WO2019068135A1

WO2019068135A1 - Synthesis of zeolites

Info

Publication number: WO2019068135A1
Application number: PCT/AU2018/050940
Authority: WO
Inventors: Yatendra Sharma; Goutam Kumar DAS
Original assignee: Neomaterials Pty Ltd
Current assignee: Neomaterials Pty Ltd
Priority date: 2017-10-04
Filing date: 2018-08-31
Publication date: 2019-04-11
Anticipated expiration: 2020-04-04
Also published as: AR113341A1

Abstract

A method (10) for the synthesis of zeolites (50), the method (10) comprising the addition of a predominantly alumina-silicate starting material (12) to a stoichiometric excess of sodium hydroxide (16), with additional water (30), and calcining (20) at a temperature of greater than about 400oC for a period of at least about 4 hours, wherein the alumina-silicate starting material (12) is the residue from a leach of a spodumene ore or concentrate to extract lithium therefrom. Also disclosed is an LTA zeolite formed by the method (10).

Description

"Synthesis of Zeolites"

Field of the Invention

[0001 ] The present invention relates to a method for the synthesis of zeolites. More particularly, the zeolite of the present invention is synthesised in the form of Linde Type A zeolite.

[0002] The present invention further relates to the synthesis of zeolites from the residue of a leach of a spodumene ore or concentrate.

[0003] The zeolite synthesised in accordance with the method of the present invention is intended for use, in one form, as either a molecular sieve or an adsorbent.

Background Art

[0004] Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents, molecular sieves and catalysts. Their structure is based on a three dimensional network of an aluminium and silicon tetrahedral linked by shared oxygen atoms.

[0005] Linde Type A (or LTA) zeolite was the first synthetic zeolite commercialised as an adsorbent in 1953 when Union Carbide used it to remove an oxygen impurity from argon. Due to specific pore sizes and large surface areas, LTA Zeolites are used in the various applications noted above, as each of adsorbents, molecular sieves, and catalysts.

[0006] Zeolites have the chemical formula M2 nOAl2O3.xSiO2.yH2O, where the charge-balancing non-framework cation M has valence n, x is 2.0 or more, and y is the moles of water in the voids. The Al and Si tetrahedral atoms (T-atoms) form a three dimensional framework comprising AIO4 and S1O4 tetrahedra linked by shared oxygen ions. [0007] The chemistry of zeolite synthesis is subject to the presence of impurities in the source materials. Such contaminants may remain insoluble during the

crystallization and cause undesired species to nucleate. These species may be soluble and result in formation of different silicate or metallosilicate species in solution, or they may cause an insoluble silicate species to precipitate, adversely affecting the yield of zeolite. Therefore, it has been considered desirable to apply pure chemicals as starting materials. This is however costly.

[0008] The process of the present invention has as one object thereof to

overcome substantially one or more of the above mentioned problems associated with the prior art, or to at least provide a useful alternative thereto.

[0009] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. This discussion is not an

acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0010] Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Disclosure of the Invention

[001 1 ] In accordance with the present invention there is provided a method for the synthesis of zeolites, the method comprising the addition of a predominantly alumina-silicate starting material to a stoichiometric excess of sodium hydroxide, with additional water, and calcining at a temperature of greater than about 400°C.

[0012] Preferably, the alumina-silicate starting material is the residue from a leach of a spodumene ore or concentrate to extract lithium therefrom. Still preferably, the spodumene ore or concentrate is in the form of beta spodumene prior to the leach. Yet still preferably, the leach is a sulphuric acid leach.

[0013] Preferably, the calcine temperature is at least about 600°C for a residence time of at least about 4 hours [0014] Preferably, the additional water is provided in the amount of between about 1 to 4 times the weight of the alumina-silicate starting material.

[0015] Preferably, the pressure is in the range of atmospheric to about 15 psig.

