Device for producing lithium carbonate crystals

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

[0001] Device for producing lithium carbonate crystals

[0002] The invention relates in particular to a device for the continuous and controlled crystallization of lithium carbonate, but can also be used for comparable, preferably inorganic crystals.

[0003] The device according to the invention is suitable for the production of 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 and their salts by precipitation from their aqueous solutions.

[0004] 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 supersaturation. This can be achieved in various ways. One option is a precipitation reaction, in which a solution of a reactant is placed in a stirred vessel and an associated precipitant is added dropwise or otherwise 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 precipitated by adding alkali carbonates (precipitants) to a lithium salt solution (reactant). Similarly, lithium carbonate (U2CO3) can be precipitated by adding lithium salts (precipitants) to initial 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 adjusting the dosage ratios.

[0005] In another precipitation reaction, lithium carbonate (U2CO3) is produced by carbonating a lithium hydroxide (LiOH) solution, i.e., 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 metering rate of the reactants. Another precipitation process is based on the thermally induced decomposition of lithium hydrogen carbonate (UHCO3) dissolved in water. Here, a purified lithium hydrogen carbonate solution is decomposed by thermal exposure to CO2 (gaseous) and lithium carbonate (U2CO3) as the precipitate. A specific embodiment of this production of lithium carbonate is described, for example, in EP 2 536 663.In principle, this process for producing high-purity lithium carbonate starts with a lithium carbonate solution (U2CO3) (aq), which is converted into a lithium bicarbonate solution by adding CO2 (g) or CO2 dissolved in water. This solution can be purified, for example, by ion exchange. The thus purified lithium bicarbonate (aq) can be used to crystallize high-purity lithium carbonate by thermal decomposition with the release of CCh.

[0006] The method for the reaction crystallization of mineral salts on an industrial scale is described in DD 227615 and DD 26479. The reactor or crystallizer essentially consists of a cylindrical vessel, optionally with a flat, domed, or conical bottom, an axial stirrer with a guide tube, a clarification ring for separating an annular clarification chamber from the remaining suspension-filled crystallizer contents, and supply and discharge elements for the solid and liquid substances. The crystallizer in DD 227615 makes it possible to continuously mix the solid and liquid starting materials, ensure the reaction process, and achieve a high crystal density in the reaction chamber, thus producing coarse crystals that can be withdrawn from the reactor in a thickened, highly concentrated form. The liquid reaction phases in the reactor leave clarified via an overflow.The axial stirrer creates mixing through the suction effect of the stirrer, which begins at the upper end of the guide tube and is generated by the suction-generating inclined blades of the stirrer. The stirrer conveys the aspirated suspension to the bottom of the tank and, after it rises up the cylindrical tank walls, sucks it back in at the upper end of the guide tube. To prevent flow vortexes from the mixed tank from passing parallel into the annular 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.

[0007] However, this apparatus has only limited use for the crystallization of mineral salts, such as lithium carbonate, on an industrial scale. In particular, it is not suitable for the homogeneous crystal production in reactions in which crystallization is induced or assisted 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 tube introducing a reactant and / or precipitant at high temperatures (so-called "steam lance"), leads to uncontrolled crystal growth in the vicinity of, and particularly 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 insufficiently homogenized.Furthermore, problems arise with cleaning and the limited operating time of a continuous process. Maintenance intervals become shorter, the reactor becomes dirty, and the crystallization process becomes low-yielding.

[0008] The object underlying the present invention is therefore to provide an improved process and apparatus for producing homogeneous metal salt crystals with a defined, as homogeneous as possible, grain distribution and grain structure. In particular, the aim is to avoid the problems identified by the inventors, which arise from an inhomogeneous temperature distribution.

[0009] Summary of the invention

[0010] 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.

[0011] In one embodiment of the first aspect of the invention, a thermally insulated steam lance, which is a thermally insulated feed tube, 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 into the reactor at high temperature, 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 tube in process media containing dissolved salts or solids, whose solubility increases significantly with decreasing temperature. In a preferred embodiment, the steam lance comprises an insulating 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, it can be insulated by a circulating inlet and outlet liquid.

[0012] 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.

[0013] "Thermally insulated" means that at most a small, limited heat flow exists from the reactor interior to the steam lance, or to the interior of the steam lance, or in the reverse 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 occurs 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.

[0014] (ÄR / dR ) > x (Ai / di), where x >1.

