Patent Description:
The invention generally relates to the field of selectively preparing highly pure lithium carbonate.

Lithium carbonate (Li<NUM>CO<NUM>) is typically produced commercially from two sources: (<NUM>) the extraction from pegmatite mineral sources such as spodumene, lithiophyllite, or lepidolite, which can be obtained through traditional mining; and (<NUM>) extraction from lithium-containing brines, such as those found in the Salar de Atacama in Chile, Silver Peak Nevada, Salar de Uyuni in Bolivia, or the Salar de Hombre Muerte in Argentina. There are alternative brine sources, such as, geothermal, oilfield, Smackover, and relict hydrothermal brines. These brines, however, have not previously been commercially exploited.

There are a number of commercial applications for lithium carbonate including: use as an additive in aluminum smelting (molten salt electrolysis); enamels and glasses; to control manic depression (when used in its purer forms); and in the production of electronic grade crystals of lithium niobate, tantalite and fluoride. High purity lithium carbonate is required for the fabrication of several materials in lithium ion batteries, such as, the cathode materials and electrolyte salts, and also in more avant-garde secondary batteries which require highly pure lithium metal.

In the case of lithium ion batteries, purified lithium carbonate may be required for the fabrication of the cathode, as well as in the active materials for cathodes such as, and without limitation, lithium cobalt oxide, lithium manganese oxide or lithium iron phosphate, as well as, mixed metal oxides, such as, lithium cobalt nickel manganese oxide.

Several processes currently exist for the removal of lithium from lithium chloride-rich brines or other lithium containing liquids. <CIT> discloses a process for producing high purity lithium hydroxide monohydrate by concentrating a lithium-containing brine for removing ions, adjusting the pH to remove cations, neutralizing the brine, purifying the brine to remove the amount of calcium and magnesium, and electrolyzing the brine to generate a lithium hydroxide solution. <CIT> is directed to a method for producing lithium carbonate from an aqueous solution containing crude lithium hydroxide, which includes purifying lithium hydroxide from the aqueous solution by filtration and crystallization, and carbonizing it in a subsequent step.

However, none of the currently employed methods are suitable for the production of lithium carbonate containing low levels of magnesium and calcium, thus limiting the ability of the lithium carbonate to be used as a battery grade lithium product without first undergoing further purification. Methods for extracting lithium carbonate from mineral sources, such as spodumene or lithium aluminum silicate ore (LiAlSi<NUM>O<NUM>), similarly produce materials that lack sufficient purity for use in batteries. The purity of the resulting material using these processes is not sufficiently pure for battery grade lithium metal production, or for pharmaceutical grade lithium carbonate. Therefore, there is a need for a method for extracting lithium from lithium-containing brines and to produce lithium carbonate of sufficient purity to produce high-purity lithium metal.

The method of the invention is defined by the appended claims.

Herein, a method for producing highly pure lithium carbonate is provided. The method includes the steps of feeding a first aqueous solution that includes a purified lithium chloride stream to an electrolyzer equipped with a membrane or a separator, and comprising an anode, a cathode, and a cathode compartment, wherein the first aqueous solution has a lithium chloride concentration of up to <NUM> % by weight to preferably form an
aqueous solution comprising at least <NUM>% by weight lithium chloride. The method includes the step of applying a current to the electrolyzer to produce a second aqueous solution in the cathode compartment that comprises greater than <NUM> wt % lithium hydroxide, wherein chlorine is generated at the anode, and hydrogen is generated at the cathode, wherein the membrane or seperator prevents cations from migrating in the direction of the cathode while selectively allowing lithium ions to pass through the membrane or seperator. The method includes cooling the second aqueous solution and supplying the second aqueous solution and carbon dioxide to a carbonation reactor to produce a third aqueous solution comprising lithium bicarbonate. The third aqueous solution is separated from the carbon dioxide and lithium carbonate solids formed using a gas-liquid-solid reactor, and filtered to remove trace impurities. Finally, the method includes the step of feeding the filtered third aqueous solution to a precipitation reactor maintained at a temperature of at least about <NUM> to precipitate highly pure lithium carbonate.

In certain embodiments, the method includes the step of supplying the third aqueous solution following the filtration step to an ion exchange column to remove divalent ions.

The characteristic novel features of the invention are set forth in the appended claims. So that the manner in which the features, advantages and objects of the invention, as well as others that will become apparent, may be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which form a part of this specification.

DEFINITIONS. As used herein the following terms shall have the following meanings:
The term "high purity lithium" or "highly pure lithium" means lithium in excess of <NUM>% purity.

The term "ultra high purity lithium" means lithium in excess of <NUM>% purity.

As used herein, the term "a total lithium carbonate concentration" includes both dissolved lithium carbonate (Li<NUM>CO<NUM>) and lithium bicarbonate (LiHCO<NUM>).

As used herein, the term "weak liquor" means the filtrate solution from the lithium carbonate recovery, which has a total lithium carbonate concentration between about <NUM> wt % and about <NUM> wt %, depending on operating mode (heating, cooling, and flow rate), operating conditions, and system design parameters.

As used herein, the term "strong liquor" means the solution from carbonation reactor having a typical total lithium carbonate concentration normally lying between about <NUM> and <NUM>% by weight, typically about <NUM>% by weight %, depending on operating mode (for example, heating, cooling, flow rate), operating conditions, and system design parameters.

