Lithium extraction method

Abstract

According to the present invention there is provided a method for the extraction of lithium from one or more lithium-containing ores such as spodumene, the inventive method comprising the steps of: milling said ore/s to a predetermined average particle size; optionally calcining the milled ore; further optionally performing a secondary milling step; providing an aqueous suspension of the one or more lithium-containing ores at a predetermined solids concentration; subjecting the one or more lithium-containing ores to an aqueous extraction medium defined by a predetermined partial pressure of CO.sub.2, a predetermined extraction temperature, over a predetermined time; and obtaining technical grade lithium carbonate/lithium bicarbonate therefrom. Optional concentration and/or precipitation/purification steps may follow.

Claims

1. A method for the extraction of lithium from one or more lithium-containing ores, said method comprising the steps of: a) milling said one or more lithium-containing ores to a predetermined average particle size to provide a milled crude ore; b) calcining said milled crude ore at a predetermined calcining temperature to obtain a calcined milled crude ore; c) providing an aqueous medium comprising a suspension of the calcined milled crude ore, at a predetermined solids concentration; d) subjecting said calcined milled crude ore to an acidic extraction medium defined by a predetermined partial pressure of CO.sub.2, a predetermined extraction temperature, over a predetermined time; and e) obtaining technical grade lithium carbonate and/or lithium bicarbonate in solution from the extraction medium.

2. The method according to claim 1, wherein the one or more lithium-containing ores comprise β-spodumene, or wherein the one or more lithium-containing ores consist essentially of β-spodumene.

3. The method according to claim 1, wherein the predetermined calcining temperature is greater than about 900° C., thereby to convert α-spodumene to β-spodumene.

4. The method according to claim 1, wherein said predetermined partial pressure of CO.sub.2 is between about 0.1 and about 300 bar; and wherein said predetermined extraction temperature is between about 20° C. and about 350° C.

5. The method according to claim 1, wherein said predetermined solids concentration is between about 0.1 and about 60% w/w.

6. The method according to claim 1, wherein said predetermined average particle size is between about 0.1 μm and about 1000 μm.

7. The method according to claim 1, wherein said predetermined time is between about 1 and about 1000 minutes.

8. The method according to claim 1, giving a yield on an extracted lithium to crude lithium basis of between about 1% and about 99%.

9. The method according to claim 1, wherein one or more impurities are extracted from said one or more lithium-containing ores; wherein said one or more impurities comprise Na, K, Mg, Ca, Mn, Fe, Al, and Si; and wherein each of said one or more impurities is present at a concentration between about 0.5% and about 40% of the lithium concentration on a molar basis.

10. The method according to claim 1, further comprising a concentration step f), wherein the technical grade lithium carbonate obtained in solution from step e) is concentrated.

11. The method according to claim 10, wherein said concentration step comprises: a concentrator, evaporation, reverse osmosis, electrodialysis, liquid-liquid extraction, selective adsorption solid state extraction or membrane separation.

12. The method according to claim 10, wherein following said concentration step g), the lithium carbonate precipitates out of solution; and wherein the method further comprises a filtration step g), thereby to separate the precipitated lithium carbonate.

13. The method according to claim 1, wherein the aqueous medium comprises water, one or more mineral acids, one or more organic acids, one or more alkaline salts, one or more ionic liquids, and combinations thereof.

14. The method according to claim 13, wherein the one of more mineral acids are supplemented with a predetermined partial pressure of CO.sub.2 between about 0.1 and about 300 bar.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a schematic of a micro-fluidised bed reactor, from which the data provided in the inventive examples have been obtained;

(3) FIG. 2 is a schematic of the integrated dissolution and RO for the production of Li.sub.2CO.sub.3 from a dilute Li stream produced by carbonic acid.

(4) FIG. 3 is a plot showing data for effect of temperature showing apparent first order kinetics and activation energy.

(5) FIG. 4 shows a grading of lithium carbonate for the battery industry.

(6) FIG. 5 shows a general process for sulfuric acid leaching of lithium from β-spodumene.

(7) FIG. 6 shows a general process for the pressure-leaching of lithium carbonate from β-spodumene.

EXAMPLES

(8) Overview

(9) The present inventors have conducted experiments in a small batch reactor in which a water-CO.sub.2 mixture is passed through a pulverised sample of β-spodumene. In the reactor, shown schematically in FIG. 1, the conditions are such that the mixture forms two phases, gas (essentially CO.sub.2) and liquid (water saturated with CO.sub.2). Some of the CO.sub.2 absorbed by the water phase is in the form of carbonic acid and it is the proton concentration associated with that acid that is responsible for the extraction of Li from the mineral sample.

