Process for production of zeolites from acid resistant mineral compositions

Abstract

The present invention provides a process for producing a zeolite from an acid resistant mineral composition, the process comprising: (a) treating an acid resistant mineral composition comprising an aluminosilicate with an alkaline solution to dissolve silicon in the aluminosilicate into the alkaline solution, thereby producing an alkaline silicate solution and an aluminiferous mineral residue; (b) separating the alkaline silicate solution from the aluminum-containing mineral residues; (c) contacting the aluminum-containing mineral residue with an acid solution to dissolve aluminum in the aluminum-containing mineral residue into the acid solution to produce an aluminum salt solution and an aluminum-poor solid residue; (d) separating the aluminum salt solution from the aluminum-poor solid residues; (e) combining at least part of the alkaline silicate solution and at least part of the aluminum salt solution to form a zeolite precursor solution; and (f) precipitating the zeolite from the zeolite precursor solution.

Description

[0001] Cross - reference to priority

[0002] This application claims priority to Australian Provisional Patent Application No. 2022902587, filed on September 8, 2022, the content of which is hereby incorporated by reference into this specification. Technical field

[0003] The present invention generally relates to a method for producing zeolites from acid - resistant mineral compositions. The method includes: treating an acid - resistant mineral composition containing aluminosilicate with an alkaline solution to produce an alkaline silicate solution and an aluminous mineral residue, contacting the aluminous mineral residue with an acid solution to produce an aluminum salt solution and an aluminum - depleted solid residue, combining the alkaline silicate solution and the aluminum salt solution, and precipitating zeolites from the combined solution. The present invention is particularly applicable to the purification of lithium leaching residues (such as β - spodumene leaching residues), and it will be more convenient to elaborate the present invention within the framework of this exemplary embodiment. Background art

[0004] The global demand for lithium is growing, especially for battery applications, which must be met more by extracting lithium from hard rock ores or concentrates containing α - spodumene (i.e., LiAl(SiO 3 ) 2 ) or other lithium - containing aluminosilicate minerals. In common processes, naturally occurring α - spodumene is converted into a more reactive β - spodumene form by calcination, and then lithium is extracted from the ore or concentrate by roasting with sulfuric acid and water - leaching the roasted product. The spodumene leaching residue accounts for about 95 wt% of the initial feed and contains HAl(SiO 3 ) 2 as the main component. Treating this grade III waste as tailings incurs huge operating costs and environmental hazards.

[0005] It is desirable to purify β - spodumene leaching residues or other lithium leaching residues to extract valuable components and offset the treatment costs. However, these materials are generally resistant to hot acids and cannot be treated by acidic hydrometallurgical processes.

[0006] Previously, it has been proposed to purify lithium leaching residues by converting them into zeolites through alkali treatment. For example, in WO 2019 / 068135, β - spodumene leaching residue was mixed with an aqueous solution of caustic soda, heated to a high temperature (about 600 °C) to form a molten solid product, and then cooled and converted into zeolite A in the presence of added water.

[0007] A significant difficulty with this method is that the selective production of a range of desired zeolite products is limited in processes involving a dissolution-reprecipitation mechanism to convert acid-resistant aluminosilicates into zeolites. In addition, there is a risk that the resulting zeolites will be contaminated by refractory impurities from the lithium leaching residue, including components such as quartz. Furthermore, the high temperatures required for the production of certain desired zeolite products by fusion with caustic soda incur substantial energy costs.

[0008] Although the above discussion has focused on the processing of lithium leaching residues, such as β-spodumene residues, it will be appreciated that similar considerations apply to the purification of a range of acid-resistant mineral compositions including aluminosilicates.

[0009] Accordingly, there has been a continuing need for methods of producing zeolites from acid-resistant mineral compositions, such as lithium leaching residues, that at least partially address one or more of the above disadvantages, or provide a useful alternative.

[0010] Patent documents or other matters mentioned herein as prior art should not be taken as an admission that such document or matter was known at the priority date of any claim, or that the information contained therein is part of common general knowledge. Summary of the Invention

[0011] According to a first aspect, the present invention provides a method for producing zeolites from an acid-resistant mineral composition, the method comprising: (a) treating the acid-resistant mineral composition comprising aluminosilicate with an alkaline solution to dissolve silicon in the aluminosilicate into the alkaline solution, thereby producing an alkaline silicate solution and an aluminous mineral residue; (b) separating the alkaline silicate solution from the aluminous mineral residue; (c) contacting at least part of the aluminous mineral residue with an acid solution to dissolve aluminum in the aluminous mineral residue into the acid solution, thereby producing an aluminum salt solution and an aluminum-depleted solid residue; (d) separating the aluminum salt solution from the aluminum-depleted solid residue; (e) combining at least part of the alkaline silicate solution and at least part of the aluminum salt solution to form a zeolite precursor solution; and (f) precipitating zeolites from the zeolite precursor solution.

[0012] The zeolite product produced according to this method crystallizes and precipitates from the zeolite precursor solution, rather than being transformed into zeolites by converting the acid-resistant mineral composition from one solid form to another (e.g., by a dissolution-reprecipitation mechanism). Advantageously, since the composition and precipitation conditions of the zeolite precursor solution can be precisely controlled, this zeolite synthesis method provides improved opportunities for preparing specific target zeolite structures with good selectivity and purity. In addition, since insoluble impurities present in the feed materials can be excluded, high-purity zeolite products can be produced.

[0013] The alkali treatment step in this method can advantageously be carried out at low temperature because the process conditions of this step are not decisive factors for the selection of the final zeolite product. Therefore, the high energy consumption and capital costs associated with the high-temperature alkali treatment of acid-resistant mineral compositions can be avoided.

[0014] Furthermore, the method disclosed herein can be flexibly applied to recover a high proportion of metal values from an acid-resistant mineral composition feed even when silicon is in stoichiometric excess relative to the zeolite product. Thus, for example, a high-purity silica product can be easily recovered from a solid residue with low aluminum content, or an aluminum source such as boehmite can be added to improve the conversion of dissolved silicon to the desired zeolite product.

[0015] In some embodiments, the acid-resistant mineral composition comprises an acid-treated mineral residue.

[0016] In some embodiments, the acid-resistant mineral composition comprises a leaching residue from a lithium leaching process. The leaching residue can comprise a β-spodumene leaching residue.

[0017] In some embodiments, the acid-resistant mineral composition comprises HAl(SiO 3 ) 2 , for example, in an amount of at least 50 wt% of the acid-resistant mineral composition.

[0018] In some embodiments, the aluminum-containing mineral residue comprises one or more acid-extractable phases selected from sodalite, cancrinite, and zeolite, for example, in a total amount of at least 50 wt% of the aluminum-containing mineral residue.

[0019] In some embodiments, the acid-resistant mineral composition is treated with an alkaline solution at a temperature below 300 °C, or below 200 °C, for example, below 150 °C.

[0020] In some embodiments, the pH value of the aluminum salt solution produced by contacting an aluminum-containing slag with an acid solution is below 3.5.

[0021] In some embodiments, the aluminum-depleted solid residue comprises silica, for example, in an amount of at least 50 wt%. Before separating the aluminum salt solution from the aluminum-depleted solid residue, silica can be coagulated by controlling or adjusting the pH value of the aluminum salt solution to 3 to 5 (for example, 3 to 4). The pH value of the aluminum salt solution can be adjusted by alkalizing the aluminum salt solution initially produced by contacting the aluminum-containing mineral residue with the acid solution. Optionally, the initially produced aluminum salt solution is alkalized with a partial alkaline silicate solution.

[0022] In some embodiments, the method further comprises at least one of the following: (i) extracting residual silicon from the aluminum-depleted solid residue to produce high-purity silica, and (ii) dissolving the residual silicon in the aluminum-depleted solid residue in an alkaline solution or an alkaline silicate solution.

[0023] In some embodiments, the method further comprises adding an aluminum source, optionally boehmite, to supplement the aluminum from the acid-resistant mineral composition present in the zeolite precursor solution.