[0016] In one form of the present invention the leach residue comprises hydrogen Catena-Aluminodisilicate, Hydrogen Tecto-Aluminodisilicate and silica as the predominant components thereof.

[0017] Preferably, the leach residue has a Pso of about 75 μιη.

[0018] Preferably, the molar ratio of silicon to aluminium in the leach residue is adjusted to about 1 .0:1 .1 prior to calcining. Still preferably, the molar ratio of silicon to aluminium in the leach residue is adjusted through the addition of AI(OH)3 to the leach residue.

[0019] An amount of an NaOH solution is preferably added to the leach residue prior to calcining. Preferably, the NaOH solution is a 50% w/w solution.

[0020] Still preferably, the NaOH solution is added with a stoichiometric sodium requirement of between 3 and 4 times. Most preferably, a 50% w/w solution of NaOH is added with a stoichiometric sodium requirement of 4 times.

[0021 ] The method of the present invention further comprises a cooling step.

[0022] The method of the present invention still further comprises a subsequent grinding step. The resulting material is preferably added to a volume of water in a water leach and thereby provides a zeolite yield. The water leach is preferably conducted over a period of between about 1 to 2 hours.

[0023] Preferably, the synthesised zeolite is in the form of an LTA zeolite.

[0024] In one form of the present invention the LTA zeolite comprises

Nai2[(AI02)i2(Si02)i2].27H₂0. [0025] Preferably, an aging step is provided immediately after the water leach. The aging step is preferably conducted in two periods. Collectively the two periods preferably provide a residence time of between about 36 to 48 hours. At least a part of the aging step is still preferably conducted at elevated temperature. Still further preferably, one of the periods of the aging step is conducted at about room temperature.

[0026] The elevated temperature of the aging step is preferably 50°C or higher. Still preferably, the elevated temperature of the aging step is in the range of 50°C to 70°C.

[0027] In one form, the aging step comprises a first period conducted at about room temperature for a period of between 22 to 24 hours, and a second period conducted at a temperature in the range of 50°C to 70°C for a period of between 15 to 24 hours.

[0028] In accordance with the present invention there is further provided a method for the synthesis of zeolites as described hereinabove in combination with a leach of a spodumene ore or concentrate, wherein a residue from the leach is utilised as the predominantly alumina-silicate starting material.

[0029] In accordance with the present invention there is still further provided an LTA zeolite formed by the method described hereinabove.

Brief Description of the Drawings

[0030] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a scanning electron micrograph (SEM) of an LTA zeolite formed in accordance with a first embodiment of the method of the present invention, showing the crystal structure thereof;

Figure 2 is a diagrammatic representation of a method for the synthesis of zeolites in accordance with the second embodiment of the method of the present invention; Figure 3 is an X-Ray Diffraction (XRD) trace of an LTA zeolite formed in accordance with the second embodiment of the present invention, including aging of the leach slurry at 50°C for 1 5 to 16 hours;

Figure 4 is an X-Ray Diffraction (XRD) trace of an LTA zeolite formed in accordance with the second embodiment of the present invention, including aging of the leach slurry at 70°C for 1 5 to 16 hours;

Figure 5 is an X-Ray Diffraction (XRD) trace of a pure reference LTA zeolite, utilised for comparison purposes in the traces of Figures 3 and 4;

Figure 6 is a Scanning Electron Microscope (SEM) image of the LTA zeolite of Figure 3; and

Figure 7 is a Scanning Electron Microscope (SEM) image of the LTA zeolite of Figure 4.

Best Mode(s) for Carrying Out the Invention

[0031 ] The present invention provides a method for the synthesis of zeolites, the method comprising the addition of a predominantly alumina-silicate starting material to a stoichiometric excess of sodium hydroxide, with additional water, at a

temperature of greater than about 400°C for a period of at least about 4 hours. The reaction that occurs as a result of this addition may be referred to as 'fusion'.

