Lithium production processes and systems

Abstract

A process and system for producing a lithium product from a solution containing lithium nitrate is disclosed. A solution containing lithium nitrate is obtained by reacting a lithium-containing metal silicate with nitric acid. The process and system include subjecting the solution containing lithium nitrate to a first heat treatment step (in one or more heated vessels) to remove water and nitric acid (if present), whereby the resulting lithium nitrate-rich crystalline slurry is heated to produce a molten liquid. The process and system also include passing the molten liquid to a second heat treatment step (in a further heated vessel) to heat the molten liquid to substantially decompose the lithium nitrate to lithium oxide.

Description

[Technical field]

[0001] A process and system are disclosed for producing lithium products from solutions containing lithium nitrate. The solutions containing lithium nitrate are typically produced by a process that uses nitric acid to extract lithium from lithium silicate minerals. The lithium products may also be converted to products desired by users of lithium chemicals, particularly lithium carbonate and lithium hydroxide. Lithium metal may also be produced. [Background technology]

[0002] Lithium is widespread throughout the Earth's crust, with an average concentration of roughly 20 parts per million, making it less abundant than other valuable metals such as iron and aluminum, but far more abundant than precious metals such as gold and platinum. One of the fastest growing end uses of lithium is the battery industry. The use of lithium-ion batteries for electric vehicles (EVs) is expected to continue to drive the lithium market as the demand for EVs continues to grow as well. Additionally, there is an increasing demand for lithium for other applications, including energy storage systems, and as an alloying metal. Ultimately, for lithium supplies to keep up with the ever-increasing demand, a sustainable process for producing lithium is needed.

[0003] The concentration of lithium in seawater is so low (less than 0.2 parts per million) that recovery of lithium from seawater is not believed to be economically feasible, even though seawater contains more than 200 billion tonnes of lithium in total.

[0004] Currently, lithium production from brines accounts for the majority of lithium produced worldwide. Most of these brines are extracted from South American salt lakes (salars) in the so-called "lithium triangle" region, which spans Argentina, Bolivia, and Chile. However, the lithium market's heavy reliance on South American brines as the main source of lithium has several drawbacks: sovereign risk issues, environmental issues, and uncertainties regarding the amount of economically recoverable lithium contained in these brines. Furthermore, when solar evaporation is used as a step to recover lithium from the brines, the processing times are large (up to several years), meaning that these processes are slow to respond to fluctuations in lithium demand.

[0005] The world's lithium supply is increasingly being met by extracting lithium from lithium-bearing hard-rock silicate minerals. Traditional means of recovering lithium from hard-rock silicate minerals are costly, complex, hazardous and environmentally challenging. Until recently, there has been little interest in pursuing these sources of lithium.

[0006] The present inventors have invented an improved process for recovering lithium from silicate minerals using nitric acid (WO2017 / 106925), improving upon the prior art of over half a century ago. The relevant content of WO2017 / 106925 is incorporated by cross-reference into this disclosure. The process of WO2017 / 106925 provides a "closed" process in which the main chemical used to extract lithium content from metal silicates, i.e., nitric acid, can be recovered for reuse in further extracting lithium content from metal silicates. WO2017 / 106925 describes a method in which lithium nitrate formed as a result of the reaction of metal silicates with nitric acid can be purified and further converted to lithium products (i.e., lithium carbonate and lithium hydroxide) for use in lithium battery manufacture. WO2017 / 106925 also describes a method in which the lithium oxide intermediate product can be converted (i.e., reduced) to lithium metal. However, in the process of WO2017 / 106925, purification of lithium nitrate requires subjecting the lithium nitrate solution to a crystallization step in which an intermediate lithium nitrate crystal is produced. This intermediate is a virtually pure lithium nitrate crystal product which is then further processed to lithium hydroxide. Crystallization is an energy intensive process and does not necessarily provide any additional benefit in terms of the purity required for the intended end use of the final product.

[0007] Other considerations in lithium production include the geographic location of the mined ore source, the type of processing plant, consumer demand, and the costs associated with transporting lithium between each source, plant, and consumer. For example, transporting lithium as an ore is not as economical as transporting lithium on a lithium basis as an oxide. Furthermore, transporting lithium as an oxide is more economical than transporting lithium on a lithium basis as a hydroxide or carbonate. A staged process, where part of the process is performed near the ore source and the rest near or adjacent to the battery plant, can provide a means to minimize lithium transportation costs. For example, ore can be mined and processed into lithium oxide products in a processing plant near the mine. The lithium oxide is then transported to the battery plant for further processing into hydroxide, etc.

[0008] The reference to the above background art is not an admission that such art forms part of the common and / or general knowledge of the person skilled in the art, nor is the above reference intended to limit the application of the processes and systems disclosed herein. Summary of the Invention [Means for solving the problem]

[0009] In a first aspect, the present specification discloses a process for producing a lithium product from a solution containing lithium nitrate. The solution containing lithium nitrate can be obtained by reacting a lithium-containing metal silicate with nitric acid. For example, the solution containing lithium nitrate can be obtained by the process disclosed in WO2017 / 106925. Here, the term "lithium product" can include lithium nitrate, lithium oxide, lithium carbonate, lithium hydroxide, and lithium metal (among other products containing lithium).

[0010] The process can include subjecting a solution containing lithium nitrate to a first heat treatment step. The first heat treatment step can remove water and nitric acid (if present). The resulting lithium nitrate-rich crystal slurry can be heated to produce a molten liquid. The heating to produce the molten liquid can be performed in a separate vessel / stage.

[0011] The process may also include passing the molten liquid to a second heat treatment step, in which the molten liquid may be heated to substantially decompose the lithium nitrate to lithium oxide. As noted above, lithium oxide may be the "lithium product" produced by the process, or the lithium oxide may be further processed to produce, for example, lithium carbonate, lithium hydroxide, and / or lithium metal (among other products).

[0012] The processes and systems disclosed herein have distinct advantages over the prior art in that they can produce battery grade lithium hydroxide and market grade lithium carbonate from solutions containing lithium nitrate using a relatively simple flowsheet. For example, the processes and systems can require fewer purification steps, lower capital / operational costs, and reduced operational complexity than conventional processes known in the prior art (including Applicant's process disclosed in WO2017 / 106925).

[0013] Moreover, due to their relative simplicity, the processes and systems disclosed herein can be installed adjacent to existing lithium mines and / or beneficiation plants. For example, the processes and systems can be "modularized / containerized" as described in more detail below. The process and system facilities can be owned and operated by the same owner / operator as the mine / beneficiation plant, allowing for added value to be added to the initial product. The flexibility of the processes and systems allows the owner / operator to terminate the process at a stage where, for example, lithium oxide is the final product. Because lithium oxide contains a high percentage of lithium by weight, the transportation of the lithium oxide product ensures even greater transportation cost savings than the transportation of the more known final lithium products (hydroxide / carbonate). The lithium oxide can be sold directly, for example, to a battery plant, which can convert the lower purity oxide to higher purity lithium hydroxide at their own facilities as needed. Alternatively, the owner / operator may decide to process the higher purity lithium hydroxide (and carbonate) on-site by simply adding additional equipment (e.g., a lithium hydroxide crystallizer).

[0014] In some embodiments, in the second heat treatment step, the lithium oxide produced during the decomposition of lithium nitrate may be floated to the top of the molten liquid, resulting in an overflow of a lithium oxide and lithium nitrate slurry and an underflow of the lithium nitrate liquid. Such a flotation step may facilitate the separation of the lithium nitrate from the lithium oxide.

[0015] In this regard, in some embodiments, the process may further include passing the lithium oxide and lithium nitrate slurry to a separation step, in which the lithium nitrate may be substantially removed from the lithium oxide, for example, the separation step may produce lithium oxide crystals.

[0016] For example, in some embodiments, the separation step may include a liquid removal step in which the lithium nitrate is substantially removed as a liquid from the lithium oxide solids, thereby producing lithium oxide crystals. For example, the liquid removal step may include a screw press.

[0017] In some embodiments, the lithium oxide crystals may be sent to a sludge step, where a controlled amount of water may be added to the lithium oxide crystals, thereby producing a solution containing lithium hydroxide monohydrate. The solution containing lithium hydroxide monohydrate may constitute the product of the process.

[0018] In some embodiments, the solution containing lithium hydroxide may be subjected to a crystallization step (e.g., to produce a purer form of lithium hydroxide monohydrate), in which the solution of lithium hydroxide may be concentrated and crystallized to form crystalline lithium hydroxide monohydrate.

[0019] In some embodiments, the crystallized lithium hydroxide monohydrate may be separated from the solution to produce a substantially liquid-free crystallized lithium hydroxide product. For example, separation may be achieved by centrifugation. The resulting lithium hydroxide monohydrate crystals may constitute the product of the process.

[0020] In some embodiments, the lithium nitrate solution removed from the lithium oxide during the separation step may be collected for further processing. For example, the further processing may include the addition of a carbonate compound to the lithium nitrate solution (e.g., in a lithium carbonate precipitation step) such that the lithium reacts with the carbonate, thereby producing lithium carbonate. The further processing may be carried out under conditions that promote the precipitation of lithium carbonate.

[0021] In some embodiments, the lithium carbonate precipitate may be separated from the solution. For example, separation may be accomplished by using a dewatering centrifuge. The lithium carbonate precipitate may constitute a product of the process.

[0022] In some embodiments, the solution separated from the lithium carbonate precipitate may be recycled as an alkaline solution, which may be used in the process step of reacting the lithium-containing metal silicate with nitric acid, or may be used as a neutralization solution.

[0023] In some embodiments, the carbonate compound may include sodium carbonate and / or potassium carbonate, such as may result from adding sodium carbonate or potassium carbonate as the carbonate compound.

[0024] In some embodiments, the solution separated from the crystallized lithium hydroxide monohydrate may be sent to further processing of the carbonate compound. For example, the separated solution may be sent to a lithium carbonate precipitation step.

[0025] In some embodiments, the first heat treatment procedure may include a two-stage heat treatment. The two-stage heat treatment may include a first heating stage in which a solution containing lithium nitrate is heated to near boiling to remove water and nitric acid (if present). The two-stage heat treatment may further include a second heating stage in which the resulting near boiling slurry of lithium nitrate is heated to a temperature of about 400° C. to melt the lithium nitrate in the slurry. Typically, the stages (e.g., vessels) are separate since they operate at different temperatures. However, the stages may also be performed within a single vessel operated under different conditions.

[0026] In some embodiments, the first heat treatment step may produce a vapor stream that includes water and nitric acid (if present). The vapor stream may be collected and condensed. For example, the condensed vapor stream may provide process water and / or a dilute nitric acid solution.

[0027] In some embodiments, the temperature in the molten lithium nitrate in the second heat treatment step may be about 600° C. Such temperatures may decompose the molten lithium nitrate into lithium oxide and nitrogen oxides. The gas stream containing the nitrogen oxides may be collected and sent, for example, to a nitric acid production process. The nitric acid may be recycled back into the process to extract more lithium from the lithium silicate mineral feedstock.

[0028] In some embodiments, the lithium nitrate containing solution sent to the first heat treatment step may be substantially free of contaminants, for example, the lithium nitrate solution may have been processed according to the purification procedure described in WO2017 / 106925.

[0029] For example, the solution containing lithium nitrate sent to the first heat treatment step may be produced by an extraction process in which a lithium-containing metal silicate is reacted with nitric acid. The extraction process may include mixing the silicate mineral with nitric acid. The extraction process may include subjecting the mixture to a leaching process having conditions such that the lithium content of the silicate mineral is leached into the aqueous phase as lithium nitrate.

[0030] The extraction process may further include passing the leach solution through a solid-liquid separation stage to remove residual solids.

[0031] The extraction process may further include optionally heating the separated leachate to distill off water and nitric acid as a vapor stream. The water and nitric acid vapor stream may be collected and used to regenerate nitric acid, which may be recycled to extract more lithium from the lithium silicate mineral feedstock.

[0032] The extraction process may further include subjecting the leachate to a series of reaction conditions such that the contaminants substantially precipitate out of the solution. The extraction process may finally include passing the solution through a filtration step to remove the precipitate, thereby producing a substantially contaminant-free solution comprising lithium nitrate, which may then be sent to a first heat treatment step.

[0033] In some embodiments, the nitric acid produced from the vapor stream of the second heat treatment step may form at least a portion of the nitric acid mixed with the silicate minerals in the extraction process.