[0024] In some embodiments, the alkaline solution comprises an alkali metal hydroxide selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, and mixtures thereof. In some embodiments, the alkaline solution comprises sodium hydroxide.

[0025] In some embodiments, the acid solution comprises an acid selected from sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof.

[0026] In some embodiments, the method further comprises: separating the precipitated zeolite from a depleted solution comprising an alkali metal sulfate or an alkali metal chloride salt; and regenerating the alkali metal hydroxide base for the alkaline solution by bipolar membrane electrodialysis or electrolysis of the depleted solution.

[0027] In some embodiments, the process of precipitating zeolite from the zeolite precursor solution comprises selectively precipitating a target zeolite by controlling precipitation process parameters including the Si:Al ratio in the zeolite precursor solution. The Si:Al ratio can be controlled by at least one of the following: (i) controlling the relative amounts of the combined alkaline silicate solution and the aluminum salt solution in the zeolite precursor solution, and (ii) adding an aluminum source to the zeolite precursor solution.

[0028] In some embodiments, the process of precipitating zeolite from the zeolite precursor solution comprises maintaining the zeolite precursor solution at a temperature of 60°C to 110°C.

[0029] In some embodiments, the zeolite is selected from the group consisting of zeolite A, zeolite X, zeolite P, and combinations thereof.

[0030] When the terms "comprises", "comprising", and "containing" are used in the specification (including the claims), they should be construed as specifying the stated feature, integer, step, or component, but not precluding the presence of one or more other features, integers, steps, or components or combinations thereof.

[0031] Other aspects of the invention are described in the detailed description of the invention below. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Embodiments of the invention will now be described by way of example with reference to the drawings.

[0033] Figure 1 is a block flow chart schematically depicting a method for producing zeolite from an acid-resistant mineral composition, illustrating some embodiments of the present invention.

[0034] Figure 2 is a graph showing the variation of dissolved aluminum and silicon present in an alkaline solution over time when treating the β-spodumene leaching residue with a 4M NaOH solution in Example 2.

[0035] Figure 3 is a graph showing the variation of dissolved aluminum and silicon present in an alkaline solution over time when treating the β-spodumene leaching residue with a 10M NaOH solution in Example 2.

[0036] Figure 4 shows the X-ray diffraction (XRD) pattern of zeolite X precipitated at 70 °C from a zeolite precursor solution (Si:Al = 2.3) produced by combining a synthetic alkaline silicate solution and a synthetic aluminum sulfate solution in Example 5.

[0037] Figure 5 shows the XRD pattern of zeolite A precipitated at 70 °C from a zeolite precursor solution (Si:Al = 1.6) produced by combining a synthetic alkaline silicate solution and a synthetic aluminum sulfate solution in Example 5.

[0038] Figure 6 shows the XRD pattern of zeolite P produced by subjecting zeolite X to an alkali treatment at 95 °C in Example 5.

[0039] Figure 7 shows the XRD pattern of zeolite A precipitated at 70 °C from a zeolite precursor solution (Si:Al = 2.2) produced by combining an alkaline silicate and an aluminum sulfate solution of the β-spodumene leaching residue according to the embodiment in Example 6 of the present invention.

[0040] Figure 8 shows the XRD pattern of zeolite X precipitated at 70 °C from a zeolite precursor solution (Si:Al = 1.0) produced by combining an alkaline silicate and an aluminum sulfate solution of the β-spodumene leaching residue according to the embodiment in Example 6 of the present invention. Detailed Embodiments

[0041] The present invention relates to a method for producing zeolite from an acid-resistant mineral composition containing aluminosilicate. The method at least includes the following steps (a) to (f).

[0042] Step (a). Treat an acid-resistant mineral composition containing aluminosilicate with an alkaline solution to dissolve silicon in the aluminosilicate into the alkaline solution. As a result, an alkaline silicate solution and an aluminous mineral residue are produced. The alkali treatment changes the aluminosilicate phase originally present in the mineral composition such that the resulting aluminous mineral residue is no longer resistant to acid extraction.

[0043] Step (b). Separate the alkaline silicate solution produced in step (a) from the aluminous mineral residue.

[0044] Step (c). Then contact at least part of the aluminous slag separated in step (b) with an acid solution to dissolve aluminum in the aluminous slag into the acid solution. As a result, an aluminum salt solution and an aluminum-depleted solid residue are produced.

[0045] Step (d). Separate the aluminum salt solution produced in step (c) from the aluminum-depleted solid residue.

[0046] Step (e). Then combine at least part of the alkaline silicate solution separated in step (b) and at least part of the aluminum salt solution separated in step (d) to form a zeolite precursor solution.

[0047] Step (f). Precipitate zeolite from the zeolite precursor solution.

[0048] Figure 1 The methods of some embodiments are schematically described in the form of a block flow chart. In the alkali treatment unit 100 for performing step (a), an acid-resistant mineral composition 102 containing aluminosilicate is treated with an alkaline solution 104 under conditions where silicon is dissolved from the aluminosilicate into the alkaline solution. The acid-resistant mineral composition 102 may optionally be the leaching residue of β-spodumene mainly containing HAl(SiO 3 ) 2 as the aluminosilicate. The alkaline solution 104 may optionally be an aqueous solution of caustic soda (NaOH).

[0049] After the alkali treatment, the resulting slurry 106 is sent to a separation unit 110 for step (b), such as a filtration unit, where the alkaline silicate solution 112 and the aluminous mineral residue 114 are separated. Generally, the aluminous mineral residue 114 contains one or more new aluminosilicate phases, such as sodalite and / or various zeolite phases.

[0050] Then the aluminous mineral residue 114 is sent to an acid extraction unit 120 for step (c), where it is contacted with an acid solution 122 under conditions where aluminum in the aluminous mineral residue is dissolved into the acid solution. The acid solution 122 may optionally be an aqueous solution of sulfuric acid, hydrochloric acid or nitric acid.

[0051] After acid extraction, the resulting slurry 124 is sent to a separation unit 140, such as a filtration unit, for step (d), where an aluminum salt solution 142 and an aluminum-depleted solid residue 144 are separated. In some embodiments, the slurry 124 initially produced in the acid extraction unit 120 will contain amorphous silica. Optionally, the slurry 124 is alkalized with a base 132 in a separate pre-filtration unit 130 as shown or in a final stage in the acid extraction unit 120 to coagulate the amorphous silica present in 124 prior to separation.

[0052] In a zeolite precursor preparation unit 150 for carrying out step (e), at least a portion of the alkaline silicate solution 112 separated in the separation unit 110 is mixed with at least a portion of the aluminum salt solution 142 separated in step (d) to form a zeolite precursor solution 152. Generally, by selecting the relative amounts of the alkaline silicate solution 112 and the aluminum salt solution 142 to provide a desired Si:Al ratio in the zeolite precursor solution 152, such as an Si:Al ratio of 2.5:1 to 1.0:1.

[0053] Subsequently, in step (f), under conditions suitable to promote zeolite formation, zeolite 162 is precipitated from the zeolite precursor solution 152 in a separate precipitation unit 160 as shown or in a combined zeolite synthesis unit for carrying out steps (e) and (f). The desired zeolite can be formed by controlling parameters (such as the Si:Al ratio and temperature of the zeolite precursor solution), adding seed materials or templating agents, or subjecting the initially precipitated zeolite to conditions suitable to induce a solid-state phase change. Thereby, zeolites with good purity (such as zeolite A, zeolite X, and zeolite P) can be prepared.

[0054] The precipitated zeolite 162 can be separated from a depleted solution 164 that may contain sodium sulfate, sodium chloride, or sodium nitrate (if sulfuric acid, hydrochloric acid, or nitric acid solution 122 is used) in a subsequent separation unit (not shown), and the depleted solution 164 can optionally be treated in a regeneration unit 180 by bipolar membrane electrodialysis or electrolysis to at least regenerate the base 182 for recycling to the alkaline solution 104.

