AU2021221391A1

AU2021221391A1 - A Method for Treating a Co-Product

Info

Publication number: AU2021221391A1
Application number: AU2021221391A
Authority: AU
Inventors: Guoping Hu; Eric Freemantle MAY; Gongkui XIAO
Original assignee: Mineral Resources Ltd
Current assignee: Mineral Resources Ltd
Priority date: 2021-08-23
Filing date: 2021-08-23
Publication date: 2023-03-09
Also published as: CN115710001A

Abstract

A method for treating a co-product comprising the steps of: (a) forming a mixture comprising leached spodumene co-product, an alkaline compound and at least a wetting quantity of water; (b) activating the mixture from step (a) under determined relatively low temperature conditions for a determined activation time period in the presence of water vapour to form an activated mixture; (c) forming a solution by introducing water to the activated mixture; and (d) hydrothermally crystallising zeolites from the solution under time and temperature conditions effective to synthesise the target zeolite.

Description

A METHOD FOR TREATING A CO-PRODUCT TECHNICAL FIELD

[0001] This invention relates to a method for treating a co-product in the form of a method for synthesis of zeolites, for example from a leached spodumene co-product, also known as a lithium slag, leached spodumene residue or delithiated residue, or delithiated beta spodumene, produced during leaching of a calcined spodumene ore.

BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The 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.

[0003] Lithium is one of the most essential metals due to the expanding demand for lithium-ion batteries. Lithium can be produced from various sources and naturally occurring spodumene is a major source due to its high content of lithium.

[0004] The state-of-the-art technology for the extraction of lithium from spodumene involves several steps: 1) roasting the natural spodumene at about 1000 °C to transform the monoclinic a-spodumene to tetragonal p-spodumene. This crystal structure transformation increases the chemical reactivity of the spodumene so that the spodumene can react with acid or alkali at moderate temperature; 2) roasting the treated spodumene with sulphuric acid at 250 - 300 °C. The sulphation roasting induces the replacement reaction to generate soluble lithium sulphate and leached spodumene co-product. The soluble lithium sulphate is collected and further treated in a lithium refinery to produce desired lithium products, such aslithium hydroxide monohydrate, while the leached spodumene co-product - which is produced in relatively high volume, at about 0.8 tons leached spodumene co-product per ton of spodumene ore - requires proper management to reduce the environment footprint of a lithium refinery.

[0005] Currently, some of the leached spodumene co-product is used as a raw material for various applications, for example in the construction industry. More typically, leached spodumene co-product is disposed of either by landfill or by open piling, which poses an environment issue. Therefore, the realisation of high value-added utilisation of leached spodumene co-product is needed to open up new ways of efficient utilisation for the sustainable development of the lithium industry.

[0006] Leached spodumene co-product is rich in silicon and aluminium and its ratio is suitable as a raw material for the synthesis of zeolites - which may be used as adsorbents, molecular sieves or catalysts. Zeolite molecular sieves have potential for use as phosphorus free detergents, thus providing a significant potential revenue stream as well as addressing the leached spodumene co-product disposal challenge.

[0007] Dan Chen, Xin Hu, Lu Shi, Qun Cui, Haiyan Wang, Huqing Yao, Synthesis and characterization of zeolite X from lithium slag, Applied Clay Science, 59-60 (2012) 148 151 reported a method for zeolite X synthesis from lithium refinery co-product by alkaline fusion with hydrothermal reaction. The co-product consists of quartz and leached spodumene, and the mass percentages of SiO 2 and A1203 are 71.73% and 25.16% respectively. This means that the molar ratio of Si/Al is 2.42. The mixture of NaOH and the co-product with a weight ratio of 1.5 was milled and fused in a platinum crucible at 600 0C for 4 h. The fused mixture was cooled to room temperature, ground further and mixed with water in a container. The slurry thus obtained was stirred mechanically for 30 minutes, aged in the container at room temperature for 12 h and then was kept at 950 C for 8 h without stirring. The resultant precipitate was then repeatedly washed with distilled water to remove excess sodium hydroxide, filtered and dried. It was claimed 94.31% of the starting material was converted to zeolite X. This method requires several processing steps and has a high energy consumption due to high temperature roasting.

