Inquarted gold then AR losses

[autumnwillow]

From my assay, I am now up to 8% losses. Before it was only about 1% loss from assay. Not sure why. I'll explain further.

The only thing that changed from my process before and from my process now is using recycled nitric. I use recycled nitric from silver chloride wastes and H202 scrubbers treated with silver nitrate.

When I digest this inquarted gold in 50% nitric then 50% recycled nitric + 10ml H202 then proceed with AR I am left with a lot of solids in a filter paper? Maybe the nitric digestion wasn't enough? But I'm pretty sure it is already about 95% gold (powder). From what I understand, AR can digest all or most of the gold? As long as it is about 95%+ gold.

I also washed the powder a lot of times before proceeding with AR, before I was getting a silver chloride precipitate which I assumed to be covering some of the gold powders but this time there was no white precipitate and still I had a huge loss.

Tomorrow, I'll do a sulfuric + iron on the solids that was left by the AR. Then proceed with nitric then AR again. If there is no gold recovered then it could probably be my staff stealing from me. If there is gold recovered then something is wrong with my process.

Which could be:
1) Not enough digestion in nitric or something wrong with the way I digest in nitric? I premix everything in a beaker then pour slowly, as soon as the red smoke reaches the top of the reactor I stop pouring, then add again if the red smoke starts to fade in color, I keep adding until there is little red fumes.
2) I use about 1:1 ratio of HCL and water in AR, maybe this one? But I was using this method before.
2) Assay is wrong? (I doubt but I'm willing to test on 4N bar)

 

[Palladium]

First thing to question in the equation is the assay. That's where the numbers all start from. Explain your assay method and procedures please.

 

[nickvc]

It could be me getting old but if you are using nitric that has chlorides in it surely that's the reason for your additional missing gold, it has dissolved some of your gold, try to precipitate the nitric and see if it has gold dissolved in it.

 

[autumnwillow]

First thing to question in the equation is the assay. That's where the numbers all start from. Explain your assay method and procedures please.

After melting the entire lot and pouring into a bar, a small sample is taken. About 0.5g - 1.0g.
This sample is then first assayed in a touchstone. The following is the amount of silver added based on the touchstone assay:
At least 21kt above: x3
At least 14kt above: x2
At least 10kt above: x1
8kt and below: x0.5

The silver and the sample is then melted carefully in a clay crucible using a torch at low pressures with a small amount of borax.
After the melt, the sample is then rolled thin while carefully annealing during the process.
The sample is then digested in a 10ml water and 5ml nitric.
Sample is filtered, and a second digest of 10ml water and 10ml nitric is performed.
Filter and wash with boiling hot water.

Melt the filter paper with the gold in a clay crucible with a little borax. After the melt, roll twice to remove borax. Weigh.

The weighing scale has only about 0.001g accuracy.

Now I know the assay performed isn't that accurate but it shouldn't be off by 8%. I have performed multiple tests using a 4N 10g bar, alloying them differently and the results came out with 1% margin for error.

I do have an idea of how to perform a fire assay properly. I just can't justify the costs of buying the required equipments for it yet.

To add, another weird thing. The sample that was assayed, we rolled it very thin and then digest it in AR along with the lot and it doesn't digest it!

It could be me getting old but if you are using nitric that has chlorides in it surely that's the reason for your additional missing gold, it has dissolved some of your gold, try to precipitate the nitric and see if it has gold dissolved in it.

I do think that this could also be a probable cause, maybe I should heat the solution while adding silver nitrate along with a mixer but the last lot that had loss, I checked the nitric solution with stannous and it was negative for gold.

 

[4metals]

You are doing an "assay" by actually refining a small sample of the material which you have in-quarted. You are not doing a cupellation only inquartation and parting, is this correct?

What was the touchstone preliminary assay you used to determine the quantity of silver to inquart? What was the expected karat of the material you started with? (That is actually the same question asked 2 ways but the answer can matter.)

 

[autumnwillow]

You are doing an "assay" by actually refining a small sample of the material which you have in-quarted. You are not doing a cupellation only inquartation and parting, is this correct?

Yes

What was the touchstone preliminary assay you used to determine the quantity of silver to inquart? What was the expected karat of the material you started with? (That is actually the same question asked 2 ways but the answer can matter.)

Touchstone assay resulted in 12k
The sample was 1.082g
I added 2.0g of silver

 

[autumnwillow]

Only three chemicals was changed from my process before.

H20 from distilled to RO. Checked with a TDS meter. Reads at 5ppm.
Recycled chloride wastes. Removed chlorides with silver nitrate.
HCL. Changed supplier. Not sure how to check yet.

 

[autumnwillow]

On the solids that was not digested by AR. We proceeded with sulfuric + iron, wash, then nitric, wash, then ar, then wash. All in all the loss was down to 2% from assay.

I guess not enough nitric digestion. But what happened is weird.

 

[autumnwillow]

Update on this. As it turns out that the HCL container was not sealed properly thus evaporating some of the chlorine content.
It was easily solved by adding more HCL to the AR digest.

 

[anachronism]

Would somebody be able to clarify something for me please? I understand the theory behind the 1/10 /20 and the karat of of gold when calculating the gold content however is the weight used the weight of the gold foils or the weight of the item itself - for example a watch band.

 

[nickvc]

If you are talking about gold filled or rolled gold as we call it the maths are these, I will use 10 grams of it for the examples, this is the gold and its base metals alone not springs etc.
10 grams 1/10 9k = 0.375 grams of gold
10 grams 1/20 9k = 0.1875 grams of gold
If the items are new and clean the figures should be reasonably accurate but not spot on, if well worn they can be considerably lower by as much as 25 percent.

 

[anachronism]

Thanks Nick but for clarity would you apply those calculations to the complete watch strap as it sits in your hand or to the pm bearing caps when removed from the strap?

 

[FrugalRefiner]

In the case of watch bands, it only applies to the caps. In other items, like eyeglass frames, it applies only to the metal frames. There is usually additional weight from screws, nose pads, ear pads, etc. In jewelry, it's going to apply to the weight of the finding, not including stones and such.

Dave

 

[anachronism]

Thanks Dave.