[0055] Based on the stoichiometry of the target zeolite product, the silicon introduced into the process through the acid-resistant mineral composition 102 is typically in excess relative to aluminum. In some embodiments, the process is carried out such that the excess silicon enters the aluminum-depleted solid residue 144. This material separated in the separation unit 140 can optionally be treated in a silica recovery unit 170 to recover the silica value. The amorphous silica that is typically present can be readily separated from the acid-resistant impurities by known methods.

[0056] In other embodiments, the stoichiometric imbalance between silicon and aluminum is addressed by introducing an aluminum source 189 (e.g., gibbsite) into one or more process steps. For example, an aluminum source 192 can be added to the alkali treatment unit 100, the acid extraction unit 120, or the zeolite precursor preparation unit 150. This can advantageously allow a greater proportion of the silicon in the acid-resistant mineral composition 102 to be converted into recyclable zeolite 162.

[0057] Acid-resistant mineral composition containing aluminosilicate

[0058] In its most common form, the present invention provides a method for producing zeolite from any acid-resistant mineral composition containing aluminosilicate. As used herein, an acid-resistant mineral composition containing aluminosilicate refers to an acid-resistant mineral composition containing aluminosilicate that is difficult to be subjected to hydrometallurgical processing by acid treatment to recover valuable substances therefrom. In such compositions, the aluminosilicate may mainly exist in one or more phases, and a large amount of aluminum cannot be extracted from these phases using strong mineral acid leaching agents such as sulfuric acid, hydrochloric acid, or nitric acid.

[0059] Non-limiting examples of acid-resistant mineral compositions containing aluminosilicate include acid-treated mineral residues (including residues generated by extraction hydrometallurgical processes using acidic leaching agents), clays (e.g., kaolinite), mica, feldspar, and fly ash.

[0060] In some embodiments, the acid-resistant mineral composition contains an acid-treated mineral residue, such as the leaching residue of a lithium leaching process. Lithium can be extracted by acid-treating ores or concentrates containing various lithium aluminosilicate minerals (including spodumene, eucryptite, lepidolite, triphylite, and petalite), which can be optionally calcined before extraction. In each case, the residue of the lithium extraction process will be an acid-resistant mineral composition containing aluminosilicate.

[0061] In some embodiments, the acid-resistant mineral composition is a spodumene leaching residue, particularly a β-spodumene leaching residue. The β-spodumene leaching residue can be a lithium residue extracted from an ore or concentrate containing α-spodumene, which includes a step of calcining to form β-spodumene, and a step of sulfuric acid roasting and leaching the roasted β-spodumene product to extract lithium. Spodumene leaching residues produced by other acid-based processes (e.g., nitric acid processing as proposed in WO 2017 / 106925) can also be used.

[0062] In some embodiments, the acid-resistant mineral composition contains HAl(SiO 3 ) 2 , for example, in an amount of at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt%, at least 60 wt%, or at least 70 wt% of the acid-resistant mineral composition.

[0063] The acid-resistant mineral composition can include various other components, such as those expected in ore or concentrate processing residues. These components can include one or more of minerals selected from feldspar minerals (such as sodalite, orthoclase), quartz, and gypsum (which can be formed by reaction of calcium in the mineral after sulfuric acid treatment).

[0064] The acid-resistant mineral composition is preferably in particulate form to facilitate processing according to the methods disclosed herein. In some embodiments, the acid-resistant mineral composition has a particle size distribution represented by the P80 value, which is less than 100 μm or less than 60 μm (such as about 45 μm).

[0065] Alkali treatment using an alkaline solution

[0066] The methods disclosed herein include the steps of treating the acid-resistant mineral composition with an alkaline solution to dissolve silicon in the aluminosilicate into the alkaline solution, thereby producing an alkaline silicate solution and an aluminous mineral residue.

[0067] The alkaline solution is generally an alkaline aqueous solution, and its pH can be greater than 10, or greater than 12, or greater than 13. The alkaline solution can include various suitable bases, including but not limited to alkali metal hydroxides. For example, it is also contemplated that certain alkaline earth metal hydroxides can be used. In some embodiments, the alkaline solution includes an alkali metal hydroxide base selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, and combinations thereof. The alkali metal hydroxide can be selected at least in part based on providing the desired alkali metal cation or cation mixture in the final zeolite structure.

[0068] In some embodiments, the alkaline solution includes sodium hydroxide, such as at a concentration higher than 0.1 M, such as 1 M to 15 M, or about 4 M to about 10 M. It has been found experimentally that such an alkaline solution converts acid-resistant aluminosilicates (such as the aluminosilicate phase found in β-spodumene leaching residues) into acid-extractable aluminosilicate phases at moderate temperatures with high conversion rates and controllable selectivity.

[0069] Thus, the acid-resistant mineral composition can be contacted with a pre-formed alkaline solution. However, it should be understood that the acid-resistant mineral composition can also be treated with an alkaline solution of the desired concentration by other methods, including preparing a slurry of the acid-resistant mineral composition in water and adding concentrated base or solid base to the slurry.

[0070] In some embodiments, the acid-resistant mineral composition is treated with an alkaline solution at a temperature below 300 °C, or the temperature is below 250 °C or below 200 °C, or below 150 °C, or below about 100 °C, such as 50 °C to 100 °C. In some embodiments, the temperature is equal to or below the normal boiling point of the alkaline solution. Advantageously, in the presently disclosed method, there is no need to subject the acid-resistant mineral composition to a high-energy-consuming high-temperature treatment. Further, when using low-temperature alkali processing conditions, the cost of high pressure and associated pressure-rated equipment can be avoided. In some embodiments, the acid-resistant mineral composition is treated with an alkaline solution at low pressure (e.g., below 5 bar, below 2 bar or about atmospheric pressure).

[0071] The alkali treatment step can be carried out by generating a slurry of the acid-resistant mineral composition in an alkaline solution, the slurry having an appropriate solids concentration to permit silicon dissolution and the desired aluminosilicate phase transformation. In some embodiments, the solids concentration of the slurry ranges from about 10% w / w solids to about 30% w / w solids.

[0072] The acid-resistant mineral composition can be treated with an alkaline solution for a time sufficient to convert the acid-resistant aluminosilicate into an acid-extractable phase and to dissolve the excess silicon component associated with the aluminosilicate. It should be understood that the required time may depend on various parameters such as the composition and physical form (e.g., particle size) of the acid-resistant mineral composition, the composition of the alkaline solution, and the treatment temperature. In some embodiments, the time is less than 10 hours, or is about 2 hours to about 6 hours.

[0073] The alkali treatment step converts the acid-resistant aluminosilicate initially present in the acid-resistant mineral composition into one or more acid-extractable phases. Depending on the process conditions, these acid-extractable aluminosilicate phases can include aluminosilicate phases such as sodalite (e.g., hydroxysodalite (Na 8 Al 6 Si 6 O 24 (OH) 2 .xH 2 O)), cancrinite (e.g., hydroxycancrinite (Na 4 Al 3 Si 2 O 12 OH.xH 2 O)); and / or zeolite phases such as zeolite A (Na 12 Al 12 Si 12 O 48 .27H 2 O) and zeolite P1 (Na 6 Al 6 Si 10 O 32 .12H 2O). It has been experimentally found that under conditions favorable for maximizing the extraction of silicon, such as by using highly alkaline solutions and longer contact times, the sodalite and hydroxyl cancrinite phases predominate. In contrast, under conditions where a less alkaline solution is used and the solid concentration in the slurry is high and silicon dissolution is limited, zeolite P with a higher Si:Al ratio is more favorable. Without wishing to be bound by any theory, it is proposed that the alkali treatment initially produces a zeolite phase, which subsequently transforms into sodalite and hydroxyl cancrinite.

[0074] In some embodiments, the alkali treatment step is carried out under conditions suitable for forming zeolites, optionally making the zeolite the most abundant aluminosilicate phase in the aluminous mineral residue.

