Method for extracting lithium salt from a raw material mixture comprising lithium containing limestone

Abstract

The invention relates to a method of extracting lithium salt from a raw material mixture comprising lithium containing limestone.

Description

The invention relates to a method of extracting lithium salt from a raw material mixture comprising lithium containing limestone. Various methods are known for recovering alkali metals, such as Li, Rb and Cs from silicates, aluminosilicates, phosphates and other minerals, such as lepidolite, zinnwaldite, spodumene, petalite, pollucite and amblygonite. WO 2018 / 228618 and WO 2022 / 167970 describe methods for recovering alkali metals including lithium from a raw material that contains a silicate mineral raw material containing lithium and optionally further alkali metals. The raw material further contains an alkaline earth metal mineral, and a reagent being capable of releasing chlorine during a thermal treatment. The raw material mixture is subjected to heat treatment in a kiln, which results in that the structure of the silicate mineral decomposes while releasing lithium and other alkali metals which combine with the released chlorine to form volatile alkali metal chlorides that may be further processed. The enormous need of Li-containing battery materials necessitates the production of LiOH from lithium ore such as spodumene. In a first step the lithium mineral is reacted to Li2CO3. On industrial scale, lithium carbonate is then converted to lithium hydroxide (LiOH) by adding calcium hydroxide (Ca(OH)2) to an aqueous solution of lithium carbonate. In this conversion, limestone (CaCOs) is obtained as by-product product, according to the following reaction: Li2CO3 + Ca(OH)2^ 2 LiOH + CaCOsT It has now been found that the limestone obtained by said conversion (hereinafter “byproduct limestone”) still contains residual amounts of lithium. By the industrial production of LiOH high volumes of CaCOs are generated. Usually, the thus produced limestone is deposited in landfill under strict regulations. CaCOs is an essential raw material component in the cement clinker and / or slag production. It was surprisingly found by the inventors that the lithium containing CaCOs (by-product limestone) can be advantageously used in a process for the production of burnt lime e.g. for the cement industry, while simultaneously the remaining lithium residues can be extracted from the by-product limestone. Accordingly, the use of by-product limestone as raw material component according to the invention allows the efficient recycling of a waste product as follows: i. the by-product limestone is advantageously used as raw material for conversion to cement clinker / slag and ii. the residual lithium contained in the by-product limestone is simultaneously extracted and recovered from the material for further processing, e.g. in Li-containing battery materials, in an energy-neutral process. Thus, the process of the invention allows for a sustainable and energy-saving separation of valuable components such as lithium at minimum waste generation, offering both economic and ecological benefits in the efficient extraction of valuable lithium material from a raw mixture. Thus, in a first aspect the present invention provides a method for extracting lithium salt comprising the steps of a. providing a raw material comprising i.at least one lithium-containing limestone, ii.optionally at least one silicate or phosphate mineral which may contain alkali metals such as lithium; and iii.at least one chlorine source, b. treating the raw material at a temperature in the range of 800°C to 1700°C, preferably in the range of 900°C to 1100°C, preferably in a rotating device, to form alkali metal chlorides in gaseous form, c. collecting exhaust gases obtained from step b) containing alkali metal chlorides in gaseous form and dust particles, d. quenching the exhaust gases obtained from step c), e. isolating solid materials obtained after step d), f. dispersing the solid materials obtained after step e) in aqueous medium, to form an aqueous solution containing at least one alkali metal chloride, and g. isolating lithium salt obtained after step f). The raw material comprises at least one lithium-containing limestone. According to the present invention the at least one lithium-containing limestone is preferably a limestone which is obtained as by-product during lithium hydroxide production (by-product limestone). According to the present invention the at least one lithium-containing limestone has a lithium-ion concentration of at least 0.1 wt.-%, preferably of at least 0.3 wt.-% and most preferably 0.2 wt.-% to 0.4 wt.-% based on dry limestone. Preferably, the moisture content of the at least one lithium-containing limestone is at least 20 wt.%, preferably at least 25 wt.%, most preferably 20 wt.%- 45 wt.-%. Preferably the lithium containing limestone is used directly from LiOH production after industrial filtration. Further, the at least one lithium-containing limestone preferably comprises a CaCOs concentration of at least 80 wt.