FI63923C - FOERFARANDE FOER UTVINNING AV LITIUMKARBONAT I REN FORM - Google Patents

Description

The present invention relates to a process for the recovery of pure lithium carbonate from calcined lithium-containing silicate ores.

The most important raw material for lithium extraction has in recent times been lithium-containing silicate ores, such as spodum, petalite and lepidolite, but also lithium-containing salt solutions, so-called "brines". Starting from these foxes, a number of methods for the extraction of lithium have been presented, but only a few have been applied in practice.

The most common method for extracting lithium from, for example, spodum is the so-called sulfuric acid method. In this process, α-spodum is first converted to 6-spodum by heating the material to temperatures around 1000 ° C.

By then treating the material with sulfuric acid at approx. 200 ° C-300 ° C, L12SO4 is formed, which, by leaching the material with water, is transferred into the liquid phase. In the sulfation process, other components in water-soluble form, such as iron, aluminum, sodium, calcium, magnesium, etc. are also partially obtained. Upon a subsequent increase in the pH of the solution with, for example, a calcium hydroxide suspension, many of the contaminating metals are precipitated. hydroxides. Remaining calcium and magnesium in the solution precipitate as carbonates upon addition of After all the solid material has been removed from the LijSO ^ solution, it is concentrated as needed and I₂CO₂ is precipitated by the addition of a saturated Na 2 CC> 3 solution. The precipitation is carried out in the temperature range of 80-100 ° C, as the solubility of 1 CO 2 is at least in this range.

In another method, this process has been modified so that, instead of a sulfuric acid treatment of the material, a treatment is carried out at about 1000 ° C with I₂SO ^ and / or Na₂SO ^ to obtain Li treatment transferred in 1 CC.

2 6 3 9 2 3 For the preparation of a LiOH solution starting from the lithium-containing ore, a method has been presented, among which spodum and a CaCO 3 suspension (CaO, Ca (OH) 2) blend is dosed and treated under roasting conditions at 1000-1200 ° C, with LiOH being formed after leaching with water. The solid material is separated from the suspension and the crude LiOH solution is concentrated and reacted with, for example, CC₂ gas, precipitating Li₂CO₂.

The ore can also be roasted under chlorinating conditions with CaCl2 and CaCO3 (or KCl + CaCO3) in the temperature range of 1100-1200 ° C, with LiCl accompanying the exhaust stream and when contacted with water, LiCl transfers into water-soluble form. The crude LiCl solution is then reacted with, for example, a Na2CO3 solution, whereby Li2CO3 is precipitated.

Naturally occurring brines, "brines" containing LiCl, are often heavily contaminated by, for example, sodium, potassium, calcium and magnesium. The solutions are concentrated and calcium and magnesium are precipitated until Na2CC> 3 is added to the LiCl solution and Li2CC> 3 is precipitated.

CA patent 643,843 discloses a process for the recovery of Li2CO3 from β-spodum. The principle of this process is evidenced by the diagram in attached Figure 2. In this process, the 6-spodumen is treated in an autoclave with a Na 2 CO 3 solution in the temperature range 200-220 ° C and at a pressure of about 5 MPa, whereby Li shape (step 10). In the autoclave, the following reaction occurs: H2 °

Li20-Al203 * 4Si02 + Na2CO3 - = - »Li2CO3 + Na20 · A1203 · 4Si02 · 2H20 To separate the formed solid Li2CO3 from the other solid (lacquer residue), the suspension is cooled and CO 2 gas is initiated under a pressure of about 1 MPa , wherein the Li2CO3 is poured into a water-soluble LiHCO3 form (step 11) and the solid is filtered off (step 12). Thereafter, the CO 2 ~ 63923 gas is expelled from the lithium-containing solution by heating to about 95 ° C, with Li 2 CO 3 precipitating, with subsequent crystalline separation (step 13).