[0075] In some embodiments, the alkali treatment step is carried out under conditions suitable for forming sodalite (e.g., hydroxyl sodalite) and / or hydroxyl cancrinite as the most abundant aluminosilicate phases in the aluminous mineral residue. It is believed that when the β-spodumene leaching residue is transformed into hydroxyl sodalite, the main reaction that occurs is shown in Equation (1).

[0076] 6HAl(SiO 3 ) 2 + 20NaOH → Na 8 Al 6 Si 6 O 24 (OH) 2 + 6Na 2 SiO 3 + 12H 2 O (1)

[0077] Thus, the alkali treatment step dissolves part of the silicon initially present in the acid-resistant aluminosilicate phase in the alkaline solution. The silicon is dissolved in the form of one or more silicate anions (e.g., SiO 3 2- ), thereby producing an alkaline silicate solution with a pH value usually greater than 12. It can be understood that the maximum amount of soluble silicon is limited by the chemical composition of the initial aluminosilicate phase present in the acid-resistant mineral composition and the transformed phases present in the aluminous mineral residue. It has been experimentally found that up to 37% of the silicon initially present in the β-spodumene leaching residue can be dissolved in a high-concentration caustic soda solution, which is consistent with the fact that most of the initially present HAl(SiO 3 ) 2 (Si:Al = 2:1) is mostly transformed into an aluminosilicate with an Si:Al ratio of about 1:1.

[0078] The amount of silicon dissolved in the alkaline silicate solution can be intentionally limited, for example, by adding an aluminum source, such as boehmite, i.e., Al(OH) 3Thus, the excess silicon released by the aluminosilicate phase change reacts with the added aluminum to form more acid-extractable aluminosilicate solids in the aluminum-containing mineral residue. The degree of silicon dissolution can be controlled in this (or other) manner to provide the desired stoichiometric ratio of silicon dissolved in the alkaline silicate solution to acid-extractable aluminum in the aluminum-containing mineral residue. Thus, the amount of silicon required in step (e) can be provided in the alkaline silicate solution, while the excess silicon is transferred to the aluminum-depleted solid residue after the acid treatment in step (c).

[0079] The alkali treatment step can be carried out in conventional mineral processing equipment that is corrosion-resistant to the solutions used and generated under the process conditions employed.

[0080] Separate the alkaline silicate solution from the aluminum-containing mineral residue

[0081] After the alkali treatment step, the alkaline silicate solution is separated from the aluminum-containing mineral residue. This can be accomplished by conventional separation methods in mineral processing, such as filtration, centrifugation, concentration, or clarification.

[0082] The separated aluminum-containing mineral residue can optionally be washed with water in one or more washing steps to remove the alkaline silicate solution remaining in the wet solid. Optionally, the wash liquor can be remixed with the main portion of the alkaline silicate solution.

[0083] As Figure 1 shown, the separation step can be carried out in a dedicated separation unit (e.g., a filtration unit or a thickener) downstream of the alkali treatment unit. However, it should be understood that the alkali treatment and separation steps can also be integrated in a single processing unit.

[0084] The separated aluminum-containing mineral residue can be selectively classified, for example, to exclude coarser particles (e.g., >180 μM, or >90 μM, or >45 μm) that have been found to contain a higher proportion of impurities. Then, the remaining portion of the aluminum-containing mineral residue containing a higher proportion of the acid-extractable aluminum-containing phase can be sent to the acid extraction step.

[0085] Perform acid extraction using an acid solution

[0086] After the separation step, at least part, optionally all, of the aluminum-containing slag is contacted with an acid solution to dissolve the aluminum in the aluminum-containing slag into the acid solution, thereby producing an aluminum salt solution and an aluminum-depleted solid residue.

[0087] The acid solution is typically an aqueous acid solution with a pH value that can be below 2, for example below 1. The acid solution can include mineral acids selected from sulfuric acid, hydrochloric acid, and nitric acid. In some embodiments, the acid solution contains hydrochloric acid (HCl), for example at a concentration of 5% w / w HCl to 50% w / w HCl, such as about 5% w / w HCl to about 20% w / w HCl. In other embodiments, the acid solution includes sulfuric acid (H 2 SO 4 ), for example at a concentration of 5% w / w H 2 SO 4 to 50% w / w H 2 SO 4， such as about 5% w / w H 2 SO 4 to about 10% w / w H 2 SO 4 . It has been found experimentally that such an exemplary acid solution can extract a high proportion of aluminum from the aluminum-containing mineral residue produced by alkali-treated β-spodumene residue.

[0088] The aluminum-containing slag can be contacted with a pre-formed acid solution. However, it can be understood that the aluminum-containing slag can also be contacted with an acid solution of the desired concentration by other methods, such as preparing a slurry of the aluminum-containing slag in water and adding concentrated acid to the slurry.

[0089] The aluminum-containing mineral residue can be contacted with the acid solution under conditions suitable for dissolving a high proportion of aluminum in the aluminum-containing mineral residue. Since aluminum is typically a limiting component in zeolite synthesis, a high extraction degree of aluminum is particularly desirable. In some embodiments, at least 80% or at least 90% (such as at least 95%) of the aluminum in the aluminum-containing mineral residue is dissolved.

[0090] In some embodiments, the aluminum-containing mineral residue is contacted with the acid solution at a temperature below 100 °C, such as about 20 °C to about 80 °C.

[0091] The acid extraction step can be carried out by producing a slurry of the aluminum-containing mineral residue in the acid solution, which has an appropriate solid concentration to allow aluminum dissolution. The maximum solid concentration may be limited by the need to maintain the fluidity of the slurry. In some embodiments, the solid concentration of the slurry is 1% w / w solid to 20% w / w solid, such as 2.5% w / w solid to 10% w / w solid.

[0092] The aluminum-containing mineral residue can be treated with the acid solution for a sufficient time to dissolve the aluminum into the acid solution. It should be understood that the required time may depend on various parameters, such as the composition of the aluminum-containing mineral residue, the composition of the acid solution, and the temperature. In some embodiments, the time is less than five hours, or less than two hours. Based on experimental observations, at least in some cases, 30 minutes may be sufficient.

[0093] When the acid solution contains sulfuric acid, hydrochloric acid, and nitric acid respectively, the aluminum dissolved from the aluminum-containing mineral residue produces an aluminum salt solution containing aluminum sulfate Al 2 (SO 4 ) 3 , aluminum chloride AlCl 3 or aluminum nitrate Al(NO 3 ) 3 . The pH value of the aluminum salt solution produced after fully dissolving aluminum can be lower than 3.5, or lower than 2.5, such as 1 to 2. At such a final pH value, most of the extractable aluminum will dissolve.

[0094] In some embodiments, the aluminum-containing mineral residue is contacted with a sulfuric acid solution to dissolve aluminum. When sodalite hydroxide (an exemplary acid-extractable aluminosilicate present in the aluminum-containing mineral residue) contacts sulfuric acid, the main reaction believed to occur is shown in Equation (2).

[0095] Na 8 Al 6 Si 6 O 24 (OH) 2 +13H 2 SO 4 →4Na 2 SO 4 +3Al 2 (SO 4 ) 3 +6SiO 2 +14H 2 O (2)

[0096] The aluminum in the aluminum-containing mineral residue dissolves in the acid solution, leaving an aluminum-depleted solid residue, which usually contains silicon from the acid-extractable aluminosilicate phase in the aluminum-containing mineral residue and insoluble impurities from acid-resistant mineral compositions (such as quartz and feldspar).

[0097] As can be seen from Equation (2), the aluminum-depleted solid residue contains silicon in the form of silicon dioxide (SiO 2 ). Experimental findings show that when the acid extraction step is carried out at a pH value lower than 3 (for example, 1 to 2), this silicon dioxide forms amorphous silica gel. Therefore, the large amount of silica gel formed in the slurry may complicate the subsequent separation of the aluminum salt solution from the aluminum-depleted solid residue.