[0034] In some embodiments, the lithium-containing metal silicate may include spodumene (LiAlSi2O6). The lithium-containing metal silicate may also include petalite (LiAlSi4O 10 , eucryptite LiAlSiO4, amblygonite (Li,Na)AlPO4(F,OH), and lepidolite K(Li,Al,Rb)3(Al,Si)4O 10 (F,OH)2 and Zinnwaldite KLiFeAl(AlSi3)O 10 It may also include any of the other lithium-containing silicate minerals, including, but not limited to, various minerals of the mica group, including (OH,F)2. The lithium-containing metal silicate may include the lithium boron mineral jadarite LiNaSiB3O7(OH), or may be written as Na2O.Li2O.(SiO2)2.(B2O3)3.H2O.

[0035] Also disclosed herein, in a second aspect, is a system for producing lithium products from a solution containing lithium nitrate. As described above, the lithium products produced by the system can include lithium nitrate, lithium oxide, lithium carbonate, lithium hydroxide, and lithium metal (among other lithium-containing products). The system includes one or more heated vessels capable of heating the solution containing lithium nitrate to an extent that water and nitric acid (if present) are removed as vapor and the resulting lithium nitrate-rich crystalline slurry can form a molten liquid.

[0036] The system may also include a heated vessel capable of heating the molten liquid to substantially decompose the lithium nitrate to lithium oxide.

[0037] In some embodiments, the further heated vessel may be configured as a flotation cell, in which lithium oxide may float as the lithium nitrate decomposes, thereby resulting in an overflow of a lithium oxide and lithium nitrate slurry and an underflow of lithium nitrate, the overflow may be sent to a solid-liquid separation stage.

[0038] In some embodiments, the further heated vessel may produce a gas stream comprising oxides of nitrogen. The further heated vessel may be sealed to prevent such gas from escaping to the atmosphere. In some embodiments, the further heated vessel may be indirectly heated, such as by electrical induction.

[0039] In some embodiments, the solid-liquid separation stage may include a screw press in which the lithium oxide may be substantially separated from the lithium nitrate.

[0040] In some embodiments, the one or more heated vessels may include an evaporator, in which the solution containing lithium nitrate may be heated to evaporate water as vapor along with nitric acid, if present, thereby producing a supersaturated solution of lithium nitrate.

[0041] In some embodiments, the one or more heated vessels may further include a melting vessel into which a saturated to supersaturated solution of lithium nitrate is delivered, where the supersaturated solution of lithium nitrate may be heated to melt the lithium nitrate. The melting vessel may be directly heated or indirectly heated, such as by electrical induction.

[0042] As noted above, the heated vessel or vessels may include an evaporator separate from the melting vessel, although in some embodiments, evaporation and melting may occur within a single vessel operated under different conditions.

[0043] In some embodiments, the system may further include a nitric acid plant. The gas stream containing primarily nitrogen oxides produced by the further heated vessel may be sent to the nitric acid plant to produce nitric acid. As noted above, the nitric acid may be recycled to extract more lithium from the lithium silicate mineral feedstock.

[0044] In some embodiments, a condenser may be positioned to collect and condense vapor from the heated vessel or vessels and, if present, from the evaporator.

[0045] In some embodiments, the system may further include an apparatus configured to produce a crystalline lithium hydroxide product from the lithium oxide produced by the heated vessel.

[0046] In some embodiments, the system may further include an apparatus configured to produce a lithium carbonate product from the lithium nitrate-containing underflow. The apparatus may be configured to produce a lithium carbonate product from the lithium nitrate produced by the solid-liquid separation step. [Brief description of the drawings]

[0047] Embodiments of processes and systems will now be described, by way of example only, with reference to the following drawings: [Figure 1] FIG. 1 is a general block flow diagram of an overall process for recovering lithium products from lithium-containing silicate minerals. [Diagram 2] FIG. 1 is a schematic diagram of a process flow diagram for a process for recovering lithium from a solution containing lithium nitrate. [Diagram 3] FIG. 2 is a schematic diagram of a process flow diagram for a first heat treatment procedure. [Figure 4] FIG. 2 is a schematic diagram of a process flow diagram for a second heat treatment procedure. [Diagram 5] FIG. 1 is a schematic diagram of a process flow diagram for a nitric acid production facility. [Figure 6]FIG. 1 is a schematic diagram of a process flow diagram for the lithium hydroxide production area where lithium oxide is converted to lithium hydroxide monohydrate. [Figure 7] FIG. 1 is a schematic diagram of a process flow diagram for the lithium carbonate production area where lithium nitrate is converted to lithium carbonate. [Figure 8] and [Figure 9] FIG. 3 is a schematic diagram of a process flow diagram in which purified lithium nitrate is produced from lithium-containing silicate minerals, the purified lithium nitrate being fed into the process of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] In the following detailed description, reference is made to the accompanying figures, which form a part of the detailed description. The illustrative embodiments described in the detailed description, illustrated in the drawings, and defined in the claims are not intended to be limiting. Other embodiments may be utilized and other changes may be made without departing from the spirit or scope of the presented subject matter. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings, may be modified, substituted, combined, separated, and designed in a variety of different configurations, all of which are contemplated by the present disclosure.

[0049] In the following description, an embodiment of a process and system for recovering lithium products from a solution containing lithium nitrate is disclosed. At least three lithium products (lithium oxide, lithium hydroxide, and lithium carbonate) and nitric acid can be produced from the solution containing lithium nitrate. The process and system are designed to be added to an upstream process that leaches lithium from a lithium-containing metal silicate to form a solution containing lithium nitrate. An example of this upstream process is described below with reference to Figures 8 and 9. The process and system have an advantage over the prior art in that it does not require the lithium nitrate to be crystallized before the production of the lithium products.

[0050] Figure 1 is a conceptual flow diagram of a process 10 for lithium extraction from a lithium-containing metal silicate 12 and nitric acid 18 to produce a solution containing lithium nitrate 22, shown in simplified block diagram form. The process 10 for lithium extraction and production of purified lithium nitrate solution 22 is illustrated and described in more detail below with reference to Figures 8 and 9.

[0051] The lithium extraction process 10 is supplemented by a process 20 for recovering the lithium product from the purified lithium nitrate solution 22. Process 20 is described in further detail below with reference to Figures 2-7.

[0052] Typically, process 10 for the extraction of lithium from lithium-containing metal silicates using nitric acid would be the first step of the process outlined in Applicant's process described in WO2017 / 106925, the relevant contents of which are incorporated herein by reference. In this regard, after initial purification of the solution containing lithium nitrate, the solution is sent to the first heat treatment step of process 20 instead of being sent to the crystallizer of WO2017 / 106925.

[0053] However, it will be appreciated that the lithium nitrate containing solution can also be produced by other means, for example by chemically treating a lithium-containing brine using the methods disclosed in Applicant's co-pending patent WO2020 / 107074, the relevant contents of which are incorporated herein by reference.

[0054] It should be appreciated that the process 10 and process 20 depicted in Figures 1-9 can be modularized / containerized, whereby each module / container defines a separate stage of the overall process. Furthermore, each module / container can be manufactured and assembled primarily in a factory environment and then transported to the new lithium refinery site where it can be quickly and conveniently assembled. This is an attractive option because lithium ore refineries are typically located in remote locations (e.g., next to a host mine or dressing plant). In remote locations, the cost of building a refinery is typically much higher than in a populated area. Furthermore, in remote locations, it is more difficult and expensive to secure qualified operators, and inclement weather can cause significant delays in construction. On the other hand, at least for process 10 and process 20 depicted in Figures 1-9, the advantages of building a refinery adjacent to or in close proximity to a host lithium ore mine and dressing plant are clear. For example, this uniquely and virtually eliminates the need to transport large quantities of expensive and hazardous chemicals from the mine / dressing plant to remote processing sites, and also eliminates the need to transport the largely worthless chemical by-products resulting from the use of the chemicals to suitable, non-hazardous disposal sites. Similarly, the only residue from Process 10 and Process 20 of Figures 1-9 is the leached spodumene concentrate, which is an inert, well-draining, finely divided solid that can be easily returned to the host mine site where it can be mixed with the mine dressing plant wastes that are typically produced in larger quantities.

[0055] As an example, at pilot scale, a modular / containerized plant can consist of up to four modules. The process equipment can be installed on three skids, each with the floor area of ​​a standard "twenty foot" (TEU) shipping container. The TEU dimensions can be set so that all process equipment is less than 2.8 meters in height, allowing for road transport. The equipment can be fixed to an acid-resistant FRP base / floor. The base frame can be formed into a protective barrier to contain spills and leaks. The floor can be reinforced to withstand the operating weight of the equipment and normal operating stresses.

[0056] Modules / containers can be assembled in sequence. For example, this allows an upstream process (e.g., process step 10 in Figures 8 and 9) to be evaluated and its performance to be demonstrated while subsequent modules / containers are being constructed. The first module / container can be operational within 3 months of the decision to proceed with construction, and further modules / containers can be added sequentially (e.g., at 4-6 week intervals), allowing the entire process to be demonstrated within 6 months of the decision to proceed with construction.

[0057] Production of purified lithium nitrate rich pregnant leach solution (PLS) As generally described in WO 2017 / 106925 and illustrated in further detail in Figures 1, 8, and 9, to produce a purified lithium nitrate solution 22 for use in the process 20 of Figures 2-7, a metal silicate containing lithium-12, such as alpha-spodumene, is first activated, such as by calcination, to produce primarily beta-spodumene. The beta-spodumene (Figure 8) forms the starting material 800 for the process illustrated in Figures 8 and 9.

[0058] Digestion of spodumene in nitric acid (module 1 of the pilot-scale plant) Beta spodumene 800 is fed to a feed mixer 802 where it is mixed with a stream of concentrated nitric acid 804, which is nominally 50%, but may range from 28% to 68%, in excess (e.g., this is shown in FIG. 1 as stream 18). Nitric acid 804 may be produced in a nitric acid production plant 50 (described below).

[0059] Once the batch is mixed in the feed mixer 802, the contents of the feed mixer are discharged to a feed holding tank 806, which takes the form of a covered polypropylene tank fitted with an agitator to prevent uneven distribution of the feed material. In tank 806, the contents are mixed and maintained at ambient temperature (e.g., ∼25°C). In process 10, tank 806 may serve to provide a flow "buffer" whereby its contents are intermittently replenished but then continuously fed to digester reactor 820 where the β-spodumene is "digested", or leached, with nitric acid.

[0060] In the digester reactor 820, the mixture of nitric acid and beta-spodumene is subjected to high temperatures and pressures, releasing the lithium from the beta-spodumene matrix and producing a solution containing lithium nitrate and other impurities. Other contaminants present in the beta-spodumene, which may be leached at the same time as the lithium and form part of the solution, include iron, aluminum, silica, potassium, and sodium.

[0061] The contents of the tank 806 are pumped from the tank to the digester reactor 820 via a suitable reactor feed pump 808. The pump 808 may consist of a peristaltic pump fitted with a variable speed drive to regulate the flow of the beta-spodumene / nitric acid slurry to the digester reactor 820. The pump 808 typically pressurizes the slurry to 6-8 bar gauge and passes it through a regenerative spiral heat exchanger 810 (a suitable spiral heat exchanger is supplied by Alfa Laval in titanium). In the heat exchanger 810, the hot slurry stream 812 exiting the digester reactor 820 preheats the beta-spodumene / nitric acid slurry so that it can reach temperatures of up to around 180°C as it passes through the digester reactor 820. An auxiliary electric heater 814 may be provided. Generally, the electric heater 814 is only used during start-up and process upsets. In any event, the heat exchanger 810, and optional electric heater 814, combine to increase the slurry feed temperature to the digester reactor 820 up to 180°C.

[0062] The digestion reactor 820 as shown consists of a three-chamber autoclave (substantially made of titanium). During normal operation, approximately one-third of the total volume of the reactor 820 is dedicated to the gas phase. The autoclave digestion reactor 820 can also be operated at substantially lower liquid:gas phase volumes, allowing the exploration of lower residence times. The nominal residence time of the slurry in the autoclave digestion reactor 820 is a maximum of 60 minutes. Accurate filling of the reactor 820 is ensured by continuously monitoring the reactor's operating weight, and if this deviates from the set point, the speed of the reactor feed pump 808 is adjusted accordingly.

[0063] In operation of digester reactor 820, the free nitric acid concentration of the aqueous phase of the reactor contents moving along its length is progressively reduced, dropping from its feed end. The operation of digester reactor 820 is fully continuous. During operation, excess water vapor and nitric acid are distilled off as stream 809, which can be sent, for example, to nitric acid plant 50, for regeneration of concentrated nitric acid for reuse in digester reactor 820. Additionally or alternatively, stream 809 can be condensed to provide (e.g., weak acid) process water, the use of which is described below.

