WO2024251991A1 - Device for producing lithium carbonate crystals - Google Patents

Abstract

The invention relates to a device and to a process for the continuous, controlled crystallization of metal salt crystals, in particular lithium carbonate crystals. These crystals can be produced with a high degree of homogeneity and on a large scale.

Description

Device for producing lithium carbonate crystals

The invention particularly relates to a device for the continuous and controlled crystallization of lithium carbonate, but can also be used for comparable, preferably inorganic crystals.

The device according to the invention is suitable for producing crystals with defined grain size, particle distribution and grain structure, especially of lithium carbonate, but also in particular of other metal hydroxides, metal carbonates, metal sulfates, metal nitrates, amino and carboxylic acids as well as their salts by precipitation from their aqueous solutions.

The basic principle of crystallization or precipitation of solids from an aqueous solution is to cause supersaturation of the dissolved solid in the aqueous solution in order to carry out the crystallization or precipitation process in a controlled manner by reducing the supersaturation. This can be done in various ways. For example, there is the possibility of a precipitation reaction, in which the solution of a reactant is placed in a stirred vessel and an associated precipitant is added dropwise or otherwise dosed while stirring. Ideally, the precipitated particles should have a homogeneous particle size and uniform particle structure. Even in continuous processes in which reactant and precipitant are continuously added, it is important to ensure homogeneous reaction conditions in the stirred vessel and to avoid uncontrolled crystal formation. In the case of lithium carbonate production, for example, lithium carbonate (U2CO3) can be produced by adding alkali carbonates (precipitant) to a lithium salt solution (reactant). The precipitation of lithium carbonate (U2CO3) is also possible by adding lithium salts (precipitant) to alkali carbonates (reactant). In continuous processes, lithium salt solutions and alkali carbonate salt solutions can be continuously added to a solution and/or suspension in the reaction vessel or reactor. The reaction can be controlled by increasing or decreasing the temperature and optionally by the dosing ratios.

In another precipitation reaction, lithium carbonate (U2CO3) is produced by carbonating a lithium hydroxide (LiOH) solution, ie, by introducing CO2 (g) or CO2 dissolved in water into a lithium hydroxide solution. In continuous processes, LiOH solution and CO2 (g) or CO2 dissolved in water can be continuously fed into a solution and/or suspension in the reaction vessel or reactor. The reaction can be controlled by increasing or decreasing the temperature and the rate of addition of the reactants. Another precipitation process is based on the thermally induced decomposition of lithium hydrogen carbonate (UHCO3) dissolved in water. In this process, a purified lithium hydrogen carbonate solution is decomposed by thermal exposure into CO2 (gaseous) and lithium carbonate (U2CO3) as a precipitate. A specific embodiment of this production of lithium carbonate is described, for example, in EP 2 536 663. In principle, this production of high-purity lithium carbonate can start from a lithium carbonate solution (U2CO3) (aq), which is converted into a lithium hydrogen carbonate solution by adding CO2 (g) or CO2 dissolved in water, which can be purified, for example, by ion exchange. The lithium hydrogen carbonate (aq) purified in this way can be used to crystallize high-purity lithium carbonate by thermal decomposition with release of CCh.

The method of reaction crystallization of mineral salts on a large scale is described in DD 227615 and DD 26479. The reactor or crystallizer essentially consists of a cylindrical container, possibly with a flat, curved or conical bottom, an axial stirrer with guide tube and a clarification ring for separating an annular clarification chamber from the remaining suspension-filled crystallizer contents, as well as supply and discharge elements for the solid and liquid substances. The crystallizer from DD 227615 makes it possible to continuously mix the solid and liquid starting materials, ensure the reaction process, achieve a high crystal density in the reaction chamber and thus a coarse crystallizate, which can be withdrawn from the reactor in a thickened, highly concentrated form, while the liquid reaction phases in the reactor leave clarified via an overflow. The axial stirrer leads to mixing through the suction effect of the stirrer, which starts at the upper end of the guide tube and is generated by the suction-in inclined blades of the stirrer. The stirrer conveys the suctioned suspension to the bottom of the tank and sucks it back in again after it rises up the cylindrical tank walls at the upper end of the guide tube. To ensure that no flow vortex can pass from the mixed tank parallel to the ring-shaped clarification zone ("clarification ring"), a specific flow deflection is provided by an annular installation in the form of a deflection ring with a roof-shaped cover and, if necessary, a transfer of solids separated in the clarification chamber to a central part of the reactor.

However, this apparatus has only limited use for the crystallization of mineral salts such as lithium carbonate on a large scale. In particular, it is not suitable for the homogeneous production of crystals in reactions in which crystallization is induced or supported by increasing the temperature. The inventors of the present invention were faced with the problem that a local increase in temperature, e.g. with at least one additional pipe that introduces a reactant and/or precipitant at high temperatures (so-called "steam lance"), leads to uncontrolled crystal growth in the vicinity of and in particular on the surface of the steam lance. Heat input via the outer walls of the crystallizer or by pumping the reaction medium through an external heat exchanger leads to comparable problems. As a result, product losses occur because the resulting crystal particles are not sufficiently homogenized. Furthermore, problems arise with cleaning and with the limited execution time of a continuous process. Maintenance intervals become shorter, the reactor becomes dirty, and the crystallization process becomes low-yielding.

The object underlying the present invention is therefore to provide an improved process or an improved apparatus for producing homogeneous metal salt crystals with a defined, as homogeneous as possible grain distribution and grain structure. In particular, the problems identified by the inventors, which arise from an inhomogeneous temperature distribution, must be avoided.

Summary of the Invention

The object is achieved according to the invention by a reactor comprising at least one reactor element which enables the supply of liquid or gaseous starting substances (e.g. medium, reactant and/or precipitant) into the reactor chamber at an elevated temperature without creating an inner surface in the reactor chamber at which a temperature gradient to the reactor solution or reactor suspension is created.

