WO2019210351A1

WO2019210351A1 - Improved mica processing

Info

Publication number: WO2019210351A1
Application number: PCT/AU2019/050318
Authority: WO
Inventors: Gary Donald Johnson; Mark Daniel Urbani; Nicholas John VINES
Original assignee: Silica Technology Pty Ltd
Priority date: 2018-04-30
Filing date: 2019-04-10
Publication date: 2019-11-07
Also published as: AU2019262080A1; AU2019262080B2

Abstract

A process for the processing of mica rich minerals, the process comprising passing an ore or concentrate (1) containing a mica rich mineral to a pre-treatment phase, the pre-treatment phase including a size separation step (20) to produce a coarse fraction (4) and a fine fraction (5), whereafter the coarse fraction (4) is passed to an acid leach step (50, 60, 70, 80) in which the coarse fraction is contacted with at least sufficient acid, on a stoichiometric basis, to react with the mica rich mineral contained in both the coarse (4) and fine fractions (5), the fine fraction (5) subsequently being added to the acid leach step (70) whereby the mica in the fine fraction (5) is also leached, the leach step (50, 60, 70, 80) producing a leach slurry (15) that is passed to a separation step (90) forming a pregnant leach solution (17) and a leach residue (18), the pregnant leach solution (17) in turn being passed to one or more recovery steps.

Description

“Improved Mica Processing”

Field of the Invention

[0001 ] The present invention relates to a process for the improved processing of mica rich minerals.

[0002] In one form, the process of the present invention is intended to facilitate the extraction of lithium, and optionally potassium, rubidium and caesium, from lithium rich mica minerals, including but not limited to lepidolite and zinnwaldite.

Background Art

[0003] The major sources of commercially mined U2CO3 have historically been brine solutions and spodumene containing ores. Lepidolite, a lithium containing mica, is present in many pegmatite deposits, and co-exists with spodumene in some pegmatites. The presence of lepidolite is problematic for refineries that produce U2CO3 from spodumene concentrate. As such, the lithium content of lepidolite holds no value and is rejected at the spodumene concentrator.

[0004] Lepidolite can contain up to 7.7% U2O. The lepidolite in pegmatite bodies can be separated from the gangue minerals by flotation, or classification. However, this separation is not 100% efficient and results in gangue minerals present in the concentrate.

[0005] A process to extract lithium from lepidolite, a phyllosilicate mineral, and to produce U2CO3 is described in International Patent Application PCT/AU2015/000608 (WO 2016/054683). In the process of International Patent Application PCT/AU2015/000608, lepidolite is preferably milled to produce a product having a particle size of <Pso 75 micron. This process requires fine grinding of the lepidolite to achieve acceptable results. The milled lepidolite is leached in sulfuric acid under atmospheric pressure and temperatures up to boiling. The leach stage produces a pregnant leach solution, which is subjected to a series of process steps in which one or more impurity metals are removed, prior to recovering lithium as a lithium containing salt product.

[0006] The process of the present invention has as one object thereof to substantially overcome the problems associated with the prior art or to at least provide a useful alternative thereto. [0007] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia or any other country or region as at the priority date of the application.

[0008] 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.

[0009] Throughout the specification and claims, unless the context requires otherwise, the word “mica”, “micas” or obvious variations thereof will be understood to refer to the group of complex hydrous aluminosilicate minerals that crystallise with a sheet or plate-like structure. Specifically, the mica referred to herein is to be understood to refer to lithium containing mica.

Disclosure of the Invention

[0010] In accordance with the present invention there is provided a process for the processing of mica rich minerals, the process comprising passing an ore or concentrate containing a mica rich mineral to a pre-treatment phase, the pre treatment phase including a size separation step to produce a coarse fraction and a fine fraction, whereafter the coarse fraction is passed to an acid leach step in which the coarse fraction is contacted with at least sufficient acid, on a stoichiometric basis, to react with the mica rich mineral contained in both the coarse and fine fractions, the fine fraction subsequently being added to the acid leach step whereby the mica in the fine fraction is also leached, the leach step producing a leach slurry that is passed to a separation step forming a pregnant leach solution and a leach residue, the pregnant leach solution in turn being passed to one or more recovery steps.

