Field of Art The invention relates to a method for recovering compounds of lithium and optionally of further alkali metals from silicate raw materials.

Background Art Alkali metals, especially rare ones such as Li, Rb and Cs, and also K and Na as minor components, can be obtained from silicates, aluminosilicates, phosphates and other minerals, such as lepidolite, zinnwaldite, spodumene, petalite, pollucite and amblygonite, by several methods.

A first method is autoclave leaching at high temperatures and pressures in acidic medium, often using mineral acids, such as sulfuric acid, hydrochloric acid or other acids. Usually, sulfuric acid is used because it is the cheapest and most accessible leaching agent. Typical leaching agents for autoclave leaching in alkaline medium are solutions of NaOH or Na ₂ C0 ₃ . There are well known methods of autoclave leaching in neutral medium, for example in solutions of NaCl, Na ₂ S0 ₄ , CaCl ₂ and other salts. At an increased temperature and pressure, anion parts are dissociated from the structure of minerals and alkali metals are dissolved. A silicate or aluminosilicate residue, respectively, is precipitated on the bottom of the autoclave. In alkaline medium at an increased temperature, a part of the silicate anion dissolves as well. After leaching and discharging the leaching solutions out of the autoclave, a partly dissolved Si0 ₂ is precipitated in the form of silica gel, using C0 ₂ , often directly from the air. The disadvantages of the autoclave method are high CAPEX, necessity of decrepitation or of fine milling before leaching in autoclaves, low productivity and formation of aluminosilicate leaching residues, which are often unusable and end up in tailing dumps.

A second, probably the most common, method for recovering alkali metals is sintering minerals containing alkali metals with different sintering agents, mainly CaC0 ₃ , CaO, (Ca,Mg)C0 ₃ , MgC0 ₃ , MgO, CaS0 ₄ , CaCl ₂ , Na ₂ S0 ₄ , NaCl, NaOH, Na ₂ C0 ₃ , K ₂ S0 ₄ , or with other chemicals or their mixtures at different ratios. Sintering takes place in a furnace at a temperature within the range of from 700 to 1150 °C. During sintering, decomposition of the structure of silicates, aluminosilicates or phosphates occurs, and that leads to formation of insoluble compounds of alkali metals, separation of anion parts into an insoluble form or binding of the anion parts of alkali metal compounds on insoluble silicates, aluminosilicates or phosphates. The resulting sinters are water leached. Some sinters disintegrate when getting into contact with water when they are still hot. Some sinters disintegrate before leaching when exposed to air. For some sinters, milling is needed before leaching. In Czechoslovakia from 1958 to 1967, sintering zinnwaldite concentrate from Cinovec area with K ₂ SO ₄ in a rotary furnace took place at the industrial scale. Li extraction was low, at around 55 %. Besides Li, no other alkali metals were recovered. Therefore, the production was terminated in 1967. There is a known method, according to a patent document which describes sintering zinnwaldite with sintering agents and subsequent aqueous leaching of the sinters in order to increase the yield of Li, Rb and Cs in the leaching liquors. The patent document CN103979809 describes a method of utilizing leaching residues after Li recovery from lepidolite sinters as a constituent in production of white Portland cement, by milling the leaching residues together with white Portland clinker, gypsum and lime. This method provides utilization of otherwise hardly utilizable waste products after recovery of Li and other alkali metals from silicate minerals. This way to utilize waste is not feasible under current legislation in force in the EU.

Both high pressure autoclave leaching methods and sintering methods require high investment and operational expenditure. Besides high energy demands, the disadvantages of sintering methods are production of large emission of C0 ₂ and of solid inert hard-to-utilize leaching residue. For these reasons only lithium-rich minerals like pollucite, spodumene and amblygonite ores are processed on the industrial scale. The currently known methods are not economical and efficient for processing low grade silicate ores such as zinnwaldite, polylithionite, lithionite, Li-muscovite and other ores. The newest methods appear to be leaching and sintering methods in combination with mechanochemical activation. Especially leaching processes in acidic media using those methods have achieved considerable progress that allows leaching without complicated and expensive autoclaves and dissolution can occur in mixing tanks at the atmospheric pressure and at a temperature below the boiling point of water. Eventually processes involving milling simultaneously with leaching silicate minerals were tested. The method requires high energy and acid-resistant materials for the system of mill-reactors in which leaching is performed. These processes proceed slowly and generate a considerable amount of hard-to-utilize wastes, similar to those from high- pressure leaching.

Currently brines are the world's main resource from which lithium is obtained mainly by precipitation, solvent extraction and ion-exchange methods. From other resources only lithium-rich source rocks, especially spodumene and amblygonite concentrates obtained from mining and processing bigger pegmatite bodies, can compete with brines due to high energy demands for extraction using traditional known methods. However, pegmatite mines are usually not large. Besides the brines, the biggest sources of lithium and other alkali metals are mainly large accumulations of greisen and lithium bearing granites, such as zinnwaldite, polylithionite and Li muscovite.