Broadly described herein are methods of producing high purity lithium carbonate (Li<NUM>CO<NUM>). In a first comparative example, the process includes reacting an aqueous solution that include technical grade Li<NUM>CO<NUM> (such as the Li<NUM>CO<NUM> that can be purchased from a chemical supplier, for example, Chemetal, FMC, SQM, or other such suppliers) with carbon dioxide (CO<NUM>) at temperatures above the freezing point of the solution, typically between about -<NUM> and <NUM>, more particularly around about room temperature, to produce an aqueous solution that includes lithium bicarbonate (LiHCO<NUM>) and lithium carbonate (Li<NUM>CO<NUM>) dissolved therein. The step of contacting the lithium carbonate with carbon dioxide is preferably at as low a temperature as possible. The lowest temperature possible without using external energy to achieve an altered temperature is employed, for example at room temperature. Alternatively, a leachable ore solution that includes lithium may be treated with carbon dioxide at a temperature of between about -<NUM> and <NUM>, to similarly generate a solution that includes both lithium bicarbonate and lithium carbonate. Such lithium bicarbonate/lithium carbonate solutions may be used in the methods as described herein. This solution is often referred to as the strong solution, and can, for example, have a concentration of lithium compounds up to about <NUM>/L, typically having a concentration of at least about <NUM>/L at a temperature of about <NUM>. The reaction can be conducted in a single reactor, but is preferably conducted in two agitated reactors arranged in sequence, or in series of reactors, optionally including a cooling system to maintain the reaction temperature at a temperature that is above the freezing point of the solution, preferably about <NUM>° C. The mixture from the last of the reactors can be fed to a separation tank, where undissolved lithium carbonate, solid impurities, lithium bicarbonate containing solution, and carbon dioxide can be separated from each other. Stirred tank reactors may be used to prepare the mixture, but other gas-liquid-solid contacting reactors may also be used. The solid can be recycled preferably to the first or, optionally to a second carbonation reactor, if present, where the gases can be recovered and recycled back to the carbonation reactor. In embodiments wherein more than one carbonation reactor is employed, recovered carbon dioxide can be recycled to one or more carbonation reactors. The liquid stream can then be fed to a filtration system which can be configured to remove any insoluble impurities that may be present, such as, silica, iron, magnesium, calcium and like compounds. In certain embodiments, the filtration can utilize of a series of filters designed to progressively remove finer particles, such as for example, filters designed to remove particles having diameters of <NUM>, <NUM>, <NUM>, <NUM>, or in an alternate examlpe, a microfiltration system can be employed that is suitable to prevent colloidal iron (III) from contacting the ion exchange media in the subsequent step. Such a microfiltration system can be tangential (also known as flow by microfiltration) or perpendicular (also known as flow through microfiltration).

The filtration step is followed by the use of a divalent selective ion exchange resin, to adsorb soluble divalent or trivalent ions, such as magnesium, calcium, iron and the like, by selective ion exchange or other similar methods. Following the removal of the soluble divalent or trivalent ions by selective ion exchange, the temperature of the solution can then be raised or otherwise extracting or partially extracting the CO<NUM> to precipitate pure Li<NUM>CO<NUM> in a second zone and preferably returning at least a part of the solution to the carbonation reaction zone (items <NUM>, <NUM> and <NUM> in <FIG>) for economic reasons. This can be done by, for example, by creating a vacuum and bubbling an inert gas, such as, nitrogen, air, argon, or the like, through the solution. Carbon dioxide can be recovered and recycled to the carbonation step. Undesirable monovalent cation impurities present remain in solution and approximately <NUM>% of the solution can be recycled back to the lithium carbonate dispersion step at the beginning of the process and the unrecycled solution is recovered for use in the regeneration of the ion exchange media. During the filtration step of the process, lithium carbonate can be recovered by suitable methods, such as, rotary filtration, band filtration or the like. Recovered solid lithium carbonate can then be subjected to washing, such as, counter current washing, and can include separate filtration zones for the recovery of the filtrate (weak liquor) and the washing solutions. Approximately <NUM>% of the washing solution can be removed and combined with the recycled lithium carbonate solution and supplied back to the initial dispersion step of lithium carbonate.

The ion exchange resin captures primarily divalent ions, such as, calcium and magnesium; however, other divalent ions that are present can also be captured by the ion exchange resin, The final step of filtration includes an iron (III) selective filtration system, which can prevent the iron (III) coming in contact with the ion exchange media. This is significant because if iron (III) is not removed prior to contacting the ion exchange resin and is captured by the ion exchange resin it is difficult to displace them from the ion exchange resins by standard methods of regeneration of ion exchange resins. Once the ion exchange resin capacity becomes exhausted, the solution can be switched to a second ion exchange column to continue filtration of the solution and capture of divalent ions.

The purity of the lithium carbonate can be controlled by ratio of the recycle to bleed of the weak liquor (i.e., the amount of the filtrate from the separation of lithium carbonate that is withdrawn). The weak liquor may have a lithium carbonate concentration of about <NUM>/L. As the bleed ratio is varied between about <NUM>% and <NUM>%, the quantity of soluble monovalent cations and some anions build up in the recycle solution. Thus, at greater bleed rates, a higher the purity of lithium carbonate product can be obtained. For example, it has been found that at a bleed ratio of about <NUM>%, <NUM>% pure lithium carbonate can be obtained. Similarly, a bleed ratio of less than about <NUM>% typically results in the production of lithium carbonate of about <NUM> % purity, which is sufficient for electrochemical/battery grade production lithium carbonate. Furthermore, the degree of washing greatly influences the purity of the lithium carbonate product and its final purity. Different wash ratios to product through put can be used to produce different grades of product purity.