[0064] The reaction time for leaching of lithium content in digester reactor 820 is short. For example, extraction of lithium content from calcined spodumene concentrate is ensured by using a large excess of nitric acid and typically exceeds 95% within 15 minutes. Alternatively, digester reactor 820 may be operated with a longer reaction time to promote secondary reactions such as the autohydrolysis of iron nitrate. Importantly, under conditions characterized by a large excess of nitric acid, the equilibrium for the autohydrolysis of iron nitrate remains (desirably) on the left side:

[0065] Fe(NO3)3+3H2O→Fe(OH)3+3HNO3

[0066] However, depending on how much nitric acid is added beyond the stoichiometric amount needed to leach the lithium from the spodumene concentrate, and how much of this excess acid is used to leach other metals, particularly iron and aluminum, into solution as nitrates, the overall free nitric acid concentration can be reduced to such an extent that the equilibrium of the above reactions begins to shift to the right, leading in particular to the formation of iron hydroxide precipitates, even though there is still a significant amount of free nitric acid in solution.

[0067] The hot slurry stream 812 exiting the digester reactor 820 is rapidly cooled in the regenerative spiral heat exchanger 810 to below 100° C. using countercurrent flow with the incoming digester reactor feed slurry. This cooling further inhibits digestion of impurity metals in the leached spodumene by excess nitric acid.

[0068] The slurry leaving the spiral heat exchanger 810 is depressurized to ambient pressure through a pressure reduction control valve 816 and then flows into a covered, agitated filter feed tank 818. The effective volume of the feed tank 818 is sufficient to hold up to two hours of reacted slurry flow under the operating parameters of the process. From the filter feed tank 818, the partially cooled and atmospherically pressured reacted slurry is pumped via a tailings filter feed pump 822 to a tailings filter press in the form of a plate and frame filter press 824.

[0069] At the start of each filtration cycle, the filter feed pump 822 turns on and fills the plate and frame filter press 824. Completion of filling is established when the backpressure in the filter press 824 rises to substantially equal the backpressure in the inlet line to the filter feed pump 822, at which point the filter feed pump turns off. The plate and frame filter press 824 is used to filter out solids present in the partially cooled product slurry from the digester reactor 820, forming a filter cake in the filter press.

[0070] The filter cake is then washed by opening the solenoid valve 826 to admit hot wash water 824 for the desired wash time. The amount of wash water employed is set by the extent of filter cake washing required, but typically at least as much wash water as the filter cake is employed. Once washing is complete, the wash water supply valve 826 is closed and the solenoid controlled air flow valve 830 is opened to allow compressed air 832 to flow into the filter press 824, thereby removing excess water from the filter cake. Although various control protocols can be followed, the preferred filtration method is to continue the washing and / or air drying cycles until sufficient slurry has accumulated in the filter feed tank 818 for the next complete filtration cycle. At the end of the final drying cycle, the air flow valve 830 is closed and the filter press 824 is opened for cake discharge. The low moisture filter cake (leached spodumene concentrate) is discharged from the filter fabric and collected in a hopper or other container, thereby forming a lean residue / tailings stream 834. It can then be disposed of (e.g., by using it as a feedstock in cement production). At least a portion of the wash water stream 828 can also be recycled for use in other parts of the process.

[0071] The filtrate from filter press 824 is periodically discharged as pregnant leach liquor (PLS) stream 836, which is a substantially clear solution of lithium nitrate, aluminum nitrate, small amounts of iron nitrate, the alkali metals sodium and potassium, calcium, and small amounts of other metals and nitric acid, resulting in a pH value below zero. Stream 836 is collected in a raw PLS holding tank 838 (e.g., a separate polypropylene tank fitted with a dust cover). From tank 838, the stream is periodically transferred by a raw PLS transfer pump 840 to the purification stage of the process (described below with reference to FIG. 9).

[0072] Purification of pregnant leachate (Module 2) Referring now to Figure 9, the raw PLS (pregnant leach solution) 900 containing lithium nitrate and other impurities is pumped via transfer pump 840 to a series of purification and neutralization stages. In these stages, reagents are added to promote precipitation of base metals and neutralize remaining nitric acid. Solid precipitates are removed by sending the solution and precipitate to solid-liquid separation stages. The end result of these purification and neutralization stages is a substantially contaminant-free solution 22 containing lithium nitrate. Solution 22 is also substantially free of nitric acid. The general concentrations of residual contaminants and suitability of solutions containing lithium nitrate as feedstocks for process 20 are also described in more detail below with reference to Example 1.

[0073] As described above, the filtrate 838 from the tailings filter press 824 (i.e., the raw PLS) is pumped out of the raw PLS holding tank 838 by transfer pump 840 as a hot (near boiling) aqueous solution of lithium nitrate, along with nitrates of other metals leached from the ore by the nitric acid, i.e., aluminum, residual iron and other transition metals, calcium, magnesium, sodium, potassium, phosphate ions, as well as any residual free nitric acid surplus needed to convert various cations leached from the concentrate to nitrates, along with wash water added by the tailings filter press 824.

[0074] This hot raw PLS 900 enters an electrically heated PLS evaporator 904 (i.e., heated via electrically heated jacket 902) where most of the volatiles, i.e., water and nitric acid, are boiled off as stream 906. The PLS evaporator 904 may be a multiple effect evaporator consisting of three or more effects in a commercial-scale plant, or a multi-stage flash system with 12 or more stages, and is made large enough to accommodate up to an hour's worth of concentrate, allowing time for the hydrolysis of most of the aluminum and ferric iron to be nearly complete, as shown below.

[0075] The PLS evaporator system 904 is operated until the residue is primarily a saturated solution of lithium nitrate and its crystals, forming a dense but pumpable slurry. The evaporation is essentially at atmospheric pressure, but because of the large increase in boiling point of the highly concentrated and saturated nitrate solution, the temperature of the final saturated solution can exceed 180° C. before the slurry becomes unpumpable. Test work has demonstrated that, before this point is reached, the very high deliquescence of lithium nitrate will cause nearly all of the free nitric acid to evaporate away; i.e., the strong attraction of lithium nitrate to the water will cause the nitric acid to boil preferentially. In practice, the PLS evaporator 904 is operated such that the concentration of soluble material in the PLS does not exceed the point at which the PLS ceases to be a pumpable slurry or when lithium nitrate crystals begin to form (e.g., when the temperature of the boiling liquid reaches approximately 180° C.).

[0076] The combined nitric acid-rich vapor phase 906 boiled at a temperature of about 120° C. in the PLS evaporator flows to the nitric acid production stage 50 (e.g., located in module 3, described below) at near atmospheric pressure. In an embodiment with an evaporation system such as a multi-effect or multi-stage flash, multiple phases ranging from virtually pure water vapor to concentrated nitric acid vapor can be produced, rather than just one nitric acid-rich vapor phase. These separate phases can be condensed separately or in combination with others and recycled to various parts of the overall process 10 and 20, including to the direct feed mixer 802, to the nitric acid plant 50, or to various holding tanks that hold process water or nitric acid solutions of various concentrations.

[0077] Removal of most of the unreacted (excess) nitric acid from the liquid phase in the evaporator system 904 reduces the pH concentration of the PLS (i.e., the pH value increases), but only to a pH of about 1-2. This allows autoprecipitation of most of the iron and aluminum content that was extracted from the spodumene concentrate and brought into solution as nitrates by the nitric acid in the digester reactor 820. More specifically, the equilibrium of the following reversible reaction is shifted to the right (it can be seen that the equilibrium for ferric iron above is virtually the same):

[0078] Al(NO3)3+3H2O←→Al(OH)3+3HNO3

[0079] This formula is a simplification, as the "hydroxide" is probably best described as hydrated lithium aluminate, with a chemical formula close to LiAlO(OH)2. The aluminum hydroxide contains significant lithium content, approximately 5% of the value recovered from the beta spodumene in the digester reactor 820.

[0080] The process seeks to recover this lithium as well. In this regard, the saturated liquid / crystal slurry from the PLS evaporator, containing a load of iron and (mainly) aluminum hydroxide crystals, is pumped by a suitable positive displacement pump 908 to a filter feed tank 910, in this embodiment a sealed, stirred storage vessel. The filter feed tank 910 is maintained at a pressure of 6-8 bar and a temperature of ~180°C. The filter feed tank 910 is operated with a flow of sufficient hot wash water 910 to dilute the PLS liquid to redissolve the lithium nitrate crystals and to ensure that no crystallization of lithium nitrate or other nitrates occurs at temperatures up to 80°C. The flow rate of the wash water 912 is controlled via a solenoid valve and non-return valve pair 914 to maintain the nitric acid concentration in the aqueous phase below 5% HNO3. By pressurizing the mixture in the tank 910, the boiling point temperature can be maintained above 180°C. The pressure in tank 910 can also be controlled / regulated via compressed air line 916 (compressed to ~1,000 kPa) controlled via solenoid valve and check valve pair 918.

[0081] If necessary, a weak nitric acid feed stream 920 may be diverted to tank 910 via solenoid and check valve pair 922 to maintain the nitric acid concentration in tank 910 at a desired level of less than 5%. The weak nitric acid itself may be produced and held in holding tank 924, and prepared by feeding strong nitric acid stream 926 (produced in another part of the process, e.g., plant 50) via valve 928. Strong nitric acid 926 is mixed with a portion of hot wash water 912 in holding tank 924, with the feeding of the hot water portion controlled via valve 930. Produced weak nitric acid 920 is pumped out of holding tank 924 via pump 932.

[0082] Under the high temperature and pressure conditions maintained in the pressurized filter feed tank 910, the dilute nitric acid (residual from the PLS evaporation step / stage 904) leaches the lithium content in the aluminum hydroxide precipitate, forming more lithium nitrate in solution. The residence time provided in the filter feed tank 910 is approximately 2 hours, which is sufficient time for further aluminum content to precipitate and for all lithium content to be completely leached out of them.

[0083] The liquid phase from filter feed tank 910 flows under pressure through check valve and control valve pair 934 to a further filter press 936 (other filtration or arrangements including centrifugation are possible). In a similar manner to filter press 824, filter press 936 is supplied with hot wash water from stream 912 and compressed air from line 916 through respective solenoid and check valve pair 938. Weak nitric acid 920 for filtrate wash (i.e., to flush the filter cake of residual nitrates) can also be supplied to filter press 936 through respective solenoid and check valve pair 938.

[0084] The filter cake 940 from the filter press 936 is periodically discharged from the filter fabric and collected in a hopper or other container, thereby again forming a lean residue / tailings stream 940. This stream 940 may be combined with the tailings residue from the leaching stage (Module 1, FIG. 8) and then similarly disposed of.

[0085] Filtrate stream 942 from filter press 936 is sent to a subsequent purification stage. As shown, the purification stage consists of a series of three stirred precipitation tanks arranged to sequentially remove species such as residual aluminum (i.e., from the downstream product process) by the addition of lithium hydroxide solution 944.

[0086] Such a first precipitation tank 946 is configured for Al(OH)3 precipitation. The second (next) precipitation tank 947 is configured for Mg(OH)2 precipitation. The third (next) precipitation tank 948 is configured for CaCO3 precipitation.

[0087] Filtrate stream 942 is sent to a first precipitation tank 946 where the pH of the solution is raised to about 2-3, causing the remaining aluminum content to precipitate as hydroxide (due to the high concentration of lithium nitrate, the hydroxide precipitates as a filterable crystalline solid, rather than a gel). The resulting supernatant liquid is then sent to a second precipitation tank 947 where the pH of the solution is raised to about pH 9.5, causing the magnesium content to precipitate as insoluble magnesium hydroxide according to the following:

[0088] Mg(NO3)2+2LiOH→2LiNO3+Mg(OH)2

[0089] If desired (or required), residual calcium is removed by precipitation as insoluble calcium carbonate (calcite) in a third precipitation tank 948, but this time with the addition of an appropriate amount of lithium carbonate 950 (i.e., from a downstream product process). The lithium carbonate stream 950 causes the following reaction:

[0090] Li2CO3+Ca(NO3)2→2LiNO3+CaCO3

[0091] The passage of liquid through the precipitation tanks 946, 947, 948 is driven by the polishing filter feed pump 952 (i.e. pump 952 draws liquid through tanks 946, 947, 948). Once the liquid has passed through all three tanks (and pumped out via the polishing filter feed pump 952) any precipitated solids that have accumulated within the liquid are sent to a fourth agitated tank, the filter feed tank 954. By this stage, any precipitated solids present are removed and washed by passing the liquid from the filter feed tank 954 through a suitable polishing filter 956. Also, due to the high concentration of lithium and nitrate ions, any solids that precipitate will precipitate as dewaterable crystalline solids, rather than a gel. The solids filtered by the polishing filter 956 are collected and fed to the combined tailings stream from the leaching stage and filter press tailings 940 as stream 958 for disposal.