[0015] 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.

[0016] 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.

[0017] 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. For 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 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 is preferred; however, larger layer thicknesses are possible.

[0018] 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.

[0019] Particularly preferably, the insulation jacket consists of several layers. The outer layer serves to prevent heat loss, which is transferred to the cooling medium. An inner layer prevents the cooling of the medium flowing through the steam lance. In principle, this design is also suitable for introducing cold process media into a hot environment within the reactor without creating a significant temperature gradient to the surface of the steam lance. In this case, unwanted deposit formation on the surface of the feed pipe can be avoided when processing media containing dissolved salts or solids, whose solubility increases significantly with rising temperature.

[0020] The temperature gradient between the surface of the steam lance and the reactor interior should be less than 1 K, preferably less than 0.1 K, and ideally not measurably small. In this way, temperature-induced crystal deposits, such as Li2CO3 crystals, on the surface of the steam lance can be reduced or, preferably, completely avoided. Heat loss is, in principle, of minor importance as long as no crystal formation is induced.

[0021] According to the invention, no deposit formation of crystals, e.g. of U2CO3, occurs on the surface of the steam lance, ie the deposit formation of crystals, e.g. of U2CO3, on the surface of the steam lance is limited to a deposit formation speed of maximum T10' 5 m / h, preferably to a maximum of T10' 6 m / h. At a temperature gradient between the surface of the steam lance and the reactor interior of less than 1 K, preferably less than 0.1 K, a maximum of T10 -5m / h, preferably maximum T10' 6 m / h. Without thermal insulation, a temperature gradient of 10 K or more was observed in U2CO3 crystallization experiments, and a deposit formation rate of less than 1 mm / h or T10' 3 m / h cannot 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 draft tube, in the area between the draft tube and the clarification ring at the height of the draft tube's upper edge, or in the interior of the clarification ring on or below the process medium surface. Solids are introduced into the latter area directly onto the process medium surface.

[0022] In a particularly preferred embodiment of the invention, the reactor comprises at least one external recirculation line. The recirculation line has an inlet at the upper end of the reactor and an outlet at the lower end of the reactor, wherein the inlet and outlet can optionally be provided with heatable and / or coolable sleeves. In a preferred embodiment, the recirculation 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 recirculation stream.

[0023] The present invention offers several advantages over conventional processes and devices. The reactor according to the invention and the associated process according to the invention are low in incrustations, thus requiring little maintenance. The reactor-induced homogenization during the crystallization process results in a regular and narrow particle size distribution and thus improved filterability and washability. The resulting crystallizate contains smaller amounts of water-insoluble, non-leachable impurities. The production output per apparatus is increased, the reactor service life is extended, and maintenance intervals are longer. For example, lithium carbonate can be provided as spherical crystallizate, which is particularly easy to wash out and further process.Lithium carbonate as a spherical crystal 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 the limit value for the lower and 0.20 mm to 0.80 mm for the upper 10 of 100 mass percentiles. Particularly preferably, a particle diameter of 0.20 mm with an even narrower distribution of 0.169 mm as the limit value for the lower and 0.255 mm for the upper 10 of 100 mass percentiles. Detailed description of the invention.

[0024] Figure 1 describes a device ("reactor") for the crystallization of mineral salts, in particular lithium carbonate, comprising a cylindrical vessel, preferably with a straight, curved, or slightly conical bottom, with a centrally arranged axial stirrer (6) in a guide tube (3) that generates a flow directed towards the vessel bottom, 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 assist the clarification. Optionally, the reactor comprises a wall baffle (5) to interrupt any possible tangential flow. An underflow (10) is provided for suspension discharge. Such a reactor is known in the prior art.

[0025] In one embodiment, the device of the present invention is characterized by at least one thermally insulated feed pipe (7) (ie 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.

[0026] In preferred embodiments, the ratio of the height of the vessel to the diameter of the vessel 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 under consideration, the required continuous tests are preferably carried out in volumes between 20 and 400 liters. Scaling is carried out using the factors for component dimensions specified for this reactor type, related to the reactor diameter. U2CO3 is typically crystallized at a specific crystallization rate of 5–40 kg of product per 1 m 3 Reactor volume per 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 U2CO3 production rate.

[0027] In principle and depending on the static conditions, the reactor can be operated with a volume greater than 300 m 3be built, but there is currently no practical operating experience.

