AR without Inquartation

[HansW]

Hi - New to this forum. After spending an hour on this forum I realise that inquartation before nitric followed by AR is the way to go. You are an outcast, or at least a rebel if you don't follow this rule.
I have a whole bunch of scrap jewellery and don't feel like sorting it and working out the exact proportions to get it to 25% Au. I have seen members on this forum going straight to AR, then washing off the AgCl coating with concentrated Na-thiosulphate. The process is repeated. That should be fine if I work in a continuous stream instead of a single batch.
Questions:
- Is that feasible?
- Am I not loosing Au in the thiosulphate leach?
- How do I recover the Ag from the thiosulphate?
Thank you!

 

[FrugalRefiner]

Hans, welcome to the forum. Inquartation isn't necessarily always required. You're not an outcast or a rebel if you don't do it.

Inquartation is only important if your scrap contains more than around 10% silver. If the silver content is lower than 10%, AR will usually provide satisfactory results. If you choose to inquart, you don't need to calculate an exact 25% gold content. If the gold content is lower than 25%, the granulated/cornflake gold may not hold together as well and may crumble into finer bits, but the gold will still be there. If the gold content is higher than 25%, the nitric may not leach the silver and base metals from the center of the granulated/cornflake gold, but it will work itself out once you go to AR.

Yes, you can dissolve the AgCl with thiosulfate or ammonia, then cycle back to AR as needed. If you use ammonia, be sure to promptly reacidify the solution to avoid creating explosive compounds.

But be aware that the silver chloride can trap some gold. Just as having too much gold in inquarted material can prevent the nitric leach from reaching the silver and base metals, the silver chloride can prevent the AR from reaching all the gold. Just be aware and deal with any residue after dissolving any AgCl in any of the processes.

Dave

 

[nickvc]

Hans may I ask if this is a one off deal and exactly how much scrap you have ?
As Dave pointed out inquarting is only really necessary if you have more than 10% silver within the alloy which is rarer than many think, British, not Italian, 9 carat yellow does and some white gold alloys do but most do not, you can simply add more copper and melt it all and pour shot which will allow the AR to work or even use nitric to remove the silver and most base metals and then use AR, the cost is more nitric for it to work in either case , the question about volume was because the more silver chloride you produce the harder it is to rinse any gold chloride out of it, even using good vacuum filtering some will remain trapped not much but some.
One other reason to inquart is if you suspect platinum group metals as they will dissolve with the silver making their recovery easier and producing better fine gold.
The AR process has fallen out of use for most larger refiners but in the past assays were done to determine both gold and silver contents and lots were mixed to under 10% silver to avoid this problem.

 

[HansW]

Dave & Nick - thanks to both of you!
I plan to do that as a continuous process, not one batch only. So I can recycle everything. As you said, most alloys have less than 10% Ag, so AgCl shouldn't be too much of a problem. I am just worried about getting swamped with Cu when throwing everything straight into AR. I believe Cu tends to partly precipitate with the Au when you get to the SMB precipitation (I plan to get rid of most nitrate with sulfamic acid).

I appreciate your time - I am sure everything has been dealt with in your forum, and I will get there, slowly, just need some quick answers.
Can you recover the Ag from the thiosulphate leach of AgCl?
My background is chemistry and I have extensive experience with cyanidation, but acid leaching is new to me.

 

[FrugalRefiner]

I am just worried about getting swamped with Cu when throwing everything straight into AR. I believe Cu tends to partly precipitate with the Au when you get to the SMB precipitation (I plan to get rid of most nitrate with sulfamic acid).

As long as you don't over do on the SMB, copper precipitation shouldn't be a problem. There is always a bit of drag down, but proper washing should remove it.

Dave

 

[4metals]

One of the issues many refiners have is dealing with the chlorides. It can be done, and often is, but it is a bit of a hassle. When you factor the probability of gold retention in the chlorides which leads to gold in your silver after reduction of the chlorides, it comes down to a question of scale. If you are setting up to do this on a reasonable scale and repetitively, then you will eventually set up a silver cell and recovery of the gold is easier. If you recover your gold by dissolving the silver bar in nitric, you are getting into a chemical wasting loop because of the inefficiency of getting all of your gold back which was retained in the chlorides.

A big factor in the determination of your method is the cost of nitric acid in your neck of the woods.

I have set up relatively small scale refiners to process up to 10 kilo's per day of karat scrap using inquartation. The benefit is you can recover all of your silver from the solution as a metal by cementation and the gold remains insoluble (with any platinum which may be in the settings) Another big factor is the ability to control the reaction. If you take a 10 kilo scrap gold bar and inquart it, and add all of the nitric at once, you will get a substantial red cloud which is not easily dealt with without some equipment specific to scrubbing NOx. Judging that you don't really want to bother with calculating the actual quantity of gold to inquart properly, I doubt the technical aspect of fume scrubbing in on your radar. But once the reaction with your inquarted alloy sees the nitric, the reaction begins. And the reaction is proportional to the amount of nitric available to create silver nitrate. Most inquarters of scale use a controlled delivery of nitric from a simple drip system to deliver the nitric to the reaction over an extended period and can usually get by without that telling red cloud. Most allow the reaction to proceed overnight and come in to a solution ready for filtration and further processing. After you do this a number of times you will determine the proper flow rate that works for you so you can feel confident adding nitric acid while you are home sleeping.

Some refiners remove the visible settings to separate the platinum from the dissolve entirely. They come out of the process with gold without PGM's and by selectively fluxing the gold when melting can remove the major contaminants of silver and copper to produce a .999 gold product without ever using aqua regia. If you are selling your refined gold to a refiner, that may be all you need to do.

Inquarting has the added advantage of recovering all of the silver from the alloy and reducing it to a meltable metal easily without hanging up gold.

I am not trying to favor one method over another and I have worked with large scale inquartation as well as large scale aqua regia, I am just trying to point out some of the issues you will encounter as you figure out what works best for your feedstock.