Chuca,
In my response to the question of natural physical forces moving microclusters, I was using experience of myself, others and a little guessing. The origional question posed some interesting ideas. A number of processes that are commercially used to get metals utilize properties that happen in nature to commercially exploit values from natural mineral suites. Gravity concentration is only one such analogy. Streams do it, man does it. Yet gravity is not the only mechanism that moves and concentrates gold, tin, PGMs and other heavy minerals in streams.
You asked if the flotation is a similar process. That is physically moves the gold by attracted surface contacts. Basically, yes. Flotation processes can be simple and they can be more complicated. In theory, the surface of the partical being sought after and other similar reactive mineral surfaces are treated so they will adhere to air. The water is treated so it will maintain strong surface tension (support bubbles). The combination of these wetting agents, oils and air cause the desired product to rise to the top of the tank when exposed to bubbles that rise in the slurry of ore, water and conditioners. The bubbles with their products are skimmed off the surface. It works for gold, silver, copper, lead, zinc and other metals and their sulfides as well as the non-metals like fluorspar and certain metal oxides. It is interesting to note here that gold can follow both sides here. Some of the gold can be collected with gold specific collectors, other gold gets collected by sulfide collectors and still a third gold is collected by oxide collectors. All from the same sample. Sure seems to support the idea of different kinds of gold although I must admit, surface coatings on the gold particles can account for the differences. Just depends on what you want to believe. I once milled ore that had a small amount of osmarium AuOs which was about 50% gold and 50% osmium. It was a white barite like powder that would not float by any method we tried. It was collected in by gravity. In that mill there were 3 kinds of gold. Gold that followed the sulfide circuit, the oxide circuit and the gravity circuit. The sulfo tellurous gold went with the sulfides. A very small amount of the gold followed the fluorspar or calcium fluoride circuit and the remainder was collected in jigs followed by tables. Not a simple circuit but you do what it takes to get the stuff out.
Selective flotation is used for complex ores. Complex ores are defined in this context as ores having more than one product to be collected. Examples are lead and zinc sulfides together in one ore. The slurry of ore and water is treated to collect one mineral by flotation and than retreated (conditioned) to collect the other metal. The purpose of treating the ores to produce different products was to be able to market the zinc to a custom zinc plant and the lead to a custom lead plant. With some ores the gold follows the zinc in flotation, in others it follows the lead, or copper, etc. Send that product with the gold to where the custom plant pays best for gold. At least that was the way it was.
In summary, the gold in flotation is collected and deposited by physical attachment means. I suspect that PGM and gold microclusters might follow the oxide collectors like oleic acid. Just a hunch that should be taken lightly.
Chuca, don't you sleep either? mike
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