The operation of the ion exchange system is heavily influenced by the velocity of the strong solution through the ion exchange and by varying the velocity of the strong solution, lithium carbonate of varying purity can be obtained.

The lithium carbonate granulometry and morphology can be managed by increasing the degree of agitation and the residence time in the precipitation vessel. As used herein, granulometry generally refers to the particle size and morphology generally refers to the shape of the lithium carbonate compounds. In general, enough agitation is necessary to ensure that insoluble particles are suspended in solution, however excessive agitation can, in certain embodiments, result in a decrease in the average particle size. Increased agitation can be achieved by increasing the recirculation rates. Alternatively, it can also be increased by the addition of a mechanical agitator to the precipitation vessel.

The residence time can be increased or decreased by either the volume of liquid contained in the vessel or by altering the flow rate. The vessel can have a fixed size; however the amount or rate of addition of liquid to the tank can be used to control the residence time of the liquids, thereby indirectly controlling the granulometry of the lithium carbonate particles, and to a lesser extent, the morphology of the lithium carbonate particles. Moreover, the morphology of the lithium carbonate can be modified by the addition of various metal ions to the mixture which provoke an altered crystal growth. The lithium carbonate particles can have an average diameter of less than about <NUM>, alternatively less than about <NUM>, alternatively less than about <NUM>.

The process described above does not remove phosphate or borate from the lithium carbonate product as both phosphates and borates typically precipitate with lithium carbonate. It is therefore envisaged that phosphates and borates can be removed from the strong lithium bicarbonate liquor by passing the liquor through a phosphate adsorbing media such as alumina, or by utilizing a suitable ion exchange media such as AMBERLITE™ IRA743 or alternatively by solvent extraction.

The initial sulfate content in technical grade lithium carbonate obtained from brines is typically about <NUM> ppm. The sulfate concentration in high purity lithium carbonate can be reduced in a single pass to only <NUM> ppm, assuming a recycle ratio of weak liquor of about <NUM>%. The sulfate concentration of the lithium carbonate can be further reduced by additional recycling of the lithium carbonate through the whole process. For example, a product lithium carbonate stream that has been twice cycled through the process described above twice can have a sulfate concentration of less than about <NUM> ppm.

An alternative approach reducing the sulfate concentration is to increase the bleed ratio to between about <NUM> and <NUM>%, rather than the more optimum process of <NUM> to <NUM>%.

The lithium carbonate can be filtered with a band filter at a temperature of between about <NUM> and <NUM>, alternatively between about <NUM> to <NUM>, onto a filter with a specially designed distributor. The filter cake can be washed in a counter current manner to ensure that the purest lithium carbonate is contacted with fresh deionized water. The wash water is recovered and can be used to wash lower purity lithium carbonate. This water can be used to wash the lithium carbonate multiple times to minimize dissolution of lithium carbonate in the water. The water recycle step can be particularly important if pure water is scarce. The final wash of the solid lithium carbonate is with hot deionized water, which can be supplied through one or more spray nozzles, at a temperature of between about <NUM> and <NUM>, alternatively at a temperature of about <NUM>. It has been determined that washing the lithium carbonate product with water at temperatures of greater than about <NUM> results in the water turning to steam and washing is ineffective. The first wash can be completed in a recycle mode, the wash water from the final wash can be added to the wash water recycle system, thereby allowing for a much larger volume of water to be used, but not consumed. As a consequence of the recycling of the wash water, there is a bleed of the wash water, and a part of the wash water can be added to weak liquor recycle to the lithium carbonate dispersion vessel. The first wash water
can be contacted to the lithium carbonate solid at <NUM> to <NUM>.

In an alternative comparative example a process for producing high purity lithium chloride from a lithium chloride solution containing up to about <NUM>% by weight lithium is
described. The lithium chloride containing solution can be a geothermal brine, other brine solution, or other chloride containing solution. Step one of the process includes treating the lithium chloride solution to adjust the pH to between about <NUM> and <NUM>, alternatively between about <NUM> and <NUM>, alternatively between about <NUM> and <NUM> with a base, such as for example, lime, sodium hydroxide, ammonia, or the like,) to precipitate salts of calcium, manganese, or zinc. The solution is then optionally treated with a sodium carbonate solution or with a weak liquor obtained from the bleed of the weak liquor solution. The lithium chloride solution is then supplied to ion exchange media that is operable to remove traces amounts of divalent ions (typically on the order of parts per billion, or ppb), and then to a secondary column that is operable to remove any borate compounds present. The lithium chloride is then concentrated by evaporation or by a combination or reverse osmosis and thermal evaporation (including by natural evaporation from an evaporation pond), to produce a highly concentrated lithium chloride solution, having a lithium chloride solution of up to about <NUM>% by weight lithium chloride (the exact concentration is temperature dependent). During the process, the sodium chloride concentration in the solution can be reduced from greater than <NUM>,<NUM> ppm to less than <NUM> ppm.

The resulting lithium chloride solution, preferably having a LiCl concentration of less than <NUM> ppm, can then be reacted at low temperatures with a gaseous mixture of ammonia and carbon dioxide to produce high purity lithium carbonate. The temperature of the solution can then be increased to degas the solution, thereby generating ammonia and hydrochloric acid gases. These gases are separated by known methods or by membranes.

The present invention is directed to a method of producing high purity lithium compounds, wherein the method includes the following steps:.