[0028] In regular embodiments, the bottom of the vessel is straight. In other preferred embodiments, the bottom of the vessel 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 baffles. The clarification ring (1) according to the reactor of the present invention, which serves to clarify the reactor overflow, preferably has 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.

[0029] In a further preferred embodiment, the clarification ring comprises a horizontal slit near the lower clarification edge.

[0030] The overflow channel (2) (here also referred to as "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 lid so that any fine material that may have settled in the overflow channel can be flushed out.

[0031] The draft tube (3) of the reactor of the present invention serves to create the desired flow conditions. The draft tube diameter is preferably 0.23 to 0.36 in relation to the vessel diameter. The draft tube length is preferably 0.49 to 0.82 in relation to the vessel height. The installation height of the draft tube preferably ends at a height of 0.092 to 0.42 in relation to the vessel height above the floor.

[0032] 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 center of the reactor). The inclination is preferably up to 30° from the vertical.

[0033] The wall baffle (5), optional in the reactor of the present invention, serves to prevent tangential flow. The width of the wall baffle is preferably up to 0.1 in relation to the vessel diameter. The installation height is preferably in the range between 0.046 and 0.128 in relation to the vessel height, in the lower vessel half. The agitator of the reactor of the present invention is preferably a 6-pitched blade agitator. The agitator diameter is preferably 0.21 to 0.33 in relation to the vessel diameter. The installation height of the agitator is preferably 0.08 to 0.020 in relation to the vessel height, with a agitator blade height of preferably between 0.042 and 0.066 in relation to the vessel diameter. The inclination of the agitator blades is preferably between 30°C and 60°C.

[0034] The thermally insulated feed pipe (7) (i.e. the thermally insulated steam lance (7)) is suitable for introducing media, reactants and / or precipitants having a temperature of 0°C up 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.

[0035] 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.

[0036] During crystallization and / or dissolution, concentrations of 50 to 450 kg of solids per cubic meter at the reactor underflow are adjusted for suspensions containing lithium carbonate by adjusting the withdrawal rate at the reactor underflow. The preferred solids concentration at the reactor underflow is between 150 kg and 300 kg / m 3 . This is particularly preferably between 180 and 250 kg / m 3 when lithium carbonate is produced from lithium chloride solutions. The mass flow of dissolved lithium salt required for precipitation is introduced through the feed pipe.

[0037] Economic considerations run counter to the aspects of lithium carbonate quality, since as the specific crystallization or dissolution rate decreases, the reactor volume and thus the investment costs increase. The preferred crystallization or dissolution rate results from the aspects of product quality and economics. Specific crystallization and dissolution rates between 5 and 25 kg / (m) are preferred for lithium carbonate. 3 h). In the case of very high purity requirements or very narrow particle size distributions, a specific crystallization rate of less than 15 kg / (m 3 h).

[0038] Precipitation processes according to the invention comprise the precipitation of lithium carbonate by adding a lithium salt solution as a precipitant to an alkali carbonate solution (the reactant). Similarly, an alkali carbonate solution can be added as a precipitant to a lithium salt solution (the reactant). Preferably, the alkali carbonate solution and the lithium salt solution are introduced into the reactor through two different feed pipes.

[0039] 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 charged in the reactor so that solid lithium carbonate is precipitated by adding lithium carbonate solution as a precipitant. Preferably, the lithium salt solution and the lithium carbonate solution are introduced into the reactor through two different feed pipes. In a further embodiment, carbon dioxide (as a precipitant, in gaseous form, or as an aqueous solution) is introduced into a lithium hydroxide solution. Similarly, a lithium hydroxide solution can be introduced into an aqueous carbon dioxide solution. Preferably, the lithium hydroxide solution and the carbon dioxide (in gaseous form or as an aqueous solution) are introduced into the reactor through two different feed pipes.

[0040] In a particularly preferred embodiment of the present invention, hot water or steam is introduced into a lithium bicarbonate solution. The precipitant, hot water or steam, causes the precipitation of lithium carbonate from the lithium bicarbonate solution, forming carbon dioxide. This reaction can also be assisted by pressurizing a lithium bicarbonate solution present in the reactor. Likewise, a lithium bicarbonate solution can be added to hot water in a reactor. Preferably, the lithium bicarbonate solution and hot water or steam are introduced into the reactor through two different feed pipes.

