AU2014259596A1 - Process for the treatment of kaolin - Google Patents

Abstract

The invention discloses a process for the treatment of run-of-mine kaolin feed material. The kaolin feed material is subjected to a de-gritting step whereby quartz grit and any other solid aggregates are removed from the kaolin feed material to produce kaolin. Thereafter, in a leaching step, the kaolin is leached with hydrochloric acid to produce a residue, which contains silica, and a leachate, which contains aluminium chloride salt. Subsequently the aluminium chloride salt is precipitated from the leachate and subjected to a calcination step wherein the aluminium chloride salt is formed into alumina. Figure 1 12 14 16 2610 I > IAZ N 32 30< W~s' ~Pxt&34 ---- ------ - rA~ ga -J8 rcc i1 .s-C4 Figure 2 12 14 16 26 100 !: Itlenite 18 Cr0 ~removal Omf oC ---- --- -- ------ 52 , F Gr, Zrd rrdrct -- --- ---- 22... -~ .. -) 32 2 2 c kj Pre heated J 40 -1advro 50 tPrier ----oio -~ . - v T--------- 38 - - - - - - -- - --- - - -(Fitter' ------ 44taatv for------- Aerd Recory 36 . ----- reevahrrtro ard T4- ----- t- rR~crer46 .. ...- ------ 'Alvrrr'a rovey 48 Aluminra wavi~er . Alrrrva dryer - -*cl 1 -t~n -------------