%, preferably at least 85 wt.%, most preferably at least 95 wt.%, more preferably 85 wt.%-99.8 wt.-%. The at least one silicate or phosphate mineral may preferably contain lithium (Li) and, optionally, further rare alkali metals such as Rubidium (Rb) and Caesium (Cs). In another embodiment the at least one silicate or phosphate mineral is free of lithium. The silicate or phosphate mineral preferably contains phyllosilicate, such as mica, more preferably lithium containing phyllosilicate, such as lithium containing mica. Further, according to the present invention the at least one lithium containing silicate or phosphate mineral is preferably present in the form of a pegmatite. Preferred examples of the at least one lithium containing silicate mineral are selected from the group consisting of lepidolite, zinnwaldite, spodumene, petalite, eucryptite, hectorite, and jadarite. Further, preferred examples of the at least one lithium containing phosphate mineral are selected from the group consisting of amblygonite, montebrasite, and lithiophilite. In a preferred embodiment the concentration of lithium-ions in the at least one silicate or phosphate mineral is at least 0.2 wt.%, preferably at least 0.4 wt.%, more preferably at least 0.9 wt.% and most preferably 0.3-1.5 wt.-%. The raw material further comprises at least one chlorine source. According to the present invention the at least one chlorine source is a substance able to release chlorine in its free form or in a bonded form. Preferably, the at least one chlorine source releases chlorine during and due to a thermal treatment. Preferred embodiments of the at least one chlorine source are selected from at least one metal chloride other than an alkali metal chloride, such earth alkali chloride, e.g. CaCh, HCI or a free chlorine (CI2). According to some embodiments of the invention, the at least one chlorine source may be or may comprise chlorinated organic compounds, such as chlorinated polymers (for example polyvinylchloride, polychloroprene), polychlorinated biphenyls or chlorinated oils or solvents. With regard to the composition of the raw material, a preferred embodiment of the invention provides that the at least one lithium-containing limestone component (i) is present in the raw material mixture in an amount of 55-75 wt.-%, the at least one silicate or phosphate mineral component (ii) which may contain lithium is present in the raw material mixture in an amount of 20-35 wt.-%, and the at least one chlorine source component (iii) is present in the raw material mixture in an amount of 5-10 wt.-%, with the proviso that the sum of the relative amounts of components (i), (ii) and (iii) is 100 wt.-%. In a preferred embodiment, the weight ratio of component(i):component(ii) in the raw material is 0.5-5:0.5-5, preferably 3.5-4.5:0.5-1.5, most preferably 4:1. According to a further preferred embodiment, the amount of the at least one chlorine source is adjusted to the lithium concentration and, optionally, to the further alkali metal concentration in the raw material mixture. Preferably, the molar ratio of alkali metal ion:chlorine in the raw material is 0.5-1.5:4.5-5.5, preferably 1:5. According to the method of the invention, the mixture of raw material is treated in step b) at a temperature in the range of 650°C to 1700°C, preferably 800°C to 1700°C, preferably in the range of 900°C to 1100°C. In the thermal treatment the raw material is melted, at least partially, whereby the lithium and optionally the further alkali metals contained in the raw material mixture combine with the chlorine released by the at least one chlorine source to form an alkali metal chloride in gaseous form. Limestone obtained as by-product during lithium hydroxide production (by-product limestone) was found to contain residual Li2CO3. In the heat treatment of step b), the residual Li2CO3 content of the by-product CaCOs is converted to Li2O by the reaction: Li2CO3(s) Li2O(s) + CO2(g) Li2O efficiently reacts with the at least one chlorine source of the raw mixture, in particular with the earth alkali chloride, e.g. CaCh, HCI or a free chlorine (CI2), to obtain lithium chloride in gaseous form. The reaction of the chlorine source with the Li2O extracted from the by-product limestone, is more efficient than the reaction with the lithium contained in the at least one silicate or phosphate mineral, such as spodumene, as the diffusion of chlorine source inside the mineral's structure is not necessary. This might be an explanation, that the extraction of lithium from by-product limestone can even be run at lower temperatures such as 650°C-1700°C, thereby allowing additional energy savings, particularly in case wherein only by-product limestone and no component (ii) is used in the raw material. The thermal treatment is preferably performed in a rotating device, such as a rotating furnace or reactor, preferably in a rotary kiln or a fluidized bed reactor. According to a very preferred embodiment of the invention the thermal treatment of the raw material is performed in a