[0008] International Patent Publication No. WO 2019/068135 and Goutam Das, Dianne Bedell, Yatendra Sharma, Chris Reed, Value added product recovery from leached spodumene leach residue, ALTA 2020 Lithium & Battery Technology Conference, ALTA Metallurgical Services, 2020, pp. 72-87, also describe a synthesis of zeolite 4A (Linde Type A or LTA) from leached spodumene co-product involving a high temperature alkali fusion with dry sodium hydroxide. The lithium slag had a Si/Al molar ratio of about 2.97 and, as the Si/Al molar ratio in the leached spodumene co-product was not close to 1, the stoichiometric Si/Al ratio in zeolite A, gibbsite (AI(OH)3) was added to the residue to synthesise zeolite 4A. The mixture of leached spodumene co-product, gibbsite and sodium hydroxide was calcined at 600 0C for 4 to 6 hours and then ground to a powder following cooling. The powder was then mixed with water and settled with aging at room temperature for 24 hours before further aging/crystallisation at 50-70 0C for 15 to 16 hours, a long synthesis time. Again, the high temperature fusion indicates high energy consumption. The long synthesis time also means that zeolite productivity per unit time is limited.

[0009] Wenfu Yan, Binyu Wang, Li Ren, Jihong Yu, Ruren Xu, X zeolite molecular sieve and preparation method thereof, China Patent No. 110950351 and Wenfu Yan, Binyu Wang, Li Ren, Jihong Yu, Ruren Xu, A zeolite molecular sieve and preparation method thereof, China Patent Application No. 110894074, 2021 disclose a method for synthesising type X and type A zeolites from leached spodumene residue having an Si/Al molar ratio of 2.8. In these methods, the leached spodumene residue is first mixed with a dry sodium-containing alkaline compound and an aluminium compound at room temperature. This mixture is then activated at 180-2200C in a sealed container. After cooling to room temperature, the activated material was mixed with water to form a soluble gel. The soluble gel then underwent a hydrothermal reaction, for example at 100-120 0C, for crystallisation of the type X and type A zeolites. These methods do not require high temperature roasting or fusion (typically at 6000C) for activation of the leached spodumene residue. Therefore, the energy consumption of these methods is lower than conventional zeolite synthesis methods. However, as the dry activation method only generates a low pressure in the sealed container, a relatively high 0 is still required to convert the Si/Al bonding from 6 temperature of 180-220 C coordination to 4-coordination for further crystallisation.

[0010] Xiaoqin Pu, Lu Yao, Lin Yang, Wenju Jiang, Xia Jiang, Utilization of industrial waste lithium-silicon-powder for the fabrication of novel nap zeolite for aqueous Cu(II) removal, Journal of Cleaner Production, 265 (2020) 121822 reported the synthesis of P zeolite from lithium-silicon powder from a plant that produces lithium carbonate. The Si/Al molar ratio in the raw material was 2.26. To prepare the zeolite, the raw material was first mixed with sodium hydroxide and deionised (DI) water. Afterwards, the slurry was stirred for 12 hours at 250 C, sealed in a hydrothermal synthesis reactor at 60-1200 C for 1 to 20 hours. The obtained slurry was then filtered and washed continuously with DI water until its pH was approximately equal to that of the DI water. Subsequently, the slurry was dried overnight at 100 0C to obtain the P zeolite. Compared to other methods for zeolite synthesis from leached spodumene co-product, this method can synthesise zeolite at relatively low temperatures but the time required for synthesis is excessively long; therefore, it is not practical for industrial scale zeolite synthesis.

[0011] From the above background, it is apparent that current methods for zeolite synthesis from leached spodumene co-product have one or more of the following limitations: 1) requiring high temperature activation of the starting material with alkali, typically sodium hydroxide; 2) requiring several synthesis steps; and 3) requiring a long time for aging and crystallisation. These limitations are constraints to industrial application of leached spodumene co-product to zeolite synthesis. In addition, the prior methods are constrained to specific Si/Al molar ratios in the raw materials; therefore, the methods cannot be effectively applied to materials with different Si/Al ratios.

[0012] It is an object of the present invention to provide a method for synthesis of zeolites from a leached spodumene co-product alternative to processes as described above.