The patent US2627452 describes a process of sintering a mixture of spodumene, calcium carbonate, and eventually sand and calcium chloride at an unspecified ratio, at temperature from 1100 °C to 1200 °C, which leads to volatilization of lithium chloride and its separation from the Portland clinker. This patent has several major disadvantages. The first disadvantage is that at temperatures in the described interval, a good Portland clinker with required properties according to current standards is not formed, but a mixture of quicklime and clinker minerals with dominantly dicalcium silicates without glassy phase and additional common minerals of Portland clinker is formed instead. The high content of quicklime also entirely disqualifies a solid sinter after sintering according to patent US2627452 as a main source for production of building materials. The reason is that temperature from 1100 °C to 1200 °C is too low for formation of Portland clinkers. Another disadvantage is that low temperature leads to evaporation of a significant portion of lithium, but of only a small portion of chlorides of other alkali metals, especially potassium, which remains in the sinters and depreciates their useful properties as binders. Further, a low efficiency of recovering chlorides of alkali metals with high boiling points makes this process unsuitable for processing zinnwaldite and other mica minerals with high content of K, Rb and Cs. The invention also does not take into account the possibility of feeding chlorine into the furnace in other form than CaCl ₂ , especially as chlorine gas or chlorine from fuels, which contain chlorinated organic compounds, such as PVC, chloroprene rubber and others. In addition, this patent does not deal with the possibility of utilization of calcareous rocks with low content of CaC0 ₃ , for example clay limestone and marl. This aspect is very important, because lithium rich sources are not always located close to sources of sufficiently pure limestone. Another patent US 1202327 describes a possibility of recovering alkali metal compounds during production of Portland clinker, using fuels containing sulfur in the presence of water steam in the calcination zone of the furnace. This invention is not practical due to the formation of hydrated and very sticky salts of alkali metals, which complicates the subsequent processing of the salts. The patent US2776202 deals with decreasing of the temperature from the interval between 1100 °C and 1200°C to the interval between 850 °C and 1000 °C for sintering petalite and spodumene together with limestone by adding lepidolite with increased fluorine content. However, alkali metals are not separated from the obtained clinkers by volatilization but by water leaching. The technical solutions according to the patents US3024082 and US3024083 for recovering chlorides of Li and of other alkali metals are probably the closest solutions to the invention proposed in this patent application. The solutions deal with recovering Li and optionally other alkali metals only from spodumene, and not from phyllosilicate minerals, as the by-products from clinker production when the use of precalcination of the raw mixture is required. The ratio between individual components of the raw materials mixture is not specified. It is evident that only Portland clinker is considered in the proposed process but possibilities of recovering compounds of alkali metals from sintering calcium-poor minerals to obtain basic or acidic slag are not considered. The temperature range, during which the volatilization of chlorides of alkali metals takes place, is specified only in the latter patent. Only calcium chloride is used as a source of chlorine for extraction of alkali metals in these patents. Possibilities of processing minerals other than spodumene are not considered. The patents do not offer possibility of selective recovery of individual alkali metals or recuperation of thermal heat from condensation of alkali metal chlorides. The patents do not take into account the influence of fluorine on decreasing sintering temperature for clinkers or slag melt or on phase composition of clinkers. The patent US3087782 describes possibilities of volatilization of Li and other alkali metals from lithium bearing ores at a high temperature under vacuum. The patent has the same drawbacks as the two previous patents. The patent US4285194 describes a solution for recovering Li adsorbed on a clay mineral, also a type of phyllosilicate, by sintering the mineral with CaO or CaC0 ₃ in the presence of H ₂ 0-HC1 vapours at temperature range of from 450 °C to 950 °C. Besides the same drawbacks as in patents US 3024082, US 3024083 a US 3087782, the patent has an additional disadvantage that the obtained sinter is not utilizable in building industry, because at the given temperature range and with the given chemical composition a full-value material, such as Portland clinker or hydraulic or air lime, cannot be formed.

There is a known method for recovering alkali metals from silicate minerals which is based on addition of silicate minerals containing alkali metals, as a corrector, to limestone in order to prepare a mixture for burning Portland clinker. During burning of solid alternative fuels in a conventional cement rotary kiln, equipped with a chloride by-pass, Cl ₂ is formed and reacts with alkalis in the cement mixture to form chlorides which preferably go to the chloride by-pass as a chloride by-pass dust together with some dust sucked from the kiln. There are very similar known methods for production of Portland clinkers with low content of alkali metals and simultaneous recovery of alkali metals. The conventional chloride by-pass systems do not have a sufficient capacity for efficiently processing larger quantities of raw materials containing alkali metals, including lithium, and allow processing only relatively small quantities of those raw materials. Adding larger quantities of the raw material as a corrector leads to high losses of alkali metals into cement clinkers and at the same time to degradation of clinkers due to disproportionately high contents of alkali metals in the clinker. There is a number of known documents which address the production of low alkali clinkers with simultaneous recovery of alkali metals or deal with Li recovery from silicate ores by the volatilization method (CN 101607796 A; CN 201530782 U; GB 891784A; GB 804962 A). None of the above listed documents addresses directly the issues related to processing of phyllosilicate ores with low Li content and low content of other alkali metals, and to highly effective recovery of rare alkali metals when processing larger quantities of low-grade lithium silicate ores at a low ratio between calcium and silicon/aluminum. The documents do not address the influence of fluorine on sintering or melting temperature as well as the phase composition of clinkers. None of the above listed patents or patent applications address issues related to selectively recovering individual alkali metals contained in fractions of gas phases from the kiln space. At the same time, the listed documents do not address the loss of thermal heat, which can be essential for the process economics. In the case of valuable alkali metals such as Li and Rb, their loss is significant and the above listed methods are less efficient for the recovery of these metals. In addition, there are losses of alkali metals which partially pass into the clinker, and the manner of condensation of gas emissions containing volatilized compounds of alkali metals is also not adequate. Cooling is achieved in a mixing chamber by suction of cold air from the outside atmosphere. This leads to significant loss of heat, which is not fully utilizable for preheating and especially for precalcination of the raw materials mixture containing CaC0 ₃ . The patent US 7265254 addresses a method of utilization of wastes with high chlorine content even when the whole system contains a small amount of alkaline earth metals. In this case, the alkali metals pass into glass phase to a large extent, because the mixture does not contain the necessary minimal quantities of Ca or other alkaline earth metals. In order to eliminate the drawbacks of the above mentioned methods of recovering alkali metals, especially from low-grade lithium silicate ores, an energetically and environmentally friendly solution for the recovery of alkali metals from low grade phyllosilicate ores was developed as described below.