rotary kiln. The components (i), (ii) and (iii) of the raw material are introduced into the rotating device, preferably into the rotary kiln, separately or in a premixed form. In step b) the heat is generated by electrical heating connected to the rotating device or by burning a fuel, preferably fuel gasses, which is fed to the device together with the raw material. The fuel may be selected from gas, oil, sludge or pulverized solid fuel. In a most preferred embodiment, the fuel used for treating the raw material in step b) is selected from the group consisting of natural gas, propane, hydrogen, coal, petroleum coke. In a further preferred embodiment, the fuel comprises the at least one chlorine source which is burnt to emit chlorine. In this embodiment the fuel preferably comprises a chlorinated organic compound such as chlorinated polymers (polyvinylchloride, polychloroprene), polychlorinated biphenyls, or chlorinated oils. In the rotating device, in particular in the rotary kiln, the raw material is thermally and mechanically processed, thereby producing at least partially dust particles. In step b) of the method of the invention exhaust gasses are formed containing alkali metal chlorides in gaseous form, dust particles and optionally fuel gasses. Preferably the dust particles have an average particle diameter of d50= 30-90 pm, e.g. measured by laser diffraction. In subsequent step c), the exhaust gases obtained in step b) are collected and separated from the raw material in the rotating device. For extraction of the alkali metals, and in particular lithium from the raw material, it was found that collection of the exhaust gas is improved if gaseous alkali metal chlorides are drawn off from the rotating device together with the dust particles generated from the processing of the raw material mixture. This allows quenching the exhaust gas obtained in step c) together with the dust particles and the gaseous alkali metal chlorides, thereby condensing the alkali metal chlorides on the surface of the dust particles. According to a preferred embodiment of the invention, the exhaust gases are collected in step c) by applying a negative or positive pressure within the rotating device. In order to provide an additional surface for enhancing condensation of the alkali metal chlorides in the exhaust gas on the surface of the dust particles, a preferred embodiment of the invention provides the addition of inert dust during the quenching step d). For example, the inert dust is preferably a fine marl or additional limestone. The inert dust may preferably be introduced or sprayed directly into the quenching chamber or in the device inlet. In a preferred embodiment, the inert dust has an average particle size of d50 in the range of 30-90 pm. With regard to the quenching step d), a preferred embodiment of the invention comprises cooling the exhaust gases obtained in step c) to a temperature of below 600 °C. Quenching to temperatures below 600 °C may be performed in the presence of a heat exchanger in the quenching chamber or by directing fresh air towards the exhaust gas stream. After quenching, the solid material obtained in step d), in particular the dust particles with the condensed alkali metal chlorides adhering on their surface are isolated from the exhaust gas in an isolation step e). The isolation in step e) may be performed by means of a cyclone separator or by use of filter elements, particularly ceramic filter elements. The isolated solid material obtained after step e) is then dispersed in an aqueous medium, preferably in water, to form an aqueous solution containing at least one alkali metal chloride, such as lithium chloride. The solid material is dispersed in the aqueous medium in a ratio between 1:2 and 1:10. As the alkali metal chlorides are highly soluble, they are present in the liquid phase. In step g) of the method of the invention the liquid phase is subjected to filtration or centrifugation. The obtained aqueous solution of alkali metal chlorides, in particular lithium chloride, can be considered the final product of the process of the invention. Optionally, the alkali metal salt, particularly the lithium salt, may be concentrated in the aqueous solution, preferably by evaporation. Preferably, the solution of alkali metal chlorides can be concentrated using excessive heat from the thermal treatment of step b) or contained in the exhaust gases in step c). The method of the present invention may preferably further comprise a pre-heating step carried out before the thermal treatment b). In the pre-heating step, the raw material mixture is preheated to a temperature preferably between 600°C and 900°C, preferably between 600°C and 750°C, i.e. to a temperature slightly lower to the temperature when alkali metal chlorides in gaseous form are formed. The preheating step may be performed in the same rotating device as the method of the present invention or in an upstream cyclone preheater. The excessive heat contained in the exhaust gas collected in step c) may be used as a primary source of heat for preheating