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Wednesday, February 1, 2012

Cleaning up Concentrates containing Gold and Platinum

Hematite particles forming ferro-fluid with a rare earth magnet beneath a sheet of glass.

One of the problems in the recovery of gold,silver and platinum from concentrates of stream heavies is the removal of iron oxides that make up the majority of heavies. Most of the other heavies are composed of silicates and in rare cases oxides of various elements. In the case of iron oxide there are two types present in most heavies. The most easily removed is magnetite because it is attracted to an ordinary magnet with the best being an Alnico magnet. This will quickly remove the magnetite that is the easiest to remove. Hematite is the second iron oxide in heavies that is not attracted to an ordinary magnet, but is attracted to a rare earth magnet that can be ordered on the internet. The remaining heavies composed of mineral silicates and oxides being much less dense and having a far lower specific gravity then gold, silver or platinum that is left behind in the pan.

The iron oxides can be removed in two stages; the first is removing magnetite. There are commercial magnetic separators available, but for the small amount usually encountered an ordinary magnet will suffice. A small amount of concentrate that has been thoroughly dried is placed on a sheet of paper and the magnet is passed over the concentrate just above its surface, but high enough not to touch the concentrate. The magnetite present will stick to the magnet so you will have to periodically remove it from the magnet.

The hematite is removed in the second step by using a small rare earth magnet by repeating step 1 using the more powerful magnet the remaining concentrate containing heavies, gold, silver and platinum group metals. This concentrate is poured into a separate container for further work in the process.

Although geologists know ways of separating heavies using dense fluids, but they are all highly toxic and shouldn’t be used by an untrained layman. The best way to remove them is with a small ten inch gold pan immersed in water using conventional panning methods. Its tedious work, but the pan full of concentrate can be worked down until the only thing left in the pan is gold, silver and platinum group metals (PGM).

The remainder in the pan is gold, silver and PGMs that are saved for further processing; because of the length of the whole process we are going to divide it into several articles we will publish in the near future. Watch for them!


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