to the ferrous (or ferric) sulfate feed 10.

The reactor body 22 can be constructed of a high thermal conductivity material such as nickel-chromium alloy steel or commercial alloys such as Incoloy, Hastelloy or Inconel 600, alloys that are not attacked by SO2 or SO3. The total pressure of the gas 60 inside the reactor 22 is kept close to 1 atmosphere by a gas duct 25 and a conventional hydraulic seal 26.

Sulfated calcine 27 discharges from reactor 22 and passes through a conventional gas seal 28 such as a rotary star valve and discharges 29 to a conventional calcine cooler 30, such as a water-cooled rotary drum 31 to cool them to 50 - 80 ^Q C. If necessary, the calcine can be ground under 100 mesh (-0.15 mm) or finer in a conventional mill.

The calcine 33 is leached with water 74 and mother liquor 35 (from the precipitation stage lithium carbonate) in a conventional stirred tank 34 at a temperature between 5 and 95 ^Q C, preferably between 30 - 60 ^Q C, with 1 to 25% solid, preferably between 5 and 15% and a leaching time between 0.5 and 5 h, preferably between 1 - 2 h.

The leached pulp 36 is thickened in a conventional thickener 37. The thick low flow (discharge) 38 is filtered in a conventional filter 39 such as a drum filter by washing the solid cake with 1 volume of water 122 on the filter. The filtrate 41 together with the clear liquid 40 coming from the thickener 37 are taken 43 to a reactor 44 for the precipitation of aluminum as alumina (AI2O3) and lithium in the form of soluble lithium hydroxide (LiOH), using a 5% excess on the stoichiometric of milk of lime (Ca (OH) 2) according to the following reactions: (xv)

(xvi)

CaSC> 4 precipitates (solid) as CaSC> 4 2H2O along with insoluble alumina. The reaction is carried out in a conventional stirred reactor 44 by adding milk of lime 45 (Ca (OH) 2) prepared in a conventional stirred tank or reactor 46, in which lime, calcium oxide (CaO) 47 and water 48 are added. the temperature in the reactor 44 is kept between 5 and 90 ^Q C, preferably 15 to 50 ^Q C, with a reaction time of between 0.25 to 2 h, preferably from 0.5 to 1 h.

The resulting pulp 49 is thickened in a conventional thickener 50 and the low flow (discharge) 52 is filtered in a conventional filter 53 washing the cake in the filter with a volume of water 54. Solid cake with CaSC> 42H2O + AI2O3 58, can be discarded.

The clear liquid 51 and the filtrate 55 containing the lithium as hydroxide 56 are taken to a lithium carbonate precipitation stage in one or more conventional reactors stirred in series 85 at a temperature between ^20-95 ° C, preferably between 60-90 ° C. ^Q C, since lithium carbonate has inverse solubility with temperature, with a reaction time between 0.2 - 4 h, preferably between 0.5 - 2 h using a sodium carbonate solution or soda ash ( Na2CC> 3) 84 from 24 to 30 g / L concentration, prepared in a conventional agitated pond 83 to which water 81 and sodium carbonate 82 are fed. The reaction that occurs is the following:

2UOH + Na ₂ C0 ₃ = U2CO3 + 2NaOH (xvii)

The hot pulp generated in the reactor (s) 86 continuously discharges to a conventional thermally insulated thickener 87, from which the low pulp flow (discharge) 88 containing the precipitated lithium carbonate and is carried to a filtration stage in a conventional filter 90, where the solid lithium carbonate cake was washed with 2 volumes of hot water 93-60 - 90 ^Q C, preferably between 70 and 85 ^Q C, with a reaction time between 0.2 to 4 h, preferably between 1 at 2 h recirculating part of the resulting liquid (mother liquor) to the calcine leaching stage and another part discarding it to avoid the accumulation of soluble impurities.

The washed lithium carbonate cake 91 is dried in a conventional rotary dryer 78 or another appropriate one at ^110-150 ° C for a time of 1 to 4 h, preferably between 2 to 3 h, and the dry lithium carbonate 79 is brought to packaging 80 as it is hygroscopic.

