29 June 2015
23 October 2017
HPA process description
Run of mine (ROM) kaolin ore will be loaded into standard sea containers and trucked from the Meckering site in Western Australia to Fremantle port, before being shipped to Tanjung Pelepas port, Johor, Malaysia. Upon arrival at Tanjung Pelepas the containers will be either stored at the port, or directly trucked to Altech’s HPA plant site in the Tanjung Langsat Industrial Complex.
At the HPA plant loaded shipping containers will be discharged into a wet screening circuit consisting of a drum scrubber, a filter and various screens. This operation ensures kaolin particle size is reduced to <300μm and the majority of oversize silica/quartz will be removed.
Bulka bags of beneficiated kaolin will be unloaded at the HPA process plant’s bag unloading station and the kaolin will be fed by conveyor into the kiln feed bin, the bin will have a storage capacity of ~24 hours of feed demand. In the first stage of the process, kaolin will be calcined at around 600° C in an indirect rotary kiln to convert the crystal structure of the clay to a more reactive form. The kiln will be indirectly fired by natural gas with associated cyclone and baghouse to collect off-gas fines. The calcine will be cooled, screened and any oversized crushed to a particle size of <500µm. ><500um.
The resultant beneficiated kaolin will be calcined at around 700°C in an indirect rotary kiln to convert the crystal structure of the clay to a more reactive form (meta kaolin) for
leaching. The kiln will be indirectly fired by natural gas with associated cyclone and bag-house to collect off-gas fines. The calcine will be cooled, screened and any oversized material crushed to a particle size of <300μm.
Leaching follows, during which the calcine will be mixed with recycled wash liquor containing hydrochloric acid (HCl) at up to 36% w/w. Leaching follows, during which the calcine will be mixed with recycled wash liquor containing hydrochloric acid (HCl) at ~30% w/w. The leach reaction is exothermic and the oxide components (except silica) are converted to soluble chlorides, producing a high concentration of aluminium chloride (AlCl3) solution. The leach reaction is exothermic and the oxide components (except silica) are converted to soluble chlorides, producing a high concentration of aluminium chloride (AlCl3) in solution. The leached slurry is then pumped to leach residue filtration. The leached slurry is then pumped to leach residue filtration. The silica residue slurry will be filtered and the silica residue neutralised before being disposed of to local vendors, such brick works or cement plants. The silica residue slurry is filtered and the silica residue neutralised before being provided to local vendors, such as brick works or cement plants. The pregnant liquor solution, known as “PLS” is directed to crystallisation where aluminium chloride hexahydrate (AlCl3 .6H2O also known as “ACH”) is crystallised out of solution. The pregnant liquor solution (PLS), from leach residue filtration is directed to crystallisation where aluminium chloride hexahydrate (AlCl3 .6H2O or ACH) is crystallised out of solution. This will be achieved by increasing the acid concentration of the liquor (ACH is insoluble at strong acid concentrations) by bubbling anhydrous HCl gas. ACH crystals are then filtered and washed from the solution. This is achieved by increasing the hydrochloric acid concentration of the liquor (ACH is insoluble in concentrated HCl) by bubbling in anhydrous HCl gas. ACH crystals are then centrifuged and washed from the solution.
The resultant ACH filter cake will be transferred to a slurrying tank where the ACH crystals will be dissolved in ultra-pure water and then fed to the second crystallisation circuit. The resultant ACH solids will be transferred to a re-dissolution tank where the ACH crystals will be dissolved in demineralised water and then fed to the second crystallisation circuit. This dissolution process makes it possible to release residual impurities, which may have become trapped in the crystals during the first crystallisation. This dissolution process makes it possible to release residual impurities, which may have become trapped in the crystals during the first crystallisation. Like the first stage crystallisation, the ACH acid concentration in the liquor is increased by bubbling HCl gas and crystallised ACH filtered and finally washed to remove any residual acid and/or impurities. Like the first stage crystallisation, the ACH acid concentration in the liquor is increased by bubbling in HCl gas, and crystallised ACH is centrifuged and finally washed to remove any residual acid and/or impurities. The third stage of crystallisation is identical to the second. The purified ACH cake is heat treated in two stages via natural gas fired rotary kilns. The third stage of crystallisation is identical to the second, however the centrifuge has no washing stage and the ACH crystals are not redissolved. The first stage involves heating the ACH to around 600° C in order to decompose the ACH to a mixture of basic aluminium chlorides (oxychlorides) and alumina. Most of the chloride is liberated as HCl, recovered and reused in the process. The purified ACH crystals are heat treated in two stages via natural gas fired rotary kilns. The first stage involves heating the ACH to around 700°C in order to decompose the ACH to alumina, with trace amounts of basic aluminium chlorides (oxychlorides). Almost all of the chloride is liberated as HCl gas, recovered and reused in the process. The partially-calcined solids from the roaster fall directly into the second rotary kiln that then heats the solids further to remove the remainder of the HCl and water (H2O) to produce highly pure alpha (α) alumina (Al2O3), in other words, HPA. The HPA will discharge to a cooler and is then fed directly to a final acid leach stage to remove surface trace impurities. The solids from the roaster fall directly into the second rotary kiln that then heats the solids further to remove the remainder of the HCl and water (H2O) to produce HPA: highly pure alpha alumina (- Al2O3).
The HPA is washed and filtered in two stages and dried before feeding to a fine grinding mill to produce product with a particle size of <10um. The milled HPA will be bagged into 20kg plastic-lined paper bags stored for dispatch to customers.
The HPA will discharge to a cooler and is then fed directly to a final wash stage to remove surface trace impurities. The flexible product finishing line is designed to initially grind all HPA to an average particle size of less than 1 micron by wet milling using bead mills. Upon the milled HPA achieving the designated particle size range it will be dried via a conventional spray drier. The finely ground, dried HPA will then be aggregated in beads for heat treatment in a tunnel kiln; the finished product being HPA beads for use in the synthetic sapphire industry. Alternatively, the finely ground HPA will be fed to a de-agglomeration unit (microniser) to produce fine HPA powder for use in the lithiumion battery industry. Both products will be bagged via an automated bagging machine.
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