gold wont precipitate?

[luddefog]

So I am doing a school project and in which i recycle gold from computer scrap, something that you all seem familiar with, I used two separate methods to dissolve the gold foils from "goldfingers" and pins from CPUs. The first method was aqua regia and the other method involved muriatic acid and sodiumhypochlorite. These tasks both seemed to go well seeing as how the gold foils was dissolved in both of these solutions. However, after the foils had been dissolved I wanted to precipitate the dissolved gold (HAuCl4/ NaAuCl4) So i addded potasiummetabissulfite, expecting to see the brown gold powder fall to the bottom. This did not happen. The solution started bubbling and darken, but there was NO powder falling to the bottom. I do not understand why there is no precipitation.
I fear that there is, in fact, no/not enough gold in the solution. I will test the contents of both solutions with stannous chloride tomorrow. However, if there is gold in the solution I would like any help or tips on how to get the gold out of the solution (reduce the gold(III)). I Would sincerely appreciate any advice that any of you have.

Thanks in advance!

 

[FrugalRefiner]

I used two separate methods to dissolve the gold foils from "goldfingers" and pins from CPUs.

I fear that there is, in fact, no/not enough gold in the solution.

How many goldfingers and pins did you dissolve?

Dave

 

[luddefog]

I used two separate methods to dissolve the gold foils from "goldfingers" and pins from CPUs.

I fear that there is, in fact, no/not enough gold in the solution.[/quote]

How many goldfingers and pins did you dissolve?

Dave
[/quote]

Hard to say exactly, however when i had seperated the foils from the PCBs with a sodiumchlorite/hydrogen peroxide soultion the total mass of the gold foils and pins were 5 grarm which were then divided into to different beakers

 

[butcher]

Once you had the gold oxidized into solution, how did you deal with any excess oxidizing agent, that was left in solution?

 

[luddefog]

Once you had the gold oxidized into solution, how did you deal with any excess oxidizing agent, that was left in solution?

I Added the potasiumsulfite to both of the solutions after oxidixing the gold, without any step in between except for filtering out parts of scrapmetal. is the excess oxidising agent (excess aqua regia for example) prohibiting the formation of solid Au? If so is there any way to fix this?

 

[butcher]

What kind of school project uses dangerous processes they do not understand?

Should not part of the learning process includes some type of study before doing something so dangerous or foolish as to put metals into a dangerous acid without knowing what happens?

This study part of the process should come before the experiment, otherwise, how will you ever know how to go it right, or what to expect, or how to correct a problem, much less know how to work safely without harming yourself or poisoning your neighborhood.

How will you safely deal with the hazardous toxic waste generated from this school project?

The dangerous gases involved in the solution will keep your gold dissolved, nitrosyl chlorides, Chlorine gas...

Filtering out scrap-metal parts before filtering? Hmm, I wonder, you may not have in gold in this toxic mess?

 

[kernels]

What do you mean by 5g of Gold foils and pins ? I get that together they are 5g, but do you mean base-metal pins that have had their Gold stripped ?

If you dissolved the Gold foils with Aqua Regia, as in 3:1 HCl and HNO3, then you likely have a very very very large amount of excess HNO3 in that solution, preventing any Gold from precipitating. The general recommendation is to cover the material with HCl and add small amounts of HNO3 until the Gold is dissolved. Even then, you usually still have to remove the excess HNO3 before precipitation, this is most often done with Sulfamic acid.

But really, if you didn't start with at least 250g of closely cut fingers, then there is likely so little Gold there that it makes it very hard to work with for someone without experience. The yield from close cut Gold fingers is usually only around 4g per kg.