[0011 ] Preferably, the mica rich mineral includes lepidolite and/or zinnwaldite.

[0012] Still preferably, the pre-treatment phase further comprises one or both of a concentration step and a milling step. The concentration step may be a flotation step. The milling step may preferably be a fine milling step. [0013] Still preferably, the fine milling step produces a product having a particle size of: a. Rdo <250 micron; b. P8o <150; or c. Rdo <75 micron.

[0014] Preferably, the size separation step comprises the separation of milled material by particle size, thereby producing the coarse fraction and the fine fraction.

[0015] Preferably, the size separation step produces a coarse fraction having a particle size of predominantly +25 micron and a fine fraction having a particle size of predominantly -25 micron.

[0016] Still preferably, the size separation step produces a coarse fraction having a particle size of predominantly +15 micron and a fine fraction having a particle size of predominantly -15 micron.

[0017] The size separation step preferably produces more fine fraction than it does coarse fraction, on a w/w basis.

[0018] Preferably, acid may be added to the leach step at or about the time the fine fraction is added thereto, in an amount such that the stoichiometric amount of acid to leach both the coarse and fine fractions is not exceeded.

[0019] The acid leach step is preferably carried out with an excess of H2SO4.

[0020] The amount of acid added to the coarse fraction in the leach step may preferably be about 1000 g/L.

[0021 ] Still preferably, the total sulfate concentration is close to the saturation limit of the solution at the leaching temperature. For example, this may be about 6.0M S at >90°C.

[0022] The coarse fraction is leached in the leach step for a period of time, to produce a pregnant liquor containing a high concentration of sulfuric acid, prior to addition of the fine fraction to the leach step. Preferably, the concentration of sulfuric acid in this pregnant leach liquor is >500 g/L. [0023] The fine fraction is preferably added to the leach step and the contained mica is leached with the acid in the coarse pregnant liquor.

[0024] Preferably, the leach slurry from the leach step contains a free acid concentration of greater than about 150 g/L H2SO4. Still preferably, the free acid concentration of the leach slurry is about 200 g/L.

[0025] The leach step preferably results in at least a proportion of the contained lithium, potassium, aluminium, rubidium, fluorine and caesium being extracted into solution, thereby forming the pregnant leach solution (“PLS”).

[0026] Preferably, the leaching step is conducted under atmospheric conditions.

[0027] The leaching step is preferably conducted at a temperature close to boiling. Still preferably, the leaching step is conducted at up to 120°C, for example at or about 105°C.

[0028] Preferably, the leach step comprises four leach stages, with leach slurry being passed progressively from a first of the four leach stages through to the fourth thereof. Still preferably, the fine fraction is added to the third of the four leach stages.

[0029] The retention time in the four leach stages is preferably: a. between about 12 to 24 hours; or b. about 18 hours.

[0030] Still further preferably, in the leach step greater than about 90% lithium extraction is achieved.

Brief Description of the Drawings

[0031 ] The process of the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which:-

Figure 1 is a flow sheet depicting the process of the present invention; and

Figure 2 is a graph showing two plots of lithium extraction versus time, wherein one plot represents a process in which a finely milled product is simply leached in acid for 24 hours, whereas the second plot represents a process conducted in accordance with the present invention, wherein a lepidolite concentrate was pre-milled to Pso 75 micron then separated in +25 micron and -25 micron fractions, and then the coarse fraction is leached for 8 hours, after which the fine fraction was added to the reactor, without additional acid, and the leach run out to 24 hours.

Best Mode(s) for Carrying Out the Invention

[0032] The present invention relates to a process for processing of mica rich minerals. More particularly, the process of the present invention is intended to allow the extraction of lithium, and optionally also potassium, rubidium and caesium, from lithium rich mica minerals. The lithium rich mica minerals include, but are not limited to, lepidolite and zinnwaldite.