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NO: LODGED: COMPLETE SPECIFICATION LODGED: ACCEPTED: PUBLISHED: RELATED ART: NAME OF APPLICANT: Australian Resource Management Group Pty Ltd (CAN 166 661 490) ACTUAL INVENTOR: Bernardus Willem Ziegelaar ADDRESS FOR SERVICE: LORD AND COMPANY, Patent and Trade Mark Attorneys, of PO Box 530, West Perth, Western Australia, 6872, AUSTRALIA. INVENTION TITLE: "PROCESS FOR THE TREATMENT OF KAOLIN" DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S: Australian Provisional Patent Application Number 2013904483 filed 20 November 2013 The following Statement is a full description of this invention including the best method of performing it known to me/us: TITLE PROCESS FOR THE TREATMENT OF KAOLIN FIELD OF INVENTION [0001] The present invention relates to a process for the treatment of kaolin. [0002] More particularly, the present invention relates to a process for the treatment of kaolin to produce quartz grit, high purity kaolin, ultra-pure alumina and ultra-pure silica. BACKGROUND ART [0003] Natural deposits of the mineral kaolinite, also known as kaolin or china clay, are found in abundance in a number of locations throughout Australia and the world. Kaolin is a layered silicate mineral with a chemical composition (used in mineralogy) of Al 2 Si 2 5 0(OH) 4 and is found as a clay deposit. [0004] Kaolin is treated by many production processes to extract quartz grit, alumina and other products which are used in various fields including industrial, electrical, cosmetic and agricultural technologies. Problems arise with such kaolin treatment using known acid leaching processing techniques due to environmental dangers associated with tailings and other inefficiencies due to wasted by-products. [0005] The kaolin deposits found in Western Australia are largely concentrated in the south west wheat belt, east of the laterite deposits found in the Darling Range. Given the ease of accessibility of such kaolin deposits, commercial treatment of commercially lesser valuable parts of the deposits, such as quartz grit, becomes viable. [0006] The present invention attempts to provide improvements over previous methods used in treating and processing kaolin. 2 SUMMARY OF THE INVENTION [0007] According to the invention, there is provided a process for the treatment of run of-mine kaolin feed material, the process comprising: a de-gritting step wherein quartz grit and any other solid aggregates are removed from the kaolin feed material to produce kaolin; a leaching step wherein the kaolin is leached with hydrochloric acid to produce a residue, which contains silica, and a leachate, which contains aluminium chloride hexabydrate; a precipitation step wherein aluminium chloride salt is precipitated from the leachate; and a calcination step wherein the aluminium chloride salt is calcined to form alumina. [0008] The de-gritting step may include crushing the kaolin feed material before scrubbing and wet-screening the koalin feed material. [0009] The de-gritting step may include removing titaniferous minerals and/or iron titanate particles from the kaolin feed material using magnetic separation means. [0010] The quartz grit that is removed from the kaolin feed material may be further washed under high pressure water to produce a cleaned quartz grit. [0011] The process may include the recovery of any kaolin contained in the water used to wash the quartz grit. [0012] The kaolin obtained from the de-gritting step may be dried and heated to a temperature being below 200'C. [0013] The leaching step may comprise leaching the kaolin in a high pressure environment, thereby to raise the temperature during the leaching step to between 170*C and 200'C. 3 [0014] The process may include a de-hydroxylation step before the leaching step, wherein the kaolin is converted into an amorphous meta-kaolin. [0015] The de-hydroxylation step may be conducted by flash calcination. [0016] The flash calcination may be performed by heating the kaolin to a temperature between 650'C and 700*C. [0017] The meta-kaolin may be subjected to the subsequent leaching step. [0018] The leaching step may include the use of hydrochloric acid having a molarity between 6 mol/L and 9 mol/L, preferably being about 6 mol/L. [0019] The leaching step may include agitation of the hydrochloric acid. [0020] The precipitation step may include increasing the acidity of the leachate until aluminium chloride salt crystals are formed which precipitate from the leachate. [0021] The acidity may be increased by sparging the leachate with a sparging gas containing hydrochloric acid. [0022] The sparging gas may further contain nitrogen being adapted to cause inert agitation of the leachate to reduce early precipitation of the aluminium chloride salt. [0023] The aluminium chloride salt may be re-dissolved and recycled to the leachate thereby to be re-precipitated from the leachate. [0024] The calcination step may be conducted in a two-stage process, whereby the aluminium chloride salt is heated to a temperature of about 400'C in a first stage and subsequently heated to a temperature of about 8004C in a second stage. [0025] The process may comprise a purification step wherein the silica containing residue is washed with sulphuric acid to remove any remaining impurities. 4 [0026] The process may produce a high-grade quartz grit having a purity of between 95% and 98% and having a particle size range between 50pj and 5000p and a particle size distribution greater than 45p. [0027] The process may produce an ultra-pure alumina having a purity rating grade of 4N, 5N or 6N and ranging in particle size from I to 40 micron. [0028] The process may produce an ultra-pure silica having a purity rating grade of 4N or 5N and ranging in particle size from 1 to 40 micron. BRIEF DESCRIPTION OF DRAWINGS [0029] The present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which: Figure 1 shows a flow diagram of a first embodiment of a process for the treatment of kaolin according to the present invention; and Figure 2 shows a flow diagram of a second embodiment of a process for the treatment of kaolin according to the present invention. DETAILED DESCRIPTION OF THE DRAWINGS [0030] Referring to the drawings, there are shown alternative processes for the treatment of kaolin in accordance with the invention, with the first process being generally indicated by reference numeral 10 and the second process being generally indicated by reference numeral 100. Both processes 10 and 100 involve many similar steps and therefore these are indicated with the same reference numerals. [0031] The following description uses the term "leachate" in a broad sense to include any liquid or liquor that extracts solutes, suspended solids or any other component of the material through which it is