the raw material. In a most preferred embodiment of the invention, the rotatory device of the invention is a rotary kiln and in particular a rotary kiln of the type used for producing cement clinker in a cement manufacturing plant. When producing cement clinker, the preheated and optionally pre-calcined cement raw meal is introduced into the inlet of the rotating device, which is arranged opposite to the outlet. The preferred tubular drum of the rotating device has an inclination of a few degrees relative to the horizontal, so that material introduced through the inlet can be slowly transported to the outlet by the effect of gravity and according to the rotational speed of the device while being sintered. The burner is arranged at the outlet, so that exhaust gases are travelling through the rotary drum in counter-current flow to the clinker and leaves the drum via the inlet. According to the method of the invention, as mentioned above, once lithium and optionally the other alkali metals are extracted from the raw material after step c), the remaining (partially) melted raw material is further heated to a temperature above 1150°C, preferably to a temperature in the range of 1150°C-1700 °C, most preferably in the range of 1150°C - 1500°C. Subsequently the material is cooled to form slag or clinker and collected from the rotatory device by flowing out from the device. Accordingly, the resulting material can be used as a synthetic mineral component in cement compositions. In order to produce the highest quality of a synthetic mineral component, it is advantageous to avoid slow cooling of the material. At the same time, the temperature of the melt shall not fall below the melting temperature before the melt flows off the device or kiln through the device or kiln outlet. Therefore, a specific temperature control is preferred, wherein the melt is collected from the rotating device or rotary kiln having a temperature still above the melting point, and then once collected abruptly cooled. To this end, a preferred embodiment provides that the main burner of the rotating device or rotary kiln is arranged outside of the device or kiln to assure that the flame starts at the border of the rotating device or rotary kiln and that the cooling zone is as short as possible. The rotating device may preferably be operated at a rotary speed of between 1 and 10 rpm. According to a second aspect, the invention provides lithium salt obtained by a method according to the invention as described above. A third aspect of the invention relates to a slag or clinker obtained by a method according to the invention as described above. A still further aspect of the invention relates to the use of at least one lithium-containing limestone as described above as a raw material in a method for extracting lithium salt and producing cement clinker, preferably in a co-process of extracting lithium salt and producing cement clinker, more preferably in a continuous co-process. Example: By-product limestone having a content of Lithium of 0.203±0.005 wt.-% and spodumene (Li2O content of 5.6 wt.-%; average particle size < 100 pm) was mixed in a weight ratio of limestone:spodumene of 3.25:1. CaCL was added at 20% excess over the stoichiometric Li amount. The mixture was roasted at 1250-1450°C for 45 min. The gases were continuously sucked and cooled by an air cooler and a water cooler before treatment in a gas scrubber with water. The overall Li yield was determined to 98.2 ± 1 %. Lithium was extracted from both starting materials, spodumene and byproduct limestone. The present invention is defined by the following items: 1. A method for extracting lithium salt comprising the steps of a) providing a raw material comprising i. at least one lithium-containing limestone, ii. optionally at least one silicate or phosphate mineral which may contain alkali metals such as lithium; and iii. at least one chlorine source, b) treating the raw material at a temperature in the range of in the range of 800°C to 1700°C, preferably in the range of 900 °C to 1100 °C, preferably in a rotating device, to form alkali metal chlorides in gaseous form, c) collecting exhaust gases obtained from step b) containing alkali metal chlorides in gaseous form and dust particles, d) quenching the exhaust gases obtained from step c), e) isolating solid materials obtained after step d), f) dispersing the solid materials obtained after step e) in aqueous medium, to form an aqueous solution containing at least one alkali metal chloride, and g) isolating lithium salt obtained after step f). 2. Method according to item 1, wherein the at least one lithium-containing limestone is obtained as by-product of lithium hydroxide production. 3. Method according to item 1 or 2, wherein the at least one lithium-containing limestone has a lithium ion concentration of at least 0.1 wt.-%, preferably at least 0.3 wt.-% and most preferably 0.2 wt.-% to 0.4 wt.-% based on dry limestone. 4. Method according to any one of items 1-3, wherein the moisture content of the at least one lithium-containing limestone is at least 20 wt.