The clear liquid 89 from the lithium carbonate thickener 87, as well as the filtrate 92 from the filter 90 are collected 95 and a part (30 to 50% of the volume) is carried 35 to the stirred tank 34. Another part is discarded 94 to avoid accumulation of impurities.

Solid 42 from filter 39 contains between 35 to 40% iron as magnetite (Fe3Ü4), a commercial product, and is carried through one or more conventional wet magnetic 75 concentration stages to obtain a magnetite 76 concentrate for sale with about 62% iron. Final residue 77 contains essentially silica (S1O2) and can be discarded.

As an alternative to using two separate reactors, it is possible to use only one calcination-sulfation reactor, as indicated in Figure 5. In this, the spodumene concentrate 97 is fed through a conventional gas seal system 98 such as a rotary star valve to a conventional reactor 96 such as an externally heated rotary kiln with conventional gas, oil or other fuel burners 106. The hot gases 107 coming from the heating system of the reactor 96 pass to a pipeline 108 where part of the gas 110 is mixed with air 111 and 112 is introduced into a conventional hydrated iron sulfate dehydration reactor 113 such as a rotary kiln, in which is fed at the other end the hydrated iron sulfate 114 which is dehydrated in its interior 115 to anhydrous FeSÜ4 (or Fe2 (SC> 4) ₃ ) and discharges 100 through a conventional gas seal 101 such as a rotary star valve to a common duct 102, where the spodumene is also fed. Additional air can be added via duct 111.

The mixture of anhydrous spodumene and ferrous (or ferric) sulfate 99 reacts 103 inside the reactor 96 and discharges at the end of it 104 through a conventional gas seal such as a rotary star valve 105 to be processed the calcine in the same way as that described in the case of using two separate reactors.

Excess flue gases, if any, are evacuated to environment 109. Process gases 116 from reactor 113 are cleaned in a conventional system such as one or more cyclones 117 and then vented to environment 118. Collected dust 119 can be returned to dewatering reactor 113 along with feed 114. The total pressure within reactor 96 is maintained at approximately 1 atmosphere using a conventional gas line 120 and hydraulic gas seal 121.

Since calcining spodumene aa spodumene b requires 900 to 1200 ^Q C, aluminum sulfate decomposes over 950 ^Q C, if reactions calcination + sulfation in the single reactor 96 occur above this temperature, no sulfate is formed of aluminum and this remains in the calcine as alumina, which also reduces the consumption of ferrous sulfate, since the lithium sulfate formation reaction only occurs according to:

2LiAI (S¡0 ₃ ) 2 + FeS0 ₄ + 0.25O ₂ = U2SO4 + 0.5Fe ₂ O ₃ + Al 0 ₃ + 4S¡0 ₂ (xviii)

Optionally, this process can also operate with other lithium minerals such as petalite, amblygonite and lepidolite.

Another preferred configuration is the use of a double concentric rotary reactor system in which decomposition is carried out in the inner reactor according to the reactions for ferrous (or ferric) sulfate, and from which the gases generated (S0 ₃ and SO2 ) sulfate the spodumene that reacts in the outer reactor, concentric with the previous one. In this way, two separate products are obtained: a sulfated calcine containing lithium sulfate that follows the process and a virtually pure (over 95%) high-grade hematite concentrate (Fe2Ü ₃ ) that goes on sale directly. Figure 6 shows a diagram of the equipment and process for this technological option.

The spodumene 187 concentrate, normally of a grade higher than 90% of spodumene and of particle size under 100 ASTM mesh (-0.15 mm) is feeds through a conventional gas seal 128 to a calcination reactor 124, such as a rotary kiln or other suitable conventional directly heated with oil or other fuel 125 in conventional manner. This calciner is operated at temperature between 600 to 1300 ^Q C, preferably from 900 to 1200 ^Q C to transform the spodumene from monoclinic crystalline form its tetragonal crystalline form aa b. The reaction time of the material (spodumene) 123 in the calcination reactor 124 ranges from 0.5 - 6 h, preferably between 2 to 4 h.

