This is just the first phase of a metallurgical project. This phase is aimed at quantifying the recovery of kaolin clay via wet processing, to eliminate quartz gangue.
If the objective is HPA, then the flow sheet's next component is likely thickeners, to recover the kaolin from the slurry, prior to calcining the kaolin to activate (dehydrate it) prior to feeding into the hydrochloric acid leach stage. This is a relatively straightforward process, and at lab scale they would just filter it and dry it out prior to the leach tests.
The key deliverables is a quantification of recovery of aluminium oxide (contained within the kaolin), and quantification of the contaminant elements within the kaolin, especially Fe, Na, Mg, Ti.
SO, in the new year the dry paste will be calcined at ~350 to ~650 degrees C, to test at what temperature the kaolin needs to be calcined to drive off the water of crystallisation. The objective is to maximise the dehydration and adsorbtive characteristics, while minimising energy inputs - ie; if you can do it at 450°C instead of 650°C it saves $1,000/t or more in energy costs.
The calcine will then be dissolved in HCl, and the solution and residues assayed; this will provide a prima facie raw recovery of aluminium, as the residue will be discarded and the aluminium will remain in the pregnant leach solution (PLS) as aluminium hexachlorohydrate (ACH), which is the intermediate aluminium salt that can be serially purified. Ideally, recoveries of 92-95% would occur, depending on how much aluminium is held within more refractory phases such as illite, montmorillonite, or remnant feldspars that don't dissolve in acid.
The PLS is then gas sparged with HCl to precipiate the ACH;, and the remaining solution discarded. The precipiate is then washed and dried and assayed; the ideal situation will see sodium, iron, magnesium levels reduced (titanium would rarely make it into the PLS in appreciable amounts). The precipitate is then dissolved again in dilute hydrochloric acid.
This process is repeated as many times as it takes to drive the sodium down to <100ppm, delivering 99.999% HPA, ideally. This could be 3 to 5 stages of serial purification. IMO might use some proprietary tricks such as ion exchange resins, or doping the solution with ions to force sodium out of solution, but generally the serial purification steps would be sufficient to achieve the 99.999% level.
Rule of thumb, you want 99.999% in the final intermediate salt before you calcine, because half or more of the ACH molecule is water and chlorine, which are removed during the final calcination (and recovered into circuit as hydrochloric acid vapors in a commercial setting). This means that impurities within the intermediate product are concentrated during the calcination phase, so you need to start with better than 4N intermediate precipitate to get to a 4N HPA aluminium oxide product.
So, RMX is at stage 1 of this process. It will take steady step-wise work over the next 2-3 months to get to a HPA product in the lab setting.
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