# oxyhydrogen PGM smelting



## nalexandrov (Jun 11, 2011)

I have a high output (2kw) electrolytic oxyhydrogen generator I built. This flame will destroy all kinds of crucibles, the secret to a nice oxyhydrogen furnace is using a zro2 coated (at flame contact point) graphite crucible which is properly insulated (easy when your combustion gas "implodes"). I have been researching this technology for years and have a few other tricks if anyone is interested.

I am interested in using this to fire assay/smelt PGM from cats. Most protocols I have seen involve using lead oxide to lower the melting point of the PGM during the smelting process and act as a collector metal upon reduction. Since my furnace is not limited by temperature what would be the most optimal composition? I have heard of silver, copper and other metals to collect the material. Do any of these simplify the process compared to lead oxide? What are the pros and cons of various PGM collection metals? I want something that is selective to PGM and will have limited impurities, and being easy to extract would be nice.

So what im asking is if you were not limited by flame temperature what would your optimal composition be for this process?

I know that there are a lot of books and patents that touch on the subject but nothing compares to advice from experience.

Also a pro question: in this type of smelting is it preferable to have the heat source coming from the bottom where the metal collects or from the top?

Also an oxyhydrogen flame trained directly on a refractory material would reach temperatures of 2000C+, is there any way to leach the PGM by directly heating the ceramic carrier material? Or maybe a very simplified process?


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## Oz (Jun 12, 2011)

You have several questions asked in rather broad terms. I will answer 1.

Silver and gold is used as a collector for converter catalyst in some assays, however gold is preferred. I have never heard of these being used as a standard recovery process though, just in assay work.


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## Lou (Jun 12, 2011)

A 2KW oxyhydrogen flame source is rather small and will limit you doing perhaps 500 g of converter material at a time. Also consider that just because your power supply is 2 KW, does not mean that the current efficiency of the cell will give you anywhere close to a 2KW flame. In all likelihood, you're probably making less than 1K BTU. Your furnace is limited by temperature. Just because you're getting a very hot flame does not mean you'll be able to get the material anywhere near that close in temperature. Given that the converter substrate is alumina and itself melts above the melting point of platinum, I think your little setup at present is inadequate to do these in volume if you're in it for a profit.

You want no graphite in contact with the _platinum group_ metals because they form carbides that will grey up the metal and make it brittle, it will also readily oxidise away. Your furnace should be insulated with 3-5" 2500 F insulating castable with a 1-2" layer of bubble alumina refractory with a final zirconia insert. In any case, you won't be a profitable operation.


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## Harold_V (Jun 13, 2011)

Lou said:


> You want no graphite in contact with the precious metals.


Lou,
Would you clarify, please? I am of the opinion that graphite is perfectly acceptable for silver and gold. Are you including these in your comment? (I realize the topic doesn't revolve around silver and gold, but some may take the message out of context and apply it across the board).

Harold


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## Iridium chaser (Jan 9, 2019)

I personally smelted all PGMs with my 150 l/h HHO torch except osmium;although I managed to melt rhenium metal from powder with that torch!And for flux I used alumina mixed with zirconia:alumina melted quite fast and zirconia was staying in the bottom with rhenium powder,than when reaching temperature of 2740°C zirconia melted it still stayed in the bottom and protected rhenium when alumina boiled(which was quite cool to look at through a good eye protection)-and finally when all alumina boiled away the rhenium powder suddenly started to decrease in volume and became a single button as I wanted it to!So the weight was 5 grams-which is quite a lot in this case!And as for PGMs most of them don't lose that much to oxidation and vaporization;iridium for example can be smelted without any flux at all and not to lose a smallest fraction of it's weight!There was an experiment where a sample of iridium was melted and kept molten for a substantial amount of time in different atmospheres including pure oxygen and even pure fluorine gas(!!!)-and so it was proven that iridium metal being the most corrosion resistant of all elements in normal conditions but still was possible to somehow either tarnish or even be consumed but on contrary when molten it becomes completely resistant to all chemicals including fluorine gas at all temperatures and all pressures.


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