[0041] In a further embodiment, in a reverse reaction to the previous embodiment, carbon dioxide (gaseous) is introduced into a lithium carbonate suspension. Similarly, an aqueous solution containing carbon dioxide can be induced to form solid lithium carbonate by adding a lithium carbonate suspension. This results in a lithium bicarbonate solution.

[0042] Figures 2 to 11 show preferred embodiments of the invention. Combinations of the various embodiments shown here are also possible.

[0043] Fig. 2 shows a reactor according to the invention with one, optionally two, feed tubes (steam lances) (7a), (7b). If two feed tubes are present, they can be installed symmetrically to the axis of the stirrer in the guide tube (3), as shown here. The opening at the tip of the feed tube protrudes into the interior of the guide tube.

[0044] According to Fig. 3, 1 asymmetrically mounted thermally insulated feed pipe (7a), (7b) are provided, wherein one thermally insulated feed pipe (7a) projects into the interior of the guide pipe (3), the other does not, ie the thermally insulated feed pipe (7b) with opening at the tip of the feed pipe is introduced in another area of ​​the reactor.

[0045] According to Fig. 4, the thermally insulated feed pipes (7) (i.e. 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. Preferably, the cooling or heating circuit is fed with an aqueous medium or with air. In a particularly preferred embodiment, the insulation jacket consists of three layers which enclose 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 having a low thermal conductivity.These 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.

[0046] As shown in Fig. 5, the thermally insulated feed pipe is connected to a feed line leading out of the reactor, forming a recirculation line (12). Optionally, the thermally insulated feed pipe (7) can also be fed by one or more additional feed lines.

[0047] According to Fig. 6, which 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 relative to the remaining part of the pipe in a manner similar to that described for the steam lance.

[0048] According to Fig. 7, which shows 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 designs. Preferably, the reaction temperature in the feed tube is also set in the static mixer. The process parameters 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, a temperature between 10°C and 25°C can be set.The flow velocity and thus the speed of mixing can be adjusted by the circulating volume flow for a given dimensioning of the static mixer.

[0049] Fig. 8 shows preferred entry points, highlighted by hatching, where the entry tubes (7) can introduce aqueous solutions and / or steam or CO2 into the reactor vessel. In principle, it is possible to install the openings at the respective tips of the entry tubes (here referred to as "entry points") on the surface within the clarification ring (1), in the space between the clarification ring (1) and the guide tube (3), or in the guide tube (3) itself. Particularly preferred is the introduction into the guide tube (3) of at least one entry point.

[0050] 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 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 in the reactor overflow in the clarifier and return them to the reactor, thereby positively influencing grain growth. Furthermore, 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, thus increasing the velocity of the solution flowing up to the overflow.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. This is because the intensified classification effect means that the retention probability 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 a reactor without a downstream clarifier. This contributes to a further increase in the upstream flow velocity in the clarification section of the reactor and enhances the classification effect. The clarified solution can be separated in the external clarifier (9).

[0051] 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 thus insulated from the outside so that the external temperature of the steam lance does not exceed, and preferably does not fall below, the reactor temperature in the reactor medium. 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 optionally fed with a cooling or heating circuit. In the particularly preferred embodiment shown, the insulation jacket consists of three layers, which encloses the CO2 feed lance in a ring. 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 a lithium carbonate suspension when, for example, dissolved lithium bicarbonate is to be decomposed and crystallized as lithium carbonate. Steam (D) or an aqueous solution can be passed through the central tube.

[0052] Fig. 11 shows a combination of two apparatuses of the present invention, such as can be used, for example, to purify lithium carbonate. In standard reactor 1, contaminated lithium carbonate is dissolved. For this purpose, an aqueous suspension containing 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 impurities also remain in the reactor; after a specified operating time, the suspension is discharged from the underflow (10) of the reactor and filtered to prevent excessive impurity buildup. The solid lithium carbonate discharged with the solution overflow (2) is collected in a downstream clarifier and returned to standard reactor 1 with the clarifier underflow.The clarifier overflow flows to a fine filter to remove even the finest particles from the lithium bicarbonate solution stream. The setup up to the fine filter ensures that, with temperature and pressure control, a lithium bicarbonate solution with a consistently constant lithium bicarbonate concentration is produced. Since a sufficient amount of lithium carbonate solids is always available, the solution is always concentrated to near the solubility limit of lithium bicarbonate. The dissolved amount of U2CO3 is replenished by the Li2CC>3 suspension, so that the solids concentration in standard reactor 1, and thus also the conversion rate, is maintained, preferably at 15-25 kg / m³. 3h), remains constant. Ion exchangers following the fine filter serve to remove multivalent cations such as calcium, magnesium, or aluminum and / or borates, which are also dissolved by the CO2, from the lithium hydrogen carbonate solution. Lithium carbonate is then recrystallized in the unit reactor 2 with the addition of steam using the inventive setup, drained off at the underflow of the unit reactor 2, and the solid lithium carbonate is separated with a centrifuge and sent for drying. The solution overflowing from the clarifier is collected and, depending on the permissible concentration of other dissolved impurities such as sodium, potassium, chloride, or sulfate, used in whole or in part to suspend contaminated lithium carbonate.