Disclosure of the invention

The object of the invention is a method for recovering lithium compounds and optionally further alkali metal compounds, wherein a mineral from the group of phyllosilicates containing lithium and optionally further alkali metals as well as at least 0.2 wt. %, preferably at least 0.9 wt. %, of fluorine, undergoes a thermal treatment in a furnace at a temperature within the range of from 1100 °C to 1700 °C, preferably at a temperature within the range of from 1220 °C to 1700 °C, at a pressure within the range of from 20 KPa to 150 kPa for a period of 15 to 360 minutes, in the presence of a reagent which contains a) at least one substance from a group comprising carbonates, oxides, hydroxides, sulfates, sulfites and chlorides of alkaline earth metals, preferably of calcium; and b) at least one substance capable of releasing chlorine and/or hydrogen chloride and/or sulfur trioxide and/or sulfur dioxide during the thermal treatment, wherein the molar ratio of the total amount of sulfur trioxide and/or sulfur dioxide expressed as S0 ₃ and/or of chlorine and/or hydrogen chloride expressed as Cl ₂ to the total amount of alkali metals including lithium , released from the silicate mineral in the reaction space of the furnace, is at least 0.5; the content of alkaline earth metals, preferably of calcium, expressed as their oxide content, in the mixture of the phyllosilicate mineral with the reagent is at least 20 wt. %, and the fluorine content in the mixture of the phyllosilicate mineral with the reagent is from 0.1 to 2 wt. %, preferably from 0.2 to 2 wt. %, for decomposition of the structure of the phyllosilicate mineral and volatilization of lithium compounds and optionally of further alkali metal compounds from the thermally treated phyllosilicate mineral; the compounds of lithium and optionally of further alkali metals are subsequently recovered by condensation by drawing off from one or more different places with different temperatures within the internal space of the furnace from 50 to 100 vol. % of flue gases formed in the furnace , wherein the rate and volume of the drawn-off flue gases from different places can be different for the selective recovery of compounds of individual alkali metals or their groups.

Preferably, the weight ratio of the total amount of alkaline earth metal oxides, in particular calcium oxide, to Si0 ₂ in the mixture of the silicate mineral with the reagent is at least 1.

Preferably, the weight ratio of the total amount of alkaline earth metal oxides, in particular calcium oxide, to the total amount of Si0 ₂ , A1 ₂ 0 ₃ and Fe ₂ 0 ₃ in the mixture of the silicate mineral with the reagent is equal to at least 1.7.

Preferably, the mineral from the group of phyllosilicates containing Li and optionally further alkali metals, alone or with the reagent or with at least one substance contained in the reagent, is subjected before the thermal treatment to a mechanochemical activation in a high-speed countercurrent two- rotor mill at a rotating circumferential rotor speed of at least 180 m.s \

Preferably, the mineral from the group of phyllosilicates containing Li and optionally further alkali metals is continuously or periodically stirred during the thermal treatment in the presence of the reagent. Preferably, the mineral from the group of phyllosilicates containing Li and optionally further alkali metals alone or with the reagent or with at least one substance from the group containing carbonates, oxides, hydroxides, sulfates and sulfites is subjected to a thermal pretreatment at a temperature within the range of from 700 °C to 1000 °C, leading to dehydroxylation of the phyllosilicate mineral and to dehydration and/or decarbonization of substances in the reagent.

Preferably, a raw materials mixture containing at least the phyllosilicate and a component a) of the reagent, optionally also a component b) of the reagent is subjected to milling in a high-speed countercurrent mill before the thermal treatment. Milling in the high-speed countercurrent mill has several advantages over other milling methods, such as acceleration of the reactions due to prevention of formation of aggregates. Aggregates can be formed in other milling methods for example due to hygroscopicity of some components (e.g. CaCl ₂ ), and the countercurrent mill usually also helps to remove water from the milled mixture.

In some embodiments of the invention, the substance capable of releasing chlorine and/or hydrogen chloride during the thermal treatment may be chlorinated organic compounds, such as chlorinated polymers (for example polyvinylchloride, polychloroprene), polychlorinated biphenyls, or halogenated oils. These compounds can be burnt as alternative fuels and their emissions contain chlorine and/or hydrogen chloride. Utilization of these flue gasses, which would otherwise need to be removed, in an industrial process and chlorine fixation are very desirable from the economic and environmental point of view. Preferably, from each place in a furnacefrom which the flue gasses are drawn off, the flue gasses are drawn off to a separate air-cooled condenser/heat exchanger system, in which the flue gasses are cooled to a temperature within the range of 100 °C to 900 °C, leading to condensation of volatile alkali metal compounds contained in the flue gasses. The condensed alkali metals compounds are removed from the condenser mechanically and/or pneumatically and/or hydraulically, wherein the air heated in the condenserheat exchanger is used as a heating air for the thermal pre -treatment of the phyllosilicate mineral containing lithium and optionally further alkali metals, alone or together with the reagent or together with at least one substance from the group containing carbonates, oxides, hydroxides, sulfates and sulfites at a temperature within the range of from 700 °C to 1000 °C; and/or the preheated air is used as a heating air for the thermal treatment of the phyllosilicate mineral together with the reagent in the furnace at a temperature within the range of from 1100 °C to 1700 °C, preferably at a temperature within the range of from 1220 °C to 1700 °C and/or for other technological operations. These technological operations may include solution concentration, evaporation, drying and heating. Preferably, a solution of at least one substance from the group of chlorides, sulfates and sulfites of alkaline earth metals, in particular of Ca, is added to the mixture of the phyllosilicate mineral with at least one substance from the group containing carbonates, oxides and hydroxides of alkaline earth metals, in particular of Ca, before the thermal treatment; or the said mixture is treated with at least one inorganic acid, in particular selected from a group comprising hydrochloric acid, sulfuric acid and sulfurous acid, or with a solution thereof; and subsequently the mixture is homogenized, dried, deagglomerated and/or milled to the particle size smaller than 50 μπι for increasing the quality of homogenization of the mixture of the phyllosilicate mineral with substances of the reagent and for increasing the effectiveness of the subsequent thermal treatment. Alkali metals including lithium, are recovered in particular in the form of halides, for example chlorides, fluorides, or in the form of sulfates or double salts, such as sulfate/aluminates, halide/aluminates (for examples chloride/aluminates).

Alkali metals shall be understood as including in particular lithium, rubidium, cesium, sodium, potassium.