In certain instances , at least a portion of the filtrate solution can be recycled back to the cathode compartment of the electrolyzer.

With the high purity lithium carbonate obtained by any of the methods described above, high purity chemicals can be made by reacting this high purity lithium carbonate with specific chemicals. As stated previously, "high purity lithium carbonate" refers to any lithium carbonate having a purity of at least about <NUM>%. Exemplary reactions include the following:.

The preparation of high purity lithium hydroxide may include supplying a lithium halide to an electrochemical cell wherein the high purity lithium hydroxide is produced by electrolysis, while also producing chlorine and hydrogen gas.

A lithium salt, for example lithium bicarbonate or lithium nitrate, may be supplied to an electrochemical cell wherein it is electrolyzed in water to produce high purity lithium hydroxide, hydrogen gas and either H<NUM>CO<NUM> or HNO<NUM>, respectively.

Alternatively, lithium sulfate can be supplied to an electrochemical cell and electrolyzed in water to produce high purity lithium hydroxide, H<NUM>SO<NUM>, and hydrogen gas.

High purity Li<NUM>CO<NUM> can be reacted with HF to produce two moles of high purity lithium fluoride and carbon dioxide. The highly pure lithium fluoride can then be reacted with PF<NUM> to produce a high purity LiPF<NUM> product.

High purity Li<NUM>CO<NUM> can be reacted with <NUM> molar equivalents HBF<NUM> to produce <NUM> moles of high purity LiBF<NUM>, as well as CO<NUM> and water.

Alternatively, high purity Li<NUM>CO<NUM> can be reacted with <NUM> molar equivalents of CF<NUM>SO<NUM>H to produce two moles of high purity Li(CF<NUM>SO<NUM>), as well as CO<NUM> and H<NUM>O.

Alternatively, high purity Li<NUM>CO<NUM> can be reacted with <NUM> molar equivalents of HClO<NUM> to produce two moles of LiClO<NUM>, as well as carbon dioxide and water.

Methods for the regeneration of the ion exchange resin are also described herein.

As used herein, the term "resin" refers to a polystyrene matrix cross linked with divinylbenzene (DVB) substituted with weakly acidic aminophosphonic or immido acetic acid active groups known by various trade names, such as, Amberlite® IRC-<NUM>/<NUM>/<NUM>, Purolite® S <NUM>, Purolite® S <NUM>, Purolite® S <NUM>, LEWATIT® TP-<NUM>, IONAC® SR-<NUM>, and the like.

One example <NUM> of an ion exchange regeneration method, shown in <FIG>, as follows:.

Alternatively, an ion exchange regeneration method may include:.

Microfilters are expensive and frequently become blocked with impurities. It is therefore necessary to recycle them. Several methods of filter recycling have been developed: the preferred methods of recycling are to use citric acid to dissolve iron which allows the iron selective filter to be recycled. Other compounds may also be used to achieve this same result, such as sodium EDTA. It is, however, more effective to use a strong acid solution, such as nitric acid (having a concentration of about <NUM> to <NUM>% solutions) to recycle the filter. To prevent contamination, the filters are then thoroughly rinsed before being placed back into service.

Referring now to <FIG> and <FIG>, <NUM> is the dispersion; <NUM> is the first reactor, <NUM> is the second reactor, <NUM> is the CO<NUM> tank, <NUM> is the gas/solid/liquid separation tank(degasser), <NUM> is the filter bags, <NUM> is the filter cartridges, <NUM> is the resin columns, <NUM> is the precipitator, <NUM> is the felt filter, <NUM> is the dryer, <NUM> is the impure carbonate stream, <NUM> is the first reactor feed stream, <NUM> is the first carbonation reactor, <NUM> is the second carbonation reactor, <NUM> is the second reactor feed stream, <NUM> is the transfer stream to decanter, <NUM> is the carbonate return stream to first reactor, <NUM> is the first carbon dioxide recycle, <NUM> is the bicarbonate stream which is supplied to coarse filtration filter bags (such as the liquid filtration bags provided by Eaton-GAF), <NUM> is the bicarbonate stream which is supplied to fine filtration cartridge filters (such as the sterilizing-grade Acrvent cartridge filters available from Millipore), <NUM> is the bicarbonate stream which is supplied to the resin, <NUM> is the bicarbonate to precipitator, <NUM> is the exchanger recirculation stream, <NUM> is a mixed stream that includes the recirculation stream plus bicarbonate stream which is supplied to the precipitator, <NUM> is the CO<NUM> evaporation stream, <NUM> is the CO<NUM> return line to tank <NUM>, <NUM> is the carbonate stream (which can include carbonate, bicarbonate or a combination thereof) supplied to filter, <NUM> is the carbonate stream that is supplied to dryer, <NUM> is the weak liquor which is recycled to the dispersion, <NUM> is the recycle wash water to that is recycled to the dispersion, and <NUM> is the wash water bleed.

Referring now to <FIG>, <NUM> is a mix tank where recycle stream <NUM> is mixed with feed stream <NUM>, <NUM> is an electrolyzer that includes a division <NUM> between cathode and anode compartments, which can be achieved with a membrane or diaphragm, <NUM> is the lithium chloride solution, <NUM> is the lithium chloride solution which is the effluent of the electrolyzer, <NUM> is the chlorine gas feed, <NUM> is the water feed, <NUM> is the hydrogen gas feed, <NUM> is the lithium hydroxide recycle stream, and <NUM> is the electrolysis lithium hydroxide product stream.

