Cleanup - Solution with gold in it, but too much acid

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snoman701

Well-known member
Joined
Oct 8, 2016
Messages
2,219
Location
SE MI
This was one of my previous mistakes, and my last "mistake" to clean up.

I dissolved an unknown quantity (probably about 100 grams) gold plated pins in AR, with an excess of both HCl and an excess of Nitric. The pins were mildly magnetic, likely a kovar center. (dsub pins)

So now I have 800 mL of black liquid, with excess acid and no precipitate. Stannous test is hard to interpret, since it starts out black.

Any suggestions for recovering the gold, and putting this nightmare to rest? I'd even be happy getting both the copper and gold to cement out!

I'd just add copper, but since I've dissolved iron, I now have ferric chloride, which can dissolve A LOT of copper....and then precipitate it back out....making a bigger mess than I already have.

Everything else has been going great! Getting better at sneaking up on the minimal amount of nitric to use with AR and have foils floating around in the cupric chloride etch.

Starting to get the hang of this stuff. Amazing what happens when you take your time and plan your steps.
 
Ok...I'm pretty sure the answer is distill off the excess solvents (free nitric, free HCl and water).

So what do I use as my endpoint for the distillation? I don't have a button large enough to use to consume the final bit of nitric.
 
Cement on copper
Dont distill, it isn't needed at all.

Yes, there is probably iron in solution, but if there is gold in situ with it, the copper will displace it out. Then it would be iron and copper in solution instead of iron and gold (and all the other junk in kovar)

Were it me, Id just throw it in the stock pot and forget about the microgram of gold until I accumulate much more.
 
snoman701 said:
So now I have 800 mL of black liquid, with excess acid and no precipitate. Stannous test is hard to interpret, since it starts out black.
Click to expand...

Ok, so is it 800ml of black crystal clear liquid or 800ml of murky black liquid?

Also you cannot just assume that 100g of pins = 0.1g of gold without knowing the provenance of said pins. The range is way too huge.
 
Black crystal clear, it's just really dark solution...no solids as far as I can ascertain.

I figured I'd stop at Salvation Army and get a crock pot. Then I can throw it outside and let it cook down for a bit.
 
snoman701 said:
I figured I'd stop at Salvation Army and get a crock pot. Then I can throw it outside and let it cook down for a bit.
Click to expand...

You are not listening to the advise being given to you :!: :!: :!:

There is NO need to evaporate :!: :!: :!:

Do as you are told --- cement it (the gold) with copper (as in stock pot) :!: :!: :!:

Yes its going to use up a lot copper (at least more then if you had used the right amount of nitric in the first place) --- but that's the price you pay for the mistake - its part of the learning curve - we have ALL gone through this same kind of learning curve - & we have ALL had to pay that kind of price to learn

Kurt
 
Think of it less at not listening, and more as thinking out loud....and feeling like you weren't listening to me. Please don't get upset, but read this whole thread.

Here's the reason I didn't want to cement....last time I did it, I put a piece of copper wire in to the flask and walked away, leaving it on heat and stirring...all night. Not a big deal in my world....leaving an active reaction running is something I'm pretty used to. (ala, stockpot)

Well, I came back in the morning to find 3" of copper powder sludge in the beaker.

Solution was nearly identical. Au, Cu, Kovar, HCl and HNO3 (and others, but those are the players).

So in retrospect (as it didn't happen when I cemented this time) what I think happened (in that case), is that by leaving it on heat, and leaving it stirring, the reaction used up all the nitric, but the Fe and Cu kept changing oxidation states...Copper Chloride and Ferric Chloride will both precipitate out copper and regenerate upon changing oxidation states. So, it not only killed all the excess nitric, precipitated the gold, but then it also used up all of the HCl.

In the end, I just washed the copper and put it in the oven (lab) to dehydrate...tried filtering it, what a mess!

In this case, I've left the busbar in there, but haven't filtered it out yet....but it doesn't appear abnormal. Today hopefully...have to find my new box of filter papers. I've been using two coffee filters and I know I'm losing gold. (or, at least losing it to the stock pot, which I don't pour, but decant)

Either way, I wanted to say that I wasn't not listening, just very hesitant to follow advice given a very messy scenario last time. But either way, thank you!
 
So to add to that...I did listen, but I was so sure that I was going to make a mess, that I tested cementation on a small sample of it first. That's when I realized the heat and surface agitation were likely what resulted in the mess last time...and realized that yes, I should just do as I'm told, but not speed cementing along with any heat or agitation!
 
Sounds very similar to the mess i made months ago, which i'm still battling to get any gold out of.

Next time an experienced person tells me to "Stock Pot It" i'm just going to say "Yes Sir. Thanks" and immediately put it in the stock pot.

Seriously, although i enjoy chemistry and running the procedures, it takes up a lot of time and effort, and gets pretty boring, especially when there's nothing to show for it.
 
butcher said:
Somehow I never found anything boring about it, even those little chemistry bubbles can keep me amazed for hours.
Click to expand...

Yeah, it's somewhat troubling how much time can be lost staring at a flask. I used to have trouble figuring out where my day went in the lab...and that wasn't even this fun!

Today, spent four hours on top of two hours yesterday trying to assay my most recent scrap acquisition. Likely as much as two ounces if it's all plated as thick as the first couple parts!

Need to build a micro sized plating cell that cleans up easy so I can run just a small amount of material.

Or just build a fire assay lab (likely what I'll do)
 
butcher said:
Somehow I never found anything boring about it, even those little chemistry bubbles can keep me amazed for hours.
Click to expand...

Hey Butcher...would you suspect that the combination of heat and stirring likely caused the previous disaster?
 
It is hard to say without seeing what all your doing, I read through what you said and I agree the ferric chloride can dissolve a lot of your copper when concentrated and heated strongly it will even dissolve silver fairly well.


You do not need to heat it, or concentrate it (that is as long as it is not just mostly water) the copper will cement the gold leaving the Iron and copper salts in solution.

I have some posts on ferric chloride that may be helpful.
 

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