Which process would you reccommend?

[bswartzwelder]

I had an AR solution which unfortunately had a fair amount of base metals in it. To precipitate the gold, I used SMB. I know all the gold precipitated (used stannous chloride and got a negative results on the spent solution),out of the solution, but I believe the precipitant also had a lot of the base metals precipitated. The precipitate is an extremely fine, almost like talcum powder. Once stirred, the powder is so fine that it takes days to settle out.

I then put the precipitated powdery sludge into a clean beaker and added fresh HCl. I was thinking the HCl might re dissolve some of the base metals and then I could just drop the gold. After sitting overnight, it doesn't appear that much of the base metals have been dissolved. Now for the question: What would be the best way to deal with this powder? I could add either Chlorox or HNO3 to the HCl which would dissolve all the metals then try to be more selective in the precipitation process by using oxalic acid or ferrous sulfate instead of SMB. By using Chlorox, I would not have a problem with excess Nitric. However, if I add the nitric a few drops at a time, I shouldn't have a problem with an excess anyhow. At any rate, a little sulfamic acid would kill off any excess nitric if I needed it. Either way, I would only add nitric or Chlorox by the dropper full until all the powder had re dissolved.

Any thoughts one which process would be greatly appreciated. Perhaps there is an entirely different process which I haven't considered.

 

[bswartzwelder]

At my age, my head hurts if I think too much, but I just thought of another possibility. What if I add a little H2O2 to the solution and bubble some air through it. To my way of thinking, everything except the gold would dissolve leaving the gold behind. Pros? Cons?

 

[Geo]

Personally, I believe you should use the bleach and let it sit overnight. Just like the nitric, add it in increments and only whats needed.

 

[jeneje]

If it were me, i would dissolve everything again using either Clorox or HNO3, ( If using Nitric - you will need to remove any excess Nitric with Sulframic acid) then drop dirty with Ferrous Sulfate, let settle, decant and re-refine and drop with SMB for a purer material.

Ken

 

[jason_recliner]

Before re-refining, give it a proper wash.
Boil in HCl > Boil in water > Repeat until clean.

It's already been sitting in AR. So my guess is that HCl alone will do little.

I ran a tiny batch of foils through HCl/Bleach last weekend. After dropping, the powder came out gunmetal grey. The HCl did nothing until I boiled it, then it turned a light tan in seconds, and not a hint of colour to the acid. But white powder appeared and it stayed even though I was boiling the HCl, and stayed even though I added 50% extra water. It was probably just salt. The separate boiling water wash got rid of it.

 

[Anonymous]

What's your estimated gold content? A rough idea?

 

[bswartzwelder]

My guessimate would be 1 to 2 grams of gold. The nice thing about working with smaller amounts is that you use less chemicals when dealing with them.

Edited to add the following:

Actually, I'm quite surprised that no one jumped on the idea of adding H2O2 to the HCl. That should get rid of the base metals and leave just the PM's behind. Since everything is in a very fine powder, it should react rather quickly AND I could toss in a dozen or so strips of finger contacts killing 2 birds with 1 stone.

 

[4metals]

My guessimate would be 1 to 2 grams of gold. The nice thing about working with smaller amounts is that you use less chemicals when dealing with them.

I think the whole notion of chemical usage and efficiency (not to mention time spent) goes into another level of understanding at that scale! Almost like physics has different rules when you get into the nitty gritty of particle physics.

You're talking a quantity of gold that can be digested in 5 to 10 milliliters of Aqua Regia. What percentage of that liquid is absorbed into the strip of filter paper when you test with stannous? It can be a loss of a few percent. Well not a loss but it is a quantity set aside for future recovery to say the least. How much liquid were you working with?

At that scale it is best to collect your concentrates (foils, black sludges, etc.) and process a quantity that will minimize your losses due to filtering and testing. Even an ounce will be digested in under 150 ml of Aqua Regia so it still is in the realm of small beakers but rinsing and recovery losses will be less.

 

[kurtak]

You're talking a quantity of gold that can be digested in 5 to 10 milliliters of Aqua Regia. What percentage of that liquid is absorbed into the strip of filter paper when you test with stannous? It can be a loss of a few percent. Well not a loss but it is a quantity set aside for future recovery to say the least. How much liquid were you working with?

I agree with 4metals --- personally I would wash it out of the beaker its in - into my settling jar that I decant my gold washes into for catching the ultra fine gold that pours off when washing my gold & then process it when the settling jar has enough in it to make it worth while processing

Kurt

 

[Anonymous]

I think that the first question that should have been asked before giving advice should have been "how much gold were you expecting?" Quantifying things can seriously change the relevant advice.

Jon