[0032] The alumina-silicate starting material is, in one particularly preferred form, the residue from a leach of a spodumene ore or concentrate to extract lithium therefrom. The spodumene ore or concentrate is in the form of beta spodumene prior to the leach. The leach is an acid leach, for example a sulphuric acid leach, or as a further example, a hydrochloric acid leach. A leach of a beta spodumene ore or concentrate is described, by way of example, in each of International Patent

Applications PCT/AU201 3/000857 (WO2014/02621 7) and PCT/AU201 5/000650 (WO201 6/1 1 9003), the entire content of each being incorporated herein by reference.

[0033] The leach residue has, for example, a Pso of about 75 μιη. [0034] The temperature of the addition of the starting material to the sodium hydroxide, or the fusion, is, for example, at least about 600°C. The additional water is provided in the amount of between about 1 to 4 times the weight of the alumina- silicate starting material. The pressure is in the range of atmospheric to about 15 psig.

[0035] In one form of the present invention the leach residue comprises hydrogen Catena-Aluminodisilicate, Hydrogen Tecto-Aluminodisilicate and silica as the predominant components thereof.

[0036] The method of the present invention further comprises subjecting the fused material to a cooling step and a subsequent grinding step. The resulting material is then added to a volume of water and thereby provides a zeolite yield.

[0037] The synthesised zeolite is in the form of an LTA zeolite, for example

Nai2[(AIO2)i2(SiO2)i2].27H₂O.

[0038] An aging step is provided immediately after the water leach. The aging step is conducted in two periods. Collectively the two periods provide a residence time of between about 36 to 48 hours. At least a part of the aging step is conducted at elevated temperature. One of the periods of the aging step is conducted at about room temperature. The elevated temperature of the aging step is 50°C or higher, for example in the range of 50°C to 70°C.

[0039] In one form, the aging step comprises a first period conducted at about room temperature for a period of between 22 to 24 hours, and a second period conducted at a temperature in the range of 50°C to 70°C for a period of between 15 to 24 hours.

[0040] The present invention further provides a method for the synthesis of zeolites as described hereinabove in combination with a leach of a spodumene ore or concentrate, wherein a residue from the leach is utilised as the predominantly alumina-silicate starting material.

[0041 ] The present invention still further provides an LTA zeolite formed by the method described hereinabove. [0042] The method of the present invention may be further understood with reference to the following non-limiting examples.

EXAMPLE 1

[0043] A spodumene leach residue having the chemical composition set out Table 1 below, is utilised as a starting material.

Table 1 : Chemical Analysis of Leach Residue

[0044] An XRD/SEM of a spodumene leach residue sample reveals the dominant presence of compounds Hydrogen Catena-Aluminodisilicate (HAIO6S12)/ Hydrogen Tecto-Aluminodisilicate (HAIO6S12) and Silica (S1O2) as the likely main phases present based on typically employed software and database search-match algorithms.

[0045] A summary of the major compounds considered to be present in the spodumene leach residue, based on the above analysis, is provided in Table 2 below:

Table 2: Presence of Major Compounds in Leach Residue

HYDROGEN CATENA -ALUMINODISILICATE MAJOR

QUARTZ MAJOR

BETA SPODUMENE MINOR

MUSCOVITE ACCESSORY

AMORPHOUS COMPOUND MINOR [0046] A summary of the likely composition of the leach residue based on the chemical analysis and mineralogy is provided in Table 3 below:

Table 3: Composition of Leach Residue

[0047] The following Table 4 illustrates the particle size distribution of the leach residue. Predominantly, it is in the range of Pso 75 μιη.

Table 4: Particle Size Distribution of Spodumene Leach Residue

[0048] 100 g spodumene leach residue was added to 200 g NaOH at 50% solution. The mixture was fused at 600°C for 4 hours in a suitable vessel, for example an oven with agitation. The resultant fused and agglomerated material was cooled to room temperature and ground to a Pso of about 75 μιη. Fused material was added to 1200 mL of distilled water in a vessel made of polymethylpentene. [0049] Zeolite yield was approximately 30 g.