The processes shown in <FIG> and in <FIG> are as follows:
The process starts in dispersion tank <NUM>, which can include <NUM> inputs. Approximately <NUM>% of the feed enters via line <NUM> as a weak liquor, which can be cooled via known means, such as a heat exchanger, to the desired temperature. Feed line <NUM> can have a lithium carbonate/bicarbonate concentration of about <NUM>/L. The mass flow rate of line <NUM> into tank <NUM> is about <NUM>/hr. Approximately <NUM>% of the feed is supplied to tank <NUM> via line <NUM> as recycled wash water, which can be cooled to the desired temperature by known means. This solution in line <NUM> can have a lithium carbonate/bicarbonate concentration of about <NUM>/L and can be supplied at a mass flow rate of about <NUM>/hr. Raw lithium carbonate can be supplied via screw feeder <NUM> at a rate of about <NUM>/L, and a mass flow rate of about <NUM>/hr, under normal operating conditions. The three inputs to tank <NUM> are mixed with sufficient agitation to maintain the insoluble lithium carbonate as a uniformly dispersed solid throughout the tank. An exemplary residence time is <NUM> minutes. The solution is then pumped from tank <NUM> via line <NUM> into the first reactor <NUM>, where CO<NUM> gas is supplied via line <NUM> and is transformed to lithium bicarbonate and therefore render the lithium soluble.

Referring to <FIG>, an exemplary reactor <NUM>, which can be similar to or the same as first and second reactors <NUM> and <NUM>, where such a transformation to lithium bicarbonate may be generated is provided. In certain embodiments, the lithium carbonate solution is supplied to reactor <NUM> via line <NUM> and the carbon dioxide gas is supplied the reactor via line <NUM>. Reactor <NUM> can be separated into various sections, for example a first section <NUM>, a second section <NUM>, a third section <NUM>, a fourth section <NUM>. and a fifth section <NUM>. Reactor <NUM> can include various plates separating the various sections, such as plate <NUM>, separating the first and second sections, plate <NUM>, separating the second and third sections, plate <NUM>, separating the third and fourth sections, and plate <NUM>, separating the fourth and fifth sections. Reactor <NUM> can also include an agitator <NUM>, positioned within the reaction vessel, such that the agitator is capable of providing sufficient mixing of the lithium carbonate and carbon dioxide. Agitator <NUM> can include various blades or protrusions <NUM> designed to provide thorough mixing. Reactor <NUM> can also include baffles <NUM>. Excess carbon dioxide exits reactor <NUM> via line <NUM> and the solution can be removed via <NUM>.

The flow rate of the carbon dioxide to the reactor can be at least about <NUM>/min, alternatively at least about <NUM>/min. Generally, at least a molar equivalent of carbon dioxide is provided, more preferably slightly greater than a molar equivalent (i.e., at least about <NUM> molar) is provided, alternatively greater than about <NUM> molar equivalent is provided. Solid lithium carbonate can be recycled from the bottom of the degasser <NUM> via pump <NUM> to the bottom of reactor <NUM>. During this stage of the reaction, the temperature can increase by about <NUM>, due in part to the exothermic chemical reaction that takes place. The solution from the first reactor <NUM> can then be fed via line <NUM>, optionally through a heater exchanger, to the second reactor <NUM> at a flow rate of between about <NUM>/hr and about <NUM>/hr. The flow rate can be at least about <NUM>/hr. A heat exchanger can be used to cool down the fluid to a temperature of about room temperature. Line <NUM> supplies a CO<NUM> to second reactor <NUM> at a flow rate of at least about <NUM>/min, alternatively at least about <NUM>/min, alternatively about <NUM>/min.