[0092] Additionally, there is an option to operate the four tanks (i.e., the three precipitation tanks 946, 947, 948 and the one filter feed tank 954) in pairs, with the first two tanks precipitating the aluminum fraction and the next two tanks precipitating the magnesium fraction.

[0093] Purification steps 946-948 produce a purified lithium nitrate solution 22. This solution can include products of the process, but typically the purified lithium nitrate solution 22 is further processed to produce lithium oxide and downstream products including lithium hydroxide, lithium carbonate, and lithium metal.

[0094] Process (20) - Recovery of lithium products from purified PLS (Figures 1 to 7). In the next section, a preferred embodiment of the entire process is described in which crystallization is avoided from the production of crude PLS to the production of solid lithium oxide. This overall description is therefore an alternative to the techniques described in U.S. Pat. Nos. 10,131,968 and 10,883,156 insofar as the production of a high purity lithium oxide intermediate required crystallization of pure crystalline lithium nitrate from purified PLS to remove the alkali metals remaining after removal of all Group 2 and Group 3 metals.

[0095] 1, the solution containing lithium nitrate 22, purified to the extent that it is free of metals other than alkali metals, is sent to a first heating step 30, which is described in more detail below with reference to FIGURE 3. In the heating step 30, water 32 is evaporated from the solution. The evaporated water 32 is collected, condensed, and stored 36 for reuse in the process. Residual nitric acid vapor may be carried along with the evaporated water 32. In the heating step 30, the resulting lithium nitrate-rich crystal slurry is heated to form a lithium nitrate melt 34 (molten liquid).

[0096] The molten lithium nitrate melt 34 is passed to a second heating step 40, which is described in more detail below with reference to Figure 4. In the second heating step 40, the lithium nitrate melt 34 is heated more vigorously to substantially decompose the lithium nitrate into lithium oxide 44 and a gas stream 42 that contains nitrogen oxides (NOx) and some oxygen.

[0097] The gaseous NOx stream 42 produced from the decomposition of lithium nitrate in the second heating step 40 is collected and sent to a nitric acid production facility 50, which is described in more detail below with reference to FIG.

[0098] As the lithium nitrate decomposes in the second heating step 40, the lithium oxide produced tends to float to the top, forming an overflow of lithium oxide-in-lithium nitrate slurry filled with bubbles of the other decomposition products, nitric oxide, nitrogen dioxide, and oxygen. The overflowing slurry first enters an annular trough where virtually all of the bubbles collapse, releasing the gaseous products and resulting in a two-phase slurry of solid lithium oxide crystals in molten lithium nitrate. This slurry flows to a solid-liquid separation system where (in an embodiment) a screw press is used to separate the undecomposed lithium nitrate liquid from the solid lithium oxide. The screw press "squeezes" the lithium nitrate-rich liquid from the lithium oxide, producing a cake of lithium oxide product 44. The lithium nitrate-rich liquid is returned to the decomposition vessel 404 for recirculation.

[0099] Because this lithium nitrate-rich liquor also contains sodium and potassium nitrates (and perhaps small amounts of rubidium and cesium nitrates to the extent that these normally rare alkali metals were present in the spodumene concentrate), these alkali metal nitrates will accumulate in the contents of the decomposition vessel 404, resulting in a steadily increasing concentration relative to the lithium nitrate as more lithium nitrate is decomposed. In practice, this process may reach a limit, since the lithium oxide cake (in this embodiment) from the screw press will inevitably contain some of these alkali metal nitrates in the interstices between the compressed lithium oxide crystals that form the cake. Eventually, a situation will arise where the amount of such alkali metal nitrates being removed from the circulating lithium nitrate liquor (from the decomposition vessel to the screw press liquor and back to the decomposition vessel) matches the rate at which these alkali metal nitrates enter this circulation as new feed to the decomposition vessel.

[0100] Thus, the lithium oxide cake formed above does not result in a pure product, but rather "raw" lithium nitrate, which requires further purification before it can be considered acceptable as a feedstock for lithium battery manufacturing.

[0101] Reference is made to previous patents granted to the inventor, such as US 10,131,968 and US 10,883,156, which describe techniques for the production of high purity lithium oxide as a key process intermediate or final product. They involve an additional process step, namely the crystallization of the partially purified pregnant leach solution (PLS), i.e. the lithium nitrate solution is purified so that the only impurity elements present in this PLS are sodium and potassium present as nitrates (and possibly rubidium and cesium if present in the spodumene concentrate fed to the refinery). However, although it is considerably simpler than the crystallization process that must be undergone in the refining process of other lithium minerals, such as the crystallization of the by-product sodium sulfate by using sulfuric acid instead of conveniently reusable nitric acid, as in the inventor's related patents and applications, the crystallization is a complex and expensive process that is not suitable for carrying out at remote mine sites.

[0102] A feature of this application is the production of battery grade lithium chemicals with a minimum of crystallization steps, and in particular, the production of pure crystals of lithium hydroxide monohydrate with only one crystallization step for the final lithium hydroxide monohydrate product.

[0103] Another feature of this application is that it allows the entire process of refining lithium-rich minerals into battery-grade lithium chemicals to be conveniently divided into two locations: the production of a raw lithium oxide product (e.g., spodumene concentrate containing 6% lithium oxide, often abbreviated as SC6) at or near the mine / beneficiation plant site that is the source of the refinery feedstock, and a "finishing" stage located at or near the lithium battery manufacturing facility where the raw lithium oxide is converted to pure battery-grade lithium hydroxide (or converted to carbonate, if desired, utilizing techniques specifically described in the inventor's U.S. Patent 10,131,968).

[0104] This is explained in more detail below with reference to FIG.

[0105] The high concentration of elemental lithium even in "raw" solid lithium oxide as produced by this version of Process 20 minimizes the transportation cost per tonne of elemental lithium, especially when compared to the transportation of spodumene concentrate, which is 94% waste. Such waste inevitably creates disposal problems for the customer / battery manufacturer. From a transportation standpoint, lithium oxide is the most convenient and lowest cost option, i.e. one tonne of pure lithium oxide contains the equivalent of over 18 tonnes of SC6 elemental lithium, even taking into account processing losses.

[0106] Whether the upstream process for production of the solid lithium oxide product 44 and the lithium hydroxide production area 60 are virtually adjacent or perhaps thousands of kilometers apart, the processes involved are described in more detail below with reference to FIG. 6.

[0107] In the lithium hydroxide production area 60, lithium oxide is mixed with sufficient water (slaked and dissolved) to form a solution of lithium hydroxide. As described below with reference to Figure 6, the lithium hydroxide is then sent to a crystallizer where the water is evaporated, thereby producing a lithium hydroxide monohydrate crystal slurry. A dewatering centrifuge is used to produce a substantially liquid-free lithium hydroxide monohydrate product.

[0108] In one embodiment, this lithium nitrate rich liquid (which may contain sodium and potassium nitrates) represents only a small portion of the total lithium nitrate fed to the decomposition reaction vessel 404, since most of the lithium is converted to solid lithium oxide in the lithium nitrate decomposition section 40.

[0109] In one embodiment, the lithium nitrate contained in the bottoms liquid 46 may undergo further processing step 70 to form a lithium carbonate product. The reason for this further processing is, first, to provide an additional marketable product, and, second, to minimize the amount of remaining lithium in what becomes a mixture of primarily lithium nitrate with sodium and potassium nitrates.

[0110] In the lithium carbonate production stage 70, described in more detail below with reference to Figure 7, soda ash and / or potash are added to the pressed residual lithium nitrate liquid 46, resulting in the precipitation of poorly soluble lithium carbonate. A dewatering centrifuge is used to remove the liquid from the lithium carbonate, thereby producing a substantially liquid-free lithium carbonate product.

[0111] Specific details of process 20 for accomplishing each of the above operational steps 30 through 70 will now be described. Figure 2 provides an overall schematic diagram of process 20. Figure 2 outlines a lithium nitrate first heating step 30 according to the present disclosure, a lithium nitrate second heating step 40 according to the present disclosure, nitric acid production 50, lithium hydroxide monohydrate production 60, and lithium carbonate production 70.

[0112] 3 through 7 show a more detailed breakdown of the individual process operations 30-70 within process 20, respectively.

[0113] Example 2 further provides preliminary calculations and design parameters for a pilot-scale plant.

[0114] Lithium nitrate first heating step 30 (Figure 3) 3, a solution 22 containing lithium nitrate (e.g., purified PLS as obtained by reacting a lithium-containing metal silicate with nitric acid in the lithium extraction process 10) is pumped to a holding tank 300 of the lithium nitrate first heating step 30. The lithium nitrate first heating step 30 is a two-stage process including an evaporator 302 and a melting vessel 320.

[0115] The holding tank 300 serves as a feed tank to the evaporator 302. The lithium nitrate containing solution 22 flows from the holding tank 300 into the main chamber 312 of the evaporator 302 when a control valve 304 is opened. The valve 304 can be partially or completely closed when it is necessary to isolate the evaporator 302 from the holding tank 300, for example, when maintenance is required, in the event of an equipment failure, or when the flow to the evaporator 302 needs to be reduced.

[0116] In the evaporator 302, the lithium nitrate containing solution 22 is heated. The evaporator 302 operates at a temperature close to the boiling point of the solution 22 at a given operating pressure of the evaporator 302. The evaporator 302 can be configured to operate at high pressure or under vacuum. At a temperature close to the boiling point of the solution 22, the water is evaporated. The evaporated water is removed as a vapor stream 306. The vapor stream 306 may contain a very low concentration of nitric acid, for example, if nitric acid is still present in the lithium nitrate containing solution 22.

[0117] The evaporator 302 also includes an outer jacket 310 that surrounds the main chamber 312 of the evaporator 302. Steam is supplied to the outer jacket 310. The steam in the outer jacket 310 condenses, thereby releasing energy. The energy released from the condensed steam 310 is transferred to the solution in the main chamber 312, thereby heating the solution and evaporating the water. The condensed steam from the evaporator jacket 310 can be collected for use as process water or returned to the boiler for reuse in the evaporator 302.

[0118] As the water and nitric acid (if present) continue to evaporate in the evaporator 302, a supersaturated solution of lithium nitrate is produced, which includes some of the lithium nitrate crystals in a slurry that collects at the bottom of the evaporator. This slurry of lithium nitrate crystals 308 is pumped out of the evaporator 302 by a pump (not shown).

[0119] Depending on the volume of lithium nitrate containing solution being treated, the evaporator 302 can be configured as either a single effect evaporator (for small volumes, such as a pilot plant) or a multiple effect evaporator (for larger volumes, such as a commercial scale system).

[0120] In a single-effect evaporator configuration, there is only one such evaporator 302, and the water vapor 306 produced by the evaporator 302 is collected immediately. In a multiple-effect evaporator configuration, several such evaporators 302 are configured in series, and the lithium nitrate-containing solution is gradually concentrated as it passes through the series of evaporators. The water vapor produced from the first evaporator in the series is used as the vapor stream for the next evaporator in the series, and so on. A small amount of make-up steam may be required for each evaporator. The last evaporator in the series produces a vapor stream 306.

[0121] The evaporator 302 (single or multiple effect) typically consists of a mechanical vapor recompression system where the steam 306 is recompressed in a compressor. The recompressed steam is then used as steam to the outer jacket 310. A small amount of make-up steam is also typically required. The use of mechanical vapor recompression can significantly reduce the overall fresh steam requirements and reduce the load required on the boiler. This allows for significant savings in both capital and ongoing costs of the process and system, especially when electricity is cheap and generated from renewable sources such as hydroelectricity.

[0122] A control valve 324 between the evaporator 302 and the melting vessel 320 allows the evaporator 302 and the melting vessel 320 to be isolated from each other. When the valve 324 is closed, the slurry 308 cannot flow from the evaporator 302 to the melting vessel 320. When the valve 324 is open, the slurry 308 of lithium nitrate crystals can be moved from the evaporator 302 to the melting vessel 320, such as by a pump.

[0123] Melting vessel 320 operates at a temperature of approximately 400° C., which is above the melting point of lithium nitrate. Melting vessel 320 is surrounded by a jacket 324 that uses electricity to indirectly heat melting vessel 320. Vessel 320 is typically inductively heated to a temperature of approximately 400° C.

[0124] The high temperature of the melting vessel 320 melts the lithium nitrate crystals present in the slurry. Other salts present in the slurry (at this stage of the process only nitrates of other alkali metals, specifically sodium and potassium, traces of rubidium and cesium, if present in the spodumene concentrate, and possibly calcium) may also melt, provided that the melting points of the salts are below 400° C. As a result, a molten liquid containing molten lithium nitrate and molten other salts is produced. The molten liquid containing molten lithium nitrate and molten other salts 34 collects at the bottom 322 of the melting vessel 320. The molten liquid 34 is sent to a second heat treatment step 40.

