Dissolving stainless in dilute sulfuric acid
Dissolving stainless in dilute sulfuric acid
(OP)
Anybody here know what would result if you put stainless steel in a dilute sulfuric acid solution? I'm thinking of processing some metallic materials from spent catalytic converters. Seems pretty easy from what I saw... but I'm new to chemistry. I'm an electric engineer by trade.
RE: Dissolving stainless in dilute sulfuric acid
If necessary, applying a protective anodic current will enable most stainless to resist the full range of composition of sulfuric acid solutions, 0-98%.
RE: Dissolving stainless in dilute sulfuric acid
RE: Dissolving stainless in dilute sulfuric acid
We're on step one right now. Just not sure if he's blowing smoke or not.
RE: Dissolving stainless in dilute sulfuric acid
That's pretty cool. So... if we used the mixture of acids that dissolve platinum and put current through the solution would the stainless stay solid?
RE: Dissolving stainless in dilute sulfuric acid
the SS behind ?
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RE: Dissolving stainless in dilute sulfuric acid
RE: Dissolving stainless in dilute sulfuric acid
Something I looked up in a non-ferrous metallurgy book for another forum:
"The wet chemistry & pyrometallurgy of assaying and refining the platinum group metals involves strong acids, including aqua regia, and thermal decompositions giving off toxic gases such as SO3. Just a hint: Nitric acid will dissolve only Pd and the less noble impurities, aqua regia will dissolve both Pd & Pt, while the residue after aqua regia leaching can be fused in molten anhydrous sodium bisulfate ca. 315 oC to form rhodium sulfate. Solubilize, filter, precipitate, dissolve, precipitate...themal decompose. Several such purifications give finely divided metal powders which can then be melted by electron beam in vacuum. So, skip the chemistry -- you might take it apart, but not be able to put it back together (in separate parts)."
http://www.finishing.com/439/83.shtml
Process flow diagram (simplified schematic) for refining precious metal ores:
http://www.implats.co.za/i/imp_flow_diagram.gif
Question: The catalytic converter shell is SS, but is the body (monolith) ceramic or SS?
RE: Dissolving stainless in dilute sulfuric acid
Thanks for the info. I'll update the thread as things progress.
RE: Dissolving stainless in dilute sulfuric acid
Why not simply CUT, with an angle grinder/zip cutter, the case of each catalytic converter, open the cases with a prybar, take out the ceramic monoliths, SELL the scrap stainless steel, and then leach the precious metals off the monoliths?!
RE: Dissolving stainless in dilute sulfuric acid
RE: Dissolving stainless in dilute sulfuric acid
A number of years back, we were involved in the process design for coating of an early generation of the metallic substrate. However, the process resulted in some coating being applied to the external surface of the can. We recovered this material with an automated brushing machine. It worked very well.
Grit blasting will also remove the PM.
RE: Dissolving stainless in dilute sulfuric acid
If you've got all the time in the world, you might get away with room (outdoor) temperature dilute sulphuric acid, periodically replenished. Add a little chloride to help. Aerate it perhaps? Someone with more time might look up corrosion rates vs concentration and advise you- I'm used to looking at the problem the other way around!
I can't imagine an easy way to electrochemically assist that corrosion given your geometry, but you might be able to come up with something if you give it enough thought.
Have you considered room temperature hydrochloric or perhaps ferric chloride instead? Would probably get rid of the stainless faster, and doubt it would dissolve much of the PM content if you left it at low temperature.
RE: Dissolving stainless in dilute sulfuric acid