[0098] The separation problem caused by silica formation can be solved or at least mitigated by coagulating silica gel. This can be achieved by adjusting the pH value of the aluminum salt solution in the slurry to 3 to 5, for example 3 to 4. At a pH value within this range, silica coagulates in the slurry, thus facilitating its subsequent separation from the aluminum salt solution by conventional solid-liquid separation techniques. When the initial pH value of the aluminum salt solution is below 3 (e.g., 1 to 2), silica coagulation can be achieved by alkalizing the solution with a base (e.g., NaOH) to raise the pH value to the desired value. Optionally, a partially basic silicate solution (e.g., produced in an alkali treatment step) can be used as the alkalizing agent. Then the alkalized slurry can be maintained at a sufficient temperature and for a sufficient time to allow silica gel to coagulate, for example, maintained at about 55 °C for 30 minutes to 4 hours, for example 1 hour to 2 hours. Experiments have found that coagulating silica in this way does not have an unacceptable adverse effect on aluminum recovery.

[0099] It has also been proposed that the desired coagulated silica form can be directly obtained by maintaining the pH value of the aluminum salt solution in the slurry at 3 to 5 (e.g., 3 to 4) throughout the aluminum extraction step. For example, this can be achieved by controlling the rate of addition of the acid solution to the aluminum-containing mineral residue slurry.

[0100] Controlling or regulating the pH value of the aluminum salt solution in this way to control the form of silica means that there is no need to pre-treat the aluminum-containing mineral residue with process steps such as ammonium ion exchange or heating before acid extraction. Therefore, in some embodiments, the aluminum-containing mineral residue does not undergo an ion exchange step before being contacted with the acid solution. In some embodiments, the aluminum-containing mineral residue is not heated at a temperature above 150 °C before being contacted with the acid solution.

[0101] Optionally, an aluminum source, such as gibbsite, i.e., Al(OH) 3 , can be added to the acid extraction step to increase the concentration of the aluminum salt solution.

[0102] The acid extraction step can be carried out in conventional mineral processing equipment that is corrosion-resistant to the liquids used and produced and the operating conditions.

[0103] Separate the aluminum salt solution from the aluminum-depleted solid residue

[0104] After the acid extraction step, the aluminum salt solution is separated from the aluminum-depleted solid residue. This can be accomplished by conventional separation methods in mineral processing, such as filtration, centrifugation, concentration, or clarification.

[0105] As described above, the aluminum-depleted solid residue can contain amorphous silica. The separation of amorphous silica can be facilitated by controlling the pH value of the aluminum salt solution before or during the separation step.

[0106] The aluminum-depleted solid residue can optionally be washed with water or the like in one or more washing steps to remove the residual aluminum salt solution in the wet solid. Optionally, the wash liquor can be remixed with the major portion of the aluminum salt solution.

[0107] As Figure 1 shown, the separation step can be carried out in a separation unit (such as a filtration unit or a thickener) located downstream of the acid extraction unit. However, it should be understood that the acid extraction and separation steps can also be integrated in a single process unit.

[0108] Production of zeolite from a zeolite precursor solution

[0109] The method disclosed herein includes the steps of mixing at least a portion of an alkaline silicate solution and at least a portion of an aluminum salt solution to form a zeolite precursor solution, and precipitating zeolite from the zeolite precursor solution. The precipitated zeolite can then be separated from the depleted solution, which contains the residual dissolved components that have not precipitated from the zeolite precursor solution.

[0110] The zeolite precursor solution can be formed by simply mixing the alkaline silicate solution and the aluminum salt solution, which are separately separated after the alkali treatment and acid extraction steps. However, it is not excluded that one or more modifications are required for the alkaline silicate solution and / or the aluminum salt solution before mixing, including pH adjustment, dilution, concentration, etc. In addition, it is not excluded that other components, such as soluble aluminum sources or silicon sources, are added to the zeolite precursor solution to adjust the Si:Al ratio.

[0111] The alkaline silicate solution and the aluminum salt solution can be combined to produce a zeolite precursor solution having a desired composition, particularly a target Si:Al ratio. Thus, the method disclosed herein can include the steps of determining the silicon concentration (and optionally the aluminum concentration) in the alkaline silicate solution and determining the aluminum concentration (and optionally the silicon concentration) in the aluminum salt solution. Then, based on these known concentrations, the alkaline silicate solution and the aluminum salt solution can be combined in relative amounts suitable for producing the target Si:Al ratio in the zeolite precursor solution.

[0112] The zeolite precursor solution can be an alkaline solution, such as having a pH higher than 12 or higher than 12.5.

[0113] For the purpose of zeolite synthesis, silicon can be stoichiometrically in excess relative to the aluminum present in the acid-resistant mineral composition. Thus, in order to obtain the desired Si:Al ratio in the zeolite precursor solution for zeolite synthesis, an aluminum source, such as boehmite, can be added to the process. As previously mentioned, one option is to add the aluminum source to the alkali treatment step, thereby reducing the amount of silicon dissolved in the alkaline silicate solution and increasing the amount of aluminum that can be dissolved in the aluminum salt solution. Alternatively (or additionally), the aluminum source can be added to the zeolite precursor solution to supplement the aluminum from the acid-resistant mineral composition, thereby reducing the Si:Al ratio to be closer to the stoichiometry of the zeolite product. The aluminum source can be suitably added to the zeolite precursor solution itself or at an earlier stage, such as during the acid extraction step or to the acidic aluminum salt solution.

[0114] By controlling the Si:Al ratio, various different zeolite products can preferably be precipitated from the zeolite precursor solution. In some embodiments, the Si:Al ratio of the zeolite precursor solution is from 3:1 to 1:1, such as from 2.5:1 to 1.0:1. Higher Si:Al ratios can also be considered to produce different zeolite products or to only allow for the excess silicon in the downstream processing steps of the zeolite precipitation step.

[0115] The properties of the zeolite product can be further controlled by the charge-balancing cations crystallized in the zeolite structure. By selecting an appropriate alkali metal hydroxide base (or base mixture) for the alkali treatment step, or by adding the desired cations to the zeolite precursor solution, zeolites with the desired metal cations or cation mixtures in the final zeolite structure can be produced.

[0116] The precipitation of the zeolite product from the zeolite precursor solution can be induced by heating the zeolite precursor solution to the desired temperature and for a sufficient time to allow the zeolite to precipitate and form a well-crystallized product. In some embodiments, the zeolite precursor solution is maintained at a temperature of 60 °C to 110 °C during the precipitation process. In some embodiments, the zeolite precursor solution is maintained at this temperature for 6 hours to one week, such as about 24 hours to about 72 hours.

[0117] In a set of exemplary embodiments, zeolite A is precipitated from the zeolite precursor solution. Experiments have shown that according to the present invention, zeolite 4A (the sodium form of zeolite A) can be selectively precipitated from a zeolite precursor solution having an Si:Al ratio of about 2.2 to 2.3 and maintained at about 70 °C. The proposed reaction for forming zeolite 4A is shown in Equation (3).

[0118] 12Na 2 SiO 3 +6Al 2 (SO 4 ) 3 +24NaOH+15H 2 O→|(Na12 (H 2 O) 27 |[Al 12 Si 12 O 48 +18Na 2 SO 4 (3)

[0119] In another set of exemplary embodiments, zeolite X is precipitated from a zeolite precursor solution. Experiments have shown that, according to the present invention, zeolite X can be selectively precipitated from a zeolite precursor solution having an Si:Al ratio of about 1.0 to 1.6 and maintained at about 70 ℃ .

[0120] It has been observed that zeolites (including zeolite A and zeolite X) precipitate more rapidly from the zeolite precursor solutions of the present invention compared to synthetic zeolite precursor solutions from pure reagents. Without wishing to be bound by any theory, it is believed that impurities present in the alkaline silicate and / or aluminate solutions from the acid-resistant mineral composition promote the zeolite crystallization process.