[0125] The water remaining in the slurry 308 is evaporated in the melting vessel 320 along with the remaining nitric acid to produce a vapor stream 314. The vapor 314 produced in the melting vessel 320 is collected and combined with the vapor 306 from the evaporator 302 (if mechanical vapor recompression is not part of the system) to form a combined vapor stream 32. The combined vapor stream 32 is collected and sent to the condenser 80 (FIG. 2). The combined vapor stream 32 is condensed in the condenser 80 and stored in the storage tank 36 (FIG. 2). The water recovered in the storage tank 36 is used as process water in other parts of the process, for example, as wash water, feed to a boiler, etc. In the condenser 80, either cooling water or cold water, such as from a cooling tower, may be used as a second cooling stream in the condenser 80. Energy is transferred from the condensed combined vapor stream 32 to the cooling water or cold water stream, resulting in a sensible heat change in the cooling water or cold water.

[0126] Lithium nitrate second heating step 40 (Figure 4) As shown in FIG. 4, the molten liquid 34 containing lithium nitrate and other molten salts from the first heat treatment step 30 is passed to a second heat treatment step 40 .

[0127] The control valve 402 is disposed between the melt vessel 320 and the second heat treatment step 40 such that when the valve 402 is partially or fully closed, the melt 34 cannot flow from the melt vessel 320. This allows the melt vessel 320 to be isolated from the second heat treatment step 40, for example, when maintenance is required or when flow to the second heat treatment step 40 is to be stopped or controlled.

[0128] When the valve 402 is opened, the melt 34 flows into the decomposition vessel 404, typically toward its upper end. The decomposition vessel 404 is surrounded by a domed roof 406 to prevent the escape of toxic gases. The inner surface 408 of the decomposition vessel 404 is completely lined with periclase (dead-burned magnesium oxide) tiles. Periclase is a suitable material for lining the decomposition vessel 404 because it is refractory and has no amphoteric properties, i.e., it does not react with lithium oxide. The decomposition vessel 404 operates at a temperature of about 600° C., i.e., near the decomposition temperature of lithium nitrate. A jacket 410 surrounds the decomposition vessel 404. The jacket 410 indirectly heats the decomposition vessel 404 by electrical induction, thereby maintaining a temperature of about 600° C.

[0129] The contents of decomposition vessel 404 (i.e., molten liquid 34) are maintained at a temperature of about 600° C. to promote the decomposition of lithium nitrate into lithium oxide crystals according to the following reaction:

[0130] 2LiNO3 → Li2O+NO+NO2+O2(1) Lithium sulfate Lithium oxide Nitric oxide Nitrogen dioxide Oxygen

[0131] Usually, more NO than NO2 is produced. NO and NO2 are collectively called NO x It is called.

[0132] Although a significant amount of the lithium nitrate present in the melt 34 decomposes in the decomposition vessel 404, some of the molten lithium nitrate remains. The residual lithium nitrate can be removed from the decomposition vessel 404 as an underflow 422 by carefully opening a control valve 424, as described below.

[0133] The decomposition vessel 404 is configured to simultaneously function as a flotation cell, even though the flotation cell is designed to operate at high temperatures and be capable of handling the chemicals involved in the process. The melt feed 34 enters the decomposition vessel 404 via feed port 412 toward the top of the decomposition vessel 404.

[0134] The lithium oxide crystals formed during the decomposition of lithium nitrate are less dense than the residual lithium nitrate, and therefore tend to migrate (i.e., "float") upward 416 through the vessel 404 to the upper portion 418 of the vessel.

[0135] When lithium nitrate decomposes, NO x The suction and oxygen gas form gas bubbles 414 within vessel 404, thereby replicating the gas bubbles introduced by aeration in conventional flotation cells. The gas bubbles 414 travel upwards 416 within the vessel until they reach the top 418 of the vessel. The upward movement of the gas bubbles 414 also helps promote the separation of the less dense lithium oxide crystals.

[0136] Lithium oxide crystal, NO x The upward movement of oxygen bubbles 414 causes bubbles of lithium oxide crystals in the lithium nitrate-rich gas bubbles to form above the residual lithium nitrate slurry. The bubbles form the overflow stream of the decomposition vessel 404 and overflow into a peripheral collection trough 420. The residual lithium nitrate slurry forms an underflow 422 that can be removed from the decomposition vessel 404 by opening valve 424.

[0137] Collection trough 420 directs the overflow of lithium oxide crystals in the lithium nitrate-rich bubbles to outlet port 425 and pipe 426. As the overflow is directed to outlet port 425 and pipe 426, the bubbles burst, forming a concentrated slurry of lithium oxide crystals in the molten lithium nitrate.

[0138] The cover 406 of the decomposition vessel 404 extends over the collection trough 420 and the exit port 426 and is adapted to accommodate NO x and oxygen are prevented from escaping into the atmosphere. x and oxygen stream 42 is directed to outlet pipe 438. x The oxygen stream 42 is sent to a nitric acid production facility 50 (FIGS. 1 and 5).

[0139] The concentrated slurry of lithium oxide crystals in molten lithium nitrate is delivered to a screw press conveyor 428. Depending on the capacity required, one or more screw press conveyors operating in parallel can be used.

[0140] In the screw press conveyor 428, the molten lithium nitrate is squeezed from the lithium oxide crystals. The remaining molten lithium nitrate collects at the bottom outlet 430 of the screw press conveyor 428. The molten lithium nitrate collected from the screw press conveyor is combined with the lithium nitrate underflow 422 from the decomposition vessel 404, thereby forming a combined lithium nitrate stream 46. The combined lithium nitrate stream 46 is pumped to the lithium carbonate precipitation stage of the lithium carbonate production section 60 (FIGS. 1 and 6).

[0141] As the molten lithium nitrate is squeezed from the lithium oxide crystals, the lithium oxide crystals are compressed into a mass of lithium oxide crystals with virtually no liquid phase. The lithium oxide crystals 44 are collected from the top of the screw press conveyor 428.

[0142] The screw press conveyor 428 is a variation of a type commonly used to extract edible oil from oilseeds, modified as necessary to withstand the process conditions. The rotors are high chromium steel covered with periclase applied using plasma technology, and the stators are made of porous sintered periclase. Other surfaces are lined with periclase as necessary, including but not limited to where the surfaces may come into contact with the molten liquid.

[0143] In one version of the process, lithium oxide crystals 44 are the final product. The lithium oxide contains 46.5% lithium by weight. This represents the highest content of elemental lithium compared to other lithium products (hydroxides, carbonates, etc.) and is significantly higher than the lithium content of the original ore. The transportation costs of the lithium-based lithium oxide product are relatively low; for example, it may be economically transported by air from distant operating sites.

[0144] The lithium oxide crystalline product 44 is also an ideal precursor for lithium metal production. Depending on the purity of the initial lithium nitrate solution, the lithium oxide crystalline product may not be capable of producing battery grade lithium hydroxide monohydrate by simply adding water, i.e., a lithium hydroxide monohydrate crystallization step may be employed. Ending the process with a lithium oxide crystalline product reduces capital and operating costs up to this point in the process (i.e., no crystallizer is required).

[0145] Furthermore, the process naturally lends itself to being split into two parts. In the first part, nearly pure lithium oxide is produced, which, due to its high lithium content, leads to the majority of the refinery being built adjacent to the host lithium mine / beneficiation plant, and the transportation costs of shipping the lithium portion as lithium oxide to the battery plant are particularly low due to the high lithium content per weight. In the second part, the remainder of the process (crystallization of lithium hydroxide monohydrate) may take place at the battery plant or at a secondary refinery.

[0146] In processes such as those shown, the lithium oxide crystals are typically further processed to produce crystallized lithium hydroxide monohydrate. In this version of the process, the liquid-free lithium oxide crystals 44 are sent to a lithium hydroxide production section 60 (FIGS. 1 and 6).

[0147] Nitric acid production 50 (Figure 5) As shown in FIG. 5, gaseous NO produced by decomposition of lithium nitrate in decomposition vessel 404. x and oxygen stream 42 is sent to nitric acid production facility 50. The gas stream may also contain water vapor and trace amounts of nitric acid.

[0148] Gas stream 42 first passes through cooler / condenser 502, where cold water 504 passes countercurrent to gas stream 42. Energy (heat) is transferred between gas stream 42 and cold water 504, thereby producing cooled gas stream 506 and hot water 508. Some or all of the water and nitric acid present as vapor in gas stream 42 may be condensed in cooler / condenser 502.

[0149] The cooled gas / liquid stream 506 (which may also contain condensed water and acid) then passes through a nitric acid synthesis heat exchanger 508. In the heat exchanger 508, cooling water 510 passes countercurrent to the cooled gas stream 506. Energy (heat) is transferred between the cooled gas stream 506 and the cooling water 510, thereby further condensing the gases in the gas stream and cooling it to ambient temperature. The cooling water 510 is simultaneously heated. The heated cooling water 512 is returned to be used as make-up water for the chiller.

[0150] As the cold gas stream 506 cools further and condenses, the following reactions occur:

[0151] 2NO + O2 → 2NO2(2) Nitric oxide, carbon dioxide, nitrogen

[0152] 3NO2+ H2O → 2HNO3+NO (3) Nitrogen dioxide Water Nitric acid Nitric oxide

[0153] The NO formed in reaction (3) reacts with additional oxygen to form more NO2 via the first reaction. Because the cooled gas stream 506 consists primarily of reactants and little or no diluent gas, reactions (2) and (3) proceed quickly enough that nitric acid production is virtually complete within the heat exchanger. Small amounts of oxygen gas may be added to maintain oxidizing conditions within the heat exchanger.

[0154] The nitric acid produced from reaction (3) is transferred to a nitric acid storage tank 514, which is capped and airtight to prevent leakage of vapors to the atmosphere. Make-up nitric acid 52 is added to the storage tank 514 as needed to maintain the acid concentration in the storage tank 514 at approximately 50% nitric acid (by weight). Nitric acid 18 from the storage tank 514 is pumped by pump 516 to the process 10 for producing a solution containing lithium nitrate from the reaction of lithium-containing metal silicates with the nitric acid.

[0155] Lithium hydroxide monohydrate production 60 (Figure 6) 6, the lithium oxide crystals 44 (from the FIG. 4 process), i.e., liquid-free from the screw press 428, are gravity fed into the lithium oxide slaking tank 602 of the lithium hydroxide production section 60 (FIGS. 1 and 6). Water 604 is also added to the slaking tank 602. The water 604 is typically demineralized water with very low impurity levels, which results in a high purity lithium hydroxide product.

[0156] One option is to add enough water 604 to the sludge tank 602 such that an anhydrous lithium hydroxide product is produced. The process then ends and anhydrous lithium hydroxide is sold as the final product. The lithium oxide crystals 44 react with the water 604 to produce anhydrous lithium hydroxide according to the following reaction:

[0157] Li2O + H2O → 2LiOH (4) Lithium oxide Water Anhydrous lithium hydroxide

[0158] The advantage of ending the process with such a lithium hydroxide product 608 is that the process is simpler and less costly as no further equipment or processing is required. Slaking is controlled to produce anhydrous lithium hydroxide with a very fine crystal size. The anhydrous lithium hydroxide product 608 contains approximately 29% elemental lithium, making it cheaper to transport on a lithium basis than the original ore. Thus, the anhydrous lithium hydroxide product 608 can be economically transported elsewhere for further processing.

[0159] Generally, however, a stoichiometric excess of water 604 is added to the sludge tank 602. In the sludge tank 602, the lithium oxide crystals 44 react with the excess water 604, thereby producing a solution of lithium hydroxide monohydrate according to the following reaction:

[0160] Li2O + 3H2O → 2LiOH.H2O (5) Lithium oxide water Lithium hydroxide monohydrate

[0161] Excess water 604 is also required to ensure the production of a pumpable, solids-free solution of lithium hydroxide monohydrate 608. The sludge tank 602 further includes an agitator 606 to promote homogeneity within the sludge tank 602.

[0162] The solution of lithium hydroxide monohydrate 608 is pumped by pump 610 to a lithium hydroxide crystallizer 612. In the crystallizer 612, the solution is heated 618 causing the evaporation of water, thereby forming a vapor stream 616 and a concentrated, crystallized lithium hydroxide monohydrate crystal slurry 614.

[0163] Steam stream 616 is combined with the combined steam stream from the first heat treatment step 316 (FIG. 3) and sent to condenser 80. In condenser 80 (FIG. 1), the steam stream is condensed, thereby producing process water that is stored in storage tank 36. The process water is reused in other parts of the process, if desired.

