Help with Wohlwill Process

[mikemrtwin]

Hello everyone, I have been experimenting with the Wohlwill process in many different ways. I have seen others example of making Gold Chloride and the method building and operating the cell. My problem with it is i get a high amount of Si ( Selenium ) in the final product. Maybe trace amounts of something else but I'm trying to figure out where its coming from. I have refined mostly jewelry to up to 99.75% +/- with and average of 0.085 Si and other impurity.

When making Gold Chloride, the gold to be dissolved for it does it have to be 99.99%? Can it be made from 99.25%?

Can Selenium and other contaminants be introduced when using cheap HCI and SMB? A lot of it?

Do i have to use a 99.99% as a cathode? can i use cathodes made from Titanium or Stainless Steel?

I have felt filter that I'm planing to use. I also read into ceramic filters as other possible add on. I'm sure of all the purity readings from my portable XRF Analyzer.

Id like to know if there are any better ways to prepare the solution, look out for what I'm using and or refine this processes i just described better?

 

[Yggdrasil]

I don't know a whole lot about the Wohlwill process.
But Si is Silicone (Silisium)
And Se is Selenium.

XRF is notoriously inaccurate with respect to some elements.
Depending in the library at hand.
Regards Per-Ove

 

[Lino1406]

Se is soluble in HNO3 while gold is not

 

[nickvc]

To make your electrolyte i would advise using the highest purity you can obtain and only use 95%+ feedstock.
Do you use a filter bag on your anode and what grade of material are you feeding the cell?

 

[Elemental]

Three quick questions:

1. Can you clarify if you are having issues with Selenium (Se, Element 34) or Silicon (Si, Element 14).

2. What is the source of your raw stock? This will allow some insight in to where your contamination is coming from.

3. What method are you using to determine your contamination? I'm assuming XRF, but I don't want to assume.

Elemental

 

[mikemrtwin]

Thanks Yggdrasil
I'm still waiting on a rep from Thermo to help me with the library. All I can see are library v.8.4C_900 witch is a list off different classes of general metals, not really the XRF's element ability range.

Thanks Lino1406
Yes I was just reading up on that about using HNO3 on the gold to remove Selenium.
What would be the method on using NHO3 on the gold bar or sponge state?

Thanks nickvc
I have 1 Micron Polyester Felt bag but i did not use it when i did it the first time. I was afraid to put such an absorbent filter into an extremely expansive electrolyte. I wanted to see what the results would be without the bag. Only picked up Se and nothing else not even a trace witch was good that the setup worked even at a barbaric level. The feedstock you can see in the attachments. the sponge is what i use for the feedstock witch is 99.26%
Do you recommend any other types of filter bags?

Thanks Elemental
1, Yes the element in question is Selenium. Attached are the XRF reading.
2, The raw stock is scrap gold filled jewellery and packet watches.
3, Yes by XRF by Thermo Scientific recently updated and calibrated.


Let me know what you guys think and thanks for all the supper help!

By the way, in one of the pictures you'll see a bar that i started to strip in the cell. what would be causing it to have that texture? Is it the Se right?

 

[butcher]

I question the XRF it doesn't sound right.

Metals are often etched with acids to reveal their crystal structure, often done with metallurgical tests.

 

[olawlor]

Regarding the neat texture developing on your gold anode bar, I've seen a similar crystalline pattern develop on copper anodes after using them for copper plating. I attributed it to electrolysis being slightly slower on the broad monocrystalline surfaces of the metal (possibly a steric effect?), so the crystal corners get eaten away first and the biggest crystal planes last the longest. But since electrolysis removes metal atom by atom, it might just be uniformly exposing crystal structures that are always present inside the metal but are difficult to see otherwise.

(I have zero experience with gold electrochemistry though, your effect might be unrelated!)

 

[orvi]

i will question the XRF first. some elements have overlaying absorption bands in XRF, thus making the machine uncertain about some combinations of elements, faultly assuming that element is present when it´s actually not.
in the past, i had this issue with reading the silver purity on one old (uncalibrated trashy one) XRF, where allways around 1-1,5 % of Sn showed up. tin wasnt present, and test with other callibrated accurate machines proved, that silver was 99.8% pure, with some minor copper.
if you have some reference standard (like gold bar/round of stated 99.9% purity at least), get it zapped in the same mode as this questioned sample. and you will see if it is some error of the machine, or it is the real deal.
selenium and tellurium are similar to sulfur. and gold posses high affinity for these elements. deffinitely, presence of these elements could be real.

from my point of wiew, i will firstly question the analytics, than move to more elaboration, with confirmed contaminant