(10) When lithium is extracted into the aqueous phase, the concentration of protons is suppressed and further extraction of lithium becomes slower. This effect increases as the concentration of Li increases, with the result that it becomes impractical to allow the lithium concentration to become very high; experiments undertaken to date suggest that the maximum practical concentrations that can be achieved are of the order of 100 ppm (wt/wt; or ˜0.015 mol/L) which is very low compared with the concentration of lithium carbonate that would be needed to bring about precipitation of lithium carbonate under the reaction conditions (˜0.7 mol/L, ˜5000 ppm) at 150° C. and 100 bar. Therefore, additional processing steps are needed before lithium carbonate could be produced.

(11) The inventors have demonstrated that reverse osmosis (RO) is suitable for concentrating dilute Li (˜50 ppm, dosed as LiNO.sub.3) up to the concentration required to precipitate lithium carbonate at process conditions. As the process is already at pressure, the use of RO is well suited to this process. RO also has the benefit in that it produces a purified permeate stream which can be recycled through the CO.sub.2 extraction process, as shown in FIG. 2. The recycle of the leachate water minimises the water consumption in the process while also facilitating the maintenance of dilute extraction conditions.

(12) Extraction of lithium in carbonic acid also extracts some of the sodium and potassium that are invariably present in the mineral; in addition, some silica and aluminium are extracted. Typically, the molar ratios of the extracted elements are:
Li:Si:Na+K:Al=1:0.20:0.02:<0.01

(13) Silica and alumina can be removed relatively easily by flocculation and precipitation as SiO.sub.2 and Al.sub.2O.sub.3 or other means. However the relative molar concentration of Na+K needs to be reduced by a factor of ˜200 to a value <0.0001 in order to achieve the purity of lithium (99.99% lithium carbonate) needed for the highest-value applications. Without wishing to be bound by theory, the inventors believe that a combination of low-cost membrane techniques can achieve the desired outcome of a concentrated solution of high-purity lithium; progress is ongoing in this regard.

(14) General Method Employed

(15) The use of carbonic acid in the extraction of lithium from β-spodumene was demonstrated on a laboratory scale. A 1 g sample of milled β-spodumene (sieved to lie in the size range ˜20 to ˜75 μm) was held in a tubular reactor. A water flow of 1 g/min was passed through the reactor at a temperature of 150° C. and a pressure of 100 bar. The aqueous reactor effluent was sampled at regular intervals and analysed for the presence of lithium and other metals extracted from the spodumene charge.

(16) With only water flowing through the reactor, a gradual release of lithium was observed, but this was accompanied by aluminium and silicon in proportions close to their respective stoichiometric proportions in spodumene. However, when CO.sub.2 in the amount of 3.7 mol/kg water was also fed to the reactor, a relatively greater proportion of lithium surprisingly appeared in the product samples; the concentration of lithium in the product samples increased by a factor of 5 or more, while the concentrations of aluminium and silicon were markedly reduced by comparison.

(17) During optimisation experiments, the Inventors varied the temperature of the extraction medium between about 25 and about 200° C. The rate at less than about 100° C. is low; there was observed a large increase in rate in going to 150° C., but no further increase was observed upon raising the temperature to 200° C. Significantly, the purity of the extract is reduced significantly in going from 150 to 200° C.

(18) The extraction of lithium from the milled β-spodumene sample was more than 85% complete after 5 h. Other metal ions detected in the extract were Na, K, Mg, Ca, Mn, Fe, Al, and Si. Overall, lithium constituted >85% of the metals extracted from the spodumene sample, on a molar basis. The dominant impurity was silicon (˜12%), followed by sodium (˜1.5%) and potassium (˜1%, on a molar basis).

(19) The reaction was also detectable in a batch reactor sparged with CO.sub.2 at room temperature and atmospheric pressure.

(20) The general method employed above amply demonstrates that the use of carbonic acid as an extraction medium for lithium carbonate from spodumene ore is surprisingly efficacious. As rationalised above, this finding is completely counterintuitive given the prevailing state of the art in which strong acids and carbonate leaching are the currently-preferred industrial methods for the extraction of lithium from pegmatitic ores such as spodumene.

Examples of the Inventive Method

(21) TABLE-US-00001 Milled Specific size Water molar Li- (μm, flow Extraction amount Example containing Extraction sieved, rate temp Pressure CO.sub.2 Time Yield No. ore* medium mean) (g/min) (° C.) (bar) (mol/kg) (h) (%) 1 Spodumene Water 20 1 150 100 3.7 8 85 2 Spodumene Water/ 40 2 180 120 3.0 6 80 acetic acid 3 Spodumene Water/ 50 1 120 140 4.0 5 90 sulfur acid 4 Spodumene Water/ 80 3 90 200 2.5 10 85 LiOH 5 Spodumene Water 100 5 190 80 4.5 3 90 *Inherently comprising impurities, as defined above

(22) In order to demonstrate the scope and reproducibility of the present invention, the following five experiments were conducted, using the general methodology prescribed above, whilst varying some of the parameters described above. The results, as shown in the “yield” column (% yield on an extracted lithium to crude lithium basis) duly demonstrate the utility of the presently-claimed method.