[0164] Depending on the volume of lithium hydroxide solution, the crystallizer 612 can be an electrically heated evaporator or can be heated using steam. Typically, an electrically heated single-effect crystallizer 612 is used in small-scale operations, e.g., pilot plants. The crystallizer 612 includes a jacket 618. Electricity is supplied to the jacket 618, thereby causing the heating of the crystallizer 612.

[0165] For larger scale operations, a steam heated crystallizer with mechanical vapor recompression is used. When the crystallizer 612 is steam heated, it also includes an external jacket 618 that surrounds the main chamber 620 of the crystallizer 612. The external jacket 618 allows steam to be supplied to and flow through the external jacket 618. The steam in the external jacket 618 condenses, thereby releasing energy. The energy released from the condensed steam is transferred to the solution in the main chamber 620, thereby heating the solution and evaporating water. The condensed steam from the crystallizer jacket 618 may be collected for use as process water or returned to the boiler.

[0166] Steam 616 is recovered and at least a portion of it is sent to a compressor 622. Compressor 622 increases the pressure of steam 616, thereby producing high pressure steam 624. The high pressure steam 624 can be reused as a steam source in the outer jacket 618 of the crystallizer 612. A small amount of make-up steam to the circuit is typically required due to losses. However, in a crystallizer with mechanical vapor recompression, the need for fresh steam is greatly reduced. This also reduces the size of the boiler required in the plant, resulting in significant savings in both capital and ongoing costs of the process / system.

[0167] Lithium hydroxide monohydrate crystal slurry 614 is discharged in a controlled manner from the bottom 617 of the crystallizer 612. The crystal slurry 614 flows to the dewatering centrifuge 626 when control valve 618 is opened. When valve 618 is closed, the crystallizer 612 is isolated from the dewatering centrifuge 626 and the crystal slurry 614 cannot flow into the dewatering centrifuge 626.

[0168] In the dewatering centrifuge 626, a lithium hydroxide monohydrate crystal product 628 is separated from the slurry. The lithium hydroxide monohydrate crystal product 628 is substantially free of liquid. The dewatering centrifuge 626 is typically operated to filter the lithium hydroxide monohydrate crystal product 628 and allow it to be washed with warm wash water 630.

[0169] In the initial filtration stage 626 , the liquid (centrate) that is separated from the lithium hydroxide monohydrate crystalline product 628 is collected and forms part of a combined collected liquid stream 632 . During washing, the interstitial liquid contained within the lithium hydroxide monohydrate crystalline product 628 is substantially replaced with wash water. The interstitial liquid (wash liquid) recovered as part of the washing cycle is collected and forms another portion of the combined collected liquid stream 632.

[0170] The amount of wash water 630 added to the dewatering centrifuge 626 is based on the amount of liquid contained in the lithium hydroxide monohydrate crystal product 628 and the desired impurity content of the interstitial liquid in the lithium hydroxide monohydrate crystal product 628. Depending on the desired moisture content of the lithium hydroxide monohydrate crystal product 628, the lithium hydroxide monohydrate crystal product 628 may be further dried prior to packaging and shipping.

[0171] The combined collected solution stream 632 is a concentrated aqueous solution containing lithium hydroxide and small amounts of sodium, potassium, lithium carbonate and nitrates. The combined collected solution stream 632 may be reused in several areas of the process as needed. A first portion can be sent back to the purification stage of the original lithium nitrate solution obtained by leaching the beta spodumene with nitric acid. A second portion can be recycled to the lithium oxide slaking tank 602. A third portion can be sent to the lithium carbonate production area 70 (FIGS. 1 and 7).

[0172] Lithium carbonate production 70 (Figure 7) As shown in Figure 7, the residual stream 46 from the screw press 430 still contains lithium nitrate (Figures 1 and 4). The lithium content of this stream is recovered as lithium carbonate. This stream is sent to the lithium carbonate production section 70 and enters the lithium carbonate precipitation tank 702.

[0173] A third portion of the combined collected solution stream 632 (FIG. 6) from the lithium hydroxide monohydrate production area 60 is also delivered to the lithium carbonate precipitation tank 702.

[0174] The lithium nitrate stream 46 from the screw press is a saturated solution of lithium nitrate with sodium and potassium nitrates. Rubidium and cesium nitrates may also be present as long as these alkali metals are present in the spodumene concentrate. As anhydrous salts, such a mixture of primarily lithium, potassium and sodium nitrates may find application as a molten salt thermal storage and heat transfer medium in solar thermal power plants. The presence of lithium content can reduce the melting point of the eutectic mixture of sodium, potassium and lithium nitrates to below 100 °C while remaining stable at temperatures above 500 °C. Thus, one option is to further concentrate the mixed lithium nitrate 46 and recovery solution 632 streams to form a mixed nitrate product.

[0175] Typically, however, the lithium nitrate stream 46 and the recovery solution stream 632 are further processed to recover the lithium content. This is done by precipitating the lithium as less soluble lithium carbonate. To accomplish this, a combination of soda ash (Na2CO3) and / or potash (K2CO3) 704 is added to the lithium carbonate precipitation tank 702. The tank 702 is continuously agitated by an agitator 706 to promote mixing between the lithium nitrate stream 432, the centrate / wash solution 632, and the added soda ash and / or potash 704.

[0176] When the streams are mixed in tank 702, any lithium nitrate present reacts with the soda ash, thereby forming lithium carbonate (Li2CO3) and sodium nitrate (NaNO3) according to reaction (6). Any lithium nitrate present also reacts with potash, thereby forming lithium carbonate and potassium nitrate (KNO3) according to reaction (7).

[0177] 2LiNO3+Na2CO3→Li2CO3+2NaNO3(6)

[0178] 2LiNO3+K2CO3→Li2CO3+2KNO3(7)

[0179] The tank conditions (temperature, pressure, reagent additions) are selected to optimize the precipitation out of solution of lithium carbonate formed by reactions (6) and (7). For example, because the solubility of lithium carbonate decreases with increasing temperature, lithium carbonate precipitation tank 702 can be heated to increase the temperature of the contents, thereby increasing the mass of lithium carbonate precipitate formed in lithium carbonate precipitation tank 702.

[0180] Lithium carbonate is a strong base. A portion 950 of the lithium carbonate slurry from the lithium carbonate precipitation tank 702 can be recycled to the lithium extraction process 10 (FIGS. 1 and 9). This offsets the need for fresh base in the process.

[0181] In the purification stage of FIG. 9 (i.e., tank 948), lithium carbonate 950 is used to adjust the pH of the lithium nitrate containing solution, thereby precipitating contaminants in the solution to form a substantially contaminant-free lithium nitrate containing solution, which can be sent to process 20.

[0182] Generally, however, the majority of the lithium carbonate slurry is pumped from the lithium carbonate precipitation tank 702 via a slurry pump 710 to a dewatering centrifuge 708. The dewatering centrifuge 708 operates to remove liquid from the contents of the slurry, thereby producing a substantially liquid-free lithium carbonate product 712 and centrate 714. The lithium carbonate product 712, of at least marketable purity, is dried, packaged, and sold.

[0183] Centrate 714, consisting primarily of lithium, sodium and potassium nitrates, is discharged to a nitrate holding tank 716. The liquid in the nitrate holding tank 716 can be reused in other parts of the lithium recovery process 20 or the first lithium extraction process 10 (FIG. 1). However, to prevent the build-up of contaminants (e.g., sodium, potassium, rubidium, cesium) in the process, some solution must be bled off from the process. The bled off solution represents a small by-product nitrate stream.

[0184] A by-product nitrate stream is pumped from the nitrate holding tank 716 by pump 718. The by-product nitrate stream can be discharged to a waste area or can be further processed. Further processing can consist of recovery of the heavier alkali metal salts (potassium, rubidium, and cesium). These alkali metal salts can be evaporated to dryness and converted into prills for sale. For example, potassium nitrate in particular is valuable as a fertilizer. EXAMPLES

[0185] Non-limiting examples of processes and systems are described below.

[0186] Example 1 This example provides the production of a solution containing lithium nitrate that can be used as a feedstock for the above-mentioned processes.

[0187] It should be noted that the solution containing lithium nitrate was produced in a manner substantially similar to the first step of the process and system outlined in the applicant's co-pending patent WO2017 / 106925, however, the process was completed prior to the lithium nitrate crystallization step of WO2017 / 106925 (i.e. after pyrohydrolysis, pH adjustment, and lithium carbonate addition).

[0188] Unrefined PLS production The main elements of the plant and equipment employed for the extraction of lithium from calcined (β) spodumene are shown in Figure 8. The configuration in Figure 8 fed β spodumene at a rate of 1 tonne per day (maximum 50 kg / hr, dry basis) and separated the leach solids from the lithium nitrate-rich pregnant leach solution (PLS).

[0189] Beta-spodumene was added to a feed mixer (a conventional concrete mixer with a 304 L stainless steel bowl) at a rate of 50 kg / h together with 63 kg of nominal 50 wt% nitric acid to produce a 123 kg / h slurry in a volume of 75 l / h. In practice, batches of the correct ratio of calcined spodumene to nitric acid were produced periodically (e.g. hourly).

[0190] Nitric acid was added in significant stoichiometric excess up to 150% to maximize leaching of lithium from the calcined spodumene. Nitric acid concentrations ranged from 30 to 50 wt.% HNO3, the remainder water, with concentrations near the upper end of this range being preferred to minimize downstream evaporative loads. In practice, the strength of the acid used was determined by the rheological properties of the mixture of acid and calcined spodumene, taking into account the changes undergone by the aqueous phase during the leaching reaction:

[0191] LiAlSi2O6+HNO3→LiNO3+AlSi2O5(OH) -75kCal / mol.

[0192] In fact, this reaction demonstrated that a liquid (nitric acid) can be readily converted to a solid (lithium nitrate) despite its high solubility in hot water. The slurry leaving the digester reactor (essentially a three-chambered titanium autoclave) was controlled to have enough liquid phase to be pumpable, but not so much liquid that significant solid-liquid separation occurred.

[0193] The use of 50% acid was confirmed to be close to the upper safe concentration limit. The overall reaction was exothermic, converting 135 kCal / kg of total feed slurry on a basis (mol wt 63). The heat energy released heated the feed mixture from 25°C to 80°C net, consuming 35 kCal / kg of total feed slurry, the remainder (100 kCal) being consumed in boiling water and nitric acid vapours. The latter amount boiled was ~0.2 kg water equivalent, reducing 1 kg of feed (solids and liquid phase) to 0.8 kg of product, of which 0.44 kg was spodumene concentrate, and 0.36 kg was 0.12 kg lithium nitrate, 0.8 kg aluminium nitrate and other soluble nitrates, and 0.16 kg nitric acid and water mixture.

[0194] The resulting lithium nitrate slurry was depressurized and pumped to a 100 litre holding tank for storage. From the holding tank, the lithium nitrate slurry was pumped to a plate and frame filter press. The filtration method employed consisted of repeated washing and air drying cycles. At the end of the final drying cycle, the air flow to the filter press was stopped and the filter press was opened for discharge of the filter cake. The resulting low moisture filter cake (leached spodumene concentrate) was drained from the filter cloth for disposal. The amount of wash water used in the filter press depended on the extent of filter cake washing required, but initial experiments were carried out using the same amount of water as the filter cake, i.e. 16 litres per cycle or 50 litres per hour, resulting in the production of 75 litres net pregnant leach liquor (unrefined PLS) per hour. This unrefined PLS was pumped to a 200 litre holding tank.

[0195] Based on a pilot-scale plant design capacity of 50 kg beta spodumene (dry basis) per hour, the following preliminary equipment sizes and parameters were recorded for crude PLS production: Nitric acid (as 65% HNO3) flow rate to digester reactor feed mixing tank: 63 kg / hr. Feed rate to digester reactor, total: 113 kg / h. · Digestion reactor feed pump discharge pressure (at maximum operation): 8 bar gauge. · Composite feed temperature at digester reactor feed pump: near ambient temperature. Feed rate to digester and dewatering filter: 80 l / h. · Tailings weight (volume 30l / hr, 10% moisture): 50kg / hr. Hot wash water flowing into the filtrate: 27 l / h. Total filtrate (crude PLS, nitric acid and wash water, (excluding cake)): 77 kg / hr. Feed mixer, standard concrete mixer, stainless steel bowl: 200 litre bowl volume. Feed holding tank, with agitator, HDPE or PP, with cover: 0.5m diameter x 1.0m side depth. Digestion reactor (total volume 200 litres): diameter 0.35m x length 2.0m, titanium. Filter feed pump 100 l / h, working pressure up to 8 bar: peristaltic. Filter supply tank (200l, polypropylene, stirred, covered): 0.5m diameter x 1.0m side depth. Plate and frame filter press (cycle time 20 min): 5 plates of 0.5m x 0.5m each Raw PLS (Filter Press Filtrate) Holding Tank (with lid, 200L capacity): 0.5m diameter x 1.0m side depth. · Instrument air compressor capacity: 100l / h @ 8 bar, 25°C.

