Gold dusting problem

[Mooks]

Hi, im make AR with 200 cc water,400 cc hcl, and 30 cc nitric. And desolved the gold. But muly problem is:
When i add smb for 35gr, it doesnt go dark, i added 5 gr NAoH ,and surprisingly solution turns bright! And some tiny black dust. This is very odd!
I grab some of the bright solution and heat it, then turns goldish. Wtf was happened. Pls help me

 

[orvi]

Did you neutralize the excess nitric in solution with boiling it down or using sulfamic acid ? If not, nitric acid slowly oxidize sulfite to sulfate, leaving gold still in the solution. What was the quantity of gold dissolved by this procedure ? Did you tested the presence of gold with stannous chloride ?
I will not advise to add base to these kind of solutions.
When dissolving gold or anything else in AR, use increments of nitric acid while solution is hot to dissolve the metals. Using excess nitric is pain to deal with in the next steps, and you need to apply chemicals to destroy it (eg sulfamic acid) or need to evaporate down the solution to slowly degrade the nitric to nitrogen oxides and NOCl.

To recover from the mess, i will go with cementation to scavenge all values (when in doubt, cement it out), then repeat it again and do it properly you find numerous references here, depending exactly on what you are dealing with. Just use search bar and give it few minutes.

 

[FrugalRefiner]

To recover from the mess, i will go with cementation to scavenge all values (when in doubt, cement it out)

I like that! When In Doubt, Cement It Out

Dave

 

[orvi]

I like that! When In Doubt, Cement It Out

Dave

Very catchy well said, sticked to my memory instantly, helpful... Works every time.

 

[Martijn]

Welcome to the forum Mooks. Please explain 'the gold'... how much, in what form, and from which source / process did it come?
You had about 30 grams of gold to dissolve, judging the amount of nitric and smb you used.
Sounds like excess nitric. A very common beginners mistake.
What is odd, why did you add water to the AR and why did you add lye to the solution?

Martijn.