The spodumene calcine b 126 discharges hot from calciner 124 to a conventional gas seal mailbox 127 and from there through a conventional gas seal system 129, such as a rotary star valve to the sulfation reactor 154.

Part or all of the combustion exhaust gases 131 from reactor 124 are led 133 to a conventional gas cleaning system 134 such as one or more cyclones. Another part, 132 can be vented to the atmosphere or reused. The separated powder 189 is discharged through a conventional gas seal system 188, such as a rotary star valve, and is joined in a common duct 130 with the calcine 126 from the calcination reactor 124 to feed the sulfation reactor 154.

The clean hot gases 137 from the cleaning system 134 are led to a conventional dehydration reactor 140 such as a rotary kiln, which is fed with commercial hydrated ferrous sulfate (or ferric sulfate) 141 through a conventional gas seal 142 In this reactor or dehydration furnace 140, the thermal decomposition of the hydrated sulfates to their respective anhydrous sulfates 139 occurs according to the general reactions indicated above (iii) and (iv). These dehydration reactions are endothermic, and the heat required comes from the hot gases 137. The dehydration temperature of the FeS047H20 and Fe2 (S04) 3-nH20 (or any number of water molecules) is from 200 to 350 ^Q C preferably between 220-260 C ^Q and a retention time in the reactor 140 of 0.25 to 4 h, preferably between 1 - 2 h.

The inlet temperature of the hot gas 137 is controlled by the addition of cold air 135 by a conventional duct 136 to prevent ferrous sulfate (or ferric sulfate) or their sulfates Anhydrous 139 inside the reactor 140 exceed 350 ^Q C , temperature above which begins a slight decomposition of both ferrous and ferric sulfate. Anhydrous sulfates 147 discharge to a conventional gas seal mailbox 138.

The hot gases 143 from the reactor 140 are cleaned in a conventional gas cleaning system 145 such as one or more cyclones and the clean gas 144 is sent to the atmosphere, since it is essentially air and water vapor, and the collected dust 146 can be returned to reactor 140 along with feed 141. Anhydrous ferrous sulfate 147 (FeSÜ4) (or anhydrous ferric sulfate (Fe2 (SC> 4) 3)) discharges from reactor 140 through a conventional 148 gas seal such as a rotary star valve, and ferrous sulfate (or ferric) is fed through a pipeline 149 towards the decomposition reactor 157 such as a rotary kiln or other, provided with conventional closures of gases 151 and 164, in which the thermal decomposition reactions of ferrous sulfate (or ferric) 156 over 600 ^Q C, according to the reactions previously seen (v), (vi) and (vii). For example, 800 C to form magnetite ^Q Fe3Ü4 requires a partial pressure of oxygen to 10 ⁹ atmospheres. Above this value, hematite, Fe2Ü3, is formed, as observed in Figure 2.

The SO3 and SO2 generated by the decomposition of the ferrous (or ferric) sulfate exit 191 continuously from the reactor 157 through the vents or slots 158 of the body of this one and react with the spodumene b 155 in the reactor 154 to form the lithium sulfates and respective aluminum, hematite (or magnetite) and silica according to reactions (xi) and (xii) seen above.

The gaseous atmosphere inside the reactor 157 is essentially SO3 and SO2, such that in the material bed 155 the spodumene continuously reacts with these gases. Longitudinal conventional lifters 190 allow a constant spodumene shower to be maintained within reactor 157 to improve reactions with SO3 and SO2.

The central ferrous (or ferric) sulfate decomposition concentric reactor 157 rotates in conjunction with the exterior 154. The anhydrous ferrous (or ferric) sulfate is fed 150 through a pipeline 149 into the reactor 157 to decompose it into hematite SO3 and SO2 ( or magnetite and SO3) at a temperature between 600 and 900 ^Q C, preferably 700 to 800 ^Q C for a reaction time between 0.5 to 10 h, preferably 2 to 4 h.