SUMMARY OF INVENTION

[0013] With this object in view, the present invention provides a method for synthesis of zeolites comprising the steps of:

(a) forming a mixture comprising leached spodumene co-product, an alkaline compound and at least a wetting quantity of water;

(b) activating the mixture from step (a) under determined relatively low temperature conditions for a determined activation time period in the presence of water vapour to form an activated mixture;

(c) forming a solution by introducing water to the activated mixture; and

(d) hydrothermally crystallising zeolites from the solution under time and temperature conditions effective to synthesise a target zeolite.

[0014] In step (a), the leached spodumene co-product is mixed with an alkaline compound provided in a near dry state and the wetting quantity of water. Suitable alkaline compounds include sodium hydroxide and sodium carbonate with sodium hydroxide being preferred. Both compounds are typically used in the lithium refining industry and can be procured in similar manner for zeolite synthesis. The ratio of leached spodumene co-product to alkaline compound is preferably in the range 1:1 to 1:5.

[0015]As to a wetting quantity of water or moisture added in step (a), the mixture of leached spodumene co-product and alkaline compound is desirably contained at a relative humidity of between 0 and 100%. The wetting water is desirably de-ionised water. The wetting quantity of water, or moisture, enables activation of the raw materials at lower temperature, due to the additional vapour pressure generated in the autoclave by the moisture. Activation is conveniently conducted in a pressure vessel such as an autoclave.

[0016]Step (a) may be conducted at any desired temperature though ambient temperature is convenient. Pressure may be in the range 1 to 25 bar.

[0017]Step (b), activating the mixture, involves change of coordination state of the silicon-aluminium species in the leached spodumene co-product from six to four to facilitate hydrothermal crystallising step (d). The activation step (b) is conducted at a determined relatively low temperature in the sense that activation does not require a fusion process conducted at 4000 C or above. Indeed, the activation temperature is advantageously maintained in the range 60-2200 C. This provides a benefit of lower energy consumption compared to a fusion temperature of 4000 C or higher.

[0018] As to activation time period in activation step (b), this is preferably less than 6 hours, more preferably less than 5 hours and conveniently in the range of 1 to 4 hours.

[0019] The activated mixture of step (b) is preferably cooled, for example to ambient temperature, before mixing with water to forming a solution in mixing step (c). Once formed, the solution of step (c) is conveniently aged for a period of 0.5 to 4 hours at ambient temperature.

[0020] If desired, to synthesise target zeolites, Si/Al molar ratio of the mixture of step (a) may be adjusted, preferably through addition of a soluble aluminium or silicon compound to the mixture of step (a), that is, prior to activation. Examples of target zeolites include, without limitation, A-type zeolite, cancrinite, chabazite (CHA), X-type zeolite, P-type and sodalite zeolite as well as mixtures of these zeolites.

[0021] Optionally, a secondary physical separation of solids, conveniently by filtration may follow mixing step (c). This allows removal of solid impurities with the liquid phase or solution being directed to hydrothermal crystallising step (d). This optional step is also conveniently conducted at ambient temperature.

[0022] Hydrothermal crystallising step (d) is conveniently conducted of the solution of step (c) heated to a temperature of between 70 and 1800 C for a period of less than 18 hours, preferably less than 12 hours, more preferably less than 6 hours, most preferably 4 to 6 hours. Stirring may be employed if desired.

[0023] If desired, hydrothermal crystallising step (d) may involve seeding of the solution to accelerate hydrothermal crystallisation. Seeding is preferably with seeds of one or more zeolites, conveniently through seeds of the target zeolite(s).

[0024] The synthesised zeolites are recovered following hydrothermal crystallisation, conveniently by filtration. Washing and drying step(s) may follow zeolite recovery. Conveniently, drying is conducted in a temperature range of 80-1200 C.

[0025] The leached spodumene co-product may be subjected to a primary physical separation prior to step (a). Conveniently, leached spodumene co-product is washed with water and solid impurities removed through a solid-solid separation process such as settling or centrifuging. This may result in formation of an impurity solids fraction which can be separated from the feed leached spodumene co-product fraction. The leached spodumene co-product can be further washed if required and dried prior to direction to step (a). The primary physical separation step allows for removal of silica which may be done to adjust the Si/Al ratio of the mixture to be activated in step (a).

