Determination of SMBS addition into the Aqua regia solution

[Chemlab]

Dear Sir/Madam,
In the process of gold recovery using the aqua regia method, after leaching gold from e-waste, we proceed to neutralize the solution using urea. Following neutralization, we add sodium metabisulfite (SMBS) to precipitate gold dust.
However, I have encountered an issue: if an excess amount of SMBS is added to the solution, white precipitates form. Could you kindly advise on how to address this issue?
Additionally, how can the appropriate quantity of SMBS required for the precipitation process be determined?
Lastly, which reducing agent yields better results for gold precipitation: sodium metabisulfite (SMBS) or Ferrous sulfite (FeSO4)?
Looking forward to your guidance.

 

[Yggdrasil]

Dear Sir/Madam,
In the process of gold recovery using the aqua regia method, after leaching gold from e-waste, we proceed to neutralize the solution using urea. Following neutralization, we add sodium metabisulfite (SMBS) to precipitate gold dust.
However, I have encountered an issue: if an excess amount of SMBS is added to the solution, white precipitates form. Could you kindly advise on how to address this issue?
Additionally, how can the appropriate quantity of SMBS required for the precipitation process be determined?
Lastly, which reducing agent yields better results for gold precipitation: sodium metabisulfite (SMBS) or Ferrous sulfite (FeSO4)?
Looking forward to your guidance.

First of all we do not recommend using Urea.
And not neutralizing but decomposing NOx.
It works to a certain extent but has a few quirks.
It can under certain conditions form an explosive compound.
It has a relatively high pH and can if used too much neutralize the solution out of the range for Gold precipitation.
What we recommend is Sulfamic acid in a heated solution.

Regarding SMB we use what is "needed" that may be at ideal conditions as little as 1:1 gram or many times more in less favourable conditions.

Ferrous Sulfate needs a lot more but has the advantage of not giving the smell of SulfurDiOxide.
Ascorbic acid, Oxalic acid anfmd even Vitamine B can be used.

Sometimes if the solution is dirty, vementing on Copper and then dissolving without the use of Nitric may prove to be a better way.

 

[Yggdrasil]

Dear Sir/Madam,
In the process of gold recovery using the aqua regia method, after leaching gold from e-waste, we proceed to neutralize the solution using urea. Following neutralization, we add sodium metabisulfite (SMBS) to precipitate gold dust.
However, I have encountered an issue: if an excess amount of SMBS is added to the solution, white precipitates form. Could you kindly advise on how to address this issue?
Additionally, how can the appropriate quantity of SMBS required for the precipitation process be determined?
Lastly, which reducing agent yields better results for gold precipitation: sodium metabisulfite (SMBS) or Ferrous sulfite (FeSO4)?
Looking forward to your guidance.

I just noticed.
AR is not a good way of treating e-waste.
Can you elaborate how you treat it what it is and how you prepare your AR.
For e-waste Cupric Chloride etch and either HCl/bleach, HCl/Peroxide or HCl/pool Chlorine is a better solution than AR.
How much material do you treat at the time?