The spodumene calcine b from the reactor or calcination furnace 124 is fed 153 through an appropriate pipeline 130 to the spodumene sulphation reactor 154, concentric with that of the decomposition of ferrous (or ferric) sulfate 157.

The external spodumene sulfation reactor 154 is heated by conventional gas, oil or other fuel burners 169 and the heat from the reactor body 154 is transferred to the spodumene charge 155, and is further radiated to the internal reactor 157. outlet 170 are destined for other uses 171 or are vented to the atmosphere.

The sulfated spodumene calcine discharges 159 from the external rotary reactor 154 into a mailbox fitted with conventional seals 160 and through a conventional gas seal valve 161 such as a rotary star valve. The calcine 162 is processed in the manner described above.

The calcine resulting from the decomposition of ferrous (or ferric) sulfate 163 which is essentially hematite Fe2Ü3 (or magnetite, Fe3Ü4) discharges the internal reactor 157 to a conventional mailbox and from there to a conventional gas seal such as a rotary star valve 165 and calcine 166 goes to sale or processing. Conventional gas seals 151 and 152 at the feed ends, as well as at the discharges 160 and 164 of both concentric reactors allow to maintain the gaseous atmosphere with SO3 -SO2 in the complete system and a duct 167 and a conventional hydraulic seal 168 allow to maintain the internal pressure of the system close to 1 atmosphere.

Figure N ^Q 7 shows a cross-sectional diagram of the set of concentric furnaces or reactors described above. Specifically, in Figure 7 (a) the cross section of both reactors is observed, the one for sulphating the spodumene 172 in which the charge or bed of spodumene 173 reacts with the SO3 / SO2 186 gas that is generated inside the reactor 175 decomposition of ferrous (or ferric) sulfate 176. Conventional lifters 184 allow to maintain a shower of spodumene 185 in its interior, which improves the mass transfer and the sulfation reaction of spodumene with SO3 and SO2. Heat is supplied by conventional burners 182 and hot gases 183 circulate in annular space 181 outside sulfation reactor 172. An outer shell 174 surrounds the concentric reactor assembly.

In Figure 7 (b) the construction detail of the internal reactor 175 for decomposition of ferrous (or ferric) sulfate is observed, which is built with longitudinal angles 179 that are welded 177 to support rings 180 and that with its profile in Z allow the passage of gas (SO3 / SO2) through the spaces or vents between them 179. This type of profile allows the passage of gases, but not the passage of the solid towards the external reactor, and can be made of 316 steel, Inconel 600 or similar.

Application example

A spodumene will concentrate of said composition in Table 2 was calcined at 1 100 ^Q C for 2 h in a microwave cripples. The calcine obtained was cooled and then mixed with ferrous sulfate previously dehydrated to 280 ^Q C for 1 hour, in a weight ratio of spodumene / ferrous sulfate = 01/01, 63 equivalent to the stoichiometric reaction (xiv). The mixture was reacted at 800 C with a flow ^Q of 0.2 cc / sec (30 cc / min) 99.8% oxygen for 3 h. A the term calcine the reaction was cooled and triturated to size 100% - 100 ASTM mesh (-0.15 mm) and then with water lixiviarla 50 ^Q C with 15% solids for 30 minutes.

_ Table 2. Spodumene concentrate used _

Element _ Li _ Al _ S1O2 _ Fe _ Ca

% by weight 3.09_ 8.98_ 98.1_ 0.40_ 0.02

The pulp obtained after leaching was filtered and the solid cake was washed with 1 volume equivalent of water at 50 ^Q C. The liquid (filtrate) was treated with milk of lime (Ca (OH) 2) in proportion equal to the stoichiometric plus 5% excess to precipitate all the aluminum (present in the pulp as dissolved aluminum sulfate) to the alumina form (insoluble) according to reaction (xv) and transform the dissolved lithium sulfate into lithium hydroxide (soluble ) according to reaction (xvi). The resulting pulp was filtered and the solid was washed with 1 equivalent volume of water at room temperature.