This may occur at a pressure that is slightly above atmospheric pressure, but it can also be run with greater through put at increased pressure. The operating volumes of the first and second reactors can be about <NUM> liters each, although reactors having different operating volumes may also be used. The solution can be cooled to a temperature of about <NUM> and supplied to second reactor <NUM> via pump <NUM>. The heat of the reaction occurring in second reactor <NUM> increases the temperature by about <NUM> to <NUM>. Line <NUM> supplies CO<NUM> gas to reactor <NUM> at a flow rate of about <NUM>/min flow. Second reactor <NUM> can be a stage reactor similar to the first reactor <NUM>. The temperature in reactor <NUM> may increase by about <NUM> as a result of the chemical reaction. Operating second reactor <NUM> at a temperature below about <NUM> enables the addition of a higher solubility of lithium carbonate into the solution, which in turn can lead to greater productivity (i.e., greater through put and higher yield). The bicarbonate containing solution is transferred via <NUM> from second reactor <NUM> to degasser tank <NUM>. In degasser tank <NUM>, the gases, solids and liquid are separated. Solids can be pumped as a slurry via line <NUM> to first reactor <NUM>. Gases, which can include CO<NUM>, can be separated and supplied via line <NUM>, which can recycle the gas to CO<NUM> tank <NUM>, and resupplied to either first or second reactor <NUM> or <NUM>. The liquid bicarbonate is pumped via line <NUM> through at least one, and preferably two, mechanical filter <NUM>. The mechanical filter can include multiple individual filters of varying sizes, including a first filter comprising a <NUM> filter bag, a second filter comprising a <NUM> filter bag. The filtered lithium bicarbonate solution can be supplied to second mechanical filter <NUM>, which can include one or more filter cartridge, for example a first cartridge comprising a <NUM> filter and a second cartridge comprising a <NUM> cartridge. The second cartridge can be configured to prevent iron being fed to ion exchange system <NUM>. The cartridge regeneration process is discussed below. The lithium bicarbonate containing liquid solution can be pumped via line <NUM> to ion exchange resin column <NUM>. The ion exchange resin can remove soluble metal divalent ions that pass through the filter bags <NUM> and the filter cartridges <NUM>. The ion exchange <NUM> can include two columns, one column that is in operation and a second column that is being regenerated. The ion exchange columns can be switched between operation and regeneration when the operating media becomes saturated. The filtered solution from the ion exchange system is fed via line <NUM> to precipitator <NUM>. Precipitator <NUM> can optionally be heated by a recirculation system, which can include a heat exchanger. The solution from precipitator <NUM> can be fed from bottom of the tank and is pumped via line <NUM> to return line <NUM>. The solution from the ion exchange column <NUM> can be combined in line <NUM> with the heated solution from line <NUM> and supplied to the precipitator <NUM>. Precipitator <NUM> can be agitated by the flow of line <NUM>. Optionally, precipitator <NUM> can include an agitator. The solution in precipitator <NUM> can be maintained at a temperature of about <NUM>, which facilitates the separation of CO<NUM> from the bicarbonate. The solid carbonate exits precipitator <NUM> by overflow and CO<NUM> can be cooled and recovered via line <NUM>. Carbon dioxide gas can be recycled via line <NUM> to the two reactors, <NUM> or <NUM>. A product stream that includes about <NUM>% lithium carbonate by weight can be pumped via line <NUM> to filter band <NUM>. The weak liquor can be recovered in a vacuum pan system, and can be cooled and pumped via line <NUM> to dispersion tank <NUM>. A part of this liquor can be stored for regeneration of the resin. The first wash can be done with the same wash recycle water. The second wash can be done with deionized water at a temperature of about <NUM>. Water from each wash can be combined in the same tank for reuse. This water can be cooled and pumped to dispersion tank <NUM>. There is a bleed line <NUM> of this water.

Referring to <FIG>, lithium chloride feed stream <NUM>, having a concentration of between about <NUM> and <NUM>%, can be supplied to tank <NUM>, The lithium chloride can be sourced from an extraction process, including geothermal or other brines. Lithium chloride from tank <NUM> can be supplied via line <NUM> to electrolyzer <NUM>. The effluent lithium chloride solution electrolyzer <NUM> can be recycled back to tank <NUM> via line <NUM>, while chlorine gas and hydrogen gas exits the electrolyzer through outlets <NUM> and <NUM>, respectively. Water is supplied to electrolyzer <NUM> via line <NUM>. Lithium hydroxide can be recycled via line <NUM> to electrolyzer <NUM>, lithium hydroxide product stream <NUM> can be collected. In electrolyzer <NUM>, lithium ions migrate from the anode compartment to the cathode compartment by way of migration and diffusion forces.

Resin is loaded into the column, as follows. First, in a <NUM> barrel, Purolite® S <NUM> resin is mixed with deionized water. To a column having a volume of about <NUM>,<NUM> was added about a ½ volume of deionized water. Using a funnel, the resin and deionized water are manually added to the column. As needed, the valve at the bottom of the column is opened to empty a little water. The steps are repeated until approximately <NUM> of resin has been introduced to the column.

A method for the regeneration of the ion exchange resin is described herein as follows:.

Cartridge filters are very expensive and should be used only once before replacement as the plastic around the filter and the cartridges' connections are fragile. A comparative method for the in situ regeneration of cartridges is described herein. All the steps will be done in reverse flow. Referring to <FIG>, the method <NUM> is shown.

A process for making high purity lithium carbonate without first converting the lithium chloride into solid lithium carbonate according to the present invention is provided as follows:.

Test #<NUM>: The test conditions are shown in Table <NUM> below.

Nation <NUM> membranes were conditioned with a solution of <NUM>% LiOH. The output was calculated by three different manners: LiOH by titration of the catholyte, H<NUM>SO<NUM> by titration of the anolyte, and Li<NUM>SO<NUM> by either analysis with ion coupled plasma atomic emission spectroscopy or ion coupled plasma mass spectroscopy of the anolyte. The current efficiencies were measured by the measurement of three concentrations of lithium hydroxide, sulfuric acid, and lithium sulfate at, respectively, <NUM>%; <NUM>%; and <NUM>%. The average current efficiency was <NUM>%.

Test #<NUM>: Current density was lowered to <NUM> A/m<NUM> (<NUM> A), the duration was increased to <NUM> minutes to allow for a total load of more than <NUM>,<NUM> coulombs, as in Test #<NUM> above. The current efficiencies obtained were: LiOH = <NUM>%, H<NUM>S0<NUM> = <NUM>%, and Li<NUM>SO<NUM> =<NUM>%, with an average of <NUM>%,.

Test #<NUM>: The current density was fixed at <NUM> A/m<NUM> (<NUM> A) and the duration at <NUM> minutes. The current efficiencies were: LiOH = <NUM>%, H<NUM>SO<NUM> = <NUM>%, and Li<NUM>SO<NUM> = <NUM>%, with an average of <NUM>%.

The objective of the electrolysis process is to convert purified, concentrated LiCl into a concentrated LiOH solution for conversion to lithium bicarbonate, before passing the lithium bicarbonate solution through the process steps described in <FIG> at the gas-liquid-solid separation step, and through the process steps described in <FIG> to produce lithium carbonate. The limiting factor determining the efficiency of the cell is the concentration of lithium hydroxide in the catholyte, due to back-migration of the hydroxide across the membrane. The experimental program was designed to operate the cell at four different hydroxide concentrations to map its effect and determine the maximum concentrations that could be prepared.