[0121] A variety of zeolites (including zeolite A and zeolite X) can be precipitated from the zeolite precursor solution without the addition of an external templating agent. Thus, in some embodiments, no templating agent is added to the zeolite precursor solution. However, in other embodiments, a templating agent is added to induce the selective precipitation of the desired zeolite structure. The methods of the present invention provide the opportunity to use a variety of known templating agents (including organic quaternary ammonium cations), thereby influencing the zeolite structure precipitated from the Al- and Si-containing precursor solution.

[0122] Optionally, a zeolite seed material can be added to the zeolite precursor solution to induce precipitation, increase the rate of zeolite precipitation, or control the selectivity or particle size of the zeolite product.

[0123] It is also contemplated that the zeolite initially precipitated from the zeolite precursor solution can be transformed into different zeolite forms by various mechanisms, including dissolution-reprecipitation and solid-state transformation or combinations of these mechanisms. Thus, for example, the initially precipitated zeolite X of the present invention can be transformed into zeolite P by hydrothermal treatment in an alkaline solution, such as treatment in a 2M NaOH solution at 95 °C.

[0124] Treating excess silicon

[0125] As previously mentioned, the Si:Al ratio in the acid-resistant mineral composition can be higher than the Si:Al ratio in the zeolite product. For example, based on the most abundant and reactive component HAl(SiO 3 ) 2 , the Si:Al ratio in the leaching residue of spodumene can be about 2:1, while the Si:Al ratio of zeolite 4A is 1:1. Thus, there is a stoichiometric excess of silicon.

[0126] At least a portion of the excess silicon enters the aluminum-depleted solid residue in the form of amorphous silica. This silicon can optionally be extracted from the aluminum-depleted solid residue by known methods, such as to produce high-purity silica as another value-added product of the process.

[0127] Alternatively (or additionally), the aluminum from the acid-resistant mineral composition can be supplemented by adding an aluminum source (such as boehmite), thereby converting a portion of the excess silicon in the acid-resistant mineral composition into the desired zeolite product. For example, the amorphous silica produced in the acid extraction step can be recycled to the alkali treatment step to dissolve into the initial alkaline solution and / or the product alkaline silicate solution, thereby increasing the silicate concentration of the alkaline silicate solution. As described herein, an aluminum source can be added to one or more different process steps, such as the acid extraction step or the zeolite precipitation step, to react with the excess silicon in the alkaline silicate solution.

[0128] Regeneration of the depleted solution after zeolite precipitation

[0129] Zeolites are precipitated from the zeolite precursor solution, forming a depleted solution containing residual dissolved components. These residual dissolved components contain a large amount of by-product salts that ultimately originate from the alkali and acid used in the alkali treatment step and the acid extraction step, respectively. Thus, in the case where a caustic soda (NaOH) solution is used in the alkali treatment step and sulfuric acid (H 2 SO 4 ) solution is used in the acid extraction step, the depleted solution will contain sodium sulfate (Na 2 SO 4 ); see Equation (3). If a hydrochloric acid solution is used instead of sulfuric acid, the depleted solution will contain sodium chloride (NaCl).

[0130] It may be desirable to reconvert these salts into an alkali (such as NaOH), which can then be recycled, together with the residual alkali already present in the (usually alkaline) depleted solution, into the alkaline solution used in the alkali treatment step. This can be achieved by bipolar membrane electrodialysis or electrolysis of the depleted solution. For example, a depleted solution containing Na 2 SO 4 can be regenerated by bipolar membrane electrodialysis to form a sodium hydroxide solution and a sulfuric acid solution. In another example, a depleted solution containing NaCl can be regenerated by electrolysis to form a sodium hydroxide solution while forming the by-product chlorine gas. In both cases, the sodium hydroxide solution can be recycled to the alkali treatment step of the process. The regenerated sulfuric acid solution (produced by bipolar membrane electrodialysis) can be recycled to the acid extraction step.

[0131] In some embodiments, the depleted solution contains an excess of silicon in the form of silicate. Before any regeneration of the salts in the depleted solution, these silicons can be removed by adding lime to precipitate calcium silicate.

[0132] Examples

[0133] The present invention will be described with reference to the following examples. It should be understood that these examples are only for illustrating the present invention and not for limiting the present invention.

[0134] Example 1. Analysis of β-spodumene leaching residue

[0135] The β-spodumene leaching residue sample was from a commercial lithium processing plant. The residue was not neutralized with limestone, so its calcium content was low. The nominal P80 of this material was 45 μm, but its water content was 15%, and it was dried overnight at 70 °C before use. Table 1 below shows the elemental composition determined by experimental and quantitative XRD (QXRD) analysis.

[0136] Table 1

[0137]

[0138] For QXRD analysis, hydroaluminosilicate products HAl(SiO 3 ) 2 , which accounted for 77% of the residue, were simulated. Other components included residual feldspar minerals, sodalite (3.5%), orthoclase (0.9%), quartz (17.5%), and a small amount of by-product gypsum (0.9%) formed during the lithium extraction process. The QXRD analysis was consistent with the main product of β-spodumene leaching being HAl(SiO 3 ) 2 .

[0139] Example 2. Treatment of β-spodumene leaching residue with alkaline solution

[0140] In a 2 L Inconel 600 autoclave from Parr Instrument Company, the β-spodumene leaching residue was treated with caustic soda (NaOH) solution at a series of solid concentrations (10% w / w, 20% w / w, 30% w / w) and NaOH concentrations (4 M, 7 M, 10 M) for 6 h, and samples were taken at 0, 0.5, 1, 1.5, 2, 3, 4, and 6 hours. The material was loaded into a container and then sealed, and for the experiments with 4 M, 7 M, and 10 M NaOH, it was heated to the target temperatures of 107 °C, 114 °C, and 122 °C respectively. The 0-hour sample was collected after reaching the target temperature (usually within less than 20 minutes of heating).

[0141] The residual solids and leachate of the ion sample and the final slurry were separated by vacuum filtration. The main leachate was allowed to stand for at least several days after collection and analyzed after reaching an equilibrium state. The solids were thoroughly washed with deionized water, dried overnight in an oven at 65 °C to 70 °C, and then analyzed. After melting and dissolving in deionized water in a lithium metaborate-lithium tetraborate flux at 12:22, the liquid and solid samples were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) using a Varian Vista Pro instrument. The solids and liquid samples were analyzed for Al, Fe, Si, Mg, Ca, Na, and K, and the liquid samples were also analyzed for Li.

[0142] The selected solid samples were pressed in a sample holder and then analyzed by X-ray diffraction (XRD). XRD measurements were performed using a PANalytical high-resolution multipurpose powder diffractometer (Empyrean). Using cobalt K-radiation, the X-ray tube was operated at 45 kV and 40 mA. A Bragg-Brentano high-resolution monochromator was inserted into the incident beam, and a PIXcel3D X-ray detector was used to collect data in the 5-130° 2θ angular range in continuous scan mode. The instrument was also equipped with a fixed incident beam anti-scatter (1°) and divergence slit (0.5°), a fixed diffracted beam anti-scatter (0.125°) slit, and 0.02 radian incident and diffracted beam Soller slits.

[0143] Figure 2 and Figure 3 The analytical results of the solutions treated with 4M NaOH and 10M NaOH are shown respectively. The figures show the changes in the concentrations of silicon and aluminum in the alkaline solution over time. In all experiments, a large portion of silicon dissolved in the alkaline solution, while relatively less aluminum dissolved. Apparently, complete dissolution was quickly achieved at 10M, while dissolution was slower and / or incomplete at 4M. In three experiments using 4M NaOH, 15% to 34% of silicon and 0.2% to 1.3% of aluminum were dissolved in the final solution. In three experiments using 7M NaOH (not plotted), 27% to 36% of silicon and 0.9% to 1.3% of aluminum were dissolved in the final solution. In three experiments using 10M NaOH, 36% to 37% of silicon and 0.6% to 2.4% of aluminum were dissolved in the final solution.

[0144] The analysis also showed that a large amount of residual lithium and potassium present in the β-spodumene leaching residue dissolved into the alkaline solution. Iron was also extracted, especially at 10M NaOH. If left standing, iron-containing solids precipitated from the filtered alkaline solution.