[0033] In very general terms, in one embodiment of the present invention, a lithium containing mica rich mineral, lepidolite, may be pre-concentrated, if required, by a mineral separation process, for example flotation. The lepidolite ore or concentrate is then subjected to a pre-treatment phase comprising, for example, milling and size separation. The size separation step utilises screens and/or hydrocyclones to produce a slurry containing the coarse particles and a slurry containing the fine particles.

[0034] The lithium, potassium, rubidium, caesium, fluorine and aluminium present in the coarse lepidolite are extracted by strong sulfuric acid leaching in an acid leach step, producing leach liquor containing lithium, potassium, rubidium, caesium, fluorine, aluminium, a high concentration of sulphuric acid and a leach residue containing amorphous silica and unreacted gangue minerals. The fine lepidolite is introduced into the coarse leach slurry after a sufficient period to enable the coarse lepidolite to leach. The fine lepidolite is understood to be leached due to the high free acid concentration present in the coarse leach slurry.

[0035] Lepidolite is a lilac-grey or rose coloured lithium phyllosilicate (mica group) mineral and a member of the polylithionite-trilithionite series. The standard chemical formula for lepidolite is, but is not limited to, K(Li,AI)3(AI,Si)4O10(F,OH)2. It occurs in granite pegmatites, high temperature quartz veins, greisens and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl. Lepidolite can contain up to 7.7% U₂0. The lepidolite in pegmatite bodies can be separated from the gangue minerals by flotation, or classification. However, this separation is not 100% efficient and results in gangue minerals present in the concentrate.

[0036] It is envisaged that the processes of the present invention are applicable to any mica bearing ores and concentrates, but particularly lithium bearing mica ores, such as lepidolite, but also including zinnwaldite, biotite, glauconite and muscovite. Zinnwaldite is a lithium containing silicate mineral in the mica group, generally light brown, grey or white in colour, and having the chemical formula KLiFeAI(AISi₃)Oio(OH,F)_2.

[0037] In one form of the present invention the process comprises the method steps of:

(i) Separation of a mica rich mineral from gangue minerals, such as quartz and feldspar, by froth flotation, if required, to produce a mica concentrate;

(ii) Milling the mica concentrate;

(iii) Separating the coarse particles from the fine particles in the milled product;

(iv) Leaching the coarse mica in sufficient sulfuric acid solution required to leach the mica contained in the coarse and fine fractions under atmospheric conditions to enable lithium, and optionally potassium, rubidium, caesium and aluminium, to be converted to soluble sulfates, and to also optionally extract any fluorine present in the coarse fraction; and

(v) Subsequently leaching the fine mica in the coarse leach slurry, which slurry contains sufficient sulfuric acid solution to leach the mica contained in the fine fraction.

[0038] In one embodiment of the present invention, a lepidolite ore or concentrate is treated in accordance with the present invention as shown in Figure 1. The relative grades of the metals in lepidolite are described only by way of example, and the process of the present invention is expected to be able treat any lepidolite bearing material and any lithium bearing mica, independent of grade. [0039] In Figure 1 there is shown a flow sheet in accordance with the present invention and in which the embodiment depicted is particularly intended for the processing of lepidolite containing ore or concentrate 1 to extract lithium therefrom.

[0040] The lepidolite containing ore or concentrate 1 is passed to a pre-treatment phase comprising a milling step 10, with water 2, in which the ore or concentrate 1 is milled to reduce the particle size, for example to Pso <250 micron. More particularly, the particle size is reduced to Pso <150 micron or Pso <75 micron.

[0041 ] Milled lepidolite 3 is directed to a further feature of the pre-treatment phase, a size separation step, for example a size separation device 20, in a conventional process such as hydrocyclones, in which a coarse fraction, the coarse mica 4, is separated from a fine fraction, the fine mica 5. The size separation step produces the coarse mica 4 having a particle size of predominantly +25 micron, and the fine mica 5 having a particle size of predominantly -25 micron, with a 50/50 mass split between the coarse and fine fractions. Optionally, the size separation step produces a coarse fraction having a particle size of predominantly +15 micron and a fine fraction having a particle size of predominantly -15 micron. With such a size separation it is envisaged that the coarse fraction will constitute a higher proportion of the mass split than the fine fraction.