Alkaline earth metals shall be understood as including in particular magnesium, calcium. Phyllosilicates or layered silicates are a group of silicate minerals composed of flat layers of shared three-atom or four-atom molecules of Si0 ₄ of tetrahedral form. Most phyllosilicates have a platelet or leaf-like habitus (according to the direction of cleavage they are mostly thin scales or leaves) with perfect fragmentation, due to the presence of endless networks in the structure, including Si tetrahedra. The individual nets are then bound into layers by relatively weak forces. The interconnection between network layered complexes may be different - either weak electrostatic forces connected by the presence of (OH) groups, or so-called interlayer cations (usually Na, K, Ca, Mg, Rb, Li) may be located between network complexes.

According to Strunz's mineralogical classification, the phyllosilicates form the Class VIII / H. The phyllosilicates suitable for use in the method of the present invention belong in particular to mineral groups:

- group of clay minerals. In this group, the main mineral with industrial content of Li is hectorite Na _0j3 (Mg, Li) ₃ Si ₄ O ₁₀ (OH) ₂ ; however other minerals such as illite contain a high amount of K and

Rb, or montmorillonite may adsorb lithium;

- mica group which includes a variety of minerals with Li content of from about 0.4 wt. %, for example up to about 4 wt. % Li, such as lepidolite, zinnwaldite, polylithionite, trilithionite, protolithionite, Li-muskovite, Li-biotite;

- group of chlorites, in particular cookeite, borocookeite and manandonite.

The invention is based on the finding that during thermal treatment in an oxidative medium in the presence of a reagent containing alkaline earth metals, especially calcium, and also substances capable of releasing volatile gasses such as Cl ₂ , S0 ₃ and others, which may include certain types of alternative fuels, the structure of phyllosilicate minerals containing the groups (F,OH), for example zinnwaldite (KLiFe^ ⁺ Al(AlSi3)Oio(F,OH)2), decomposes. The decomposition of the phyllosilicate mineral takes place so that at first F and OH bound in the group (F,OH) are released, meanwhile oxidation of Fe ²⁺ to Fe ³⁺ and a release of one molecule of H ₂ 0 occurs, and subsequently a molecule of HF is formed. Further, in the presence of alkaline earth metal compounds, especially calcium compounds, a further destruction of the structure of the phyllosilicate occurs so that the residual amount of Si and Al reacts with the alkaline earth metal. Due to these reactions, oxides of lithium and of further alkali metals are formed. The oxides alone are not capable of being volatilized at temperatures below 1700 °C. But in the temperature range typically from 800 °C to 1000 °C, the oxides react with chlorine or S0 ₃ to form salts that are capable of being volatilized within the temperature range of from 1100 °C to 1670 °C. Unlike the previously known methods, the method of the present invention has several fundamental differences and it is based on a thermal treatment by a complete or a partial melting of the silicate mineral, during which the formation of chlorides and/or sulfates of lithium and further alkali metals and subsequent complete volatilization occur, depending on pressure/temperature conditions, the residence time of the phyllosilicate mineral containing lithium and optionally further alkali metals inside the furnace, and also on the heating rate of the raw materials mixture entering the furnace. At the same time, formation of a glassy phase occurs. This method also envisages that the phyllosilicate minerals with Li content contain an increased amount of fluorine, which leads to decreasing the temperature needed for the formation of glassy phase during the thermal treatment, often by more than 100 °C to 200 °C. At the same time, chlorides and sulfates of alkali metals are easily released from the glassy phase at lower temperatures due to its decreased viscosity, in comparison to processing minerals without fluorine content. Depending on the ratio Ca:Si, i.e., on the saturation of the system by calcium, the temperature and the duration of thermal treatment, the residue after the recovery of Li and optionally further alkali metals has a form of acidic, basic or ultrabasic glassy phase, optionally with varying percentages of crystalline phases of clinker minerals, especially belite, sulfobelite, alite and others. At the same time, the fluorine present in the system enters at the temperature range of from 1100 °C to 1300 °C several reactions, during which the formation of CaF ₂ , fluorosilicate and fluoroaluminate minerals takes place at varying degrees. At higher temperatures, where a melt is formed to a greater extent, fluorine reacts with the residual alkali metals and is volatilized together with them. This simultaneously affects the phase equilibrium between tricalcium silicate, alite, dicalcium silicate, belite and the melt, because by this way Si enters the melt. Therefore, more tricalcium silicate and more acidic melts are formed at the expense of the dicalcium silicate phase. At lower temperatures or higher pressures, mixtures of the glassy phase with clinker minerals are formed, but their content can be lower than that in the common Portland clinker. Therefore, the method of recovering lithium according to this invention is energetically and environmentally very efficient, because it requires only a small volume of raw materials, or raw materials of lower quality with lower CaO content and it also produces a smaller volume of C0 ₂ emissions, compared to the previously known methods. An additional fundamental difference is that unlike the conventional cement technology, 50 to 100% of flue gases are drawn off from the furnace space into an apparatusfor condensation of alkali metals. The traditional cement technology uses the so-called cement chlorine or alkaline by-pass to reduce the content of alkalis, CI, S and other substances in production of Portland clinker. By this system 10 wt.%, exceptionally 25 wt. % of flue gases are drawn off from the furnace in places with the highest concentration of alkalis, CI and S. No bigger volume can be drawn off due to a disproportionate increase in energy losses. In comparison with this method, the use of conventional cement technology does not allow efficient recovery of, in particular, rare alkali metals. If the weight ratio of the total amount of alkaline earth metals and, in particular CaO to (Si0 ₂ + A1 ₂ 0 ₃ ) drops below 0.2, the alkali metals dissolve in the glass phase as oxides and cannot be efficiently released from the system even with excess CI or S0 ₃ or at temperature higher than temperature for glass fining. Solid glass residual products of the thermal treatment - melting - do not contain almost any alkali and may contain very little CaO, compared to blast furnace cements. However, as fine and very fine milled, they can be used as an analog of granular blast furnace slag and must also meet all the requirements for granular blast furnace slag, especially a minimum glassy content of at least 2/3 and a minimum CaO: Si0 ₂ weight ratio of at least 1. This material also has to meet a number of other requirements given by the standard for granular blast furnace slag. The formation of the analogue of granular blast furnace slag takes place at temperatures usually above 1500 °C, but at lower pressures and with a suitable composition of the raw material mixture, in particular with an increased content of fluorine, the transition to viscous state may occur at temperatures several hundred degrees lower. In addition to the advantages of low energy costs associated with a small amount of dissociated CaC0 ₃ and low carbon footprint, this composition generates a very low hydration heat and has a very low alkali content. At the ratio CaO:Si0 ₂ below 1, so-called acidic slags are formed. They have an advantage in that they crystallize slowly and can be cooled off only by air in order to maintain the absolute dominance of the glass phase. After fine grinding, they can be used as high quality pozzolans for the preparation of pozzolanic or mixed cements. Accordingly, the solid products of this treatment are suitable for use as binders or binder components for significantly limiting the risk of alkaline reaction of the aggregate. For the preparation of hydraulic binders based on solid residual products after obtaining the Li and further alkali metals according to the invention, the use of mechanochemical activation is suitable.

