# interference



## arthur kierski (May 7, 2008)

does silica interfere in the leaching of catalists and in the leaching of ores containing precious metals?
if the answer is YES---what are the sugestions to eliminate these interference? thanks in advance


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## Lou (May 7, 2008)

You don't know the answer to this?

Silica is unaffected by acids used in refining but HF attacks it. HF doesn't not appreciably attack certain modifications of alumina. In fact, $2000 dollar HF dispensettes from Aldrich are made from teflon and sintered ultra high purity alumina. 

The only interference should be from the SiO2 encapsulating the values and preventing easy access to the leach solution.


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## arthur kierski (May 7, 2008)

Lou, before leaching car catalyst i use hf in the substrate and this reduces the weight of the substrate by 35%---many years ago i read in c. w Ammen book that this should be done----then i mix this substrate with nahso4 and withdraw all the rh and pd from the cat--then i add ar for 2 hours and the pt goes to the solution--as you see i have my way and i just made the question of the interference of sio2 because friends in this forum liked my method of extraction and are worried in using hf(which is really dangerous to use and need a good know how---many years ago i had a severe burn with hf and suffered daily for 2 months)i never extracted pgm from cats without using hf first--so i was surprised that you was surprised that i did not know if sio2 interfers or not in leaching---you just said that if pm are embedded in sio2 the leach does not attack---you was dubious


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## Lou (May 8, 2008)

I wish I spoke Portuguese. If you prefer, I do write/read fluent Spanish.


I understand what you mean by using the HF to decrease the mass. My personal belief on the utility of the HF is that it acts as a loosener of sorts and permits easy access to the values by exposing more of the PGMs on the surface. From what I understand of the construction of these things, it's all on γ-Al2O3 a particularly resistant (both thermally and chemically) modification of aluminum oxide, this is then given a wash of some sort of fine fumed silica slurry with other additives (ceria, magnesium silicates etc) that has been impregnated with the acid salts of Pt, Pd, and Rh. That means most of them are distributed on the surface of the converter in an SiO2 based matrix, while Al2O3 just serves as a bulking substrate.

I know all about HF burns, once is enough to last a lifetime, even if it is minor. 


Tell me this Arthur, do you extract the Rh with aqueous (in water) NaHSO4, or do you use a molten fusion of bisulfate?


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## Lino1406 (May 9, 2008)

Did not recommend HF


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## Lino1406 (May 10, 2008)

Sorry, Ammen did recommend HF. In fact,
I used it myself, before stopping using it
for the following reasons:
1. The advantage of reducing volume a little
doesn't look so advantageous vs.
2. H2S2F6 breathing
3. Appearance of AlF3 related crystals in the
system
4. Danger for the sewerage system


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## Lino1406 (May 10, 2008)

H2Si2F6 - not H2S2F6


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## arthur kierski (May 10, 2008)

LINO---since i became a member of this forum i receive replies from you as if i am a lier and you are testing me---i am in this forum in good faith to learn and to pass to members what i learned---i dispense replies from persons like you


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