[0026] Advantages of the method of the invention include value addition to leached spodumene co-product, even where this contains significant impurities (including calcium oxide and silica) which can be removed through primary and/or secondary physical separation steps as described above, as well as a reduced cost method for synthesis of a range of zeolites. This results from a number of considerations. First, the raw material, leached spodumene co-product, is a currently low value byproduct produced in significant volume during the production of high value lithium salts for battery production. Second, zeolites may be synthesised at a relatively low temperature and at low pressure. Third, fewer synthesis steps and shorter crystallisation time allow potential savings in capital and operating costs. Fourth, the use of leached spodumene co-product as the starting silicon-aluminium material avoids the significant cost involved in synthesising zeolites from other raw materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features of the method for synthesis of zeolites of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0028] Figure 1 is a: flowsheet for a method for synthesis of zeolites according to a first embodiment of the present invention.

[0029] Figure 2 provides a detail flowsheet of a primary physical separation step conducted according to a further embodiment of the invention.

[0030] Figure 3 provides a detail flowsheet of a secondary physical separation step conducted according to a further embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] Referring to Figure 1, leached spodumene co-product 10, also known as a leached spodumene residue or lithium slag, having an Si/Al molar ratio of about 2.4 is obtained from a lithium refinery, for example involving sulphuric acid leaching of p spodumene to form lithium sulphate, conversion to lithium hydroxide, purification and crystallisation to form lithium hydroxide monohydrate. As this process is well understood in the art of lithium refining, no further description is provided here.

[0032]The leached spodumene co-product 10 is subjected to a method 100 for synthesising zeolites as described below.

[0033] In optional step 115, and as shown in more detail in Figure 2, the leached spodumene co-product 10 is subjected to a primary physical separation. Leached spodumene co-product 10 is slurried with water 11 and subjected to a solid-solid separation, conveniently settling or centrifuging. Solids 115a, including insoluble silica for example in the form of quartz, are removed as an impurity fraction by solid-solid separation step 116 from further fraction 10a. The further fraction 10a, including both leached spodumene co-product and water, is directed to filtration and drying step 117 where water 117a is separated and recycled. The leached spodumene co-product is dried to provide a leached spodumene co-product 106 which is directed to step 120. The leached spodumene co-product may be washed several times before filtration and drying.

[0034] In step 120, dried leached spodumene co-product 106 is mixed, at ambient temperature, with a relatively small quantity of de-ionised water 15 and dry sodium hydroxide 20 to form a mixture 25. The mass ratio of leached spodumene co-product to dry sodium hydroxide is between 1:1 to 1:5. De-ionised water 15 wets or moistens the mixture 25 so that it can be held at a relative humidity of between 0 and 100%. The mixture 25 is not subjected to fusion.

[0035] The mixture 25 is then activated in activation step 130 conducted in an autoclave at temperature 60-220 0C for 1 to 4 hours and 1 to 25 bar pressure to form an activated mixture 35. These conditions are exemplary only. Activating the mixture 25 involves change of coordination state of the silicon-aluminium species in the leached spodumene co-product from six to four in order to facilitate hydrothermal crystallisation step 150.

[0036] If desired, to synthesise target zeolites, the Si/Al molar ratio of the mixture 25 may be adjusted from its first value of about 2.4 through addition of a soluble aluminium or silicon compound 42 to the activation step 130. Examples of target zeolites may include, without limitation, cancrinite, chabazite, A-type zeolite, X-type zeolite, P-type zeolite and sodalite zeolite as well as mixtures of these zeolites.

[0037] Due to the evaporation of the quantity of de-ionised water 15 from mixture 25, activation of mixture 25 occurs in the presence of water vapour and a consequential water vapour pressure that pressurises the autoclave and facilitates activation of mixture 25 to form activated mixture 35 at a relatively low temperature. The activation step 130 is conducted at a relatively low temperature in the sense that activation does not require a fusion process conducted at 4000 C or above. This provides a benefit of lower energy consumption because cost for heating is substantially less than to achieve a fusion temperature of 4000 C or higher.

[0038] Following cooling of activated mixture 35 to ambient temperature following activation step 130, activated mixture 35 is mixed with de-ionised water 40 in mixing step 140 to form a solution 45. Once formed, the solution 45 is aged for a period of 0.5 to 4 hours at ambient temperature.

[0039] Hydrothermal crystallisation step 150, for producing zeolites, is conveniently conducted with solution 45 heated to a temperature of between 70 and 1800 C for a period of less than 18 hours, desirably 4 to 6 hours. The solution 45 is desirably stirred during hydrothermal crystallisation step 150 with stirring speed being selected in the range 0 to 700 rpm.