In this known process, the Li 2 CO 3 crystals from step 10 are bonded to the solid lacquer residue, which means that the crystals must be dissolved to obtain them separated from the lacquer residue. When dissolving the Li2CO3 crystals, even unreacted Na2CO3 (in step 10, a significant excess of Na2CO3 is used) and other soluble components of the ore will be dissolved, which means that the concentration of foreign ions in the Li solution will be relatively high. -may be detrimental to the purity of the precipitated Li2CO3 crystals.

Another disadvantage of this process is that the residue must be separated from the LiHCO 3 solution, which is unstable at normal pressure. CC 2 gas is released spontaneously at normal pressure from the LiHCO 3 solution, with the result that Li 2 CO 3 precipitates. This means that the lacquer residue must be filtered out very quickly, heist in just a few minutes, which causes difficulties.

Lithium carbonate produced from any lithium-containing silicate ore or "brine" by, for example, any of the above enumerated methods contains foreign ions in some men, for which the carbonate is most often purified to meet international quality standards regarding its purity. derived from, for example, the original ore, from the additive chemicals, from the equipment material or by the contamination being built up in some circuit system in the process, depending on which method the Li2CO3 has been produced, the content of the various components will vary.

Most often, the foreign ions consist of sodium, potassium, calcium, magnesium, iron, aluminum, sulfate and chloride. When using Εΐ2003 as an additive in the cryolite melt in the production of primary aluminum through the Hall-Herault process, higher levels of phosphorus and sulfur in Li2CO3 have negative consequences in aluminum production. When processing Li 2 CO 3 4 63923 into metallic lithium, pure I 2 CO 2 should be used as a raw material and especially high levels of sodium and sulfur should be avoided. When using 1 CO 2 for pharmaceutical preparations, the carbonate should be very pure.

Purification of the precipitated LiCOCOET has been carried out by washing the crystals with an aqueous solution. In order to obtain a commercially acceptable product purity, it has been necessary to use fairly large amounts of detergent solution, especially the high content of alkali metals and sulphates, in particular, often contaminates the ³CO₂ crystals. As Large amounts of washing solution and several washing steps are used in the purification, the proportion of soluble I₂CO₂ will be high, which can cause significant lithium losses in the process. On the other hand, a return of the washing solution in the process means, among other things, that energy-demanding concentration measures should be taken and the consumption of various chemicals increased. The same is true even if a complete dissolution of I₂CO₂ is carried out with water, after which a new crystallization must be carried out.

To reduce the amount of water in the purification, the solution of LI2CO2 can be facilitated by reaction with, for example, hydrochloric acid in LiCl, which has higher solubility in water than LijCO-j. A new crystallization of Li2CO.j requires the addition of chemicals and this leads to a greater risk of the crystals becoming contaminated.

Depending on which raw material and by which method the lithium recovery takes place, the precipitated Li carbonate will be contaminated with various levels of foreign ions, for example sodium, potassium, calcium, magnesium, iron, aluminum, sulphate and chloride.

The purity requirements for commercial grade L1200® commercial grade products are as follows:

II

5 63923

Typical content Guaranteed content Li2CO3 99.1% 99.0% H2O (500 ° C, 30 min) 0.5 6 0.6

Cl 0.002 £ 0.005 S04 0.3 £ 0.4

Fe203 0.001 £ 0.003

CaO 0.01 f 0.05

Na20 0.15 £ 0.2

Insoluble (in HCl) 0.002 £ 0.005 The object of the present invention is to remove the disadvantages of hitherto known methods for the recovery and purification of lithium carbonate and to provide a simple and effective process for the purification of lithium carbonate.

This has been achieved in a very satisfactory manner by transferring impure and highly soluble lithium carbonate extracted from calcined lithium-containing silicate ores, in a more water-soluble lithium hydrogen carbonate form, by adding carbon dioxide to a water suspension of the decomposed lithium carbonate, by heating to precipitate pure lithium carbonate, which is then removed from the solution, after which it is desired, the above-mentioned purification procedure for lithium carbonate is repeated.