[0050] By way of energy dispersive spectroscopy (EDS) analysis of the resulting LTA Zeolite it was found to have a composition of Nai2[(AIO2)i2(SiO2)i2].27H2O.

[0051 ] The crystal structure of the resulting LTA Zeolite is shown in the SEM image in Figure 1 .

EXAMPLE 2

[0052] Additional two tests were performed aiming to prepare Linde Type A zeolite with a Na:AI:Si ratio of 1 :1 :1 having chemical composition Nai2[(AIO2)i2(SiO2)i2] or Nai2[(AIO2)i2(SiO2)i2].xH₂O.

[0053] The procedure adopted was substantially similar to Example 1 , here including the calcination of a spodumene leach residue mixed with an amount of AI(OH)3 solid and a volume of 50% w/w NaOH soln, water leaching of the calcined ground sample at room temperature (RT), an aging step comprising the aging of water leach slurry at RT (Aging-1 ) for a first period of 22 hours, and further aging of the Aging-1 slurry at room temperature (RT), 50°C or 70°C, separately (Aging-2), for a second period of 15 to 16 hours.

[0054] With reference to Figure 1 , depicting a method 10 for the synthesis of zeolites in accordance with the present invention and Example 2, a spodumene leach residue 12 is mixed with an amount of AI(OH)3 solid 14 and 50% w/w NaOH solution 16.

[0055] In two tests (referenced herein as Ze-6 and Ze-7), a calculated amount of the AI(OH)3 solid 14 was added to the spodumene leach residue 12 to obtain a molar ratio of Si to Al about 1 .0:1 .1 , for example 1 :1 . The 50% NaOH solution 16, produced from NaOH flakes 17 and water 30, was added to these tests with a stoichiometric sodium requirement of either: 3.1 times for test Ze-6; and

4.0 times for test Ze-7.

[0056] Initially a uniform slurry/paste 18 of leach residue, AI(OH)3 and NaOH was prepared and the slurry/paste was passed to an evaporator 19 operated at 200°C for a residence time of about 4 hours and an evaporation loss of 40 to 45%, and subsequently calcined 20 at 600°C for 4 hours. A calcined solid was cooled 22, ground 24 to a P80 of 75 μιη, and stored 26, before leaching 28 with water 30 and agitation, at room temperature for about 1 -2 hours. The leach slurry was passed to an aging step 32, in which a first period 32a is conducted at RT for a period of about 22 to 24 hours (Aging-1 ), for example 22 hours, and subsequently a second period 32b, conducted at any of RT, 50°C and 70°C for between about 15 to 24 hours (Aging-2), for example 15-16 hours. A final slurry 34 containing zeolite and excess NaOH is collected and then centrifuged 36, producing a filtrate 35 and a zeolite product, the wet zeolite product in turn being washed 38 with water by

repulping/centrifuging 40 two times. Wash solution 42 from the

repulping/centrifuging 40 is recycled to the water leach 28.

[0057] The filtrate 35 from the centrifuge 36 is passed to a concentration step 42 and in turn to a NaOH store 44. From here NaOH solution may be recycled for the preparation of the uniform slurry/paste 18 of leach residue, AI(OH)3 and NaOH.

Evaporated liquids from the evaporator 19 may be added to this recycle stream.

[0058] Solids from repulping/centrifuging 40 are passed to a store for washed, wet zeolite 46 before being passed to a drying step 48, in turn providing a Linde Type A Zeolite 50 as the final product.

