My thoughts on why halide leaches should be used?
A major reason is that they're "broad spectrum". That is, they can (potentially) dissolve pretty much all the metals etc in the ore (if it has been properly preprocessed) as opposed to, say, cyanide, which is more targetted - towards gold (and silver). Some may consider this a disadvantage, but with available ores becoming increasingly low grade and increasingly contaminated, I believe a "cover all" leach is attractive, particularly if viable separation technologies are available at the preprocessing and post-refining stages. (see Intec [Refractory] Gold Process at http://www.intec.com.au and patent US7858056.)
This makes possible additional income streams from sale of commodity "contaminants" and can decrease tailings disposal costs by converting toxic products to inert minerals.
In addition hydrometallurgical pre/leach/post processing make synergies possible where (particularly halide leach) processes can be combined (ie run in parallel).
In short, a totally hydro process makes for potentially elegant solutions BUT a broad appreciation of the science is vital.
SX techniques (if you're familiar with the background) are fairly straight-forward and needn't be technologically advanced. For example, centrifugal separation is only really necessary where the densities of the organic solvent and aqueous fraction approach each other; if they are equal, separation becomes pretty much impossible. The Minataur solvent doesn't have this problem!
Ethylhexanol is a good guess. It is superior to DBC (see patent WO2011/154603A1) in that:
- the [Au loaded] DBC phase settles very slowly from the aquaeous phase,
- the solubility of DBC is extremely high (approx 3 g/l @25 deg C), leading to reagent losses [to the aqueous fraction],
- the flashpoint of DBC is relatively low
- etc
Mintek's organic solvent has all these advantages, plus one virtually unique one, which they let slip in their Minataur description, namely it does not suffer from phase inversion. The answer should now be easy to determine for those with a reasonable grasp of chemistry. I won't post the answer on a public forum, but will let you (ie Lou) know, if necessary <g>, in PM.