Another major advantage of the solution according to the present invention is the possibility of selectively drawing off the gaseous products from different locations in the furnace at different temperatures which allows to a large extent a selective recovery of individual alkali metals or their compounds, or individual fractions of volatile compounds enriched always with one compounds of a certain alkali metal, respectively. The solution according to the present invention also envisages the possibility of heat recovery/recuperation during the condensation of the volatile alkali metal compounds which can be condensed in an air-cooled heatexchanger recuperation systems. The cooling air is heated and the heat that has been removed from the furnace together with the flue gases may enter the pre-heating treatment process of the raw material mixture in the precalciner independently or as the combustion air for the precalciner or furnace in which sintering or melting is carried out. Alternatively, this heat can be used for other technological operations, but unlike other solutions, it is utilized, and that positively contributes to the economy of the process of recovering Li and other alkali metals. The invention is further explained in the examples which should not be construed as limiting the scope of the invention.

Examples of carrying out the invention

Example 1

A raw material mixture in the ratio shown in Table 1 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, zinnwaldite concentrate from the deposit Cinovec and CaCl ₂ . The mixture is ground in a high-speed counter mill at a circumferential speed of 210 ms ¹ to the medium grain size of less than 50 μπι. It is then subjected to a particle size enlargement to 7 mm and melting in an internally heated shaft furnace at 1350 °C for 30 minutes. During the melting in the furnace, chlorides and other compounds of alkali metals are released. The furnace pressure is maintained at ~ 90 kPa. All hot flue gas carrying volatile compounds is drawn off from the furnace into a regenerative condenser in which the extracted alkali metal salts are obtained from the hot gas. The resulting mixture contains 75% of Li, 90% of K and 95% of Rb from the original batch. At the same time, due to the appropriate composition of the raw material mixture and the high content of F, a basic melt is formed, almost free of chlorine, sulfur and alkali metals, which is fast-cooled by an air flow to a temperature below 400 °C, followed by additional cooling down to a temperature below 100° C, to form a basic granular slag with a CaO: Si0 ₂ ratio of 1.02 and a (CaO + Si0 ₂ ) /(A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) ratio of 3.46. The slag can be used to produce hydraulic binders as a granular blast furnace slag analogue. The heated air from the melt cooling and from the regenerative condenser is used as combustion air for heating the shaft furnace.

Table 1 - Composition of the raw material mixture for preparation of basic granular slag in a shaft furnace

Example 2

A raw material mixture in the ratio shown in Table 2 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC and zinnwaldite concentrate from the deposit Cinovec. The mixture is ground in a high-speed counter mill at a circumferential rotor speed of 210 m.s ¹ to the average grain size of less than 30 μπι, then the ground mixture is at first calcined in a cyclone pre-calciner for about 12 seconds at a temperature of 920 °C. Due to the high content of F, this prepared mixture is melted in a rotary kiln (furnace) at a temperature of 1350 °C for 40 min to form a melt virtually free of CI, S and alkali metals. The fuel used in the rotary kiln contains 114 kg of CI per 1 tone of zinnwaldite concentrate. After rapidly cooling in air flow to a temperature below 400 °C, followed by cooling in the water spray to temperature below 100 °C, the melt with the CaO:Si0 ₂ ratio = 1.015 and the ratio of (CaO + Si0 ₂ )/(A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) = 3.51 is usable for the production of hydraulic binders as an analogue of granular blast furnace slag. The heated air from the melt cooling is used as combustion air for heating the rotary kiln. The furnace pressure is maintained at -110 kPa. All hot flue gas is drawn off from the furnace into a condenser/heatexchanger in which volatile alkali metal chlorides are obtained from the hot gas. The obtained mixture contains 85% of Li, 92% of K and 97% of Rb from the original batch. The air heated in the condenser/heat exchanger is used as calcination and combustion air in the calciner. To obtain lithium chloride-enriched gaseous fractions, a portion of the flue gases is drawn off at approximately 25% of their total volume at a distance of 7 m from the start of the rotary kiln. The rest of the flue gases are drawn off above the input ports for the raw material mixture at the start of the rotary kiln.