passed. [0032] Further, in order for the present invention to produce high purity commodities there is a requirement for a clean environment for the production, sampling and testing to 5 avoid contamination at each step of the process. Accordingly it is envisaged that a clean filtered air environment will be provided consistent with a defined ISO standard to achieve the best results, [0033] The management of trace concentration is envisaged by cation and anion exchange of the relevant side streams, thereby controlling the level of contaminants in the processes to remain below a level at which product contamination will take place. Preferably a Glow Discharge Mass Spectrometer will be used for analysing the purity of the final products. [0034] Referring now specifically to Figure 1, run-of-mine (ROM) kaolin feed material 12 is provided in any form, but is preferably provided in the form of natural rock or clay deposits which have been mined using known means. Step one: de-gitting [0035] Naturally occurring deposits of kaolin generally comprise a quartz grit (SiO2), the grit being comprised of around ninety nine percent (99%) pure quartz chips. The effective removal of the quartz grit from the kaolin feed material 12 is required to enable the production of ultra-pure silica having a fine particle size in accordance with the present invention. [0036] In a first step, the quartz grit is initially segregated, at least in part, from the kaolin by passing the kaolin feed material 12 through a grizzly separator, which preferably has a mesh screen size of about 10mm. The separated grit can then be further processed through an impact crusher before undergoing scrubbing and wet screening 14. Titaniferous minerals or iron-titanate particles, which occur naturally in kaolin deposits, found in the separated grit can also be mechanically separated out during the de-gritting step, e.g. by using a magnetic separation process 16. Preferably the magnetic separation process 16 of the present invention comprises a high gradient magnetic separator and it should be understood that the magnetic separation process 16 may minimise the necessity of later steps for removing other trace metals from the solution as further described hereafter. 6 [0037] The screened grit 18 has a commercial value as a small aggregate product used for exposed aggregate concrete, ornamental stones, pavers and bricks for example. The screened grit IS is scrubbed in a grit scrubber 20, where it is exposed to a flow of high pressure water from one or more water jets, thereby cleaning any remaining kaolin from the screened grit 18 and resulting in a cleaned grit 22. The cleaned grit 22 may undergo a subsequent wet screening process in order to grade the cleaned grit into groups of similar particle size. Preferably the grit end product will comprise a separated, graded and cleaned grit 22 that ranges in size between forty-five micron (45pt) and five hundred micron (500 g). (0038] The water used in the de-gritting step is recycled to improve the efficiency of the present invention with the de-gritted kaolin being recovered from the water in a recovery cyclone 24. [0039] It is envisaged the de-gritting step results in a high purity kaolin substantially free of quartz grit, which assists in reducing the need for further purification of the kaolin during later steps of the process 10. S two: Production of meta-kaolin [0040] In a second step, which is required in the process 10 but not in the process 100, the high purity kaolin from the first step is converted to an amorphous meta-kaolin through de-hydroxylation, thereby to enable the later dissolution of alumina in hydrochloric acid by acid leaching. [00411 Meta-kaolin is a valuable product in its own right and has many applications, such as a pozzolan or cementitious additive. In particular the finer particle size meta kaolin which is produced in the process 10 has outstanding pozzolan activity. [0042] In the process 10, the high purity kaolin is initially passed through a flash dryer 26 for removal of moisture. The temperature of the dried kaolin is preferably maintained at an elevated level while it is transferred to a flash calciner 28 where it is further heated up to a temperature in the range of 650*C (six hundred and fifty degrees) 7 to 700*C (seven hundred degrees). It has been advantageously found that the flash calcination process is preferable over a more traditional kiln calcination process because the flash calcination process maximises the conversion of the high purity kaolin to a high purity meta-kaolin. This calcination process avoids the fonnation of alumina phases that are generally produced when the calcination temperature exceeds seven hundred degrees centigrade and which are generally difficult to dissolve. [0043] The production of the amorphous meta-kaolin phase can be maximised through selection of the correct flash calcination conditions. [0044] The meta-kaolin is then arranged to undergo atmospheric pressure leaching. Stea: Extraction of calcined kaolin using hydrochloric acid [0045] In a third step, the meta-kaolin produced in the flash calciner 28 is kept at an elevated temperature at or below 700'C, thereby to maintain the alumina in the amorphous phase to facilitate extraction of the alumina by an atmospheric pressure leaching process 30 using hydrochloric acid. [0046] The leaching process 30 takes place in a two stage high and low acid strength dissolution step. The meta-kaolin material is exposed to a high strength acid for removing any additional trace elements from the meta-kaolin material prior to dissolution of the alumina. A side stream may therefore be provided for the removal of these trace elements. [0047] The selection of the one or two step dissolution process will depend upon the trace elements present in the feed of meta-kaolin material to be treated. [0048] The meta-kaolin is extracted using a leachate of hydrochloric acid having a molarity of between 6 and 9 mol/L, but preferably being about 6 mol/L. The extraction process may further comprise a mechanical activation for assisting the dissolution of alumina and minor contaminants such as iron, calcium, magnesium and other oxides. 