The resulting solution (filtrate) was then treated with a solution containing 24 g / L sodium carbonate (Na2CÜ3) at 90 ^Q C in ratio of 10% excess over the stoichiometric value to precipitate lithium carbonate (Li2CO3) according to the reaction (xvii). The solid cake was washed with 2 U2CO3 equivalent volumes of water at 90 ^Q C and then dried at a temperature of 120 ^Q C for 1 h. The final U2CO3 product had a purity of 98.8% U2CO3 (Table 3) and the overall recovery of lithium from spodumene was 91.1%.

Table 3. Lithium carbonate obtained

Element Li Mg Ca Na U2CO3

% by weight 18.55 0.31 0.08 0.40 98.8

The solid residue obtained from the first precipitation after washing had the composition indicated in Table 4.

_ Table 4. First filtration residue _

Element _ Li _ Al _ S1O2 _ Fe _ FesC

% by weight_ 0.03_ 0.1 1_ 56.1_ 21, 1_ 43.9

This residue was concentrated in three wet steps on a 600 gauss / cm ² magnetic drum. The final concentrate obtained is found in Table 5.

_ Table 5. Iron concentrate obtained _

Element _ Li _ Al _ S1O2 _ Fe _ FesC

% by weight_ 0.01_ 0.18_ 2.81_ 67.1_ 89.9

Claims

1 A process to produce lithium carbonate or other lithium chemicals from spodumene mineral concentrates, LiAI (Si03) 2, CHARACTERIZED because it comprises at least the following steps:

to. calcining the spodumene concentrate to transform its crystalline form oc crystalline form b, which operates at a temperature between 600 to 1300 ^Q C for 0.5 to 6 h;

b. dehydrate hydrated ferrous sulfate (FeS04-nH20) to the anhydrous form (FeSÜ4) using part of the exit gases from the spodumene calciner from stage “a”, mixing them with air, after cleaning them, at a temperature between 200 to 350 ^Q C for 0.25-4 h;

c. sulphation reaction of the spodumene b with ferrous sulfate in a closed reactor heated externally by a portion of the exhaust from the calciner spodumene and additional fuel by oil burners or other fuel and operating at temperature between 400 to 1200 ^Q C a reaction time between 0.5 - 6 h maintaining an atmosphere close to 1 atmosphere to form the respective lithium sulfates (U2SO4) and aluminum sulfate (Al2 (SC> 4) 3), hematite (Fe2Ü3) and / or magnetite (Fe3Ü4) and silica (S1O2);

d. cooling the sulphated calcines from the reactor that are discharged from stage "c" to a temperature between 50-80 ° C;

and. the calcine leaching with water and mother liquor from the precipitation of lithium carbonate to temperatures between 5 and 95 ^Q C, with 1 to 25% solid, and leaching time between 0.5 and 5 h;

F. thicken and filter the pulp generated in the leaching stage "e", washing the solid cake on the filter;

g. form lithium hydroxide (LiOH) and aluminum oxide (AI2O3) from the solution generated in step “f” by adding calcium hydroxide (Ca (OH) 2) using a 5% excess over the stoichiometric required to transform the sulfate aluminum (Al2 (S04) 3) to form insoluble alumina (Al2O3) and lithium sulfate (U2SO4) transform to lithium hydroxide (LiOH) in solution at temperatures between 5 to 90 ^Q C, with a time of reaction from 0.25 to 2 h.

h. thicken and filter from the pulp generated in the previous reaction step "g" washing the cake from solid with a volume of water;

i. precipitate lithium carbonate (U2CO3) from the solution generated in step “h” using a sodium carbonate solution (Na2C03) with a concentration of 24 to 30 g / L in one or more stirred reactors heated to a temperature between 20 and 95 ^Q C with a reaction time of 0.2 to 4 h; j. thickening and filtering the pulp generated in the precipitation step "i" maintaining the temperature between 20 and 95 ^Q C, washing the cake of lithium carbonate in the filter with 2 volumes of water at 60-90 ^Q C with a reaction time between 0.2 to 4 h, and recirculating part of the resulting liquid or mother liquor to the calcine leaching stage and part discarding it; Y

k. drying the precipitate of lithium carbonate 1 10-150 ^Q C an indirect dryer for a time of 1 to 4 h repacked.