Table 2 - Composition of the raw material mixture for preparation of basic granular slag in a rotary furnace

Example 3

A raw material mixture in the ratio shown in Table 3 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, zinnwaldite concentrate from the deposit Cinovec and CaCl ₂ . The mixture is ground in a high-speed two-rotor counter mill at a circumferential speed of 210 m.s ¹ to an average grain size of less than 50 μπι and then subjected to a heat treatment consisting of calcination in a pre-calcination cyclone apparatus for approx. 10 seconds at temperature of about 950 °C and subsequently melted in a shaft furnace at 1420 °C for 30 minutes. During melting in the furnace volatilization of alkali metal salts occurs. The furnace pressure is maintained at ~ 90 kPa. All hot flue gas is drawn off above the melt surface from the furnace to acondenser/heat exchanger, in which alkali metal chlorides contained in the hot gas are recovered. At the same time, the melt, free of halogen elements, sulfur and alkali metals with the CaO: Si0 ₂ ratio = 1.296 and the (CaO + Si0 ₂ )/ (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) ratio = 3.895, is formed. After rapid cooling of the melt in an air flow to a temperature below 400 °C and subsequent cooling by a water spray to a temperature below 100 °C, the product is usable for the production of mineral fibers or hydraulic binders as an analogue of granular blast furnace slag. The obtained mixture contains 90% of Li, 95% of K and 95% of Rb from the original batch. The heated air from the melt cooling is used as the primary combustion air for heating the shaft furnace. The heated air from the condenser/heat exchanger is used as secondary combustion air. Table 3 - Composition of the raw material mixture for preparation of basic granular slag in a shaft furnace with internal heating

Example 4

A raw material mixture in the ratio shown in Table 4 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC and zinnwaldite concentrate from the deposit Cinovec. The mixture is milled in a high speed two-rotor counter-rotating mill at a rate of 220 m.s ¹ to an average particle size of less than 50 microns. The milled product is further subjected to preheating and calcination in a cyclone-type precalciner for 10 s and subsequently melted in a rotary furnace (kiln) with a diameter to length ratio 1 : 15. Due to the increased content of F melting takes place only at 1420 °C in the hottest furnace zone, at pressure of 110 kPa and the furnace passage time of 38 min. During the heat treatment in the rotary kiln, a solid alternative fuel containing 114 kg of CI per 1 tone of zinnwaldite concentrate is used as a part of the fuel. During sintering and subsequent melting, alkali metal chlorides are formed, volatilized and drawn off from the furnace. At the same time, a melt, free of halogen elements, sulfur and alkali metals with the CaO: Si0 ₂ ratio = 1.1 and the (CaO + Si0 ₂ )/ (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) ratio = 3.67, is formed. After rapid cooling of the melt in an air flow to a temperature below 400 °C and subsequent cooling by a water spray to a temperature below 100 °C, the product is usable for the production of hydraulic binders as an analogue of granular blast furnace slag. The heated air from the melt cooling is used as the primary combustion air for heating the shaft furnace. The heated air from the condenser/heat exchanger is used as combustion and calcination air for the pre-calciner. The condensed mixture obtained contains 91% of Li, 94% of K and 96% of Rb from the original batch.

Table 4 - Raw material mixture for the production of melt for the production of granular slag

Example 5

A raw material mixture in the ratio shown in Table 5 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, zinnwaldite concentrate from the deposit Cinovec and CaCl ₂ . The mixture is milled in a high-speed mill at a rotation speed of 200 m.s ¹ to an average grain size of less than 70 μπι and melted at 1500 °C for 20 minutes in a continuous bathtub furnace with four parallel series of passes. During melting, compounds, mainly alkali metal chlorides, are formed, volatilized from the sintering mixture and drawn off from the furnace through the passes. The furnace pressure is maintained at 90 kPa. Flue gases removed from the furnace by the passes are discharged to a condenser/heat exchanger where condensation of volatile alkali metal compounds occurs. The flue gases removed from the furnace through the third and fourth series of passes do not contain lithium chlorides. At the same time, a melt free of halogen elements, sulfur and alkali metals, in which the CaO: Si0 ₂ ratio = 1.2 and the ratio of (CaO + Si0 ₂ ) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) = 3.67, is formed. The melt, which is rapidly cooled by air in a fluid cooler to a temperature below 200 °C, is usable for the production of hydraulic binders as an analogue of granular blast furnace slag. The heated air from the melt cooling from the condenser/heat exchanger is used as the primary combustion air for heating the bath furnace. The condensed mixture obtained contains 85% of Li, 90% of K and 92% of Rb from the original batch.

Table 5 - Raw material mixture for the preparation of a melt for the production of mineral fibers or granular slag

Example 6

A raw material mixture in the ratio shown in Table 6 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, zinnwaldite concentrate from the deposit Cinovec and calcium chloride. The mixture is milled in a high speed two-rotor counter-rotating mill to an average particle size of less than 30 μπι. The milled product is further subjected to preheating and calcination in a precalciner at the temperature of 890 °C and subsequently melted in a rotary furnace with a diameter to length ratio 1 : 17. Due to the appropriate composition and the increased content of F, the melting occurs only at 1340 °C in the hottest furnace zone, at the furnace passage time of 45 min. The furnace pressure is maintained at 110 kPa. During sintering and subsequent melting, the decomposition of zinnwaldite and calcium chloride occurs, alkali metal chlorides are formed, volatilized and drawn off from the furnace space. The drawing-off is carried out in such a way that first 10% of the volume of flue gas is drawn off from the space located 10 m from the beginning of the kiln, the other 15% is drawn off from the space located 5 m distant from the beginning of the rotary kiln and the rest of the gas is drawn off at the beginning of the rotary kiln. All gases are fed to condenser heat exchangers. The condensed mixture obtained from the first drawing-off stage contains 70% of Li, 3% of K from the original batch. The condensed mixture obtained from the second extraction stage contains 5% of Li, 80% of K and 88% of Rb from the original batch. The condensed mixture obtained immediately from the beginning of the rotary kiln contains 1 % of Li, 3% of K and 4% of Rb from the original batch. At the same time, a melt, free of halogen elements, sulfur and alkali metals, with the ratio CaO: Si0 ₂ = 0.4 and the ratio of (CaO + Si0 ₂ ) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) = 2.2, is formed in the furnace. The melt is rapidly cooled in an air flow to a temperature below 100 °C. The obtained product is usable for the production of glassy acid slag, which after milling can be used as pozzolanic additives to hydraulic binders for reducing the risk of alkaline reaction of aggregates. The heated air from the melt cooling is used as the primary combustion air for heating the furnace. The heated air of the feeder condenser is used as combustion and calcination air for the precalciner.