[0042] The use of hydrocyclones requires water to fluidise the slurry, part of which requires removal prior to leaching. The coarse mica 4 is dewatered in a conventional process, such as thickening 30. The water 7 can be returned to the size separation process device 20. The fine mica 5 is also de-watered, in step 40, and the water 8 can be returned to the size separation process device 20.

[0043] The dewatered coarse mica 6 is repulped in leach liquor providing greater than 40% solids w/w, the leach liquor containing in the order of 200 g/L free acid, before being directed to an atmospheric acid leach step, comprising a‘coarse leach’ in which it is directed to a first leach tank 50 (TK1 ) in which it is contacted with concentrated sulphuric acid, whereby a free acid level of about 1000 g/L is reached. The slurry from leach tank 50 is passed to a second leach tank 60 (TK2) in which steam 1 1 is added to maintain the reaction temperature, at or about boiling, for example 105°C. In these leach tanks or reactors at least a proportion of the contained lithium, potassium, aluminium, rubidium, fluorine and caesium are extracted from the coarse mica into solution forming a pregnant leach solution (“PLS”).

[0044] The coarse leach slurry 12 is passed to a third leach tank 70 (TK3) where it is reacted with the de-watered fine mica 8, after same is first repulped with leach liquor, which again contains in the order of 200 g/L free acid. Steam 13 is added to leach tank 70 to maintain the reaction temperature, again at or about boiling, for example 105°C. The slurry from leach tank 70 is passed to a fourth leach tank 80 (TK4) in which steam 14 is added to maintain the reaction temperature. Again, in these reactors at least a proportion of the contained lithium, potassium, aluminium, rubidium, fluorine and caesium are extracted, this time from the fine mica, in addition to the further leaching of the coarse fraction, into solution forming a pregnant leach solution (“PLS”).

[0045] A coarse and fine leach slurry 15 is passed from the leach tank 80 to a solid liquid separation step, for example a filter 90, which enables the PLS to be recovered from the leach residue at or near the leaching temperature. The solid liquid separation stage produces a PLS 17 containing the bulk of the extracted lithium, potassium, aluminium, rubidium, fluorine and caesium and a leach residue 18 with high silica content, which is washed with water 16. The wash water 16 can be combined with the PLS 17.

[0046] The PLS 17 may be passed on to one or more recovery steps in which any one or more of the contents, such as lithium and the like, may be recovered.

[0047] The present invention may be better understood with reference to the following non-limiting example.

EXAMPLE

[0048] In Figure 2 there is shown a graph of two plots of lithium extraction versus time.

[0049] The first plot describes the leaching of lepidolite concentrate, pre-milled to P8o 25 micron and leached with 1 100 kg/t sulphuric acid at 105°C over 24 hours. The second plot describes the leaching of lepidolite concentrate, pre-milled to a coarser Pso 75 micron, then separated in +25 micron and -25 micron fractions. After 8 hours of leaching of the coarse fraction the fine fraction was added to the reactor, without additional acid at that point, and the leach run to 24 hours. The total acid addition was 1 100 kg/t and the leach temperature was 105°C. As can be seen with reference to Figure 2, the‘split leach’ resulted in a higher lithium extraction despite the coarser particle size.

[0050] The total sulfate concentration in the leach steps of tanks 50 and 60 is such that it is close to the saturation limit of the solution at the leaching temperature. For example, it is understood by the Applicants that this could be 6.0M S at >90°C. With these conditions for the leaching of the coarse fraction, and the subsequent addition and leaching of the fine fraction, the Applicants have noted >90% metal, for example lithium, extraction is achieved within 18 hours and is significantly higher than leaching the mica concentrate without undergoing the size separation prior to leaching.

[0051 ] It is envisaged that the use of the leach step that comprises a number of stages, with the coarse fraction being first leached with the full stoichiometric amount of acid, or close thereto, allows more complete leaching of the coarse fraction that might otherwise not leach if the fine fraction were present immediately. The process of the invention is, amongst other things, intended to provide as little dilution of the leach liquor as the leach step progresses through the several stages thereof. This is in part facilitated by repulping of the fine and coarse fractions with leach liquor.