[0059] XRD investigation of the final samples generated from RT aging were found to be completely amorphous for both the tests Ze-6 and Ze-7, and no zeolite formation took place. Consequently, no results for the RT tests are provided herein. However, the samples generated from both the 50°C and 70°C aging of Aging-2 produced good quality Linde Type A Zeolite in both the Ze-6 and Ze-7 tests. The XRD traces of 50°C and 70°C aged sample for both these tests are provided in Figures 3 and 4, respectively. A minor silicon peak was found to be present in most cases, except 50°C aging from the Ze-7 test (with 4 times NaOH during calcination) where the silicon peak was found to be negligible.

[0060] In Figures 3 and 4 only silicon peaks are indicated (refer the straight indicator lines extending upwardly from the x-axis). The remaining peaks refer to the Linde Type A zeolite peaks, with reference to the typical XRD trace of pure Linde Type A zeolite, as per RW Thompson, shown in Figure 5.

[0061 ] The final liquors and solid analyses for the 50°C and 70°C aged tests are given in Table 5, below, for comparison. The molar ratios of AI:Si:Na in the prepared solids (as shown in Table 5) were found to be sufficiently close to 1 :1 :1 which is the intended stoichiometry of Al, Si and Na to provide the production of Linde Type A zeolite.

Table 5: Final liquors and solids analyses for 50° and 70°C aging solids for tests Ze-6 and Ze-7

[0062] The yield provided by the method set out with reference to Example 2 was better than that provided by the method as set out with reference to Example 1 , suggesting that the aging step and/or the adjustment of proportions of Na, Al and Si are of some importance in improving yield.

[0063] An overview of the XRD phases, particle size and pore volume data of the prepared zeolites are given in Table 6 below. The particle size distribution was found to be more or less similar for all the prepared samples. Table 6: Characterisation data of the prepared zeolites in both the tests Ze-6 and Ze-7

[0064] The pore volume data indicates the capacity of gas that can be adsorbed within pores of the molecules in the prepared zeolite samples. This confirms that 4 times caustic addition during calcination will produce higher pore volume capacity compared to lower caustic addition during calcination.

[0065] The SEM images for the prepared zeolite samples at 50°C and 70°C, for both the tests, were found to be very similar with marked crystallisation. The particle shape is found to be cubic in the SEM images. The SEM images of the 50°C and 70°C test samples from test Ze-6 are provided in Figures 6 and 7.

[0066] As can be seen with reference to the above description, the method of the present invention provides an alkali fusion method for the synthesis of an LTA zeolite from spodumene leach residue.

[0067] The Applicant has determined that during fusion, the majority of the phases in the leach residue material were converted into soluble sodium silicate and then converted to amorphous material through agitation. The LTA type Zeolite phase was detected in the product. During the fusion process, alumina silicate from the spodumene leach residue is understood to react with the sodium hydroxide giving rise to alumina-sodium silicate. The aged material, or fused product, was

amorphous with some residual sodium contained therein. Finally, after heating at 600°C for 4 to 6 hours, an LTA Zeolite phase with crystal system was formed with space group 1 m3m and having a lattice constant 4.29 A.

[0068] It is envisaged that the LTA zeolite synthesised using the method of the present invention may be used as a molecular sieve or an adsorbent.

[0069] The method of the present invention has found that when special conditions are observed, the yield of LTA Zeolite can be greatly improved (the yield obtained when using a fly ash starting material is known to be less than 50%, whereas when using the spodumene leach residue in accordance with the present invention the yield has been found to be greater than about 85%) and the properties of the LTA Zeolite are modified (wherein a prior art fly ash starting material ultimately produces an X Type zeolite, the spodumene leach residue in accordance with the present invention produces an LTA zeolite), thus providing a number of advantages.

[0070] These conditions involve carrying out the reaction between the alumina- silicate bearing spodumene leach residue and NaOH solution. Theoretically, the temperature can range from about 400°C to over 600°C for about 4 hours. This product is understood by the Applicants to have excellent ion-exchange properties, relative to X Type zeolites, and thus has a higher market value. It is apparent that an economic advantage lies in utilising spodumene leach residue in the preparation of an LTA zeolite as described hereinabove rather than the typical fate of such material, being dumping in pits or for use in road construction.