In an embodiment of the first aspect of the invention, a thermally insulated steam lance, which is a thermally insulated feed pipe, is introduced into the reactor of the present invention. The steam lance is suitable for introducing starting substances in the form of gases, such as steam or gaseous CO2, or aqueous solutions at high temperature into the reactor, so that thermally induced or promoted crystallization can be initiated there. The thermal insulation prevents unwanted deposits from forming on the surface of the feed pipe in process media containing dissolved salts or solids, the solubility of which increases greatly as the temperature drops. In a preferred embodiment, the steam lance comprises an insulation jacket which thermally insulates a substance-carrying inner tube in the steam lance from the reaction space in the reactor. The insulation jacket can be insulated by air or a thermally inert liquid, for example by a circulating liquid that is supplied and discharged.

In particularly preferred embodiments, the insulation jacket comprises at least one insulation layer with a cooling medium, a conventional insulation medium or a vacuum layer. In one embodiment, the insulation layer of the insulation jacket has a thermal conductivity of 0.05 W/(mK), e.g. with a layer thickness of 2 cm or more.

"Thermally insulated" means that there is a maximum of a small, limited heat flow from the inside of the reactor to the steam lance or to the inside of the steam lance or in the opposite direction. The insulation layer serves as a measure to limit this heat flow. In preferred embodiments, an inlet pipe or a steam lance is referred to as "thermally insulated" if the quotient of the thermal conductivity of the reactor medium AR and the boundary layer thickness dR on the surface of the insulation layer around which the flow takes place on the reactor side is at least a factor x greater than the quotient of the thermal conductivity of the insulation layer Ai and its layer thickness di.

(ÄR/dR ) > x (Ai/di), where x >1.

The factor x is equal to the value of the temperature difference between the inside of the steam lance and the medium temperature in the reactor. In a preferred embodiment, x is at least 5, more preferably at least 10.

The boundary layer thickness dR is a value that depends on the geometry and conditions in the reactor and is determined by the quotient of the Nusselt number and the given length of the steam lance.

Ideally, the insulation layer of the insulation jacket will have a thermal conductivity of 0.05 W/(mK) or less, preferably 0.01 W/(mK) or less, more preferably 0.005 W/(mK) or less. The layer thickness of the insulation layer is 0.1 cm or more, 0.2 cm or more, 0.5 cm or more, 1.0 cm or more, 1.5 cm or more, 2.0 cm or more; or 3.0 cm or more. With a thermal conductivity of 0.05 W/(mK) or less, layer thicknesses of 1.0 cm or more are common, preferably 1.5 cm or more, more preferably 2.0 cm or more; or most preferably 3.0 cm or more. With a thermal conductivity of For a thermal conductivity of 0.01 W/(mK) or less, layer thicknesses of 0.2 cm or more, 0.5 cm or more, or 1.0 cm or more are preferred; however, larger layer thicknesses - as mentioned above - are possible. For a thermal conductivity of 0.005 W/(mK) or less, layer thicknesses of 0.1 cm or more, 0.2 cm or more, or 0.5 cm or more are preferred; however, larger layer thicknesses are possible.

In practice, thermal insulation is achieved by introducing at least one insulating layer on the surface of the feed pipe, which contains vacuum or a coolant.

The insulation jacket is particularly preferably made up of several layers. The outer layer serves to prevent heat losses that are transferred to the cooling medium. An inner layer prevents the cooling of the medium that flows through the steam lance. In principle, this embodiment is also suitable for introducing cold process media into a hot environment within the reactor without a relevant temperature gradient occurring to the surface of the steam lance. In this case, unwanted deposit formation on the surface of the feed pipe in the case of process media with dissolved salts or solids, the solubility of which increases significantly with increasing temperature, can be avoided.

The temperature gradient between the surface of the steam lance and the interior of the reactor should be less than 1 K, preferably less than 0.1 K, and ideally not measurably small. In this way, temperature-induced deposit formation of crystals, e.g. Li2CO3 crystals, on the surface of the steam lance can be reduced or preferably completely avoided. The heat loss is in principle of minor importance as long as no crystal formation is induced.

According to the invention, no deposits of crystals, e.g. of U2CO3, occur on the surface of the steam lance, i.e. the deposit formation of crystals, e.g. of U2CO3, on the surface of the steam lance is limited to a deposit formation rate of maximum T10' ⁵ m/h, preferably to a maximum of T10' ⁶ m/h. With a temperature gradient between the surface of the steam lance and the interior of the reactor of less than 1 K, preferably less than 0.1 K, a maximum of T10 ^-5 m/h, preferably a maximum of T10' ⁶ m/h, is achieved. Without thermal insulation, a temperature gradient of 10 K or more was observed in experiments on U2CO3 crystallization, and a deposit formation rate of less than 1 mm/h or T10' ³ m/h could not be achieved. In a preferred embodiment, the reactor comprises one or more steam lances for the supply of liquid or dissolved starting substances (medium, reactant and/or precipitant), which are introduced at certain defined positions in the reaction vessel, particularly preferably within the guide tube, in the area between the guide tube and the clarification ring at the height of the upper edge of the guide tube or in the inner area of the clarification ring on or below the process medium surface. Solids are fed into the latter area directly onto the process medium surface.

In a particularly preferred embodiment of the invention, the reactor comprises at least one external circulation line. The circulation line has an inlet at the upper end of the reactor and an outlet at the lower end of the reactor, where the inlet and outlet can optionally be provided with heatable and/or coolable sleeves. In a preferred embodiment, the circulation line comprises a heating element at the inlet, which heats the supplied starting substance (such as medium, reactant, precipitant) before it enters the reactor. The inlet in this aspect of the invention is a steam lance as described above. In a preferred embodiment, the heating element consists of a T-shaped tube in which steam or another heating medium such as hot water is mixed with the circulation stream.