[0196] Purification PLS manufacturing The crude PLS from the 200-liter holding tank was then sent to several purification and neutralization stages to produce purified PLS. In these stages, reagents were added to promote the precipitation of base metals and to neutralize residual nitric acid. Solid precipitates were removed by passing the solution and precipitate through plate-and-frame filtration stages.

[0197] The raw PLS from the 200 L holding tank was pumped as a hot (near boiling) aqueous solution to an electrically heated, single-effect, 100 L evaporator made of heat-resistant glass, heated by an electrically heated jacket, and capable of storing several hours' worth of concentrate. In the evaporator, water and nitric acid were evaporated off, and the vapor stream was collected for use in other parts of the process (e.g., nitric acid production). Evaporation was carried out to 140 °C for a sufficient time to allow hydrolysis of the aluminum and ferric iron content.

[0198] A dense but pumpable slurry was pumped from the evaporator by a positive displacement pump to a 120 litre filter feed tank where it was maintained at a pressure of 6-8 bar and a temperature of ~180°C. Hot wash water was added to the tank to maintain the nitric acid concentration in the aqueous phase below 5% HNO3. Compressed air (~1,000 kPa) was added to the tank as required. The liquid residence time in the tank was approximately 2 hours, sufficient for further precipitation of the aluminium content and complete leaching of the lithium content.

[0199] The resulting liquid phase from the filter feed tank was flowed under pressure to another plate and frame filter press operated in a similar cycle of washing and air drying as the previously described plate and frame filter press. The filter cake from the filter press was periodically discharged for disposal. The filtrate stream from the filter press was sent to a purification stage consisting of a series of three stirred precipitation tanks. These were arranged to sequentially remove residual aluminum, magnesium, and calcium impurities from the PLS by the addition of lithium hydroxide solution (downstream product).

[0200] The filtrate stream was sent to a first 300 L precipitation tank configured for Al(OH)3 precipitation, where the pH of the solution was raised to approximately 2-3, thereby precipitating the remaining aluminum as aluminum hydroxide crystals. The resulting supernatant solution was then sent to a second 300 L precipitation tank configured for Mg(OH)2 precipitation, where the pH of the solution was raised to approximately pH 10.5, thereby precipitating the magnesium as insoluble magnesium hydroxide crystals. The resulting supernatant solution was then sent to a third 300 L precipitation tank, where the remaining calcium was removed by precipitation as insoluble calcium carbonate (CaCO3 - calcite). Additionally, an appropriate amount of lithium carbonate (i.e., downstream product) was added.

[0201] The resulting liquid from the precipitation tank was pumped to a 300 liter polishing filter feed tank where the liquid was held in preparation for filtration of the solids. From this tank, the liquid was pumped by a feed pump to a polishing candle filter along with the precipitated solids, which were filtered as crystalline solids that could be dewatered from the liquid. The filtered solids from the polishing filter were collected and discarded. The filtrate from the polishing filter constituted the purified lithium nitrate solution.

[0202] For purified PLS production, the following preliminary equipment dimensions and parameters were recorded: Feed to evaporator (crude PLS, 77 kg / hr): 13 kg / hr HNO3, 12.5 kg / hr LiNO3, 6.5 kg / hr other nitrates, 45 kg / hr H2O. · Evaporator off steam: 17 kg / hr HNO3, 40 kg H2O. Evaporator capacity: 52 l / h water equivalent. Evaporator load (energy input / hour): 140MJ (40kW). Cooling water (CW) flow rate to column condenser (ΔT=20°C): 2,000 l / h (0.6 l / s, requires 25 mm diameter pipe). · Crystal slurry from evaporator to filter feed tank: 25 kg / hr (12.5 kg / hr LiNO3, 2.5 kg / hr Al(OH)3, 5 kg / hr HNO3 solution). Positive Displacement (PD) pump: up to 20 l / hr. Dilution water flow rate to filter supply tank: 5kg / hr. Total feed rate to filter press: 30kg / hr. Filter supply tank (0.12m 3 , Titanium, max 10 bar): diameter 0.25m x height 2.2m. Wash water to filter press: 5kg / hour. Filter cake from filter press: 3 kg / hr. Plate and frame filter press (60 min cycle time): 2 plates of 0.5mx0.5m each. Filtrate from filter press (total): 32kg / h Precipitation tank (3 units, capacity 0.3 m each) 3 , HDPE / PP: Diameter 0.6m x Side depth 1.6m. Candle filter, (7 candles, each 60cm x 10cm OD: 0.5m diameter x 1.0m total height. Candle filter supply tank, 304L stainless steel: 0.6m diameter x 1.2m side depth. · Candle filter feed pump: 40 kg / hr, 10 bar. Purified PLS: 30 kg / hr (15 kg / hr LiNO3, 1 kg / hr K / NaNO3, 14 kg / hr water).

[0203] The resulting PLS was found to be substantially free of contaminants with only trace concentrations of impurity elements, and the purified PLS was ready to be sent to the first heat treatment step of the process described herein.

[0204] The concentrations of several elements in the purified PLS were analyzed by standard techniques, and the results of this analysis are shown in Table 1.

[0205] A portion of the PLS was then boiled and concentrated to produce a crude lithium nitrate product. No washing of the crude product was performed. The mass fractions of the same elements in the crude lithium nitrate product were also analyzed using standard techniques. The results of this analysis are also shown in Table 1.

[0206] Table 1 (concentrations (mg / L) and mass fractions (%) of the most common elements in PLS and crude lithium nitrate, respectively; lithium nitrate equivalent concentrations / fractions are also provided):

[0207] [Table 1]

[0208] Additionally, PLS contained high concentrations of lithium, which accounted for >9 wt% of the crude lithium nitrate (>98 wt% as lithium nitrate). Sodium was the most common contaminant, accounting for ~0.6 wt% of the crude lithium nitrate. The next most common contaminant was potassium, accounting for ~0.1 wt% of the crude lithium nitrate. The remaining 18 elements collectively accounted for ~0.15 wt% of the crude lithium nitrate.

[0209] Thus, sodium and potassium were the main contaminants of note in terms of affecting the purity of the final lithium hydroxide monohydrate and lithium carbonate. However, it was also determined that the presence of sodium and potassium at these concentrations in the PLS did not adversely affect the purity of the lithium hydroxide monohydrate product. The ionic radii of sodium and potassium were determined to be significantly larger than that of lithium, and therefore could not be readily incorporated into the lithium hydroxide monohydrate crystal structure. Washing the crystallized lithium hydroxide monohydrate also served to redissolve any sodium and / or potassium salts that may have co-precipitated during crystallization.

[0210] Similarly, it was confirmed that the presence of sodium and potassium does not adversely affect the purity of the lithium carbonate product. Lithium carbonate was confirmed to be poorly soluble. Its solubility is about 1.5 g per 100 mL of water at 0 °C, decreasing to about 0.7 g per 100 mL of water at 100 °C. That is, the temperature-solubility curve has a negative slope. On the other hand, sodium carbonate and potassium carbonate are very soluble in water. For example, the solubility of sodium carbonate is about 7 g per 100 mL of water at 0 °C, increasing to about 45 g per 100 mL of water at 100 °C. This means that due to the low concentrations of sodium and potassium carbonate present, these carbonates will remain in solution even as lithium carbonate precipitates. By carrying out the precipitation of lithium carbonate at a high temperature, the possibility of co-precipitation of sodium and potassium carbonate was further reduced. This had the added benefit of increasing the recovery of lithium carbonate. The co-precipitated sodium and potassium carbonate were observed to be washed away from the lithium carbonate product during centrifugation.

[0211] Thus, the process described herein has been used to produce battery grade lithium hydroxide and market grade lithium carbonate from purified PLS. It has also been confirmed that high purity lithium hydroxide and lithium carbonate can be produced from solutions containing lithium nitrate with similar properties to the PLS described above.

[0212] Example 2 In this example, several calculations and design parameters were made for a pilot plant to recover lithium products from a purified solution containing lithium nitrate using the process described in Example 1.

[0213] The purified solution containing lithium nitrate was fed to a lithium recovery process (e.g., process 20 in Figures 1 and 2) at a rate of 30 kg / hr. The solution consisted of 15 kg / hr LiNO3, 1 kg / hr of the sum of KNO3 and NaNO3, and 14 kg / hr of water. The lithium nitrate containing solution was delivered to a purified lithium nitrate holding tank with a volume of 100 L, a diameter of 0.6 m, and a side water depth (SWD) of 1.2 m.

[0214] The lithium nitrate-containing solution was discharged from the holding tank to an electrically heated single-effect evaporator (see, e.g., unit 302 in Figures 2 and 3). In the evaporator, 8 kg / hr of water was evaporated. As a result, the remaining 6 kg / hr of water, 15 kg / hr of LiNO3, and 1 kg / hr of KNO3 and NaNO3 combined were sent from the evaporator to a melting vessel (see, e.g., unit 320 in Figures 2 and 3). The melting vessel was equipped with electrical induction heating and operated to a temperature of ~400°C (i.e., above the melting point of lithium nitrate). The melting vessel removed most of the remaining water, producing a molten lithium nitrate liquid that collected at the bottom of the vessel. The molten liquid was sent to a decomposition vessel (see, e.g., unit 404 in Figures 2 and 3).

[0215] The decomposition vessel was completely lined with periclase and jacketed to indirectly heat the vessel contents by electrical induction, bringing them to a temperature of ~600 °C (the decomposition temperature of lithium nitrate). As the lithium nitrate decomposed, NOx and oxygen gases were produced. The maximum flow rate of NOx and oxygen from the decomposition vessel was 12 kg / hr of HNO3 equivalent at approximately 600 °C. The NOx and oxygen from the decomposition vessel were combined with water and nitric acid vapours from the lithium extraction process (if employed), resulting in a total gas flow rate of approximately 50 kg / hr at 300 °C to the nitric acid production facility. Of this 50 kg / hr gas flow, 29 kg / hr was HNO3.

[0216] As mentioned above, both the melting vessel and the decomposition vessel were indirectly heated. The latent heat of fusion of anhydrous LiNO3 was 0.36 kJ / kg. The heat capacity of molten LiNO3 was 0.93 J / kg / °C. The total energy required to melt 15 kg / h of LiNO3 and heat it from 60°C to 600°C (i.e., the operating temperature of the decomposition vessel) was 12.9 MJ / h. The heat of decomposition of 15 kg / h of LiNO3 was 47 MJ / h. Therefore, the total energy required to heat, melt, and decompose LiNO3 was 60 MJ / h.

[0217] In a variant, the melting vessel and the decomposition vessel were heated by gas. If the vessels were electrically heated, about 20 kW of electricity was required. If the vessels were gas heated, about 100 MJ / h of gas was required.

[0218] Concurrent with its decomposition function, the decomposition vessel could function as a froth flotation cell operating at high temperatures. Because the lithium oxide crystals formed during the decomposition of lithium nitrate were less dense than the residual lithium nitrate, the lithium oxide crystals tended to migrate upwards (i.e., "float") through the top of the decomposition vessel. In this regard, the NOx and oxygen gas produced during decomposition formed gas bubbles within the vessel that rose to the top of the vessel and trapped, thereby separating out, the less dense lithium oxide crystals.

[0219] Foam of lithium oxide crystals in the lithium nitrate-rich froth formed on top of the residual lithium nitrate slurry and overflowed into the surrounding collection trough, while the residual lithium nitrate slurry formed the underflow of the decomposition vessel. The collection trough directed the overflow of lithium oxide crystals in the lithium nitrate-rich froth through an outlet port and a pipe to a screw press conveyor (i.e., one or more screw press conveyors operating in parallel). The screw press conveyor consisted of a rotor of high chromium steel covered with periclase (applied using plasma technology) and a stator made of porous sintered periclase. Other surfaces were lined with periclase tile as required.

[0220] In the screw press conveyor, the molten lithium nitrate was squeezed from the lithium oxide crystals and collected at its bottom outlet. The combined lithium nitrate stream from the screw press conveyor was combined with the lithium nitrate underflow from the decomposition vessel and sent to the lithium carbonate precipitation stage (see, e.g., stage 60 in Figures 1, 2, and 6).