(23) Surprisingly, it has been found that the base (catalysed) reaction is relatively fast and leads to approximately congruent extraction of lithium (i.e., Li is accompanied by Al and Si, more or less in their molar proportions, 1 and 2, respectively, in the spodumene).

(24) Experimental Results for Carbonic Acid Extraction

(25) Provided below are results obtained to characterise the rates of extraction of Li and the other elements over the range of temperatures from 100-200° C. and pressures from 20-100 bar. In all the runs shown, the mass fraction of CO.sub.2 in the water-CO.sub.2 mixture was 15%; the specific mass flow rate of the mixture was of sample was in the range 0.5 to 5 kg min.sup.−1 per kg.

(26) The rate of extraction as a function of temperature was analysed at parameters of: pressure (100 bar); reaction time (4 hours); and specific mass rate (0.5 min.sup.−1). Table 1, shown below, shows the extent of Li extraction (X.sub.Li) by carbonic acid over a 4 hour period.

(27) TABLE-US-00002 TABLE 1 Extent of Li extraction (X.sub.Li) by carbonic acid over a 4 hour period T (° C.) X.sub.Li (—) 100 12.4 125 42.8 150 80.0 200 88.0

(28) The extraction is clearly activated, approaching completion only at the higher temperatures. As shown in FIG. 3, the degree of extraction follows first order kinetics with an apparent activation energy ˜30 kJ mol.sup.−1.

(29) Table 2, below, summarises results for the effects of specific mass rate and pressure on the extent of extraction and its composition. In each of these runs (2, 3, and 4), leaching was carried out for 2 hours at 150° C.

(30) Reducing the pressure from 100 (Run 2) to 20 bar (Run 3) led to a 50% reduction in the extent of lithium extraction, which is ascribed to the lower proton concentrations arising when the CO.sub.2 pressure over the solution is reduced. The Li fraction of the total extract is slightly reduced while that of matrix Si is increased correspondingly; the relative amounts of Li, Na and K in the extract are approximately constant.

(31) TABLE-US-00003 TABLE 2 Elemental composition of extract obtained after 2 hours at 150° C. Run number 2 3 4 Specific mass rate (min.sup.−1) 0.5 0.5 5 Pressure (bar) 100 20 100 X.sub.Li (%) (%) 40.4 22.7 86.7 Extracted element Li 59.44 44.66 59.21 wt %) Si 37.89 49.52 33.01 Al 0.03 0.41 0.70 K 1.02 3.12 3.80 Na 1.62 2.28 3.27

(32) Comparison of Runs 2 and 4 in Table 2 shows the effect of specific mass rate. At higher values of this parameter, the mineral sample is exposed to a greater volume of acid solution overall and the concentrations of the extracted minerals are reduced. As discussed above, a lower lithium concentration is accompanied by a higher proton concentration, with the result that the rate of extraction of lithium from the rock is higher. The more dilute conditions appear also to enhance the relative fractions of Na and K in the leachate. Clearly, there is a trade-off between the leaching time required and the degree to which the leachate must be concentrated and purified in order to be able to achieve concentrations high enough to precipitate highly purified lithium carbonate.

(33) Essentially complete extraction of lithium from β-spodumene can be achieved using carbonic acid. The treatment also extracts some silica and alumina from the rock, as well as sodium and potassium. The extraction process is faster at higher temperatures and pressures, and when the products are more dilute (<100 ppm wt/wt lithium).

(34) Economic and Environmental Implications

(35) The above examples demonstrate that, contrary to the accepted wisdom of using strong acid or base to extract lithium from one or more lithium-containing ores such as β-spodumene, lithium can also be extracted under the relatively mild conditions of a CO.sub.2/H.sub.2O extraction medium. Such a process engenders many of the advantages of traditional sulfate or Quebec lithium extraction, without the negative consequences in respect of lithium selectivity, cost, environmental damage and without the need for one or more subsequent purification/extraction steps.

(36) The inventive method of extracting lithium from lithium-containing ores such as β-spodumene engenders many advantages over the methods prescribed in the prior art. In using carbonic acid as the extraction medium at only moderate temperature, pressure—and over a relatively short reaction period, the inventive method is genuinely counterintuitive. Moreover, as compared with the representative prior art methods (e.g., concentrated H.sub.2SO.sub.4; 19 equivalents of HF, etc.), the present invention provides for an environmentally-friendly approach to what has traditionally been a somewhat damaging and wasteful pursuit.

INDUSTRIAL APPLICABILITY

(37) With ever-increasing global demand for lithium (e.g., in batteries) and, in particular, Australia's vast natural deposits of lithium-containing ores such as spodumene (around one-third of the global market), the economic implications of successfully developing and commercialising the inventive technology may be significant.

(38) Although the invention has been described with reference to specific examples it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.