The experiment measured current efficiency and energy utilization of the dialysis process as a function of hydroxide concentration. As described in the chemistry section above, Li+ ions migrate from the anolyte to catholyte under the applied electric field, while water is electrolyzed to H<NUM> and OH- at the cathode. In theory, each electron passed in the external circuit corresponds to an increase of one LiOH molecule in the catholyte, leading to an increase in concentration of LiOH over time. However, the main inefficiency of the process, back migration of OH- ions from catholyte to anolyte, is dependent on the OH' concentration of the catholyte. The experiments reported here were performed with the intention of maintaining the OH- concentration of the catholyte constant by adding water at a known rate. The efficiency of the reaction was measured by comparing the actual rate of addition of water addition with that expected on the basis of theory.

The electrolysis system consisted of the electrolysis cell, and the anolyte and catholyte flow systems. Electrolysis of LiCl solutions was carried out using an FM01 electrolyzer manufactured by ICI (a scale model of the FM21 electrolyzer used commercially in the chlor-alkali industry). The electrolyzer included lantern blade-style electrodes; ruthenium oxide coated titanium was used as anode and nickel was used as cathode. Nation® <NUM> was used as the membrane. The active surface area was <NUM><NUM> (4x16 cm), and the cell gap was about <NUM>-<NUM>. The FM01 electrolyzer was operated with the flow direction parallel to the <NUM> direction, as this improved the management of gasses (chlorine and hydrogen) evolved from the electrodes. In addition, although anolyte and catholyte flows are normally fed from opposite sides of the cell, they were fed from the same side in these tests, again to limit the effects of gas blinding.

The anolyte flow system included a feed tank, pump, degassing tank, chlorine scrubber, and collection tank. A lithium chloride solution having a concentration of about <NUM>% by weight was placed in the anolyte feed tank and heated to about <NUM>. The solution was pumped through the anode chamber of the cell in a single pass mode at a flow rate of about <NUM><NUM>/min, corresponding to a face velocity of <NUM>/s. On exiting the cell, the LiCl solution and entrained Cl<NUM> gas (produced at the anode) were passed through into a degassing tank which was equipped with a chlorine scrubber to remove chlorine. The solution was then pumped into a collection tank for storage.

The catholyte flow system included a tank, pump and water feed system. Lithium hydroxide was placed in the tank and heated to about <NUM> and was fed to the cathode chamber of the cell in recirculating mode at a flow rate of about <NUM>/min, corresponding to a face velocity of <NUM>/s. Water was added continuously to the system using a peristaltic pump to try to maintain a constant LiOH concentration. The rate of addition was monitored by the weight loss of the water tank. Nitrogen was bubbled through the catholyte recirculation tank to minimize reaction of LiOH with CO<NUM> from air.

The experimental conditions used in the four experiments are summarized in Table <NUM> below. These conditions were the same for all of the experiments. The concentration of hydroxide in the catholyte was varied from <NUM> to <NUM> between the four experiments.

Samples were collected at the catholyte inlet and outlet and anolyte outlet ports every <NUM> minutes during operation of the cell. The cell voltage was monitored at the cell terminals using a handheld multimeter. The difference between the inlet and outlet catholyte hydroxide concentrations and the cell voltage were used to calculate the efficiency and energy consumption of the cell.

Referring now to <FIG> and Table <NUM>, the results of the four experiments are summarized. <FIG> shows the difficulty in maintaining a constant LiOH concentration based solely by adjusting the rate of water addition, in the absence of a real-time measurement of the hydroxide concentration. This is believed to be because water can be consumed or added to the catholyte by a variety of mechanisms, including electrolysis, evaporation and migration across the membrane with Li' cations. In general, the data suggest that the higher the initial concentration of LiOH, the more difficult the task of maintaining the concentration constant through water addition.

The cell voltage was approximately <NUM>-<NUM> V for all of the experimental runs (shown in <FIG>), indicating that the voltage is relatively independent of hydroxide concentration. It also implies that energy consumption is largely driven by the electrical efficiency of the electrode and membrane reactions. The cell gap in the FM01 electrolyzer used in the study (<NUM>-<NUM>) is large, as compared to commercial cells (<NUM>-<NUM>), so a commercial cell would be expected to have a lower cell voltage than those measured here.

The current efficiency decreases with increasing LiOH concentration, as shown in <FIG>. This is likely due to increased back-migration of OH- anions across the membrane from the catholyte to anolyte as the LiOH concentration increases. As shown in <FIG>, this phenomenon also resulted in an increased energy consumption because all experiments were performed at about the same current density and the cell voltage was essentially constant. The data suggests that the practical limiting concentration of LiOH is about <NUM>-<NUM>, although it may be possible to identify a range of operating conditions or other membranes which would achieve a different result.

Table <NUM> summarizes the findings of this study and shows that the efficiency of LiOH production increases as the concentration of LiOH decreases, reaching an efficiency of between about <NUM>-<NUM>% for concentrations of about <NUM> (<NUM> wt %) LiOH. Cell voltage is relatively independent of LiOH concentration, so efficiency also drives the energy requirement, which decreases to about <NUM> kWh per kg LiOH produced at a concentration of about <NUM>. The LiOH production rate is also maximum (<NUM>-<NUM>/m2/hr) at <NUM> wt% LiOH concentration.

