My first gold recovery didn't go as expected

[geoffbosco]

So, this is the result of my first attempt at gold recovery mixed ICs...yeah, I'm sure you're all a bit confused, so I'll go through my process and tell you about all the mistakes I made. lol

I incinerated the chips. Didn't really do much of a job crushing or separating magnetic material. I did do some basic panning of the lightest material. Then I got everything into 35% HCL. After it seemed like the reaction was slowing I poured it off and added more. When that slowed I poured that off.

I made some poor man's nitric with battery acid and potassium nitrate (spectracide stump killer). For that I added the nitrate to the acid and heated it. I kept adding the nitrate until I saw extra nitrate so I knew all the sulfuric acid would be used up. I added a little water to the chip material and then the nitric acid. I heated this solution till the reaction slowed and then repeated the process.

At that point I poured it off (solution was the bluish color you'd expect to silver from silver nitrate and copper nitrate combined) and left a little of the nitric solution and added HCL and returned to heat. I added a little more potassium nitrate as well. The solution turned a really dark brown color. When the reaction slowed, I poured off the brown solution and did one more small round of poor man's aqua regia on the remaining material. Then finally poured that off.

Here's where on funny thing happened: I went to add some distilled water to get the remaining solution out of the chip material and a white precipitate formed instantly. Huh... Back to the rest of the solution, I knew there must be unused nitric in the solution, so my best solution was to add a piece of copper and boil the solution for a bit. When I couldn't see any reaction on the copper I assumed any excess nitric was gone.

So I took it off the heat and cooled the solution in an ice bath. I then added SMB and let it sit over night. In the morning I did see some black precipitate in the dark brown liquid, but not much. It also had an incredibly acrid smell. I didn't know what to do or what I had, so I just ended up adding some sodium hydroxide to both solutions to neutralize them. The coffee carafe on the right had the brown solution and the flask had the remaining ic material mixed with the white precipitate. The brown solution reacted quite violently.

Any ideas what I got here?

 

[Martijn]

Welcome to the forum geoffbosco.
Did you filter anywhere in between those steps? Like after adding copper? Your post is a bit confusing for me regarding what you did to which solution.
Your gold has probably displaced out on the copper after dissolving in AR. Assuming all base metals were consumed.
Very little gold would be left in solution after that.

The brown could have been gold fallen out on base metals after dissolving with leftover HCL and fliating around. Did you leave it to cool and settle or decant right away?
Test a bit of that brown (powder?) with AR and test with stannous if it contains gold.

The white precipitate:
Some metal salts are less soluble in diluted acid or in cold solutions. That's probably what happened. Might be lead or silver. Silver chloride turns dark purple to black in sunlight. Lead chloride is soluble in hot water. Test and study.
I have no experience in poor mans nitric or AR, so someone else might have other comments.

Test your solutions with stannous chloride.

Learn about waste treatment. You'll understand what the copper did.

How much did you read and study?

You are better of separating the iron legs with a magnet. Leaching in HCL should have taken care of all iron and solder though.

Martijn.

 

[butcher]

Toxic waste to deal with.
That is where I would begin, putting this mess aside in a safe spot and begin studying how to deal with this toxic mess.

You may have to dissolve the metal hydroxides nitrate salts, chloride salts, and sulfate salts back into solution,
preferably without putting any values into solution, so you may need some stannous to ensure what is in solution, use copper to cement and remove any values from the acidified solutions, using iron to remove copper and a slew of other metals before bringing the remaining solution to pH 10 to pH 11 to precipitate and remove many more toxic metals from the solution, before neutralizing the solution to pH 7 to precipitate more metals from the nitrate, chloride, and sulfate salt solution...

After studying dealing with waste, and dealing with this toxic mess, I suggest you study more to gain a better understanding before beginning again on starting another mess. You are making it harder for yourself by not having some basic understanding before jumping in with the chemicals.

 

[Martijn]

Regarding the hydroxides, dissolve a little bit from the bottom with residu in a test tube in HCL. This should redissolve the hydroxides and leave any precious metal behind. Dilute, decant, rinse the solids left behind and dissolve in AR.
Test with stannous.

(Edit i read butchers reply after posting.
While studying, only try things on a very small scale. Test tubes and pipettes.
And again, start reading dealing with waste.
Be safe.

 

[geoffbosco]

"Welcome to the forum geoffbosco.
Did you filter anywhere in between those steps? Like after adding copper? Your post is a bit confusing for me regarding what you did to which solution.
Your gold has probably displaced out on the copper after dissolving in AR. Assuming all base metals were consumed.
Very little gold would be left in solution after that."

I'm having trouble remembering which steps I filtered between. Yeah, I was aware of the reactivity series of metals so I'm not sure why I thought that was a good idea. I had been working on it all day and it was getting late by that time, So I started getting impatient.



"The brown could have been gold fallen out on base metals after dissolving with leftover HCL and fliating around. Did you leave it to cool and settle or decant right away?
Test a bit of that brown (powder?) with AR and test with stannous if it contains gold."

OK cool. I let it cool and settle overnight. I kind of freaked a bit because of the smell which is why I decided to neutralize it. I really don't have a place to let volatile liquids sit for long periods of time. But I'm working on some kind of outdoor setup.

"The white precipitate:
Some metal salts are less soluble in diluted acid or in cold solutions. That's probably what happened. Might be lead or silver. Silver chloride turns dark purple to black in sunlight. Lead chloride is soluble in hot water. Test and study.
I have no experience in poor mans nitric or AR, so someone else might have other comments."

Thanks I figured something like that, just wasn't sure which metal. It seemed like a lot of silver for the amount of material, so I knew there must be something else.

"Test your solutions with stannous chloride."

Making my own is on my list of projects.

"Learn about waste treatment. You'll understand what the copper did.

How much did you read and study?"

I mostly watched youtube videos (yes yes I know). But, I'm the type who learns more by making mistakes than studying. Currently reading Hoke, and I'll get over to the waste treatment section on here.

"You are better of separating the iron legs with a magnet. Leaching in HCL should have taken care of all iron and solder though."

I probably didn't do the hcl step as thoroughly as I could have.

Martijn.

Thanks for the reply
Geoff

 

[geoffbosco]

Toxic waste to deal with.
That is where I would begin, putting this mess aside in a safe spot and begin studying how to deal with this toxic mess.

You may have to dissolve the metal hydroxides nitrate salts, chloride salts, and sulfate salts back into solution,
preferably without putting any values into solution, so you may need some stannous to ensure what is in solution, use copper to cement and remove any values from the acidified solutions, using iron to remove copper and a slew of other metals before bringing the remaining solution to pH 10 to pH 11 to precipitate and remove many more toxic metals from the solution, before neutralizing the solution to pH 7 to precipitate more metals from the nitrate, chloride, and sulfate salt solution...

After studying dealing with waste, and dealing with this toxic mess, I suggest you study more to gain a better understanding before beginning again on starting another mess. You are making it harder for yourself by not having some basic understanding before jumping in with the chemicals.

I appreciate the response. I will be spending much time here before I attempt my next recovery. But, I did learn a lot already. I'm the type of person that if I don't just start where I am I'll never do anything. So, I try to make myself do new things. That's a tight balance to walk for a procrastinator...