The present invention offers a number of advantages over conventional methods and devices. The reactor according to the invention and the associated method according to the invention have few incrustations, which means that little maintenance is required. The reactor-related homogenization during the crystallization process results in a regular and narrow grain size distribution and thus improved filterability and washability. The resulting crystallizate contains smaller amounts of water-insoluble, non-washable impurities. The production output per apparatus is increased, the reactor service life is increased, and the maintenance intervals are longer. For example, lithium carbonate can be provided as spherical crystallizate that is particularly easy to wash out and process further. Lithium carbonate as a spherical crystallizate preferably has a diameter of 0.15 mm to 0.75 mm as a median value and a narrow particle size distribution of 0.09 to 0.65 mm as a limit value for the lower and 0.20 mm to 0.80 mm for the upper 10-of-100 mass percentile and particularly preferably a particle diameter of 0.20 with an even narrower distribution of 0.169 mm as a limit value for the lower and 0.255 mm for the upper 10-of-100 mass percentile. Detailed description of the invention

Figure 1 describes a device (“reactor”) for crystallizing mineral salts, in particular lithium carbonate, comprising a cylindrical container, preferably with a straight, curved or slightly conical bottom, with a centrally arranged axial stirrer (6) in a guide tube (3) which generates a flow directed towards the bottom of the container, as well as a clarification ring (1) for clarifying the reactor overflow, as well as an overflow channel (2) for collecting and draining the reactor overflow and an optional deflection ring (4) to support the clarification. The reactor optionally comprises a wall flow breaker (5) to interrupt a possible tangential flow. An underflow (10) is provided for the suspension discharge. Such a reactor is known in the prior art.

In one embodiment, the device of the present invention is characterized by at least one thermally insulated feed pipe (7) (i.e. a thermally insulated steam lance (7)) for media, reactants and/or precipitants, which projects into the reactor interior, preferably into the medium inside the reactor.

In preferred embodiments, the ratio of the height of the container to the diameter of the container is between 0.8 and 1.3, more preferably 0.9 to 1.2. The volume of the reactor is between 20 liters and 300 m ³ . For dimensioning taking into account the specific properties of the solution to be considered, the continuous tests required for this are preferably carried out in volumes between 20 and 400 liters. Scale-up is carried out using the factors for the component dimensions specified for this reactor type, related to the reactor diameter. U2CO3 is usually produced with a specific crystallization rate of 5 - 40 kg of product per 1 m ³ of reactor volume and hour. Ideally, a low crystallization rate promotes better quality lithium carbonate. The reactor volume and thus the dimensions of all components are determined by the specific crystallization rate for a given production rate for U2CO3.

In principle and depending on the static conditions, the reactor can be built with a volume larger than 300 ^m3 , but there is currently no practical operating experience.

In regular embodiments, the bottom of the container is straight. In other preferred embodiments, the bottom of the container comprises a straight bottom inclined at an angle of up to 5° to the bottom outlet. In a further embodiment, the bottom is domed with a curvature that preferably extends to the wall flow breakers. The clarification ring (1) according to the reactor of the present invention, which serves to clarify the reactor overflow, preferably comprises a diameter of 50% of the vessel diameter, with a preferred clarification height of 0.15 to 0.28 in relation to the vessel height.

In a further preferred embodiment, the clarification ring comprises a horizontal slit near the clarification lower edge.

The overflow channel (2) (here also "overflow") of the reactor of the present invention serves to collect and drain the reactor overflow. It is preferably inclined at an angle of 1 to 5 degrees to the outlet. The width of the overflow channel depends on the overflow volume. It is preferably provided with maintenance hatches in the reactor cover so that any fine material that has sedimented in the overflow channel can be flushed out.

The guide tube (3) of the reactor of the present invention serves to generate the desired flow conditions. The guide tube diameter is preferably 0.23 to 0.36 in relation to the container diameter. The guide tube length is preferably 0.49 to 0.82 in relation to the container height. The installation height of the guide tube preferably ends at a height of 0.092 to 0.42 in relation to the container height above the floor.

The deflection ring (4), optional in the reactor of the invention, serves to support the clarification ring. The width of the deflection ring is preferably 0.07 to 0.10 in relation to the vessel diameter. The installation height is a maximum of 0.5 in relation to the vessel height (from the top to the middle of the reactor). The inclination is preferably up to 30° to the vertical.

The wall flow breaker (5), optional in the reactor of the present invention, serves to prevent tangential flow. The width of the wall flow breaker is preferably up to 0.1 in relation to the container diameter. The installation height is preferably in the range between 0.046 and 0.128 in relation to the container height, in the lower half of the container. The agitator of the reactor of the present invention is preferably a 6-blade impeller. The impeller diameter is preferably 0.21 to 0.33 in relation to the container diameter. The installation height of the impeller is preferably 0.08 to 0.020 in relation to the container height with a stirring blade height of preferably between 0.042 and 0.066 in relation to the container diameter. The inclination of the stirring blades is preferably between 30°C and 60°C.

The thermally insulated feed pipe (7) (ie the thermally insulated steam lance (7)) is suitable for introducing media, reactants and/or precipitants with a temperature of 0°C to the boiling temperature, ideally between 40°C and 100°C, more preferably between 50°C and 85°C for precipitation processes and between 40°C and 100°C, preferably between 80°C and 100°C for boiling solutions or for thermal decomposition or precipitation processes, for example the decomposition of dissolved lithium hydrogen carbonate by steam introduction.

When dissolving lithium carbonate by reversing the crystallization processes, the feed pipe can be operated at 0°C to 30°C, preferably at ambient temperature and pressure.

During crystallization and/or dissolution, concentrations of 50 to 450 kg of solids per cubic meter are set at the reactor underflow for suspensions containing lithium carbonate by the amount removed at the reactor underflow. The solids concentration at the reactor underflow is preferably between 150 kg and 300 kg/m ³ . It is particularly preferably between 180 and 250 kg/m ³ if lithium carbonate is produced from lithium chloride solutions. The mass flow of dissolved lithium salt required for precipitation is introduced through the feed pipe.

Economic aspects run counter to the aspects of lithium carbonate quality, since the reactor volume and thus the investment costs increase as the specific crystallization or dissolution rate decreases. The preferred crystallization or dissolution rate is determined by the aspects of product quality and the economic aspects. Specific crystallization and dissolution rates for lithium carbonate are preferably set between 5 and 25 kg/(m ³ h). In the case of very high purity requirements or very narrow grain size distributions, a specific crystallization rate of less than 15 kg/(m ³ h) is particularly recommended in the case of crystallization.