Solid lithium hydroxide monohydrate was fed at approximately <NUM>/hr to dispersion tank <NUM> via line <NUM>, and recycled wash water and weak liquor are recycled via lines <NUM> and <NUM> respectively. The total flow rate to the tank being about <NUM>/min. , about <NUM>% of the flow was weak liquor and the remaining flow is wash water. The resulting mixture was a solution of lithium carbonate and hydroxide. The solution temperature was about <NUM>.

The rate of reaction for the conversion of lithium hydroxide to lithium carbonate and bicarbonate was controlled by maintaining a pH on the outlet side of the first reactor <NUM> at about <NUM>. The CO<NUM> flow to the first reactor <NUM> was adjusted to maintain this pH. The CO<NUM> flow rate was about <NUM>/min and the temperature of the solution exiting the reactor was increased to approximately <NUM>, due to the heat of reaction. The solution temperature was cooled to <NUM> by way of the heat exchanger between the first and second two reactors, <NUM> and <NUM>.

The second reactor converted remaining unconverted Li<NUM>CO<NUM> into lithium bicarbonate as CO<NUM> was fed to the second reactor at a flow rate of <NUM>/min and the temperature on the reactor outlet side increased to about <NUM> due to the heat of reaction.

The lithium bicarbonate solution was then passed through the same process and under the same conditions as in Example <NUM>. First the solution passes through to the gas/solid/liquid separator <NUM>, then through filtration <NUM> and <NUM>, ion exchange <NUM> and to the precipitator <NUM> and on to filtration <NUM> and drying <NUM>.

The lithium hydroxide monohydrate had a significantly lower concentration of calcium and magnesium than lithium carbonate. It was therefore possible to increase the time between regenerations to between <NUM> and <NUM> bed-volumes of strong liquor.

The flow rate of the second washing was adjusted to <NUM>/min of deionized water heated to <NUM>. The flow rate of the first wash was the same as in Example <NUM>.

The dryer operated as described in Example <NUM>, producing approximately <NUM>/hr of purified lithium carbonate. The chemical yield was at around <NUM>%.

In <FIG>, the system for the production of high purity and ultra high purity lithium carbonate includes dispersion tank <NUM> that is configured to provide a suspension of particles; first carbonation reactor <NUM>, second carbonation reactor <NUM>, CO<NUM> tank <NUM>, gas/solid/liquid separation tank (degasser) <NUM>, first filtration system <NUM> that includes filter bags, second filtration system <NUM> that includes filter cartridges, ion exchange columns <NUM>, precipitator <NUM>, belt filter <NUM>, and dryer <NUM>. Feed line <NUM> supplies impure carbonate to the reactor, feed to the first reactor is via line <NUM>, CO<NUM> is fed to the first reactor via line <NUM>, CO<NUM> is fed to the second reactor via line <NUM>, lithium carbonate is fed to the second reactor via line <NUM>, lithium carbonate from the second reactor is transferred to the decanter via line <NUM>, a portion of the carbonate is returned to the first reactor via line <NUM>, degassed CO<NUM> is removed via line <NUM>, bicarbonate is supplied to filter bags via line <NUM>, bicarbonate is supplied to the cartridges via line <NUM>, bicarbonate is supplied to the ion exchange resin via line <NUM>, bicarbonate is supplied to the precipitator via line <NUM>, heat exchanger recirculation is via line <NUM>, line <NUM> supplies a mixture of the recirculation from the precipitator and bicarbonate from the ion exchange resin to the precipitator, CO<NUM> separated by the precipitator is recycled via line <NUM>, CO<NUM> from recycle line <NUM> and degasser line <NUM> is supplied to holding tank via line <NUM>, carbonate is supplied to the filters via line <NUM>, filtered carbonate is supplied from the filters to the dryer via line <NUM>, weak liquor from the filters is supplied to the dispersion tank via line <NUM>, recycled wash water is supplied from the filters to the dispersion tank via line <NUM>, and wash water bleed is removed from the filters via line <NUM>.

As is understood in the art, not all equipment or apparatuses are shown in the figures. For example, one of skill in the art would recognize that various holding tanks and/or pumps may be employed in the present method.

The singular forms "a", "an" and "the" include plural referents, unless the context clearly dictates otherwise.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

Claim 1:
A method of producing high purity lithium carbonate, the method comprising the steps of:
feeding a first aqueous solution comprising a purified lithium chloride stream to an electrolyzer equipped with a membrane or a separator, wherein the first aqueous solution has a lithium chloride concentration of up to <NUM>% by weight, the electroylzer comprising an anode, a cathode, and a cathode compartment;
applying a current density up to <NUM>,<NUM> A/m2 to the electrolyzer to produce a second aqueous solution comprising greater than <NUM> wt% lithium hydroxide in the cathode compartment, wherein chlorine is generated at the anode, and hydrogen is generated at the cathode, wherein the membrane or separator prevents cations from migrating in the direction of the cathode while selectively allowing lithium ions to pass through the membrane or separator;
cooling the second aqueous solution;
supplying the second aqueous solution and carbon dioxide to a carbonation reactor to produce a third aqueous solution comprising lithium bicarbonate;
separating the third aqueous solution from the carbon dioxide and lithium carbonate solids formed using a gas-liquid-solid reactor;
filtering the third aqueous solution to remove trace impurities; and
feeding the filtered third aqueous solution to a precipitation reactor maintained at a temperature of at least about <NUM>° C to precipitate highly pure lithium carbonate.