%, preferably at least 25 wt.%, most preferably 20 wt.%- 45 wt.-%. 5. Method according to any one of the preceding items, wherein the at least one lithium-containing limestone comprises a CaCOs concentration of at least 80 wt.%, preferably at least 85 wt.%, most preferably at least 95 wt.%, more preferably 85 wt.%-99.8 wt.-%. 6. Method according to any one of the preceding items, the at least one silicate or phosphate mineral contains phyllosilicate, such as mica, more preferably lithium containing phyllosilicate, such as lithium containing mica. 7. Method according to any one of the preceding items, wherein the at least one silicate or phosphate mineral is present in the form of a pegmatite. 8. Method according to any one of the preceding items, wherein the at least one silicate mineral is selected from the group consisting of lepidolite, zinnwaldite, spodumene, petalite eucryptite, hectorite, and jadarite, and / or wherein the at least one phosphate mineral is selected from the group consisting of amblygonite, montebrasite, and lithiophilite. 9. Method according to any one of the preceding items, wherein the concentration of lithium-ions in the at least one silicate or phosphate mineral is at least 0.2 wt.%, preferably at least 0.4 wt.%, more preferably at least 0.9 wt.% and most preferably 0.31.5 wt.-%. 10. Method according to any one of items 1-7, wherein the at least one silicate or phosphate mineral is free of lithium. 11. Method according to any one of the preceding items, wherein the chlorine source is selected from at least one metal chloride other than alkali metal chloride, such as earth alkali chloride, e.g. CaCh, HCI or free chlorine (CI2). 12. Method according to any one of the preceding items, wherein the at least one chlorine source may be chlorinated organic compounds, such as chlorinated polymers (for example polyvinylchloride, polychloroprene), polychlorinated biphenyls or chlorinated oils or solvents. 13. Method according to any one of the preceding items, wherein the weight ratio of component (i):component (ii) is 0.5-5:0.5-5, preferably 3.5-4.5:0.5-1.5, most preferably 4:1. 14. Method according to any one of the preceding items, wherein the molar ratio of alkali metal ion:chlorine in the raw material is 0.5-1.5:4.5-5.5, preferably 1:5. 15. Method according to any one of the preceding items, wherein the rotating device is a rotating furnace or reactor, preferably a rotary kiln or a fluidized bed reactor, most preferably a rotary kiln. 16. Method according to any one of the preceding items, wherein the heat in step b) is generated by an electrical heating or by burning a fuel, such as gas, oil, sludge or pulverized solid fuel. 17 Method according to item 16, wherein the fuel is selected from the group consisting of natural gas, propane, hydrogen, coal, petroleum coke. 18. Method according to items 16 or 17, wherein the fuel comprises the at least one chlorine source, preferably comprises a chlorinated organic compound, such as chlorinated polymers (polyvinylchloride, polychloroprene), polychlorinated biphenyls, or chlorinated oils. 19. Method according to any one of the preceding items, wherein the dust particles of step c) have an average particle diameter of d50= 30-90 pm. 20. Method according to any one of the preceding items, wherein the exhaust gases are collected in step c) by applying a negative or positive pressure within the rotating device. 21. Method according to any one of the preceding items, wherein the quenching in step d) comprises cooling the exhaust gas obtained in step c) to a temperature of below 600 °C. 22. Method according to any one of the preceding items, wherein the quenching in step d) is performed using a heat exchanger or by directing fresh air towards the exhaust gas stream. 23. Method according to any one of the preceding items, wherein an inert dust is added during the quenching step d), preferably having an average particle size of d50 in the range of 30-90 pm. 24. Method according to any one of the preceding items, wherein in step g) the aqueous solution is subjected to filtration or centrifugation and, optionally to evaporation. 25. Method according to any one of the preceding items, wherein the raw material is preheated at a temperature of 600-750 °C before step b), said preheating being preferably performed in the rotating device or a cyclone preheater. 26. Method according to any one of the preceding items, wherein after step c) the remaining material is heated to a temperature in the range of 1150°C- -1700 °C, most preferably in the range of 1150°C - 1500 °C, and subsequently cooled to form slag or clinker. 27. Lithium salt obtained by a method according to any one of items 1-25. 28. Slag or clinker obtained by a method according to any one of items 1-26. 29. Use of at least one lithium-containing limestone as a raw material in a method for extracting lithium salt and producing cement clinker. 30. Use according to claim 29, in a co-process of extracting lithium salt and producing cement clinker, more preferably in a continuous co-process.