Precipitation processes according to the invention comprise the precipitation of lithium carbonate by adding lithium salt solution as a precipitant to an alkali carbonate solution (starting material). Likewise, an alkali carbonate solution can be added as a precipitant to a lithium salt solution (starting material). Preferably, alkali carbonate solution and lithium salt solution are introduced into the reactor through two different feed pipes.

In a further embodiment, solid lithium carbonate is precipitated from a lithium carbonate solution (starting material) by adding a lithium salt or a lithium salt solution (as a precipitant). Alternatively, the lithium salt or the lithium salt solution can be initially introduced into the reactor so that solid lithium carbonate is precipitated by adding lithium carbonate solution as a precipitant. Preferably, lithium salt solution and lithium carbonate solution are introduced into the reactor through two different feed pipes. In a further embodiment, carbon dioxide (as a precipitant, gaseous or as an aqueous solution) is introduced into a lithium hydroxide solution. A lithium hydroxide solution can also be introduced into an aqueous carbon dioxide solution. Preferably, lithium hydroxide solution and carbon dioxide (gaseous or as an aqueous solution) are introduced into the reactor through two different feed pipes.

In a particularly preferred embodiment of the present invention, hot water or steam is introduced into a lithium hydrogen carbonate solution. The precipitant hot water or steam causes the precipitation of lithium carbonate from the lithium hydrogen carbonate solution with the formation of carbon dioxide. This reaction can also be supported by pressurizing a lithium hydrogen carbonate solution in the reactor. A lithium hydrogen carbonate solution can also be added to hot water in a reactor. Lithium hydrogen carbonate solution and hot water or steam are preferably introduced into the reactor through two different feed pipes.

In a further embodiment, carbon dioxide (gaseous) is introduced into a lithium carbonate suspension in a reverse reaction to the previous embodiment. Similarly, an aqueous solution mixed with carbon dioxide can be made to form solid lithium carbonate by adding a lithium carbonate suspension. This produces a lithium hydrogen carbonate solution.

Figures 2 to 11 show preferred embodiments of the invention. Combinations of the various embodiments shown here are also possible.

Fig. 2 shows a reactor according to the invention with one, optionally two feed pipes (steam lances) (7a), (7b). If there are two feed pipes, these can be installed symmetrically to the axis of the stirrer in the guide pipe (3) as shown here. The opening at the tip of the feed pipe protrudes into the interior of the guide pipe.

According to Fig. 3, 1 asymmetrically mounted thermally insulated feed pipes (7a), (7b) are provided, whereby one thermally insulated feed pipe (7a) protrudes into the interior of the guide pipe (3), the other does not, i.e. the thermally insulated feed pipe (7b) with opening at the tip of the feed pipe is introduced into another area of the reactor.

According to Fig. 4, the thermally insulated feed pipes (7) (ie the thermally insulated steam lances (7) or here also “thermally insulated injection pipes” (7)) can be heated or cooled by a cooling or heating circuit in the insulation jacket of the respective thermally insulated Steam lance (7). The cooling or heating circuit can contain a cooling or heating liquid, a cooling or heat transfer gas or a vacuum. The cooling or heating circuit is preferably fed with an aqueous medium or with air. In a particularly preferred embodiment, the insulation jacket consists of three layers, which surrounds the thermally insulated feed pipe (7) for CO2 in a ring shape. The inner and outer layers of the insulation jacket each consist of a chamber filled with material that has a low thermal conductivity. This can be vacuum insulation panels, air or other solid or gaseous insulating materials with a thermal conductivity of less than 0.05 W/(mK), preferably less than 0.01 W/(mK), more preferably less than 0.005 W/(mK). The middle layer consists of a chamber arranged spirally around the longitudinal axis of the thermally insulated feed pipe (7), through which a cooling medium flows (see Fig. 10 below). The outer layer serves to minimize heat losses. This embodiment can also be used to cool the process medium in the crystallizer.

According to Fig. 5, the thermally insulated feed pipe is connected to a feed line that leads out of the reactor, so that a circulation line (12) is created. Optionally, the thermally insulated feed pipe (7) can also be fed by one or more further feed lines.

According to Fig. 6, when it shows a preferred embodiment of Fig. 5, the circulation line is provided with cooling (or heating) sleeves (13), which are preferably attached directly to the entry points into the circulation line (12). In this particularly preferred embodiment, the T-shaped pipe used for mixing with the circulation flow can be thermally cooled or heated on the side where the heating or cooling medium is introduced against the rest of the pipe in a similar manner to that described for the steam lance.

According to Fig. 7, which represents a further preferred embodiment of the reactor according to Fig. 5, a static mixer (8) is integrated into the circulation line. The static mixer is a device for mixing liquids, or for mixing liquids with gases, whereby a homogeneous mixture of a mixture with a desired, adjustable mixing ratio is produced. Static mixers are known in the prior art in various embodiments. Preferably, the reaction temperature in the feed pipe is also set in the static mixer. The process parameters that are generated in the static mixer are as follows: A temperature in the range from 0°C to boiling temperature is set, preferably between 40°C and 85°C, for example between 80°C and 100°C. For the dissolution of Lithium carbonate can be heated to a temperature between 10°C and 25°C. The flow rate and thus the speed of mixing can be adjusted by the circulating volume flow for a given dimension of the static mixer.

Fig. 8 shows preferred entry points, highlighted in hatching, at which the entry pipes (7) can introduce aqueous solutions and/or steam or CO2 into the reactor vessel. In principle, it is possible to place the openings at the respective tips of the entry pipes (here called "entry points") on the surface within the clarification ring (1), in the space between the clarification ring (1) and the guide pipe (3) or in the guide pipe (3) itself. It is particularly preferred to introduce at least one entry point into the guide pipe (3).