[0053] Embodiments of the invention

[0054] The present invention provides an apparatus and a crystallization process.

[0055] 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 a guide tube (3), which preferably generates a flow directed towards the container bottom, and an annular partition plate (1) (so-called "clarification ring" (1)) concentrically surrounding the axial stirrer (6) for separating a clarification 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.

[0056] 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 jacket which is fed with a cooling and / or heating medium. In a further embodiment, the jacket comprises a vacuum. Another embodiment contains air as an insulation layer. Yet another embodiment contains vacuum insulation or plastic foam. In a particularly preferred embodiment, the feed pipe is encased in three layers, wherein the inner and outer layers provide thermal insulation in the manner described and the middle layer regulates the temperature by supplying a heating or cooling medium such that no measurable temperature gradient occurs between the surface of the feed pipe and the medium into 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.

[0057] 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.

[0058] 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 from the reactor overflow (2) is introduced. Separated solid particles can be collected in the external clarifier (9) and returned to the reactor, thereby promoting crystal growth.

[0059] In a preferred embodiment, the external clarification device (9) is a clarification cone without a raking mechanism, a round thickener with a raking mechanism, a lamella clarifier, a centrifuge, or a decanter.

[0060] In another preferred embodiment, the reactor of the invention comprises two or more thermally insulated feed tubes (7). The thermally insulated feed tubes (7a, 7b) are preferably arranged axially symmetrically to the axial stirrer (6).

[0061] In another embodiment, two thermally insulated feed pipes (7) are arranged asymmetrically (7a), (7b) to the axial stirrer (6).

[0062] In a further embodiment, at least one thermally insulated feed tube (7) is mounted in the guide tube of the reactor (3), ie the feed tube opening at the tip of the thermally insulated feed tube (7) preferably projects into the guide tube.

[0063] In a further embodiment, the reactor of the present invention comprises a deflection ring (4).

[0064] In a further embodiment, the reactor of the present invention comprises a wall baffle (5).

[0065] 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-pitched blade impeller (6a). The use of four-pitched blade or propeller impellers is also possible.

[0066] In a further embodiment, the reactor of the present invention comprises a static mixer (8).

[0067] In a further embodiment, the reactor of the present invention comprises a circulation line (12), preferably a heatable and / or coolable circulation line (12).

[0068] In a further preferred embodiment, the thermally insulated feed pipe (7) is a thermally insulated steam lance (7) whose outer wall can be cooled with ambient air, or whose outer wall can be cooled or heated with a liquid medium. Preferably, the thermally insulated feed pipe (7) is surrounded by a triple insulation layer.

[0069] 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 in the reaction medium inside the reactor occurring which induces or promotes the precipitation reaction without a surface being introduced into the reactor which generates a temperature gradient to the reactor medium.

[0070] Preferably, according to the method of the present invention, a thermally insulated steam lance (7) is introduced into the reactor vessel.

[0071] More preferably, the supplied medium is supplied by means of a circulation circuit (12).

[0072] In another embodiment of the present invention, a battery of two or more devices of the present invention is provided.

[0073] In a preferred embodiment, a battery of two devices (i.e., 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 in a first device of the battery by adding CO2, which is then converted back into pure lithium carbonate in a second device of the battery by adding steam. In these embodiments, purification elements can be introduced between the two devices, 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.