8 [0049] The leaching process 30 produces aluminium chloride hexahydrate (ACH) which has a chemical composition of AICI 3 .6H 2 0 and which is insoluble at high acid concentrations. The leached kaolin is filtered to separate a substantially siliceous residue 32 from a substantially clear ACH leachate 34, The siliceous residue 32 may be further purified for producing an ultra-pure silica material 36. [0050] Ion exchange can be used to reduce the build-up of any impurities during the acid leaching. Step 4: Precipitation and isolation of ACH [0051] In a fourth step, to precipitate the ACH from the leachate 34, the leachate 34 is introduced to a concentrator 38 so that its acidity is concentrated or increased to a level where the aluminium chloride hexahydrate crystallises into a salt and becomes insoluble. Preferably the acid concentration of the leachate 34 is raised to just below the precipitation point of the ACl. The solubility versus temperature curve for ACH is substantially constant and therefore a reduction in temperature is not considered viable or necessary. [0052] During the precipitation process the concentration of entrained minor impurities within the leachate increases by a factor of 4.7. These can then be removed into a side stream 40. [0053] It is envisaged that the crystallization of ACH is capable of producing a highly pure product and therefore the crystal size is important. Because the entrained leachate percentage is larger when the crystal size is small, a larger crystal size results in less entrained leachate. The present invention may comprise the crystallization of ACH at elevated temperatures in order to produce relatively large crystals and so as to the prevent co-precipitation of impurities. In the exemplary embodiment, the most preferable crystal size is obtained when the ACH is precipitated in a temperature range of between 40'C to 60 0 C. [0054] The present invention provides several options for achieving the precipitation and isolation of crystalline ACH as follows: 9 a. The leachate 34 can be introduced into a precipitator vessel 42, where it is sparged with a sparging gas 44 containing hydrochloric acid. The sparging causes a rapid increase in acidic concentration in the leachate to around 26% and thus results in the formation of the crystalline ACH. The sparging gas 44 preferably also contains nitrogen for causing agitation of the leachate 34 and thereby reducing any isolated rapid settling out of the crystalline ACH. that may result in a decreased ACH crystal size. b. Membrane separation or reverse osmosis processes may be used to increase the acid concentration through the removal of water from the leachate 34. This method may provide significant energy savings. c. Evaporation of the leachate 34 may be employed thereby increasing the concentration of aluminium chloride hexahydrate. [0055] Subsequently the crystalline ACH is separated out from the leachate using a centrifugal process that enhances purity by maximizing the removal of entrapped leachate. Step 5: Calcination of ACH [0056] In step five, the substantially isolated crystalline ACH material obtained from the fourth step is then arranged to undergo a two-stage calcining process 46 for the removal of chloride that is residual from the acid leaching step and thereby producing an ultra-pure alumina product 48. Preferably the crystalline ACH is treated according to the present invention using a fluidized bed calciner. [0057] It has been adventitiously found that the two stage calcination of the isolated crystalline ACH material is important for lowering a total energy requirement expended during the calcination process. [0058] In a first pre-treatment stage the crystalline ACH is exposed to a temperature of around 400'C. In a preferred embodiment of the present invention, the heat used in the 10 pre-treatment stage comprises waste heat reclaimed from the flash calciner 28 of the second step above. [0059] In the second stage the pre-treated crystalline ACH is exposed to a temperature of around 800'C. [0060] The resulting product is the ultra-pure alumina (A1 2 01) product 48. Step 6 - Purification of the silica residue to produce an ultra-pure Silica product [0061] In a sixth step, the siliceous residue 32 obtained from filtering the leachate 34 in the third step will typically comprise a material consisting of approximately 98% silica, the remaining impurities will typically comprise alumina and/or titanium based compounds. [0062] In order to produce 4N grade or better silica, further purification steps are required, In a preferred embodiment of the present invention it is envisaged that the siliceous residue 32 will be washed 50 with sulphuric acid in order to remove the impurities resulting in the production of the ultra pure silica 36. Various qualities of purity and particle size may be obtained. [0063] Referring now specifically to Figure 2, as indicated above, the process 100 is substantially similar to the process 10 of Figure 1. Thus similar steps are indicated with the same reference numerals to those used in process 10. [0064] The first step of process 100 is identical to that if the process 10, whereby the kaolin is separated from the quartz grit and the latter is screened 18 and scrubbed 20 to result in the cleaned grit 22. [0065] The water used in the de-gritting step is recycled and the de-gritted kaolin recovered from the water in a recovery cyclone 24 to result in a high purity kaolin substantially free of quartz grit. 11 [0066] In the process 100, the second step of process 10 is not performed. Thus there is no conversion of the kaolin to an amorphous meta-kaolin. instead, after being dried in the flash dryer 26 for removal of moisture, the kaolin is directly passed on to the third step for acid leaching. [0067] In the third step, leaching of the pure (un-calcined) kaolin is carried out in a pressure vessel 52 under high pressure conditions in order to raise the leaching temperature to between 170'C (one hundred and seventy degrees) to 200C (two hundred degrees). It has been advantageously found that, at this temperature and pressure, up to 99% of the alumina is extracted in a time frame of under than thirty minutes duration. [0068] Similarly as in the process 10, the resultant leachate 34 is filtered to remove the substantially siliceous residue 32. [0069] In a fourth step, the leachate 34 is firstly introduced to a concentrator 38 and subsequently to a precipitator vessel 42 for sparging with hydrochloric acid gas to crystallise and precipitate the ACH salt. [0070] As shown in Figure 2, if required, the crystallised ACH may be re-dissolved 54 so that it can be recycled back to the precipitator vessel 42 and re-crystallised in order to improve the purity of the final alumina product. [0071] The remaining fifth and sixth steps of process 100 are substantially the same as those of the process 10. Further, if required, the alumina product from the calcining process 46 may be further washed and dried to produce the ultra-pure alumina product 48. [0072] It is further envisaged that the third acid leaching step of both processes 10 and 100 will be carried out in a closed vessel with recycling of the acid being in the order of 98% to reduce costs. Further, pressure relief valves are arranged to discharge into enclosed spaces to reduce any environmental impact. [0073] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. 12