Fig. 9 shows an embodiment of the invention for the crystallization of lithium carbonate with external clarification. The reactor and a connected external clarifier (9) are connected to each other via the overflow (2). The clarification overflow is collected in the external clarifier (9) and from there clarified crystals from the underflow of the external clarifier (9) are returned to the reactor via the thermally insulated feed pipe (7). According to this embodiment, it is possible to collect lithium carbonate particles entrained with the reactor overflow in the clarifier and return them to the reactor, which has a positive effect on grain growth. In addition, this embodiment enables the production of larger particles than would be possible with the reactor alone. By increasing the clarification ring diameter, the clarification area in the reactor is reduced and thus the speed of the solution flowing up to the overflow is increased. This also causes the average grain diameter of the U2CO3 particles entrained with the overflowing solution to increase. Consequently, the average grain diameter of the particles retained in the reactor also increases. As the overflowing solids are collected in the clarifier and returned, this material gradually grows to the particle size distribution prevailing in the reactor, as the intensified classification effect means that the probability of retention in the reactor is only large enough to lead to a relevant population density if the particle diameter is sufficiently large. Due to the increased solids discharge, a larger volume flow is returned from the clarifier compared to the reactor without a downstream clarifier. This contributes to further increasing the upflow velocity in the clarification area of the reactor and strengthens the classification effect. The clarified solution can be separated in the external clarifier (9).

Fig. 10 shows an embodiment of a thermally insulated feed pipe (7) (steam lance (7)) whose outer wall can be cooled with the ambient air. The outer wall is insulated from the outside in such a way that the outside temperature of the steam lance does not exceed the reactor temperature in the reactor medium and preferably does not fall below it either. In this way, incrustations on the outer wall of the steam lance are avoided. In other embodiments, the feed pipe or steam lance can be fed with either a cooling or heating circuit. In the particularly preferred embodiment shown, the insulation jacket consists of three layers, which surrounds the feed lance for CO2 in a ring shape. The inner and outer layers of the insulation jacket can each be filled with air (see A1, A3). The middle chamber, arranged spirally around the longitudinal axis of the steam lance, can be flowed through with cold ambient air (A2). This figure shows a comparatively cost-effective variant of the steam lance, for example for heating the lithium carbonate suspension, for example when dissolved lithium hydrogen carbonate is to be decomposed and crystallized as lithium carbonate. Water vapor (D) or an aqueous solution can be passed through the central pipe.

Fig. 11 shows a combination of two apparatuses of the present invention, such as can be used for purifying lithium carbonate. Contaminated lithium carbonate is dissolved in the unit reactor 1. For this purpose, an aqueous suspension with the contaminated lithium carbonate and CO2 is continuously introduced into the reactor to form lithium hydrogen carbonate. The reactor contains a sufficient amount of solid lithium carbonate, preferably with a concentration of 180-250 g/l. Coarse, insoluble contaminants also remain in the reactor, with suspension being discharged from the underflow (10) of the reactor after a specified operating time and filtered to prevent excessive accumulation of contaminants. The solid lithium carbonate discharged with the solution overflow (2) is collected in a subsequent clarifier and returned to the unit reactor 1 with the clarifier underflow. The clarifier overflow is fed to a fine filter so that even the finest particles are removed from the lithium hydrogen carbonate solution stream. The structure up to the fine filter ensures that a lithium hydrogen carbonate solution with a constant lithium hydrogen carbonate concentration is produced by controlling the temperature and pressure. Since a sufficient amount of lithium carbonate solid is always available, the solution is always concentrated to near the solubility limit of lithium hydrogen carbonate. The dissolved amount of U2CO3 is replenished by the Li2CC>3 suspension so that the solid concentration in the unit reactor 1 and thus also the conversion rate, preferably 15 - 25 (kg/m ³ h), remains constant. Ion exchangers following the fine filter serve to remove multivalent cations such as calcium, magnesium or aluminum and/or borates that have also been dissolved by the CO2 from the lithium hydrogen carbonate solution. Lithium carbonate is then Supply of steam with the inventive structure in the unit reactor 2, the solid lithium carbonate is recrystallized, drained off at the lower reaches of the unit reactor 2 and the solid lithium carbonate is separated with a centrifuge and passed on for drying. The solution overflowing from the clarifier is collected and, depending on the permissible concentration of the other dissolved impurities such as sodium, potassium, chloride or sulfate, is used in whole or in part to suspend contaminated lithium carbonate.

embodiments of the invention

The present invention provides an apparatus and a crystallization process.

According to a first embodiment, a device for thermally controlled precipitation crystallization is provided in the form of a reactor, consisting of a cylindrical container with a preferably flat, curved or slightly conical bottom, with a centrally arranged axial stirrer (6) with guide tube (3), which preferably generates a flow directed towards the container bottom, and an annular separating plate (1) (so-called "clarification ring" (1)) concentrically surrounding the axial stirrer (6) for separating a clarifying ring space from the stirred container contents and an overflow channel (2), characterized in that the reactor comprises a thermally insulated feed pipe (7) for introducing an aqueous phase or a gas phase, without having a surface in the reactor interior which has a temperature gradient to the temperature of the reactor medium.

In a preferred embodiment, the thermally insulated feed pipe (7) comprises an opening, preferably at the tip of the feed pipe, which projects into the interior of the reactor vessel, wherein the thermally insulated feed pipe (7) is thermally insulated, preferably by a casing which is fed with a cooling and/or heating medium. In a further embodiment, the casing comprises a vacuum. Another embodiment contains air as an insulating layer. Yet another embodiment contains vacuum insulation or plastic foam. In a particularly preferred embodiment, the feed pipe is covered with three layers, wherein the inner and outer layers are thermally insulating in the manner described and the middle layer has a temperature-regulating effect by supplying a heating or cooling medium such that no measurable temperature gradient occurs between the surface of the feed pipe and the medium in which it is immersed. In another embodiment of the present invention, the feed pipe is part of a circulation circuit (12) which is thermally adjustable and can preferably adjust the reaction temperature in gradual steps.

In preferred embodiments, the above-mentioned embodiments comprise a reaction vessel which further comprises means for flow deflection (4) (e.g. a deflection ring (4)) and an underflow (10) suitable for product removal at the vessel bottom.

In other embodiments, the reactor of the present invention comprises an integrated clarification zone (11). Preferably, the reactor of the invention comprises an additional external clarifier (9) (or "clarifier" (9)) located outside the reactor, into which the reactor overflow is introduced from the reactor overflow (2). In the external clarifier (9), separated solid particles can be collected and returned to the reactor, thereby promoting crystal growth.