Table 6 - Raw material mixture for the preparation of acidic glassy slag, usable as a pozzolanic additive in hydraulic binders, e.g. for reducing the risk of alkaline reaction of aggregates

Example 7

A raw material mixture in the ratio shown in Table 7 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, pure limestone from the deposit Certovy schody, zinnwaldite concentrate from the deposit Cinovec and calcium chloride. The mixture is milled in a high speed two-rotor counter-rotating mill to an average particle size of less than 30 μπι. The milled product is further subjected to preheating and calcination in a precalciner at temperature of 890°C and subsequently melted in a rotary kiln (furnace) with a diameter to length ratio 1: 17. Due to the appropriate composition and the increased content of F, sintering takes place only at 1400 °C in the hottest furnace zone at the furnace passage time of 50 min. During sintering the decomposition of zinnwaldite and calcium chloride occurs, alkali metal chlorides are formed, volatilized and drawn off from the furnace space. The furnace pressure is maintained at 110 kPa. The drawing-off is carried out in such a way that first 10% of the volume of flue gas is drawn off from the space located 10 m from the beginning of the kiln, the other 15 % is sucked from the space located 5 m distant from the beginning of the rotary kiln and the rest of the gas is drawn off at the beginning of the rotary kiln. All gases are fed to condenser/heat exchangers. The condensed mixture obtained from the first drawing-off stage contains 75 % of Li, 5 % of K from the original batch. The condensed mixture obtained from the second extraction stage contains 10 % of Li, 85 % of K and 90% of Rb from the original batch. The condensed mixture obtained immediately from the beginning of the rotary kiln contains 1 % of Li, 5 % of K and 7 % of Rb from the original batch. At the same time, an alitic Portland clinker, free of halogen elements, sulfur and alkali metals, with the ratio CaO: Si0 ₂ = 3.091 and the ratio of (CaO) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ + Si0 ₂ ) = 2.042, is formed in the furnace. The clinker is rapidly cooled in an air flow to a temperature below 200 °C. The obtained product is usable for the production of Portland cement and other hydraulic binders. The heated air from the melt cooling is used as the primary combustion air for heating the shaft furnace. The heated air of the feeder condenser is used as combustion and calcination air for the precalciner.

Table 7 - Composition of the raw material mixture for sintering in a rotary kiln for the production of alithic Portland clinker

Example 8

A raw material mixture in the ratio shown in Table 8 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, pure limestone from the deposit Certovy schody and zinnwaldite concentrate from the deposit Cinovec. The mixture is milled in a high speed two-rotor counter-rotating mill at the at the circumferential speed of 210 m.s ¹ to an average particle size of less than 30 μπι. The milled product is further subjected to preheating and calcination in a precalciner at temperature of 890°C and subsequently melted in a rotary kiln (furnace) with a diameter to length ratio 1 :17. Due to the appropriate composition and the increased content of F sintering takes place only at 1400 °C in the hottest furnace zone at the furnace passage time of 40 min. The furnace pressure is maintained at 110 kPa. With a fuel with a content of 128 kg of CI to 1 t of the zinnwaldite concentrate, which is used to heat the rotary kiln, zinnwalidte is decomposed, HC1 and CI are released from the fuel. Calcium and alkali metal chlorides are formed, volatilized and drawn off from the furnace. All gases are fed to a condenser/heat exchanger. The mixture of alkali metal compounds and other compounds in this apparatus is further processed by known methods. At the same time, an alite-belitic Portland clinker, free of halogen elements, sulfur and alkali metals, with the ratio CaO: Si0 ₂ = 2.56 and the ratio of (CaO) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ + Si0 ₂ ) = 1.7, is formed in the furnace. The clinker is rapidly cooled in an air flow to a temperature below 200 °C. The obtained product is usable for the production of Portland cements and other hydraulic binders. The clinker together with the additives is ground in a shearing roller mill to achieve a grain size of less than 0.3 mm and subsequently in a high-speed, counter-rotating two-rotor mill to achieve the grain size below 50 μπι. The heated air from the clinker cooling is used as the primary combustion air for heating the rotary kiln and partly for the precalciner. The heated air from the condenser/heat exchanger is used as combustion and calcination air for the precalciner. The obtained condensed mixture contains 85 % of Li, 90 % of K and 91 % of Rb from the original batch.

Table 8 - Composition of the raw material mixture for sintering in a rotary kiln for the production of allitic - bellitic clinker

Example 9

A raw material mixture in the ratio shown in Table 9 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, pure limestone from the deposit Certovy schody, zinnwaldite concentrate from the deposit Cinovec and gypsum from the semi-dry flue gas desulfurization method. The mixture is milled in a high speed two-rotor counter-rotating mill at the at the circumferential speed of 240 m.s ¹ to an average particle size less than 30 μπι. The milled product is further subjected to preheating and calcination in a precalciner at temperature of 890°C and subsequently sintered in a rotary kiln (furnace) with a diameter to length ratio 1 : 17. Due to the appropriate composition and the increased content of F sintering takes place only at 1340 °C in the hottest furnace zone at the furnace passage time of 50 min. The furnace pressure is maintained at 110 kPa. All gases are fed to acondenser/heat exchanger. The mixture of alkali metal sulfate and other compounds in this apparatus is further processed by known methods. At the same time, a sulfo-belitic Portland clinker, free of halogen elements, sulfur and alkali metals, with the ratio CaO: Si0 ₂ = 2.56 and the ratio (CaO) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ + Si0 ₂ ) = 1.55, is formed in the furnace. The clinker is rapidly cooled in an air flow to a temperature below 200 °C. The obtained product is usable for the production of Portland cements and other hydraulic binders. The clinker together with the additives is ground in a shearing cylindrical mill to achieve a grain size of less than 0.3 mm and subsequently in a high-speed, counter-rotating two-rotor mill at a circumferential speed of 230 m.s ¹ to achieve a grain size below 10 μπι. The heated air from the clinker cooling is used as the primary combustion air for heating the rotary kiln and partly for the precalciner. The heated air from the condenser/heat exchanger is used as combustion and calcination air for the precalciner. The obtained condensed mixture contains 89 % of Li, 92 % of K and 94 % of Rb from the original batch.