The invention is described below with reference to the scheme of the attached Figure 1, of which the principle of the present process is embodied.

The recovery of lithium carbonate in unclean form from the β-spodum is carried out in a manner known per se (steps 1-5). As starting material in the process, in addition to the spodum, other lithium-containing silicate ores, such as petalite and lepidolite, can also be used. The β-spodumen is treated with an excess of sulfuric acid at about 250 ° C, whereby Li2SO4 is formed in solid form (step 1). The lithium content of the β-spodumen may alternatively be transferred to Li2SO4 by treatment at about 1000 ° C with K2SO4 and / or Na2SO4.

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By leaching the material with water, the Li2SO4 transfers into the liquid phase (step 2). The contaminating water-soluble components derived from the original ore are precipitated by the addition of CaO, after which all solid material is separated (step 3). Chemicals other than CaO can also be used in the solution purification. The resulting L ± 2S0 2 solution is concentrated as needed (step 4). Upon the addition of a saturated Na 2 CO 3 solution, Li 2 CO 3 crystals precipitate which are then separated (step 5).

In the purified method invented, the "impure" Li2CO3 "product is transferred into the more easily soluble lithium hydrogen carbonate form by adding carbon dioxide to a Li2CO2" suspension (step 6). For complete dissolution of Li 2 CO 3, the amount of water indicated by the solubility of LiHCO 3 under current pressure and temperature conditions is required. Carbon dioxide is expelled from the LiHCO 3 solution by heating, with Li 2 CO 3 crystals precipitating, with subsequent crystal separation (step 7). The pollutant components will hereby remain almost completely in the aqueous solution. If applicable. using pure CO 2 gas no further contaminating components are introduced.

Thus, the water demand will be lower than when dissolving Li 2 CO 3 in water under normal conditions. Since even some lithium remains in soluble form after the Li 2 CO 3 precipitation, it is preferred to return the solution in the process so as not to incur significant lithium losses.

The solubilities of Li2CO3 and LiHCO3 at varying temperatures and CO2 pressures are given in the tables below (A. Seidell: Solubilites of Inorganic and Metalorganic Compounds): h 7 63923

Table 1 Solubility of I₂CO₂ t g Li₂CO0 ° C_100 g solution 0 1.52 10 1.41

Table 2 Solubility of LiHCO 3 CO 2 pressure g LiHCO 2/100 g solution

atm_Ofc_18 ° C 40 ° C_60 ° C

1 14.13 10.56 8.55 7.33 5 16.96 12.52 8.62 10 19.91 14.90 8.68 20 - 17.29 11.48 7.53 30 - 12.23 I a preferred embodiment of the invention is carried out such that Li2CC> 3 and water, corresponding to the amount necessary for the transfer of the Li carbonate to Li hydrogen carbonate at rescue temperature and CO2 pressure, are mixed in a reactor or pressure vessel, in which CO 2 gas is introduced. Most of the Li carbonate-contaminating components are water-soluble and thus preferable at the same time in solution.

After the reaction has taken place, the solution can be rapidly filtered if any insoluble material remains. Li 2 CO 3 is precipitated out of LiHCO 3 solution by evaporating CO 2. This can be carried out in a stirred reactor in which the solution is heated to 80-100 ° C, at which temperature the Li carbonate 3 solubility is lowest. The pollutant components are in soluble form in the solution even during Li 2 CO 3 crystallization. The purified Li carbonate is separated from the solution after crystallization by, for example, filtration or centrifugation, while the clear solution, which contains some soluble lithium in soluble form, can be returned in the process to prevent lithium loss. The CO 2 gas released during crystallization can also be re-used at the dissolution stage in order to improve the economics of the purification method.

The purification can, if necessary, be carried out in successive steps with final washing of the recrystallized lithium carbonate.