[0052] Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.

Claims

Claims:

1. A process for the processing of mica rich minerals, the process comprising passing an ore or concentrate containing a mica rich mineral to a pre treatment phase, the pre-treatment phase including a size separation step to produce a coarse fraction and a fine fraction, whereafter the coarse fraction is passed to an acid leach step in which the coarse fraction is contacted with at least sufficient acid, on a stoichiometric basis, to react with the mica rich mineral contained in both the coarse and fine fractions, the fine fraction subsequently being added to the acid leach step whereby the mica in the fine fraction is also leached, the leach step producing a leach slurry that is passed to a separation step forming a pregnant leach solution and a leach residue, the pregnant leach solution in turn being passed to one or more recovery steps.

2. The process of claim 1 , wherein the mica rich mineral includes lepidolite and/or zinnwaldite.

3. The process of claim 1 or 2, wherein the pre-treatment phase further comprises one or both of a concentration step and a milling step.

4. The process of claim 3, wherein the concentration step is a flotation step.

5. The process of claim 3, wherein the milling step is a fine milling step.

6. The process of claim 5, wherein the fine milling step produces a product having a particle size of: a. P8o <250 micron; b. P8o <150 micron; or c. Rdo <75 micron.

7. The process of any one of the preceding claims, wherein the size separation step comprises the separation of milled material by particle size, thereby producing the coarse fraction and the fine fraction.

8. The process of claim 7, wherein the size separation step produces a coarse fraction having a particle size of predominantly +25 micron and a fine fraction having a particle size of predominantly -25 micron.

9. The process of claim 7, wherein the size separation step produces a coarse fraction having a particle size of predominantly +15 micron and a fine fraction having a particle size of predominantly -15 micron.

10. The process of any one of the preceding claims, wherein the size separation step produces more fine fraction than it does coarse fraction, on a w/w basis.

1 1.The process of any one of the preceding claims, wherein acid is added to the leach step at or about the time the fine fraction is added thereto, in an amount such that the stoichiometric amount of acid to leach both the coarse and fine fractions is not exceeded.

12. The process of any one of the preceding claims, wherein the acid leach step is carried out with an excess of H2SO4.

13. The process of any one of the preceding claims, wherein an amount of acid added to the coarse fraction in the leach step is about 1000 g/L.

14. The process of claim 12 or 13, wherein the total sulfate concentration is close to the saturation limit of the solution at the leaching temperature.

15. The process of claim 14, wherein the total sulfate concentration is about 6.0M S at >90°C.

16. The process of any one of the preceding claims, wherein the coarse fraction is leached in the leach step for a period of time, to produce a coarse pregnant liquor containing a high concentration of sulfuric acid, prior to addition of the fine fraction to the leach step.

17. The process of claim 16, wherein the concentration of sulfuric acid in this pregnant leach liquor is >500 g/L.

18. The process of claim 16 or 17, wherein the fine fraction is added to the leach step and the contained mica is leached with the acid in the coarse pregnant liquor.

19. The process of claim 18, wherein the leach slurry from the leach step contains a free acid concentration of: a. greater than about 150 g/L H2SO4; or b. about 200 g/L H2SO4.

20. The process of any one of the preceding claims, wherein the leach step results in at least a proportion of any contained lithium, potassium, aluminium, rubidium, fluorine and caesium being extracted into solution, thereby forming the pregnant leach solution.

21. The process of any one of the preceding claims, wherein the leaching step is conducted under atmospheric conditions.

22. The process of any one of the preceding claims, wherein the leaching step is conducted at a temperature: a. close to boiling; b. up to 120°C; or c. at or about 105°C.

23. The process of any one of the preceding claims, wherein the leach step comprises four leach stages, with leach slurry being passed progressively from a first of the four leach stages through to the fourth thereof.

24. The process of claim 23, wherein the fine fraction is added to the third leach stage.

25. The process of any one of the preceding claims, wherein the retention time in the leach step is: a. between about 12 to 24 hours; or b. about 18 hours.

26. The process of any one of the preceding claims, wherein greater than about 90% lithium extraction is achieved in the leach step.