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Trying to dissolve aluminum disc to recover platinum coating

2004

I am looking for some guidance in dissolving platinum coated discs of aluminum to recover the platinum. We are using 50% caustic liquid (sodium hydroxide) to try and flake off the platinum with little or no success. Does anyone know what I could use to dissolve the aluminum disc or the platinum for recovery?

Thanks,

Guy Jackson
hobbyist - Glen Carbon, Illinois, USA

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Must have been a good plating job because I can't imagine aluminum holding up at all once the caustic gets to it. Cut whatever they are in half so the caustic can get to the aluminum. You identify yourself as a hobbyist, but I hope this is being done by trained people in an industrial setting, Guy.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

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First: Cut the disks into pie slices, preferably with cutters that curl the pieces. The curling stress the chrome so that it can peel easily from the substrate; the smaller, the faster it works.

Second: You are not dealing with PURE aluminum, it is an alloy of aluminum, copper, boron and hand-full of other stuff to improve the thermal stability.

Third: I am using calcium hypochlorite and deionized water. That is plain swimming pool chlorine. The process is slow. The available chlorine reacts with the copper and aluminum to form stable chlorides, releasing the electro-bond of the chrome plating. Then you have calcium chloride to further corrode the aluminum and copper. It all just peels off.

Fourth: When you can't smell the chlorine, add more calcium hypochlorite granules.

Don't put the iron oxide coated disks in the mix, the iron will combine with the chlorine first and slows the reaction by a huge amount.

The chrome coating is also coated with a vapor-thin coating of silicon dioxide, making it inert to most leaches(part of the reason to cut the disks into pieces.)

Jonathan L. Boyett
- Socorro, Texas
2007

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2007

As an after-thought, the platinum content is under 1% of the chrome matrix, the rhodium/rhenium content is something less than 1% of the platinum. It takes a large lot of drives to get a paying measure of precious metal.

My method is benign to the atmosphere/environment if done in free air (outside). The only thing I have to worry about is the metal chlorides; which I use, diluted, as weed killer.

Jonathan L. Boyett
- Socorro, Texas