In a preferred embodiment, the external clarification device (9) is a clarification cone without a rake mechanism, a round thickener with a rake mechanism, a lamella clarifier, a centrifuge, or a decanter.

In another preferred embodiment, the reactor of the invention comprises two or more thermally insulated feed pipes (7). The thermally insulated feed pipes (7a, 7b) are preferably arranged axially symmetrically to the axial stirrer (6).

In another embodiment, two thermally insulated feed pipes (7) are arranged asymmetrically (7a), (7b) to the axial stirrer (6).

In a further embodiment, at least one thermally insulated feed tube (7) is mounted in the guide tube of the reactor (3), i.e. the feed tube opening at the tip of the thermally insulated feed tube (7) preferably projects into the guide tube.

In a further embodiment, the reactor of the present invention comprises a deflection ring (4).

In a further embodiment, the reactor of the present invention comprises a wall baffle (5).

In a further embodiment, the reactor of the present invention comprises an underflow (10). In a further preferred embodiment, the reactor of the present invention comprises a six-blade impeller (6a). The use of four-blade impellers or propeller impellers is also possible.

In a further embodiment, the reactor of the present invention comprises a static mixer (8).

In a further embodiment, the reactor of the present invention comprises a circulation line (12), preferably a heatable and/or coolable circulation line (12).

In a further preferred embodiment, the thermally insulated feed pipe (7) is a thermally insulated steam lance (7), the outer wall of which can be cooled with ambient air, or the outer wall of which can be cooled or heated with a liquid medium. The thermally insulated feed pipe (7) is preferably surrounded by a triple insulation layer.

Also provided is a crystallization process in a cylindrical reactor vessel equipped with a stirrer, the crystallization process comprising the following step: a) initiating a precipitation reaction by supplying at least one liquid or gaseous medium into a medium inside the reactor, the supplied medium having a different temperature, preferably a higher temperature, than the reactor medium, a temperature change occurring in the reaction medium inside the reactor which induces or promotes the precipitation reaction without a surface being introduced into the reactor which creates a temperature gradient to the reactor medium.

Preferably, according to the method of the present invention, a thermally insulated steam lance (7) is introduced into the reactor vessel.

More preferably, the supplied medium is supplied by means of a circulation circuit (12).

In another embodiment of the present invention, a battery of two or more devices of the present invention is provided.

In a preferred embodiment, a battery of two devices (ie reactors) of the present invention is provided. Preferably, a reaction and a reverse reaction take place in these two devices. In this way, for example, a contaminated starting substance can be purified. In a particularly preferred embodiment, contaminated lithium carbonate is converted into Lithium hydrogen carbonate is converted, which is converted back into pure lithium carbonate in a second apparatus of the battery using added steam. In these embodiments, cleaning elements can be introduced between the two apparatuses, e.g. one or more ion exchangers and/or one or more filters. These embodiments are particularly advantageous in that they can be carried out in continuous operation.

In another preferred embodiment, a battery of three devices (here "apparatus") of the present invention is provided. This is used, for example, to convert solid U2CO3 with a slightly overstoichiometric amount of solid Ca(OH)2 to dissolved LiOH and solid CaCOs. The selected embodiment promotes the formation of a high concentration of dissolved LiOH with minimized lithium losses that arise from undissolved or recrystallized U2CO3 in the solid product CaCOs. In these three devices of the battery, the conversion reaction preferably takes place predominantly in the first apparatus and the conversion reactions are quantitatively completed in the other two apparatuses. By reacting U2CO3 with Ca(OH)2, CaCOs, which is significantly less soluble than the two reactants, is initially formed, with lithium dissolving as hydroxide. As the reaction progresses, the concentration of LiOH in the solution increases. This reduces the solubility of both U2CO3 and Ca(OH)2, which is why when a LiOH concentration of more than 2.5 parts by mass in 100 parts by mass of solution is reached, the appearance of solid U2CO3 must be expected, which is lost from the process without further treatment with the CaCOs. The water required for the process is therefore fed into the third apparatus, so that a CaCOs suspension is formed there with a solution that is only slightly concentrated in LiOH, which is dewatered after being removed from the apparatus according to the invention. Due to the low lithium hydroxide concentration, only minimal lithium losses occur, which can be further reduced by washing the filter cake. The filtrate, the wash filtrate and the overflow from the third apparatus reach the second apparatus, which is additionally fed with the underflow of the first apparatus and the underflow of a clarifier downstream of the first apparatus. The resulting dilution effect dissolves solid U2CO3 from the first apparatus, which reacts with the unreacted Ca(OH)2 to form LiOH and CaCOs and completes the reaction. The overflow from the first apparatus is fed into a clarifier and clarified so that the clear solution flowing out of it can be further processed using known methods to form lithium hydroxide monohydrate or other products.

In another embodiment of the invention, for the purification of lithium carbonate, contaminated lithium carbonate is continuously dissolved in a unit reactor. the dissolution rate of lithium carbonate, which is preferably between 10 kg/m ³ h and 25 kg/m ³ h, fresh suspension with contaminated lithium carbonate is added so that a preferred solids concentration of between 180 kg/m3 and 250 kg/m ³ is maintained in the lower region of the reactor. In order to avoid excessive accumulation of insoluble contaminants, suspension is withdrawn continuously or at regular intervals from the underflow of the reactor so that preferably at least 95 out of 100 mass parts of lithium carbonate are dissolved in the contaminated feedstock. The criterion for the volume flow of the suspension withdrawal at the reactor underflow is to ensure the specific dissolution rate, the achievement of which can be monitored by measuring the density, refractive index or other characteristic measured variables of the solution in the lithium hydrogen carbonate solution. The lithium carbonate withdrawn from the underflow of the reactor is used for other purposes. The solid lithium carbonate discharged with the solution overflow is collected in a subsequent clarifier and returned to the standard reactor 1 with the clarifier underflow. The clarifier overflow goes to a fine filter so that even the finest particles are removed from the lithium hydrogen carbonate solution stream. These fine particles are usually contaminants and are also removed from the process. The fine filter is followed by ion exchangers which serve to remove dissolved multivalent cations such as calcium, magnesium or aluminum and/or borates from the lithium hydrogen carbonate solution. These are preferably regenerated with dilute hydrochloric or nitric acid. They are preferably conditioned with dilute lithium hydroxide solution. This avoids an enrichment of other alkali metals, which would be the case if potassium hydroxide or sodium hydroxide were used instead of lithium hydroxide. The lithium hydrogen carbonate solution purified in this way is then used to produce lithium carbonate again. For this purpose, it is crystallized with the inventive structure, with a specific crystallization rate of 10 - 25 kg/hm ³ , by supplying steam, separated with a centrifuge, washed if necessary and passed on for drying. The solution overflowing from the clarifier is collected and, depending on the permissible concentration of the other dissolved impurities such as sodium, potassium, chloride or sulfate, used in whole or in part to suspend contaminated lithium carbonate. In a particularly preferred variant of this embodiment, the solution used to suspend the contaminated lithium carbonate is cooled by means of water evaporation and the evaporated water is compressed so that it is returned to the inventive structure as heating steam, thereby reducing thermal energy consumption.