Table 9 - Composition of the raw material mixture for sintering in a rotary kiln for the production of allitic - bellitic clinker

Example 10

A raw material mixture in the ratio shown in Table 10 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, pure limestone from the deposit Certovy schody, a Li-Fe muscovite concentrate from the deposit Krasno and calcium fluoride. The mixture is milled in a ball mill to achieve the average grain size of less than 30 μπι and further subjected to preheating and calcination in a cyclone pre-calciner at 900 °C for 10 seconds and then sintering in a rotary kiln (furnace)with the internal diameter to length ratio of 1 : 17. Due to the increased content of F sintering takes place only at 1340 °C in the hottest furnace zone at the furnace passage time of 38 min under the furnace pressure of 110 kPa. A fuel with the content of 85.5 kg CI per 1 tone of the Li-Fe muscovite concentrate is used to heat the rotary kiln. During the thermal treatment, the Li-Fe muscovite decomposes, HCl and CI are released from the fuel, calcium and alkali metal chlorides are formed, volatilized and drawn off from the furnace. At the same time, an alitic-belitic Portland clinker, free of halogen elements, sulfur and alkali metals, with the ratio CaO: Si0 ₂ = 2.47 and the ratio of (CaO) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ + Si0 ₂ ) = 1.7, is formed in the furnace. The clinker is rapidly cooled in an air flow to a temperature below 200 °C. The obtained product is usable as a base for the production of hydraulic binders. The heated air from the clinker cooling is used as the primary combustion air for heating the rotary kiln and partly for the precalciner. The heated air from the condenser/heat exchanger is used as combustion and calcination air for the precalciner. The obtained condensed mixture contains 90 % of Li, 93 % of K and 95 % of Rb from the original batch.

- The composition of the feed mixture for sintering in a rotary kiln to produce a sulfobelic

Example 11

A raw material mixture in the ratio shown in Table 11 is produced by mixing calcium marl from the deposit Upohlavy of Lafarge Cement JSC, Li-Fe muscovite concentrate from the deposit Krasno and calcium fluoride. The mixture which is milled in a high-speed counter mill at a circumferential speed of 200 m.s ¹ to achieve the mean grain size of less than 50 μπι. The milled product is subjected to a thermal treatment consisting of calcination in a cyclone precalciner for about 10 seconds at temperature of about 950 ⁰ C and subsequent melting in a rotary kiln (furnace) with a ratio of internal diameter to a length of 1 : 17 at 1420 ⁰ C at the furnace passage time of 40 minutes. The furnace pressure is maintained at 110 kPa. A fuel with the content of 85.5 kg CI per 1 tone of the Li- Fe muscovite concentrate is used to heat the rotary kiln. During the thermal treatment, the Li-Fe muscovite decomposes, HCl and CI are released from the fuel, alkali metal chlorides are formed and volatilized. All hot flue gas is drawn off from the furnace into a condenser/heat exchanger in which volatilized alkali metal chlorides are obtained from the hot gas. At the same time, a melt, free of halogen elements, sulfur and alkali metals, with the ratio of CaO: Si0 ₂ = 1.06 and the ratio of (CaO+ Si0 ₂ ) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ ) = 4.48, is formed in the furnace. The melt is rapidly cooled in an air flow to a temperature below 100 °C. The obtained product is usable as an analogue of granular blast furnace slag. The heated air from the melt cooling is used as the primary combustion air for heating the rotary kiln. The heated air from the condenser/heat exchanger is used as secondary combustion air. The obtained condensed mixture contains 93 % of Li, 97 % of K and 99 % of Rb from the original batch.

Table 11 - The composition of the feed mixture for sintering in a rotary kiln to produce a sulfobelic clinker

Example 12

A raw material mixture in the ratio shown in Table 12 is produced by mixing pure limestone from the deposit Certovy schody and zinnwaldite concentrate from the deposit Cinovec. The mixture is milled in a high-speed two-rotor counter mill at a circumferential speed of 200 m-s to achieve an average grain size of less than 50 μπι. The milled product is subjected to pre-calcination in a cyclone calciner at 920 ⁰ C for 12 s. Subsequently, the pre -calcined mixture is mixed with 30 % HC1 in the ratio shown in Table 12 in order to treat the mixture with HC1 . Subsequently, the mixture is dried and subjected to deagglomeration in a two-rotor high-speed contralateral pin mill at a circumferential speed of 100 m.s \ Furthermore, the mixture is subjected to sintering in a rotating kiln (furnace) with an internal diameter to length ratio of 1 : 17. Due to a suitable composition and an increased F content of 0.71, the sintering takes place only at 1380 °C in the hottest furnace zone at the furnace passage time of 40 min. The furnace pressure is maintained at 110 kPa. All gases from the rotary kiln are fed to a condenser/heat exchanger. The obtained condensed mixture contains 92 % of Li, 93 % of Ka and 97 % of Rb from the original batch charge. The mixture of alkali metal compounds and other compounds obtained from the furnace is processed further by known methods. At the same time, an alitic-belitic Portland clinker, free of halogen elements, sulfur and alkali metals, with the ratio of CaO: Si0 ₂ = 3.07 and the ratio of (CaO) / (A1 ₂ 0 ₃ + Fe ₂ 0 ₃ + Si0 ₂ ) = 1.86, is formed in the furnace. The clinker is rapidly cooled in an air flow to a temperature below 200 °C. The obtained product is usable in the production of Portland clinkers and other hydraulic binders. The clinker, together with additives, is milled in a shear roll mill to a particle size of less than 0.3 mm, and then in a high-speed countercurrent two-rotor mill at a circumferential velocity of 220 m.s ¹ for the grain size below 40 μπι. The heated air from the clinker cooling is used as the primary combustion air for heating the rotary kiln or partly for heating the precalciner. The heated air from the condenser/heat exchanger is used as combustion and calcination air for the precalciner for drying the raw mixture after its reaction with HC1.

Table 12 - The composition of the feed mixture for sintering in a rotary kiln to produce a sulfobelic clinker