Claims

1. A method for extracting lithium salt comprising the steps ofa. providing a raw material comprisingi. at least one lithium-containing limestone,ii. optionally at least one silicate or phosphate mineral which may contain alkali metals such as lithium; andiii. at least one chlorine source,b. treating the raw material at a temperature in the range of in the range of 800°C to 1700°C, preferably in the range of 900 °C to 1100 °C, preferably in a rotating device, to form alkali metal chlorides in gaseous form,c. collecting exhaust gases obtained from step b) containing alkali metal chlorides in gaseous form and dust particles,d. quenching the exhaust gases obtained from step c),e. isolating solid materials obtained after step d),f. dispersing the solid materials obtained after step e) in aqueous medium, to form an aqueous solution containing at least one alkali metal chloride, andg. isolating lithium salt obtained after step f).

2. Method according to claim 1, wherein the at least one lithium-containing limestone is obtained as by-product of lithium hydroxide production.

3. Method according to claim 1 or 2, wherein the at least one lithium-containing limestone has a lithium ion concentration of at least 0.1 wt.-%, preferably at least 0.3 wt.-% and most preferably 0.2 wt.-% to 0.4 wt.-% based on dry limestone.

4. Method according to any one of claims 1 -3, wherein the moisture content of the at least one lithium-containing limestone is at least 20 wt.%, preferably at least 25 wt.%, most preferably 20 wt.%- 45 wt.-% and / orwherein the at least one lithium-containing limestone comprises a CaCOs concentration of at least 80 wt.%, preferably at least 85 wt.%, most preferably at least 95 wt.%, more preferably 85 wt.%-99.8 wt.-%.

5. Method according to any one of the preceding claims, the at least one silicate or phosphate mineral contains phyllosilicate, such as mica, more preferably lithium containing phyllosilicate, such as lithium containing mica.

6. Method according to any one of the preceding claims, wherein the concentration of lithium-ions in the at least one silicate or phosphate mineral is at least 0.2 wt.%, preferably at least 0.4 wt.%, more preferably at least 0.9 wt.% and most preferably 0.3-1.5 wt.-%.

7. Method according to any one of claims 1-6, wherein the at least one silicate or phosphate mineral is free of lithium.

8. Method according to any one of the preceding claims, wherein the chlorine source is selected from at least one metal chloride other than alkali metal chloride, such as earth alkali chloride, e.g. CaCh, HCI or free chlorine (CI2) and / or wherein the at least one chlorine source may be chlorinated organic compounds, such as chlorinated polymers (for example polyvinylchloride, polychloroprene), polychlorinated biphenyls or chlorinated oils or solvents.

9. Method according to any one of the preceding claims, wherein the weight ratio of component (i):component (ii) is 0.5-5:0.5-5, preferably 3.5-4.5:0.51.5, most preferably 4:1 and / orwherein the molar ratio of alkali metal ion:chlorine in the raw material is 0.51.5:4.5-5.5, preferably 1:5.10.Method according to any one of the preceding claims, wherein the heat in step b) is generated by an electrical heating or by burning a fuel, such as gas, oil, sludge or pulverized solid fuel.11.Method according to any one of the preceding claims, wherein the quenching in step d) comprises cooling the exhaust gas obtained in step c) to a temperature of below 600 °C.12.Method according to any one of the preceding claims, wherein the raw material is preheated at a temperature of 600-750 °C before step b), said preheating being preferably performed in the rotating device or a cyclone preheater and / orwherein after step c) the remaining material is heated to a temperature in the range of 1150°C - 1700 °C, most preferably in the range of 1150°C -1500 °C, and subsequently cooled to form slag or clinker.13.Lithium salt obtained by a method according to any one of claims 1-12.14.Slag or clinker obtained by a method according to any one of claims 112.

15. Use of at least one lithium-containing limestone as a raw material in a method for extracting lithium salt and producing cement clinker, particularly in a co-process of extracting lithium salt and producing cement clinker, more preferably in a continuous co-process.