[0074] 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 superstoichiometric amount of solid Ca(OH)2 to dissolved LiOH and solid CaCO3. The selected embodiment promotes the formation of a high concentration of dissolved LiOH with minimized lithium losses caused by undissolved or recrystallized U2CO3 in the solid product CaCO3. 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. The reaction of U2CO3 with Ca(OH)2 initially forms CaCO3, which is significantly less soluble than the two reactants, 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 mass parts in 100 mass parts of solution is reached, the occurrence of solid U2CO3 must be expected, which is lost from the process without further treatment with the CaCO3. Therefore, the water required for the process is fed into the third apparatus, so that a CaCO3 suspension is formed there with a solution with only a low concentration of LiOH, which is dewatered after removal 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 enter 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 CaCO3, thus completing the reaction. The overflow from the first apparatus is directed to a clarifier and clarified, so that the resulting clear solution can be further processed using known methods to produce lithium hydroxide monohydrate or other products.

[0075] In another embodiment of the invention, for the purification of lithium carbonate, contaminated lithium carbonate is continuously dissolved in a unit reactor. According to 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 to achieve a preferred solids concentration between 180 kg / m3 and 250 kg / m 3in the lower region of the reactor. To avoid excessive accumulation of insoluble impurities, suspension is withdrawn continuously or at regular intervals from the reactor underflow so that preferably at least 95 out of 100 mass fractions 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 parameters of the solution in the lithium hydrogen carbonate solution. The lithium carbonate withdrawn from the reactor underflow is used for other purposes. The solid lithium carbonate discharged with the solution overflow is collected in a downstream clarifier and returned to the standard reactor 1 with the clarifier underflow.The clarifier overflow flows to a fine filter to remove even the finest particles from the lithium bicarbonate solution stream. These very fine particles are usually contaminants and are also removed from the process. Ion exchangers follow the fine filter to remove dissolved multivalent cations such as calcium, magnesium, or aluminum and / or borates from the lithium bicarbonate solution. These cations are preferably regenerated with dilute hydrochloric or nitric acid. Conditioning is preferably carried out with dilute lithium hydroxide solution. This prevents the accumulation of other alkali metals, which would occur if potassium hydroxide or sodium hydroxide were used instead of lithium hydroxide. The purified lithium bicarbonate solution is then used to produce lithium carbonate again.For this purpose, it is supplied with steam using the structure according to the invention, with a specific crystallization rate of 10 - 25 kg / hm. 3 , crystallized, separated with a centrifuge, washed if necessary, and sent for drying. The solution overflowing from the clarifier is collected and, depending on the permissible concentration of 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 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.

[0076] 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 enriched in it. The lithium carbonate then passes into a second reactor corresponding to the described embodiments, which is equipped with at least two, preferably three, steam lances corresponding to one of the embodiments of the invention. The previously prepared lithium carbonate is preferably introduced in suspended form through one steam lance. A solution containing another metal salt is introduced through another.A medium is introduced through at least one additional vapor lance, which either leads to the supersaturation of the additional cation introduced into the reactor or, in a preferred variant, provides an additional anion that forms a precipitate with the additional cation. The precipitation of the product is driven by the lithium carbonate present. Due to the inventive structure, the lithium carbonate particles provide a large amount of growth surface area, so that the CO2 particles are uniformly coated with a layer containing 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.

[0077] 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, may also contain further cat- and anions that hinder the crystallization of a battery-suitable lithium carbonate. The embodiments and active principles described in the invention are used to initially crystallize one or more cat- and / or anions in at least two successive crystallization or precipitation steps, without lithium being co-precipitated in relevant amounts. In the last crystallization unit according to the invention, lithium carbonate is crystallized using one of the described embodiments, the crystallization or precipitationDepending on the application, precipitation of the interfering ions can be carried out in one crystallization unit according to the invention per cation or anion, or synchronously with the precipitation of multiple 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.

[0078] Examples

[0079] Precipitation of lithium carbonate by decarbonization of a lithium hydrogen carbonate solution. a) A lithium hydrogen carbonate solution containing 75 g / l UHCO3, temporarily stored at ambient temperature, is pumped at a rate of 10 liters / h through a steam-heated plate heat exchanger, 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 below 7 l / h. After flushing the plate heat exchanger with hydrochloric acid, the original solution flow rate and the targeted temperature of 95 °C were briefly reached again. Because a further significant drop in both process parameters occurred, the experiment was terminated.b) In a second test run, the same solution was introduced at a rate of 10 liters / h directly via a steam lance consisting of a simple tube into the mixed zone within the clarification ring of the reactor according to the invention with a volume of 400 liters. The system was heated with steam flowing via a steam lance consisting of a simple injection tube and extending into the draft tube of the reactor according to the invention. The process was operated for a period of 8 hours before being terminated as planned. During this time, the solids concentration increased to 3 g / l. A quantity of approximately 600 g of U2CO3 surrounded the steam injection tube. 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).