[0145] The results of the solution analysis showed that a part of the silicon (up to about 37%) in the β-spodumene leaching residue could be dissolved in the caustic soda solution, and higher caustic soda concentration and temperature were helpful for the dissolution. Relatively less aluminum was dissolved.

[0146] The elemental composition of the solid residue after alkali treatment determined by analysis is shown in Table 2 below. The results confirmed that a large amount of silicon was extracted and the sodium content increased significantly, indicating the formation of a new phase.

[0147] Table 2

[0148]

[0149] a Composition of the β-spodumene leaching residue before alkali treatment

[0150] XRD analysis was carried out to determine the main phases in the solid residue. Various aluminosilicates and zeolites existed as the main phases, including sodalite hydroxide (Na 8 Al 6 Si 6 O 24 (OH) 2 .xH 2 O), cancrinite hydroxide (Na 4 Al 3 Si 2 O 12 OH.xH 2 O), zeolite A (Na 12 Al 12 Si 12 O 48 .27H 2 O, whose structure is similar to that of dehydrated zeolite 4A), and zeolite P1 (Na 6 Al 6 Si 10 O 32 .12H 2 O). However, a small amount of quartz (SiO 2 ), sodalite (NaAlSi 3 O 8 ) and other feldspar minerals (such as orthoclase, microcline or sanidine; all are KAlSi 3 O 8 ) also existed, which originally existed in the β-spodumene leaching residue.

[0151] As shown in Table 3, the type and relative amount of the zeolite phase depend on the alkali treatment conditions. Under conditions of high NaOH concentration and low solid concentration, with NaOH in excess, hydroxysodalite and hydroxycancrinite are the main aluminosilicate phases formed. In contrast, under conditions of low NaOH concentration and high solid concentration, the availability of NaOH is limited, less silicon is dissolved, and zeolite P1 (with a higher Si:Al ratio than other zeolites) predominates.

[0152] Table 3

[0153]

[0154] Example 3. Treatment of β-spodumene leaching residue with alkaline solution added with gibbsite

[0155] According to the method of Example 2, the β-spodumene leaching residue was again treated with caustic soda (NaOH) solutions at a solid concentration of 10% w / w and different NaOH concentrations (4, 7, 10 M), except that the amount of gibbsite added to the autoclave was 10% more than the amount of silicon expected to be dissolved in the alkaline solution at the end of the reaction without the addition of gibbsite (i.e., the corresponding experiment in Example 2). As can be seen from Table 4, the added aluminum significantly reduced the amount of silicon dissolved in the alkaline solution at the end of the reaction and increased the amount of solid residue. XRD analysis of the solid residue showed the formation of hydroxysodalite and hydroxycancrinite phases.

[0156] Table 4

[0157]

[0158] The results show that an aluminum source such as gibbsite can be added in the alkali treatment step to reduce the amount of silicon dissolved in the alkaline silicate solution and increase the amount of aluminosilicate phases in the solid residue that are easily dissolved by acid. This can be carried out within the necessary range to provide the stoichiometric ratio required for the silicon content in the alkaline silicate solution and the aluminum content dissolved in the aluminum salt solution (after extraction with an acid solution), thus facilitating the formation of the final zeolite product in high yield.

[0159] Example 4. Dissolving aluminum in the alkali-treated residue in hydrochloric acid solution

[0160] Using the alkali-treated mineral residue produced by treating the β-spodumene leaching residue with a 10 M NaOH solution (solid concentration of 30% w / w) in Example 2, the dissolution of aluminum in hydrochloric acid (HCl) was studied. As shown in Table 3, this residue contains hydroxysodalite and hydroxycancrinite as the main phases. The alkali-treated mineral residue was size-fractionated; the fractions of -25 μm and +25, -45 μm were retained (together accounting for about 74% of the total mass), while the larger particle fraction containing most of the quartz and other impurities was removed. Table 5 shows the elemental composition of the various fractions and compares it with the overall composition before fractionation.

[0161] Table 5

[0162]

[0163] N / D = Not Determined

[0164] The acid dissolution experiments were carried out at a series of solid concentrations (2.5, 5, 10, 15% w / w), HCl concentrations (10, 15, 20% w / w) and temperatures (25, 50, 75 °C). Hydrochloric acid solutions of the required concentrations were mixed with the alkali-treated mineral residues in 250 mL Nalgene bottles and placed in a Grant shaking water bath set at the target temperature. In the study, a single preview test was adopted to determine the leaching time of 2 hours.

[0165] The residual solids and leachate of the final slurry were separated by vacuum filtration and analyzed as described in Example 2. The free acid was determined using the CaEDTA method, and the titration end point was detected by first derivative using Metrohm Tiamo software. The solid residue after HCl treatment was repulped in 2 L of deionized water and then decanted, and this operation was repeated until the pH of the decanted water was higher than 3 for analysis. The solid was filtered and dried at 65 °C for 24 hours.

[0166] Table 6 lists the metal extraction rates and the final free acidities obtained after the experiments. In all experiments, the solubility of aluminum obtained was very high (>93%), except for the experiment carried out at 25 °C, 10% w / w acid and 15% w / w solid, where the acid availability was limited (as can be seen from the low free acid value). Silicon mainly remained in the solid residue, and in many experiments, the silicon dissolved under the reaction conditions tended to precipitate from the post-reaction filtered solution in the form of amorphous silica gel. The solution to this problem was to dilute the filtered solution with water and refilter it before analysis in order to collect and analyze the filtrate.

[0167] Table 6

[0168]

[0169] XRD analysis was carried out on the solid residue after filtration following acid extraction. The results showed that the silicon in the residue was mainly amorphous silica, with a small amount of impurity phases such as quartz, feldspar, hematite and trace amounts of α-spodumene, which had not been transformed during the roasting process of the concentrate.

[0170] Example 5. Synthesis of zeolite from synthetic alkaline silicate and aluminum salt solution

[0171] The preparation method of the synthesized alkaline silicate and aluminum sulfate solutions is as follows. Dissolve sodium hydroxide in water, then add silicon powder and heat until the silicon dioxide dissolves, thereby preparing a sodium hydroxide solution containing dissolved silicon dioxide. Filter the solution to remove any fine insoluble components, and make up the volume to produce a synthesized alkaline silicate solution with the desired concentration. By dissolving Al 2 (SO 4 ) 3 .18H 2 O in water, an aluminum sulfate solution is prepared. Filter the solution to remove any fine insoluble components, and make up the volume to produce a synthesized aluminum sulfate solution with the desired concentration.

[0172] Zeolites are synthesized as follows: Weigh the two synthesized solutions and put them into a polytetrafluoroethylene bottle, then seal and shake. Put the homogeneous mixture into a water bath set at the desired temperature and let it stand for a selected time. Filter and collect the solid product through a Buchner funnel, filter and wash it several times, and then dry it overnight in an oven at 70 °C. Perform XRD analysis on the dried product to characterize the mineralogical characteristics of the existing phases.

[0173] Zeolite X is prepared as follows: Mix 150 mL of the synthesized alkaline silicate solution containing 106 g / L NaOH and 25.1 g / L silicon dioxide (63 mmol dissolved silicon) with 50 mL of the synthesized aluminum sulfate solution containing 292.0 g / L Al 2 (SO 4 ) 3 .18H 2 O (27 mmol dissolved aluminum), and heat at 70 °C for 72 hours. Therefore, the Si:Al ratio in the initial mixed solution is 2.3. The yield of the solid product is 5.1 g. As Figure 4 shown, XRD analysis shows that the solid product is high-purity zeolite X.

[0174] Zeolite A is prepared as follows: Mix 150 mL of the synthesized alkaline silicate solution containing 106 g / L NaOH and 17.5 g / L silicon dioxide (44 mmol dissolved silicon) with 50 mL of the synthesized aluminum sulfate solution containing 292.0 g / L Al 2 (SO 4 ) 3 .18H 2 O (27 mmol dissolved aluminum), and heat at 70 °C for 72 hours. Therefore, the Si:Al ratio in the initial mixed solution is 1.6. The yield of the solid product is 6.8 g. As Figure 5 shown, XRD analysis shows that the solid product is zeolite A with good purity (trace impurities of zeolite X and sodalite).