Compared to the process of CA Patent 643,843, the process of the present invention provides a purer Li2CO3 "product which meets international purity standards. The content of the critical pollutants Na2O, CaO, Fe2O3 and SO4 is very low. In both processes, the same reaction is used Li2CO3 + CO2 + H2O -> 2LiHCO3, but with different meanings for the processes. In the process of CA Patent 643,843, the reaction is needed to be able to separate the Li2CO3 from the lacquer residue. In the process of the present invention, the reaction is needed to dissolve the Li 2 CO 3 and get the pollutant ions in the solution. Since the lacquer residue was followed so long in the process according to CA patent 643 843, the content of foreign ions in the LiHCO-j solution will be high, which adversely affects the purity of the crystallized Li2CO3 product. In addition, in the process of the present invention, the troublesome separation of the lacquer residue is avoided from the unstable LiHCO-j solution which is unstable under normal pressure.

The invention is further illustrated by the following embodiments:

Example 1

A Li2CO2 material prepared by the sulfuric acid method contained 0.90% Na2O, 0.14% CaO, 0.001% Fe2O3 and 1.4% SO4 · Li2CO3 and water was mixed in a reactor, whereby CO 2 gas was allowed to flow through the suspension. The suspension was filtered and the solution heated to 95 ° C, evaporating CO 2 and crystallizing Li 2 CO 3. The product thus contained in 63923 0.03% Na2O, 0.03% CaO, <0.001% Fe2C> 3 and 0.08% SO4. Example 2

A 1 CO 2 material prepared by the sulfuric acid method contained 0.27% Na 2 O and 0.72% SO 4 · 100 g of the material was mixed with 1.25 kg of CO 2 saturated water at 20 ° C in a pressure vessel. The CO 2 pressure was raised to 1 MPa and the gas flow rate was 0.25 l / min. After 15 minutes of reaction time at 1 MPa, 98.8% of the Li 2 CO 3 material had abandoned in soluble form. The pressure was lowered and the solution was filtered, whereupon the clear solution was heated and Li 2 CO 3 crystallized. The product now contained 0.01% Na 2 O and <0.05% SO 4.

Example 3

A Li2CO3 material prepared by the sulfuric acid method contained 7.2% Na2O, 0.002% Al2O3, 5.4% SO4 and 0.003% Cl.

100 g of material was mixed in 1.35 kg of CO 2 saturated water at 20 ° C in a pressure vessel. The CO 2 pressure was raised to 1.5 MPa and the gas flow rate was 0.7 l / min. After 15 minutes of reaction time at 1.5 MPa, 99.2% of the material had abandoned in soluble form. The ether crystallized Li 2 CO 3 product contained 0.15% Na 2 O, 0.002% Al 2 C> 3, 0.29% SO 4 and 0.002% Cl.

Claims (4)

A process for recovering lithium carbonate in pure form from calcined lithium-containing silicate ores by converting the ore lithium content to lithium sulphate, which is introduced into the liquid phase by extraction with water followed by purification of the solution and separation of the solid which is then separated from the solution, characterized in that the crude and sparingly soluble lithium carbonate obtained is converted to a more water-soluble lithium hydrogen carbonate form by introducing carbon dioxide into the aqueous suspension of impure lithium carbonate. repeated. Process according to Claim 1, characterized in that the crude lithium carbonate is mixed with the amount of water required for the conversion of lithium carbonate into lithium hydrogen carbonate at a temperature of 0 to 60 ° C and carbon dioxide gas at a pressure of 0.1 to 3 MPa is introduced into this suspension, after which any insoluble matter is separated , followed by removal of carbon dioxide at 70-100 ° C and separation of the crystallized pure lithium carbonate by filtration or centrifugation. Process according to Claim 1 or 2, characterized in that the conversion of lithium carbonate into lithium hydrogen carbonate is carried out in a reactor vessel and in that