In a further embodiment, lithium carbonate is crystallized in a reactor according to one of the described embodiments and either separated from the mother liquor or in this is enriched. The lithium carbonate then passes into a second reactor corresponding to the embodiments described, which is equipped with at least two, preferably three steam lances that correspond to one of the embodiments according to the invention. The previously produced lithium carbonate is preferably introduced in suspended form through one steam lance. A solution with a further metal salt is introduced through another. A medium is introduced through at least one further steam lance, which either leads to supersaturation of the further cation introduced in the reactor or, in a preferred variant, provides a further anion that forms a precipitate with the further cation, the precipitation of the product being driven by the lithium carbonate present. Due to the structure according to the invention, the lithium carbonate particles provide a large amount of growth surfaces, so that the Ü2CO3 particles are evenly coated with a layer that contains the precipitate of the metal salt. The order of precipitation can be reversed if necessary, so that lithium carbonate envelops the particles consisting of a different cation or anion.

In a further embodiment of the present invention, lithium salt solutions are processed in a series of successive crystallization steps, which, in addition to lithium as a cation, can also contain other cations and anions that hinder the crystallization of a lithium carbonate suitable for batteries. The embodiments and active principles described in the invention are used to first crystallize one or more cations and/or anions in at least two successive crystallization or precipitation steps without lithium being co-precipitated in relevant quantities. In the last crystallization unit according to the invention, lithium carbonate is crystallized using one of the described embodiments; the crystallization or precipitation of the interfering ions can, depending on the application, take place in one crystallization unit according to the invention per cation or anion or synchronously with the precipitation of several cations and/or anions in one crystallization unit according to the invention (= device of the invention). Common cations that must be almost completely removed from the solution are calcium or magnesium. Common anions that influence the crystallization and purity of lithium carbonate are sulfate and borate.

examples

Precipitation of lithium carbonate by decarbonization of a lithium hydrogen carbonate solution. a) A lithium hydrogen carbonate solution with 75 g/l UHCO3 stored at ambient temperature is pumped at a rate of 10 liters/h through a steam-heated plate heat exchanger and heated to 95 °C and then introduced into a crystallization reactor according to the invention. After 25 minutes, the experiment was interrupted because only 75 °C was reached and the flow rate had decreased to less than 7 l/h. After flushing the plate heat exchanger with hydrochloric acid, the original solution flow rate and the target temperature of 95 °C could be reached again for a short time. Since a massive drop in both process parameters occurred again, the experiment was aborted. b) The same solution was introduced at a rate of 10 liters/h in a second test run directly via a steam lance consisting of a simple pipe into the mixed area within the clarification ring of the reactor according to the invention with a volume of 400 liters, and the system was heated with steam that flowed via a steam lance consisting of a simple injection pipe and extending into the guide tube of the reactor according to the invention. The process was operated for a period of 8 hours before it was terminated as planned. During this time, the solids concentration increased to 3 g/l. A quantity of approximately 600 g U2CO3 coated the steam injection pipe. c) By using a thermally insulated steam lance in the test setup and test procedure of b), no more solid U2CO3 was deposited on the steam lance surface under the same test conditions as in b).

Example 2:

For Li2CC>3 precipitation, a total of four experiments were carried out on a small pilot scale (20 litre reactor volume) in two different scenarios, each with a conventional setup with three stirred vessels operated with overflow and a draft tube and a loop reactor setup. The experimental work is summarized in the table below. All experiments were carried out at about 70 °C.

Szenario: Table: Simplified overview of the test work carried out on Li2CC>3 precipitation

Scenario:

Low-sulfate solution: The brine contains 0.9% lithium, 6.2% sodium, 13% chloride and 0.02% sulfate.

High potassium content: The brine contains 0.9% lithium, 4.2% sodium, 3.0% potassium, 12.7% chloride and 0.12% sulfate.

In scenarios 1 and 3, the lithium solutions are divided. For the first of the stirred tank cascade, the lithium solution is fed through an injection pipe at a rate of 19 liters per hour. In the second tank of the cascade, 8 liters of lithium solution per hour are introduced in a similar manner. To precipitate lithium carbonate, a solution with 30% sodium carbonate is used, which is introduced into the first stirred tank of the cascade through an injection pipe. The third stirred tank of the cascade is used to extend the residence time. The suspension leaving the stirred tank cascade is collected in a clarifier and the solid is thickened, filtered, washed to remove any caustic residues and analyzed.

Scenarios 2 and 4 are carried out in a setup corresponding to Figure 9. Heating and temperature regulation are carried out via a steam lance as shown in Figure 4, by feeding in approximately 1 liter per hour of a steam-water mixture. 8.7 liters per hour of lithium solution and 2.1 liters per hour of soda solution are simultaneously fed into the crystallization reactor according to the invention via a setup corresponding to Figure 2. From the tenth hour, 2 liters per hour of product suspension is removed from the reactor underflow and continued until test hour 32. The overflow from the reactor is fed into a clarifier in which the entrained solid particles are collected and returned to the reactor via the underflow of the clarifier. This return begins with the first test hour. The removed suspension is filtered, washed to remove any caustic soda and the product is analyzed. The following impurities are found in the product:

When using the structure according to the invention, higher purities are achieved, particularly for the elements sodium and potassium. In addition, lower residual moisture can be achieved during dewatering, which is between 6% and 8% after centrifugation with the structure according to the invention, while residual moisture is between 9% and 12% with the conventional structure. Differences also occur in the grain size distribution with a considerably larger

range for the 10% percentile and multimodal distribution and significantly lower modal values of the main distribution in the conventional setup. These are summarized in the following table:

Example 3: Production of spherical lithium carbonate by precipitation from a lithium sulfate solution.

