I couldn't manage to precipitate the gold

[yararyus]

Hello there,

I tried to get some gold from a mixture of gold fingers, gold dots, and gold plates from various PCBs.
It is obvious that I made a mistake but not sure in which step. Let me write down my steps and please tell me what I shouldn't do for the next try.

1) I put them into HCl and dissolved solder.
2) Extracted gold flakes with AP
3) Filtered the solution and put the filter paper into 400 ml, heated Aqua Regia (300 HCl, 100 HNO3).
4) After a couple of hours, I filtered the Aqua Regia solution by plugging a funnel with cotton.
5) I guess my series of mistakes start from here. I forgot to add sulfamic acid for de-NOxing and poured a bit SMB into the solution and nothing happened. I continued to add SMB like it will change anything. Then I realized that I forgot to add Sulfamic acid. With the instinct of "better late than never" I added sulfamic acid. As you can guess, the solution just buzzed and stayed same. I gave a break and started to think. Then I thought, maybe I had to add more SMB by mixing it with water. But, again, nothing happened

After I read what I wrote, I think I love adding SMB to AR :lol:

Anyways. So, can you please tell me why I couldn't precipitate gold from AR?

I have 2 guesses.

1) The volume of my AR solution was too much for that little amount of gold foils.
2) I tried to precipitate it without de-NOxing the solution.

 

[FrugalRefiner]

What did a stannous test show before you started adding SMB and sulfamic acid?

How much gold flakes did you put into your AR? We don't need an exact weight, but do you estimate it was 1 gram, 10 grams, 100 grams?

Yes, I would guess you used way to much AR. My usual advice for recovering from a mess is "when in doubt, cement it out".

Dave

 

[yararyus]

What did a stannous test show before you started adding SMB and sulfamic acid?

How much gold flakes did you put into your AR? We don't need an exact weight, but do you estimate it was 1 gram, 10 grams, 100 grams?

Yes, I would guess you used way to much AR. My usual advice for recovering from a mess is "when in doubt, cement it out".

Dave

To be honest, I didn't weigh. I lost my mind when I see those little shiny particles and forgot to note it down. But if I have to guess, It was between 1 - 4 grams.

What is your advice to me for saving my little sweet shiny gold particles from the messed up solution? Boiling ?

 

[FrugalRefiner]

As I said above, when in doubt, cement it out. You already have a soup of too much acid, too much SMB, sulfamic acid, and some base metals. Cement the values out, then re-refine them.

Dave

 

[galenrog]

Dave gave you the cheapest and easiest way out of your mess. Twice.

I have followed the adage of “when in doubt, cement out” many times. Copper is cheap. Guessing is not.

Also, test your solutions often.

Time for more coffee.

 

[g_axelsson]

For your next refining session, 100 ml nitric in your aqua regia is enough acid to dissolve more than 100 g of gold. Only add small amounts of nitric until the gold is dissolved. It's easier to add nitric if you need more than to remove it.

And I agree with Dave and galenrog, cementing is the way out of a mess, and if you are at the lower scale of 1-4 g then it can be hard to even see the gold on the bottom.

Test your solutions with stannous and only discard crystal clear solutions.

Göran

 

[yararyus]

Thank you for your advice people

 

[Advance]

Hi. I used aqua regia to dissolve gold from 2kgs scrap cell phone circuit boards. I then added urea to the filtered solution until it fizzled out. I then added 5grams of SMB and left it over night but no precipitation. I repeated stennous test and its still positive , Should I add more SMB?

 

[Martijn]

Hi advance. Welcome to the forum. Your answer is in this thread above.
Please search and read before asking a quick fix.
Study before diving in dissolving things you don't understand.

Too much HNO3 in the mix is often the problem. Save it and keep adding gold foils until they don't dissolve anymore. It may take some time... but you'll have an idea of how much gold is needed to exhaust out a certain amount of HNO3.
How much HNO3 did you use?
You can also put a piece of copper in and cement it out, wasting an amount of usefull nitric. Depending on how much HNO3 is used...
Why did you use urea?

Martijn.

 

[galenrog]

When in doubt, cement it out.

If you do not know what that means, put your toys away and study.

The answers are here.

Time for more coffee.

 

[Iamdrainbows]

When in doubt, cement it out.

If you do not know what that means, put your toys away and study.

The answers are here.

Time for more coffee.

So galenrog.... is precipitation different than cementing

 

[Iamdrainbows]

As I said above, when in doubt, cement it out. You already have a soup of too much acid, too much SMB, sulfamic acid, and some base metals. Cement the values out, then re-refine them.

Dave

I. Having the same problem. But worse. My stannous chloride showed I had gold. I added sulfamic acid chrystals and the solution didn't test positive again. Does this mean I have too much hcl or nitric? Should I add more sulfamic? Where do I go from here.

I am going to try cementing but how do I actually do this

 

[FrugalRefiner]

I am going to try cementing but how do I actually do this

Type "cementing", or "cement", or "cementation" into the search box at the top of the screen. Spend some time reading through the threads.

Dave