[0080] Example 2:

[0081] For Li2CC>3 precipitation, a total of four small-scale pilot-scale experiments (20-liter reactor volume) were conducted in two different scenarios, each with a conventional setup featuring three overflow stirred vessels with a draft tube and a loop reactor setup. The experimental work is summarized in the table below. All experiments were conducted at approximately 70 °C.

[0082] Table: Simplified overview of the test work carried out on Li2CC>3 precipitation Scenario:

[0083] Low-sulfate solution: The brine contains 0.9% lithium, 6.2% sodium, 13% chloride and 0.02% sulfate.

[0084] High potassium content: The brine contains 0.9% lithium, 4.2% sodium, 3.0% potassium, 12.7% chloride and 0.12% sulfate.

[0085] In scenarios 1 and 3, the lithium solutions are divided. For the first tank in the stirred tank cascade, the lithium solution is fed through an injection pipe at a rate of 19 liters per hour. Similarly, 8 liters of lithium solution per hour are introduced into the second tank in the cascade. A solution containing 30% sodium carbonate is used to precipitate lithium carbonate and is introduced into the first tank in the cascade via an injection pipe. The third tank in the cascade serves to extend the residence time. The suspension leaving the stirred tank cascade is collected in a clarifier, and the solids are thickened, filtered, washed to remove residual liquor, and analyzed.

[0086] Scenarios 2 and 4 are carried out in a setup corresponding to Figure 9. Heating and temperature regulation are achieved via a steam lance as shown in Figure 4, by feeding 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. Starting at the tenth hour, the withdrawal of 2 liters per hour of product suspension from the reactor underflow begins and continues until test hour 32. The reactor overflow enters a clarifier where the entrained solid particles are collected and returned to the reactor via the underflow of the clarifier. This recirculation begins with the first test hour. The withdrawn suspension is filtered, washed to remove any residual caustic, and the product is analyzed.The following impurities occur in the product.

[0087] When using the inventive structure, higher purities are achieved, particularly for the elements sodium and potassium. Furthermore, lower residual moisture contents can be achieved during dewatering, which lie between 6% and 8% after centrifugation with the inventive structure, while residual moisture contents are between 9% and 12% with the conventional structure. Differences also occur in the particle size distribution, with a considerably larger

[0088] Range for the 10% percentiles and multimodal distribution and significantly lower modal values ​​of the main distribution in the conventional setup. These are summarized in the following table:

[0089] Example 3: Production of spherical lithium carbonate by precipitation from a lithium sulfate solution.

[0090] A mass flow of 10.5 kg per hour of a solution containing 7.3% U2SO4, 13.4% Na2SO4, 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. Synchronously, 2 kg per hour of a 33% sodium carbonate solution is introduced into the interior of the draft tube via a steam lance according to the invention as shown in Figure 4 in such a way that a molar ratio of 2.21:1 is established between the amount of lithium ions introduced and 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 above conditions correspond to a specific production rate of 23.9 kg / (m 3h). 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 further washed out. Unlike other processes, the product precipitates in a spherical shape with a median diameter of 0.208 mm and a narrow particle size distribution of 0.169 mm as the lower limit and 0.255 mm as the upper 10-of-100 size percentile.

[0091] Example 4: Thermal insulation

[0092] In a reactor with a volume of 300 m 3 , which circulates a suspension of U2CO3 and an 80% saturated NaCl solution, a cylindrical steam lance protrudes with an immersion depth of 5 m.

[0093] The steam lance is operated with saturated steam at a temperature of 160 °C. The O2CO3 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. 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) and a layer thickness of approximately 2 cm is required.

Claims

Claims:

1. A reactor comprising 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 projects 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 deflection (4), a wall baffle (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 any one of claims 1-9, wherein at least one feed tube (7) projects into the guide tube 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 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 into a medium inside the reactor, the supplied medium having a higher temperature than the reactor medium, a temperature change in the reaction medium inside the reactor occurring which induces or promotes the precipitation reaction, without introducing a surface 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 the median value and 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.

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