A mass flow of 10.5 kg per hour of a solution containing 7.3% U2SO4, 13.4% Na2SC>4, 6.3% K2SO4 and traces of calcium, magnesium, rubidium and cesium is introduced into the interior of the reactor's draft tube at a temperature of 22 °C via a steam lance according to the invention as shown in Figure 5. Simultaneously, 2 kg per hour of a 33% Nat- The lithium carbonate solution is introduced into the interior of the guide tube via a steam lance according to the invention as shown in Figure 4 in such a way that the amount of lithium ions introduced is in a molar ratio of 2.21:1 to the amount of carbonate ions introduced. In this way, 477 g of lithium carbonate are crystallized per hour. By using a reactor according to the invention with a volume of 20 liters, the conditions mentioned correspond to a specific production rate of 23.9 kg/(m ³ h). After solid-liquid separation and washing, a product with a purity of 99% is obtained with sodium sulfate, potassium sulfate and lithium sulfate as the main impurities that cannot be washed out. In contrast to other processes, the product falls in a spherical shape with a median diameter of 0.208 mm and a narrow particle size distribution of 0.169 mm as the limit value for the lower and 0.255 mm for the upper 10-of-100 size percentile.

Example 4: Thermal insulation

A cylindrical steam lance with an immersion depth of 5 m extends into a reactor with a volume of 300 m ³ , which circulates a suspension of U2CO3 and an 80 % saturated NaCl solution.

The steam lance is operated with steam saturated at a temperature of 160 °C. The Ü2CO3 suspension boils at 105 °C. The solution has a thermal conductivity of 6 W/(mK). A Nusselt number of 3434 was determined for this arrangement and process configuration. In order to achieve a temperature difference of less than 0.1 K between the medium temperature and the surface temperature of the outside of the steam lance, insulation with a thermal conductivity of 0.05 W/(mK) with a layer thickness of approx. 2 cm is required.

Claims

Claims: 1. A reactor consisting of a cylindrical vessel with a centrally arranged axial stirrer (6) with guide tube (3) which generates a flow directed towards the vessel bottom, as well as an annular clarification ring (1) concentrically surrounding the axial stirrer (6) and an overflow (2), characterized in that the reactor comprises a thermally insulated feed pipe (7) for introducing an aqueous phase, solid suspension or a gas phase, which extends into the interior of the reactor vessel. 2. The reactor according to claim 1, wherein the temperature gradient between the surface of the thermally insulated feed tube (7) and the reactor interior is less than 1 K. 3. The reactor according to claim 1 or 2, wherein the thermal insulation of the feed tube prevents crystal formation on the surface of the feed tube. 4. The reactor according to claim 1, wherein the thermally insulated feed pipe (7) is part of a circulation circuit (12). 5. The reactor according to any one of claims 1-4, further comprising means for flow diversion (4), a wall flow breaker (5) and/or an underflow (10). 6. The reactor according to any one of claims 1-5, comprising an external clarifier (9) arranged outside the reactor, into which the reactor overflow from the overflow (2) of the reactor is introduced. 7. The reactor according to claim 6, wherein the external clarification device (9) comprises a clarification cone without a rake, a round thickener with a rake, a lamella clarifier, a centrifuge, or a decanter. 8. The reactor according to any one of claims 1-7, comprising two or more thermally insulated feed tubes (7). 9. The reactor according to any one of claims 1-8, wherein two feed pipes (7) are arranged asymmetrically or symmetrically to the axial stirrer (6). 10. The reactor according to one of claims 1-9, wherein at least one feed pipe (7) projects into the guide pipe of the reactor (3). 11. The reactor according to any one of claims 1-10, wherein the reactor comprises a static mixer (8) in a circulation line (12). 12. The reactor according to any one of claims 1-11, wherein the reactor comprises a heatable circulation line (12). 13. The reactor according to any one of claims 1-12, wherein the thermally insulated feed tube (7) comprises an outer wall which is heated with ambient air or with a liquid medium. 14. The reactor according to any one of claims 1-13, wherein the thermally insulated feed pipe (7) comprises an insulator jacket with an insulation layer and the insulation layer of the insulation jacket has a thermal conductivity of 0.05 W/(mK) or less. 15. A process for crystallization in a cylindrical reactor equipped with a stirrer, the crystallization process comprising the following step: a) initiating a precipitation reaction by supplying at least one liquid or gaseous medium to a medium inside the reactor, the supplied medium having a higher temperature than the reactor medium, a temperature change occurring in the reaction medium inside the reactor which induces or promotes the precipitation reaction without a surface being introduced into the reactor which creates a temperature gradient with respect to the reactor medium. 16. The method according to claim 15, comprising introducing a thermally insulated steam lance (7) into the reactor vessel, through which the supplied medium is introduced into the reactor medium. 17. A battery of reactors according to any one of claims 1-14, wherein at least two of the reactors are connected in series. 18. The battery of reactors according to claim 17, wherein a forward reaction takes place in the first reactor and a reverse chemical reaction takes place in the second reactor. 19. Use of the reactor according to any one of claims 1-14 or the process according to any one of claims 15-16 or the battery of claim 17 or 18 for producing lithium carbonate, preferably by introducing hot water or steam into a lithium hydrogen carbonate solution. 20. Lithium carbonate as spherical crystals with a median diameter of 0.15 mm to 0.75 mm as a median value with a narrow particle size distribution with a 10% size percentile between 0.09 and 0.65 mm up to a 90% size percentile between 0.20 mm and 0.80 mm and particularly preferably with a particle diameter of 0.208 mm with a particle size distribution from the 10% size percentile of 0.169 mm to the 90% size percentile of 0.255 mm.