# Hydrazine for acid solutions?



## skippy (Jul 22, 2011)

I am looking for better ways of cementing metals from catalytic converter solutions.

I have one constraint. It shouldn't involve taking the pH higher than 4, as that's where I get a lot of alumina junk precipitating out.
Ideally I would like to be able to drop the reduced metal quickly in a form that I can wash and filter easily, unlike iron or zinc reduced metals, which are a messy pain in the end. Can hydrazine sulfate be used at this pH to do a non selective precipitation?

Any other suggestions appreciated too of course.


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## lazersteve (Jul 23, 2011)

Hydrazine sulfate requires basic conditions to reduce PGMs.

Are you using zinc turnings or fine mesh powder? I use zinc turnings with excellent results and typically don't have to adjust the pH.

Neither zinc nor hydrazine are selective for PGMs so the resulting black/gray powder/sponge must be purified after either process unless you are reducing from pure solutions or salts. With zinc reduction you still have to clean up the residual zinc, but it safer to use than hydrazine in my opinion.

Steve


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## skippy (Jul 23, 2011)

What I'm looking to do is get the metals reduced then washed and filtered and then separated by the procedure outined by Lou a while back - that is nitric for dissolving palladium, H2O2+HCl for the platinum, and then refuxing sulfuric acid for the rhodium. I was having trouble with salt residue causing platinum dissolution while dissolving the palladium with nitric acid. More washing was in order but washing and filtering was as mentioned being a pain. 

I've been using powdered zinc, I will have to try the turnings now. Hopefully that does the trick. 

I always thought before I started experimenting that dissolving the metals from the converters was the real trick, but really it's just the start of the battle!

Thanks for setting me straight on the hydrazine Steve.


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## skippy (Jul 24, 2011)

Steve, your reply prompted another question. Are you saying you don't bother with the partial neutralizing of your cat solutions pre zinc reduction?




lazersteve said:


> Hydrazine sulfate requires basic conditions to reduce PGMs.
> 
> Are you using zinc turnings or fine mesh powder? I use zinc turnings with excellent results and typically don't have to adjust the pH.


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## Lou (Jul 24, 2011)

He's saying that surface area to volume ratio is low enough that you won't have too much of an exotherm and the hydrogen produced (which raises the pH) will be much less in rate than with zinc dust.

Steve makes turnings that accomplish a slower reduction. Zinc does works quick but is very hazardous.


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