[0221] By squeezing out the molten lithium nitrate, the screw press also produced a mass of compressed lithium oxide crystals that was virtually liquid-free, and the crystals exited the top of the screw press conveyor at a rate of ~3 kg / hr of lithium oxide. The lithium oxide was collected and discharged to a lithium oxide slaking tank (see, for example, tank 602 in Figures 2 and 6). The lithium oxide slaking tank had a capacity of 100 L. If dry lithium hydroxide was the end product, 1.8 kg / hr of process water was added to the slaking tank to convert the lithium oxide to dry lithium hydroxide. However, typically lithium hydroxide monohydrate was the end product, in which case 3 kg / hr of process water was added to the slaking tank to convert the lithium oxide to lithium hydroxide monohydrate. An additional 25 kg / hr of hot process water was added to the slaking tank to dissolve the lithium hydroxide monohydrate, thereby forming a pumpable solution.

[0222] This lithium hydroxide monohydrate solution was pumped to a lithium hydroxide crystallizer (see, e.g., unit 612 in Figures 2 and 6) where the water of solution was evaporated. The crystallizer was an electrically heated single effect device requiring 20 kW of power to evaporate the water.

[0223] The crystallized lithium hydroxide slurry was then sent from the crystallizer to a dewatering centrifuge (see, for example, centrifuge 626 in Figures 2 and 6) at a rate of 5 kg / h. The centrifuge produced a lithium hydroxide monohydrate crystal product, and the separated liquid formed part of the collected and recovered liquid stream. In the dewatering centrifuge, the interstitial liquid contained in the lithium hydroxide monohydrate crystal product was washed with wash water, essentially replacing it, and this interstitial liquid was also collected and recovered, forming another part of the combined recovered liquid stream. The combined recovered liquid stream was reused in other areas of the process. A first part was returned to the purification stage of the initial lithium nitrate solution obtained by leaching beta spodumene with nitric acid. A second part was recycled to the lithium oxide slaking tank. A third part was sent to lithium carbonate production (see, for example, area 70 in Figures 1, 2 and 7).

[0224] The combined lithium nitrate stream from the decomposition vessel was collected and sent to the lithium carbonate production stage (see, e.g., area 70 in Figures 1, 2, and 7). Approximately 1 kg / hr of market grade lithium carbonate could be produced.

[0225] The lithium nitrate stream, which includes the centrate and washes from the lithium hydroxide dehydration centrifuge, was first pumped to a lithium carbonate precipitation tank (see, e.g., tank 702 in Figures 2 and 7). Lithium nitrate was present in the tank along with small amounts of sodium nitrate and potassium nitrate. Small amounts of rubidium and cesium nitrates were also sometimes present.

[0226] A combination of soda ash (Na2CO3) and / or potash (K2CO3) was added to the lithium carbonate precipitation tank to precipitate lithium as poorly soluble lithium carbonate, thereby forming lithium carbonate (Li2CO3), sodium nitrate (NaNO3), and potassium nitrate (KNO3). The tank conditions were optimized for the precipitation of lithium carbonate (i.e., it was determined that the solubility of lithium carbonate decreases with increasing temperature). Therefore, the lithium carbonate precipitation tank was heated to increase the temperature of the contents, increasing the mass of lithium carbonate precipitate formed.

[0227] A portion of the lithium carbonate could be recycled to the lithium extraction process, for example, used to adjust the pH of the raw lithium nitrate solution to precipitate contaminants (e.g., calcium) in the solution. However, the majority of the lithium carbonate slurry was pumped to a dewatering centrifuge via a slurry pump. The dewatering centrifuge (e.g., see centrifuge 708 in Figures 2 and 7) was operated intermittently to remove liquid from the contents of the slurry, thereby producing a substantially liquid-free lithium carbonate product. The centrate from the centrifuge, consisting primarily of lithium, sodium, and potassium nitrates, was discharged to a nitrate holding tank (e.g., see tank 716 in Figures 2 and 7). This by-product nitrate stream was either discharged as waste or further processed to recover the heavier alkali metal salts (e.g., potassium, rubidium, and cesium).

[0228] Moreover, a pilot plant built according to these principles could employ the latest process control, automation, and monitoring techniques and operate as a fully continuous process. The pilot plant could be built in stages, allowing upstream processes to be optimized while downstream equipment was being installed.

[0229] For example, a pilot plant could be built to produce only lithium oxide product (i.e., with the highest elemental lithium content of 46.5% by weight, making the cost of transporting lithium oxide to customers relatively low). Then, depending on market conditions, anhydrous lithium hydroxide could be produced (anhydrous lithium hydroxide contains greater than 29% elemental lithium by weight). Finally, with the addition of a single-effect electrically heated crystallizer, crystallized lithium hydroxide monohydrate could be produced.

[0230] An advantage of the process and system disclosed herein is that the process can end at any stage depending on market and customer preferences. For example, a battery manufacturer may prefer to receive lithium as oxide since it allows them more control over the purity of the lithium hydroxide produced, in which case they do not need to build the rest of the plant area. As another example, a mine / beneficiation plant operator may decide to install the present process and system close to their facility. They may prefer the simplicity of the process ending with a lithium oxide product since they can avoid the cost / complexity of a lithium hydroxide crystallizer. Thus, the present process and system can provide a very high level of flexibility depending on the needs of both lithium customers and plant operators.

[0231] Further variations It should be understood that the properties of the lithium nitrate containing solution, whether produced by reaction of spodumene with nitric acid or from another source, may vary to the extent that modifications to the methods and systems described above may be appropriate.

[0232] Other unit operations may be included in the overall process, in keeping with good industrial practice, particularly for the provision of services and utilities, efficient use of waste heat, water conservation, and minimization of all waste streams.

[0233] In the following claims, as well as in the foregoing description, unless the context otherwise requires, either by express language or necessary implication, the word "comprise" and variations such as "comprises" or "comprising" are used in their inclusive sense, i.e., to specify the presence of stated features but not to exclude the presence or addition of further features.

Claims

1. 1. A process for producing a lithium product from a solution containing lithium nitrate, comprising the steps of: a. subjecting said solution containing lithium nitrate to a first heat treatment step to remove water and nitric acid (if present), thereby forming a crystal slurry containing lithium nitrate crystals, and heating the lithium nitrate crystals to produce a molten liquid; b. subjecting the molten liquid to a second heat treatment step in which the molten liquid is heated to substantially decompose the lithium nitrate into lithium oxide; A process including.

2. 2. The process according to claim 1, wherein in the second heat treatment step, lithium oxide produced during decomposition of lithium nitrate floats on top of the molten liquid, thereby resulting in an overflow of lithium oxide and lithium nitrate slurry and an underflow of lithium nitrate liquid.

3. 3. The process of claim 2 further comprising passing an overflow of the lithium oxide and lithium nitrate slurry to a separation stage where the lithium nitrate is substantially removed from the lithium oxide.

4. 4. The process of claim 3, wherein the lithium oxide in the overflow of the lithium oxide and lithium nitrate slurry comprises lithium oxide crystals, and the separation step comprises a liquid removal step, in which lithium nitrate is removed together with the liquid from the lithium oxide.

5. 4. The process of claim 3, water is added to the lithium oxide crystals, thereby producing a solution containing lithium hydroxide monohydrate; A process in which a solution of lithium hydroxide monohydrate is passed through a crystallization step to form crystalline lithium hydroxide monohydrate.

6. 6. The process of claim 5, further comprising separating the crystallized lithium hydroxide monohydrate from the solution, thereby producing a substantially liquid-free crystallized lithium hydroxide product.

7. 7. The process according to any one of claims 3 to 6, recovering the lithium nitrate removed from the lithium oxide during the separation step for further processing; The further processing comprises: adding a carbonate compound to the lithium nitrate such that the lithium reacts with the carbonate, thereby producing lithium carbonate; subjecting the lithium carbonate to a condition under which lithium carbonate precipitates; The process further comprising separating the lithium carbonate precipitate from the solution.

8. The process of claim 1, wherein the first heat treatment step comprises: i. a first heating step, heating said solution containing lithium nitrate to remove water and nitric acid (if present), thereby producing a slurry containing lithium nitrate crystals; ii. A second heating step of heating the slurry containing lithium nitrate crystals to a temperature of about 400° C. to melt the lithium nitrate in the slurry and form the molten liquid; The process includes a two-stage heat treatment comprising:

9. A process as described in any of claims 1 to 6, wherein the first heat treatment step produces a vapor stream containing water and nitric acid (if present), and the vapor stream is collected and condensed.

10. The process of claim 1, wherein the second heat treatment step is carried out at a temperature of about 600°C.

11. The process of claim 1, wherein the second heat treatment step produces a gas stream containing nitrogen oxides, which are collected and sent to a nitric acid production process.

12. The process of claim 1, further comprising, prior to step a, reacting a lithium-containing metal silicate with nitric acid to obtain a solution containing lithium nitrate.

13. 13. The process of claim 12, wherein the solution comprising lithium nitrate is a substantially contaminant-free solution comprising lithium nitrate, the process comprising: i) mixing a lithium-containing metal silicate with nitric acid to obtain a mixture; ii) subjecting said mixture to a leaching process having conditions such that the lithium content in the lithium-containing metal silicate is leached into an aqueous phase as lithium nitrate, thereby producing a leach solution; iii) passing the leachate solution through a solid-liquid separation stage to remove solids and obtain a leachate; iv) subjecting the leachate to reaction conditions such that the contaminants are substantially precipitated, thereby producing a leachate containing a precipitate; v) passing said precipitate-containing leachate through a filtration step to remove precipitate, thereby producing said substantially contaminant-free solution containing lithium nitrate for sending to said first heat treatment step. The process includes:

14. The process of claim 13, further comprising, prior to step iv), heating the leachate to distill water and nitric acid as a gas stream, and collecting the water and nitric acid gas stream for use in regenerating nitric acid.

15. The process of claim 1, wherein the lithium-containing metal silicate is spodumene, LiAlSi ２ O ６ , Petalite LiAlSi ４ O １０ , eucryptite LiAlSiO ４ , Amblygonite (Li,Na)AlPO ４ (F, OH), Lepidolite K (Li, Al, Rb) ３ (Al, Si) ４ O １０ (F, OH) ２ , and Zinnwaldite KLiFeAl (AlSi ３ ) O １０ (OH, F) ２ A process that is one or more of the following:

16. 1. A system configured to produce a lithium product from a solution comprising lithium nitrate, comprising: a. one or more vessels configured to allow a solution containing lithium nitrate to be heated to such an extent that water and nitric acid (if present) are removed as vapor and the resulting lithium nitrate-rich crystal slurry forms a molten liquid; b. a further vessel configured to heat the molten liquid to substantially decompose the lithium nitrate into lithium oxide; A system including:

17. 17. The system of claim 16, wherein the further vessel is configured as a flotation cell in which, upon decomposition of the lithium nitrate, the lithium oxide floats, thereby creating an overflow of a lithium oxide and lithium nitrate slurry and an underflow of lithium nitrate.

18. 18. The system of claim 17, further comprising a solid-liquid separation stage configured to receive an overflow of the lithium oxide and lithium nitrate slurry, the solid-liquid separation stage comprising a screw press capable of substantially separating the lithium oxide from the lithium nitrate.

19. 19. The system of any one of claims 16-18, wherein the one or more vessels include an evaporator configured to heat a solution comprising lithium nitrate to evaporate water as vapor along with nitric acid, if present, thereby producing a supersaturated solution of lithium nitrate.

20. 20. The system of claim 19, wherein the one or more vessels are configured to receive a supersaturated solution of lithium nitrate and further comprises a melting vessel capable of heating the supersaturated solution of lithium nitrate to melt the lithium nitrate.

21. 19. A system according to any one of claims 16 to 18, comprising: the further vessel is configured to produce a gas stream comprising nitrogen oxides; said further container being sealed to prevent such gases from escaping to the atmosphere; The system is The system further includes a nitric acid plant configured to receive the gas stream containing nitrogen oxides produced by the additional vessel and to produce nitric acid from the gas stream.

22. 19. A system according to any one of claims 16 to 18, comprising: The system further comprising a condenser positioned to collect and condense vapor from said one or more vessels and, if present, from said evaporator.

23. 19. A system according to any one of claims 16 to 18, comprising: The system further comprising an apparatus configured to produce a crystalline lithium hydroxide product from the lithium oxide produced by said additional vessel.

24. 19. The process of claim 17 or 18, further comprising an apparatus configured to produce a lithium carbonate product from the lithium nitrate underflow and from the lithium nitrate produced by the solid-liquid separation step.

25. 7. The process of any one of claims 1 to 6, further comprising reducing lithium oxide to form lithium metal.

26. The process of any one of claims 1 to 6, wherein the solution contains lithium nitrate prepared by the process of: i) mixing a lithium-containing metal silicate with nitric acid to form a mixture; ii) subjecting the mixture to a leaching process in which the lithium content in the lithium-containing metal silicate is leached from the lithium-containing metal silicate as lithium nitrate, thereby forming a solution containing lithium nitrate; A process including.

Images