2.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because in stage "a" of calcination of spodumene is carried out in a conventional reactor of the rotary kiln type with direct heating.

3.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage “a” of calcination of the spodumene is carried out, preferably between 900 to 1200 ^Q C and a time between 2 to 4 h.

4.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because step “b” of dehydration of hydrated ferrous sulfate is carried out in a separate reactor of the conventional rotary kiln type using part or all of the combustion gases exiting the spodumene calcination kiln.

5.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because step "b" operates, preferably, at

220-260 ^Q C and with a reaction time of 1 to 2 h.

6.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because the reactor of stage “c” is a sulfation reactor or rotary kiln provided with conventional seals at the ends of feeding and discharge of solids to avoid loss of gases from its interior.

7.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage "c" operates, preferably, at a temperature between 700 - 900 ^Q C and with a reaction time of 2 to 4 h.

8.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because in stage “c” of spodumene sulphation, it is used, optionally, ferric sulfate (Fe2 (S04) 3).

9.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage "a" of calcination of spodumene and stage " c "reaction with ferrous sulfate is carried out in a single closed reactor with a pressure close to 1 atmosphere and external indirect heating at temperatures between 400 to 1200 ^Q C.

10.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because, optionally, the calcine of stage "d" is ground under 100 meshes, -0.15 mm, in a conventional mill.

1 1 .- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage "e" of calcine leaching is carried out preferably between 30 - 60 ^Q C with 5 to 15% solids and for 1 to 2 h.

12.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage "g" of lithium hydroxide formation operates, preferably from 5 to 90 ^Q C with a reaction time of between 0.25 to 2 h with 5% excess of calcium hydroxide with respect to the stoichiometric.

13.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage “h” operates, preferably between 20 and 95 ^Q C.

14.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because stage "j" operates, preferably, between 70 - 85 ^Q C, with a preferred reaction time between 1 - 2 h, washing the lithium carbonate cake with water between 60 - 90 ^Q C.

15.- A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because in stage "k" the lithium carbonate cake is dry from 1 10 to 150 ^Q C for a time of 1-4 h.

16. A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because, the solid containing magnetite (Fe3Ü4) generated in the stage " f "is concentrated in wet magnetic form in one or more conventional stages to have a high grade magnetite concentrate in iron.

17.- A process to produce lithium carbonate or other lithium chemicals from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because, optionally, it operates with other lithium minerals such as petalite, amblygonite or lepidolite.

18.- A process to produce lithium carbonate or other lithium chemicals from spodumene mineral concentrates, LiAI (Si03) 2, according to claim 1, CHARACTERIZED because the decomposition reactions of ferrous or ferric sulfate and the sulphation of spodumene with SO3 - SO2 are carried out in a double concentric reactor, in which the thermal decomposition of ferrous or ferric sulfate occurs in the inner reactor with generation of SO3 and SO2, and in the annular external reactor the sulphation of the spodumene occurs with the SO3 - SO2 gas generated and in which the heat required by the reactions that occur is supplied from the outside by means of conventional burners, and in which the final products of the sulfated calcine of spodumene and the hematite or magnetite are discharged separately for further processing.

19. A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claims 1 and 18, CHARACTERIZED because both the calcination of the spodumene «to its form b and the dehydration of the ferrous or ferric sulfate is carried out in separate reactors.

20. A process to produce lithium carbonate or other lithium chemical products from spodumene mineral concentrates, LiAI (Si03) 2, according to claims 1 and 18, CHARACTERIZED because the internal reactor body for decomposition of ferrous sulfate or Ferric is formed by a set of angular profiles that allow the passage of SO3 - SO2 gas.