Claims (22)

1. A process for the treatment of run-of-mine kaolin feed material, the process comprising: a de-gritting step wherein quartz grit and any other solid aggregates are removed from the kaolin feed material to produce kaolin; a leaching step wherein the kaolin is leached with hydrochloric acid to produce a residue, which contains silica, and a leachate, which contains aluminium chloride hexahydrate; a precipitation step wherein aluminium chloride salt is precipitated from the leachate; and a calcination step wherein the aluminium chloride salt is calcined to form alumina.

2. A process as claimed in claim 1, wherein the de-gritting step includes crushing the kaolin feed material before scrubbing and wet-screening the koalin feed material.

3. A process as claimed in claim 1 or 2, wherein the de-gritting step includes removing titaniferous minerals and/or iron-titanate particles from the kaolin feed material using magnetic separation means.

4. A process as claimed in any one of the preceding claims, wherein the quartz grit that is removed from the kaolin feed material is further washed under high pressure water to produce a cleaned quartz grit.

5. A process as claimed in claim 4, which includes the recovery of any kaolin contained in the water used to wash the quartz grit.

6. A process as claimed in any one of the preceding claims, wherein the kaolin obtained from the de-gritting step is dried and heated to a temperature being below 200'C. 13

7. A process as claimed in any one of the preceding claims, wherein the leaching step comprises leaching the kaolin in a high pressure environment, thereby to raise the temperature during the leaching step to between 170 0 C and 200'C.

8. A process as claimed in any one of claims I to 6, which comprises a de hydroxylation step before the leaching step, wherein the kaolin is converted into an amorphous meta-kaolin.

9. A process as claimed in claim 8, wherein the de-hydroxylation step is conducted by flash calcination,

10. A process as claimed in claim 9, wherein the flash calcination is performed by heating the kaolin to a temperature between 650'C and 700"C.

11, A process as claimed in claim 9 or 10, wherein the meta-kaolin is subjected to the subsequent leaching step.

12. A process as claimed in any one of the preceding claims, wherein the leaching step includes the use of hydrochloric acid having a molarity between 6 mol/L and 9 mol/L.

13. A process as claimed in any one of the preceding claims, wherein the leaching step includes agitation of the hydrochloric acid.

14. A process as claimed in any one of the preceding claims, wherein the precipitation step includes increasing the acidity of the leachate until aluminium chloride salt crystals are formed which precipitate from the leachate.

15, A process as claimed in claim 13, wherein the acidity is increased by sparking the leachate with a sparging gas containing hydrochloric acid.

16. A process as claimed in claim 14, wherein the sparging gas further contains nitrogen being adapted to cause inert agitation of the leachate to reduce early precipitation of the aluminium chloride salt. 14

17. A process as claimed in any one of the preceding claims, wherein the aluminium chloride salt is re-dissolved and recycled to the leachate thereby to be re-precipitated from the leachate.

18. A process as claimed in any one of the preceding claims, wherein the calcination step is conducted in a two-stage process, whereby the aluminium chloride salt is heated to a temperature of about 400CC in a first stage and subsequently heated to a temperature of about 800'C in a second stage.

19. A process as claimed in any one of the preceding claims, which comprises a purification step wherein the silica containing residue is washed with sulphuric acid to remove any remaining impurities.

20. A process as claimed in any one of the preceding claims, which produces a high grade quartz grit having a purity of between 95% and 98% and having a particle size range between 50p and 5000 p and a particle size distribution greater than 45p.

21. A process as claimed in any one of the preceding claims, which produces an ultra pure alumina having a purity rating grade of 4N, 5N or 6N and ranging in particle size from I to 40 micron.

22. A process as claimed in any one of the preceding claims, which produces an ultra pure silica having a purity rating grade of 4N or 5N and ranging in particle size from 1 to 40 micron. 15