[0040] Optionally, and as shown with reference to the embodiment of Figure 3, solution 45 is subjected to a secondary physical separation step 220 in which solution 45 from mixing step 140 is filtered in filtration step 222 to remove any remaining solid impurities 223 which are removed from the process. The liquid phase or filtered solution 45A is directed to hydrothermal crystallisation step 150. The secondary physical separation step 220 is conveniently conducted at ambient temperature. In hydrothermal crystallisation step 150, the solution 45A is hydrothermally crystallised to produce zeolites.

[0041] If desired, hydrothermal crystallisation step 150 may involve seeding 155 of the solution to accelerate the hydrothermal crystallisation. Seeding is preferably with seeds of one or more zeolites, conveniently through seeds of the target zeolite(s). However, in some embodiments, seeding may not be necessary,

[0042] The synthesised zeolites 200 are recovered following hydrothermal crystallisation 150, conveniently by filtration in step 160. Washing and drying step(s), embodied within step 160, may follow synthesised zeolite 200 recovery. Conveniently, synthesised zeolite 200 drying is conducted in a temperature range of 80-1200 C.

[0043] Zeolite product 200 can then be distributed for use, for example as a molecular sieve to be used in water treatment, gas emissions control or gas filtration.

[0044] Waste water 170 can be recycled elsewhere in a lithium refinery or treated prior to discharge, subject to regulatory contaminant limits.

[0045] Advantages of the method of the invention include value addition to leached spodumene co-product as well as a reduced cost process for synthesising target zeolites. This results from a number of considerations. First, the raw material, leached spodumene co-product, is a currently low value byproduct produced in significant volume during the production of high value lithium salts for battery production. It contains significant impurities including calcium and silicon in oxidised form. Second, zeolites may be synthesised in a relatively low temperature from this impure material though use of first and/or second physical separation steps to remove these impurities is desirable. Third, fewer synthesis steps and shorter crystallisation time allow potential savings in capital and operating costs. Fourth, the use of leached spodumene co product as the starting silicon-aluminium material avoids the significant cost involved in synthesising zeolites from synthetic though pure reagents.

[0046] Modifications and variations to the method for synthesising zeolites as described in this specification may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed to be within the scope of the present disclosure.

[0047] Throughout this specification, 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

Claims

1. A method for synthesis of zeolites comprising the steps of:

(c) forming a solution by introducing water to the activated mixture; and

(d) hydrothermally crystallising zeolites from the solution under time and temperature conditions effective to synthesise the target zeolite.

2. The method of claim 1, wherein in step (a), the leached spodumene co-product is mixed with an alkaline compound provided in a dry or near dry state and the wetting quantity of water, said alkaline compound optionally being selected from sodium hydroxide and sodium carbonate, the ratio of leached spodumene co-product to alkaline compound optionally being in the range 1:1 to 1:5.

3. The method of claim 1 or 2, wherein step (b) is conducted at an activation 0 and pressure in the range 1 to 25 bar for a time temperature in the range 60-220 C period of less than 6 hours, preferably in the range of 1 to 4 hours.

4. The method of any one of the preceding claims, wherein the solution of step (c) is aged for a period of 0.5 to 4 hours at ambient temperature.

5. The method of any one of the preceding claims, wherein Si/Al molar ratio of the mixture of step (a) is adjusted through addition of a soluble aluminium or silicon compound to the mixture of step (a).

6. The method of any one of the preceding claims, wherein a secondary physical separation of solid impurities, optionally by filtration, follows mixing step (c).

7. The method of any one of the preceding claims, wherein hydrothermal crystallising step (d) is conducted at a temperature of between 70 and 1800 C for a period of less than 18 hours, preferably less than 12 hours, more preferably less than 6 hours, most preferably 4 to 6 hours.

8. The method of any one of the preceding claims, wherein hydrothermal crystallising step (d) involves seeding of the solution to accelerate hydrothermal crystallisation.

9. The method of claim 8, wherein seeding is with seeds of one or more zeolites, optionally with seeds of the target zeolite(s).

10.The method of any one of the preceding claims, wherein the leached spodumene byproduct is subjected to a primary physical separation prior to step (a), said primary physical separation optionally including washing of leached spodumene co-product with water for removal of solid impurities.

11. A zeolite produced by the method of any one of the preceding claims.