[0071 ] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

1 . A method for the synthesis of zeolites, the method comprising the addition of a predominantly alumina-silicate starting material to a stoichiometric excess of sodium hydroxide, with additional water, and calcining at a temperature of greater than about 400°C.

2. The method of claim 1 , wherein the alumina-silicate starting material is the residue from a leach of a spodumene ore or concentrate to extract lithium therefrom.

3. The method of claim 2, wherein the spodumene ore or concentrate is in the form of beta spodumene prior to the leach.

4. The method of claim 2 or 3, wherein the leach is a sulphuric acid leach.

5. The method of any one of the preceding claims, wherein the temperature of the calcine is about 600°C and the residence time at least about 4 hours.

6. The method of any one of the preceding claims, wherein the additional water is provided in the amount of between about 1 to 4 times the weight of the alumina-silicate starting material.

7. The method of any one of the preceding claims, wherein the leach residue comprises hydrogen Catena-Aluminodisilicate, Hydrogen Tecto- Aluminodisilicate and silica as the predominant components thereof.

8. The method of any one of claims 2 to 7, wherein the leach residue has a Pso of about 75 μιη.

9. The method of any one of claim 2 to 8, wherein the molar ratio of silicon to aluminium in the leach residue is adjusted to about 1 .0:1 .1 prior to calcining.

10. The method of claim 9, wherein the molar ratio of silicon to aluminium in the leach residue is adjusted through the addition of AI(OH)3 to the leach residue.

1 1 . The method of any one of claims 2 to 10, wherein an amount of an NaOH solution is added to the leach residue prior to calcining.

12. The method of claim 1 1 , wherein the NaOH solution is a 50% w/w solution.

13. The method of claim 12, wherein the NaOH solution is added with a

stoichiometric sodium requirement of: a. between 3 and 4 times; or b. 4 times.

14. The method of any one of the preceding claims, wherein the method further comprises an evaporation step prior to calcination.

15. The method of claim 14, wherein the evaporation step is conducted at about 200°C for a period of about 4 hours.

16. The method of any one of the preceding claims, wherein the method further comprises a cooling step after calcination.

17. The method of claim 16, wherein the method still further comprises a

subsequent grinding step.

18. The method of claim 17, wherein the material resulting from the grinding step is added to a volume of water in a water leach and thereby provides a zeolite yield.

19. The method of claim 18, wherein the water leach is conducted over a period of between about 1 to 2 hours.

20. The method of claim 18 or 19, wherein the synthesised zeolite is in the form of an LTA zeolite.

21 . The method of claim 20, wherein the LTA zeolite comprises

Nai2[(AI02)i2(Si02)i2].27H₂0.

22. The method of any one of claims 18 to 21 , wherein an aging step is provided immediately after the water leach.

23. The method of claim 22, wherein the aging step is conducted in two periods, collectively the two periods provide a residence time of between about 36 to 48 hours.

24. The method of claim 22 or 23, wherein at least a part of the aging step is

conducted at elevated temperature.

25. The method of claim 23 or 24, wherein one of the periods of the aging step is conducted at about room temperature.

26. The method of claim 24 or 25, wherein the elevated temperature of the aging step is: a. 50°C or higher; or b. in the range of 50°C to 70°C.

27. The method of any one of claims 22 to 26, wherein the aging step comprises a first period conducted at about room temperature for a period of between 22 to 24 hours, and a second period conducted at a temperature in the range of 50oC to 70oC for a period of between 15 to 24 hours.

28. A method for the synthesis of zeolites in combination with a leach of a

spodumene ore or concentrate, wherein a residue from the leach is utilised as the predominantly alumina-silicate starting material, the method for the synthesis of zeolites being in accordance with any one of the preceding claims.

29. An LTA zeolite formed by the method of any one of the preceding claims.