[0175] Zeolite P was prepared by mixing 10 g of zeolite X with 100 mL of 2 M NaOH solution and then heating at 95 °C for 240 hours. The yield of the product was 8.3 g. As Figure 6 shown, XRD analysis indicated that the solid product was mainly zeolite P, with a small amount of zeolite X and sodalite also present.

[0176] Example 6. Synthesis of zeolite from β-spodumene leaching residue

[0177] 108 g of β-spodumene leaching residue (as described in Example 1) was treated with 2295 g of 3.88 M NaOH solution (mass ratio of NaOH to residue = 310 g:108 g; the leaching residue in the slurry was 4.5 wt%). The mixture was stirred at 105 °C for 6 hours. After filtration, 93 g of the treated solid was recovered. The composition (g / L) of the reacted alkaline silicate solution (2182 g recovered) was as follows: Li (0.126), Na (76.6), K (0.198), Al (0.127), and Si (5.68).

[0178] A portion of the treated solid (84 g) was made into a slurry with 995 g of water, and then 101 g of concentrated sulfuric acid was added. A slurry containing 7.1% w / w solids and 8.8% w / w H 2 SO 4 was mixed and heated to 55 °C. The resulting slurry formed finely dispersed silica gel. The pH of the slurry was adjusted from 1.4 to 3.2 by adding concentrated NaOH solution to coagulate the silica gel, and the final slurry was conditioned for about 2 hours. After filtration, 61 g of solid residue was recovered. At this time, aluminum sulfate was dissolved in the acid solution (840 g of the recovered solution), and its composition was as follows (g / L): Li (0.012), Na (16.2), K (0.032), Mg (0.064), Ca (0.254), Al (8.2), Si (0.172), and S (20.3).

[0179] Zeolite A was prepared by mixing 81 mL of alkaline silicate solution (16.4 mmol of dissolved silicon, 0.4 mmol of dissolved aluminum) with 54 mL of solution containing acidic aluminum salt (0.3 mmol of dissolved silicon, 16.4 mmol of dissolved aluminum), and heating to 70 °C for 24 hours. Thus, the Si:Al ratio in the initial mixed solution was 1.03. As Figure 7 shown, XRD analysis indicated that the recovered solid product was mainly composed of zeolite A and contained trace amounts of zeolite X and sodalite.

[0180] Zeolite X was prepared by mixing 116 mL of an alkaline silicate solution (23.5 mmol of dissolved silicon, 0.5 mmol of dissolved aluminum) with 33 mL of a solution containing an acidic aluminum salt (0.2 mmol of dissolved silicon, 10.0 mmol of dissolved aluminum), and heating to 70 °C for 24 hours. Thus, the Si:Al ratio in the initial mixed solution was 2.30. As Figure 8 shown, XRD analysis indicated that the recovered solid product was high-purity zeolite X and contained trace amounts of sodalite.

[0181] The time required to produce the two zeolites using the solution from the β-spodumene leaching residue was shorter than that required using the synthetic solution (Example 5). Without wishing to be bound by any theory, it is believed that impurities in the actual solution enhanced the rate of zeolite formation.

[0182] Those skilled in the art will recognize that the present invention can have other variations and modifications in addition to those specifically described. It is to be understood that the invention includes all variations and modifications that fall within the spirit and scope of the present invention.

Claims

1. A method for producing zeolite from an acid-resistant mineral composition, the method comprising: (a) treating the acid-resistant mineral composition containing aluminosilicate with an alkaline solution to dissolve silicon in the aluminosilicate into the alkaline solution, thereby producing an alkaline silicate solution and an aluminous mineral residue; (b) separating the alkaline silicate solution from the aluminous mineral residue; (c) contacting at least part of the aluminous mineral residue with an acid solution to dissolve aluminum in the aluminous mineral residue into the acid solution, thereby producing an aluminum salt solution and an aluminum-depleted solid residue; (d) separating the aluminum salt solution from the aluminum-depleted solid residue; (e) combining at least part of the alkaline silicate solution and at least part of the aluminum salt solution to form a zeolite precursor solution; and (f) precipitating zeolite from the zeolite precursor solution.

2. The method according to claim 1, wherein the acid-resistant mineral composition contains an acid-treated mineral residue.

3. The method according to claim 1 or 2, wherein the acid-resistant mineral composition contains a leaching residue from a lithium leaching process.

4. The method according to claim 3, wherein the leaching residue contains a β-spodumene leaching residue.

5. The method according to any one of claims 1 to 4, wherein the acid-resistant mineral composition comprises HAl(SiO 3 ) 2 , and its content is preferably at least 50% by weight of the acid-resistant mineral composition.

6. The method according to claim 5, wherein the acid-resistant mineral composition comprises at least 50% by weight of the acid-resistant mineral composition of HAl(SiO 3 ) 2 .

7. The method according to any one of claims 1 to 6, wherein the aluminous mineral residue includes one or more acid-extractable phases selected from sodalite, cancrinite and zeolite.

8. The method according to any one of claims 1 to 7, wherein the acid-resistant mineral composition is treated with the alkaline solution at a temperature below 300 °C.

9. The method according to any one of claims 1 to 8, wherein the pH value of the aluminum salt solution produced by contacting the aluminous mineral residue with the acid solution is lower than 3.

5.

10. The method according to any one of claims 1 to 9, wherein the aluminum-depleted solid residue contains silica.

11. The method according to claim 10, wherein silica is coagulated by controlling or adjusting the pH value of the aluminum salt solution to 3 to 5 before separating the aluminum salt solution from the aluminum-depleted solid residue.

12. The method according to claim 11, wherein the pH value of the aluminum salt solution is adjusted by alkalizing the aluminum salt solution initially produced by contacting the aluminous mineral residue with the acid solution.

13. The method according to claim 12, wherein the initially produced aluminum salt solution is alkalized with part of the alkaline silicate solution.

14. The method according to any one of claims 1 to 13, further comprising at least one of the following: (i) extracting residual silicon from the aluminum-depleted solid residue to produce high-purity silica, and (ii) dissolving the residual silicon in the aluminum-depleted solid residue in an alkaline solution or an alkaline silicate solution.

15. The method according to any one of claims 1 to 14, further comprising adding an aluminum source to supplement the aluminum from the acid-resistant mineral composition present in the zeolite precursor solution.

16. The method according to any one of claims 1 to 15, wherein the alkaline solution includes an alkali metal hydroxide selected from lithium hydroxide, sodium hydroxide, potassium hydroxide and mixtures thereof.

17. The method according to any one of claims 1 to 16, wherein the acid solution comprises an acid selected from sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof.

18. The method according to claim 17, wherein the method further comprises: separating the precipitated zeolite from the depleted solution comprising an alkali metal sulfate or an alkali metal chloride salt; and regenerating the alkali metal hydroxide base for the alkaline solution by bipolar membrane electrodialysis or electrolysis of the depleted solution.

19. The method according to any one of claims 1 to 18, wherein the process of precipitating zeolite from the zeolite precursor solution comprises selectively precipitating a target zeolite by controlling precipitation process parameters, the process parameters including the Si:Al ratio in the zeolite precursor solution.

20. The method according to claim 19, wherein the Si:Al ratio is controlled by at least one selected from the following: (i) controlling the relative amounts of the combined alkaline silicate solution and the aluminum salt solution in the zeolite precursor solution, and (ii) adding an aluminum source to the zeolite precursor solution.

21. The method according to any one of claims 1 to 20, wherein the process of precipitating zeolite from the zeolite precursor solution comprises maintaining the zeolite precursor solution at a temperature of 60 °C to 110 °C.

22. The method according to any one of claims 1 to 21, wherein the zeolite is selected from the group consisting of zeolite A, zeolite X, zeolite P, and combinations thereof.

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