Glittery precipitate while dissolving with HCl/Cl (bleach)

[KreAture]

Just thought I should ask as I can't seem to find a good description of this.
Basically I've run the classic Hcl/H2O2 leech to release gold foils from ram fingers.
I managed to keep the solution very low in volume this time and feel quite happy about that. It was barely covering the fingers the whole time and all foils released nicely.

Filtering was fine and I had a nice pile of foils after rinsing with clean HCl and de-ionized water. (I know I could have skipped the water.)

When dissolving I kept the foils in the filter and used 4.7% concentration bleach sparingly but have now added a total of 3ml to a HCl volume of approx 30ml. (This is a small test batch as I am testing a new setup and a scrubber.) The coffee filter has disappeared but there is a tiny bit of a foggy mess left and I wonder if the filter had impurities.

The odd thing is the gold, although a lot has dissolved, does not appear to finish. Instead it is almost like it is precipitating back out as microscopic crystals or flakes so the solution although being very dark yellow is also shimmering like it is full of mica. You can see it dance in there. It's beautiful but I was expecting to reach a clear solution with some debris I could filter before dropping. I have been helping things along a bit with some heat, but as soon as I let off it appears to immediately fall out of solution and starts shimmering even more.

Maybe I should film it...

 

[FrugalRefiner]

Have you tried adding a bit more water, HCl, and/or bleach? You mentioned a "nice pile of foils". It's possible you've saturated your solution. When you cool, it precipitates. There is often nickel along with the foils. You may be seeing a cementation.

Dave

 

[KreAture]

It's a good question FrugalRefiner.
I was also pondering if it was saturated but I really don't know since AR can hold a very high amount while it appears from my reading that HCl/bleach tend to create salts and it appears to have other limits.

I have tried adding a bit more HCl and I think it moved forward a tiny bit on the gold. I also added bits of bleach and it fizzes when added and I am unsure how much progression there is.
I also tried heating and it seems to help a bit but only while hot.

The crystals are more brownish than white so I am unsure if it is gold or salts.


The "nice pile of foils" is relative and I estimate I am trying to dissolve 80 mg of gold in a solution of only 35ml.
That would equate to approx 2g/liter and I think that should be ok.

 

[anachronism]

You need more liquid. Don't be stingy with it. Also make sure you have some free water there otherwise you will get salt precipitating out.

Jon

 

[FrugalRefiner]

Yep.

Dave

 

[butcher]

Bleach is a caustic solution (to keep the hypochlorite in the solution of water), when mixed with HCl they will produce sodium salts water and chlorine gas (the oxidizing agent to dissolve gold into the salt water solution).

HCl + NaClO --> NaCl + H2O + Cl2

Water will dissolve the table salt.

 

[FrugalRefiner]

That is also some nasty brown solution. I've never seen that when dissolving foils. Looks like iron in solution. Please tell us what all went into this whole process.

Dave

 

[KreAture]

Hurray. You appear to have hit the nail (no nails in there) on the head.
I added some distilled water to see and it did clear up some crystals.

So, to limit the volume I used more HCl and it appeared to clear it up. It still didn't dissolve much gold though so I added more bleach in small increments. (0.5ml)
I'm now at almost double the volume I had when I had the massive crystallization but I am dissolving gold again and apart from the fine particulate (looks like very fine cellulose) left from the filter it is lighter and brighter yellow.

 

[KreAture]

By the way, I think the color balance on the camera is quite a bit off on the pic as it looked deep yellow/orange in real life not brown.
It's finally filtering now though and is a very clear yellow.

 

[KreAture]

Just wanted to follow up on what happened during the removal of excess Cl in the solution.
As I drove off the Cl gas by heating it (through a bubbler/scrubber) it quickly started glittering again.
This is after it had been filtered and diluted by adding about 20% distilled water.
Then as it heated more it drove of more gas and gold started floating on surface and dropped down. After 20 mins I had gold cake in the bottom!
Is this due to very poor HCl or something else, as I ended up adding an excess bleach at the end to get it to dissolve all the gold.

The color is pale vs real life but that is definitely :G
I want to repeat that this came from heating a filtered solution with what I believe is excess bleach and it was very nice bright yellow before I started.

 

[KreAture]

Just wanted to post a pic before I dry and melt it hopefully tomorrow.
The good thing is nothing dissolved in the washings, so not salt.
I don't have an exact weight yet but it is approx 80mg which seems spot on.

And yes, that is a tiny vial. Isn't it cute?

 

[KreAture]

Just as a note for posterity:
I used Potassium Metabisulfite as it was more easily available to me in pure form, but since I had such issues dissolving the gold I also had issues precipitating it. I used an excess PMB so I threw off my stannous tests completely. Expecting to recover only 80mg gold I was still seeing new precipitate forming after adding over 4 grams. Just putting it back on heat quickly precipitated out a lot more gold so something was holding it back even after a lot of fighting to get it out. There was definitely an excess bleach in there that took a long time to boil off. I am still unsure what blocked my initial dissolving of the Au. At one point I had salts forming that did dissolve with addition of more HCl or more water.