getting started 50/50 braze alloy

[ItsASecret]

Greetings all.

I have been accumulating scrap with high PM content for several decades and now want to cash out.

I am hoping some of you would be willing to share insights you may have on how I might best achieve parting of the PMs. I would like to increase my return with a modest investment of time and money for PPE, glassware, etc. as well as risk - all endeavors have it. By my estimation the cost of the needed PPE and handling / processing equipment are easily justified by the increased return. I have a suitable hood / ventilation system as well that will handle the fumes.

The most immediate questions are:

??-What concentration of Nitric Acid should I purchase? This is in light of the 'special circumstance' below. I understand that I can 'always' dilute but concentration costs...
??-How much Nitric acid at the purchased concentration should I anticipate needing? Of course I would like to minimize waste and disposal issues.
??-Is my overall assessment of methods (below)correct?

I have something like 2000 grams of high purity alloy that is a mix of Au / Cu. Some is 50/50 and some 35/65. I can't reliably distinguish between the two. I also have a similar weight of Ag /Cu high purity alloy and some much smaller quantities of alloy that contain unknown portions Ag, Au, Cu and possibly other metals. All are 'high purity' virgin alloys that are used in the electronics industry. None contain tin or lead etc. All of the material is in wire and foil forms that are thin so, there is a high surface area per unit weight/volume.

According to my research so far, which is primarily focused on the highest return lot of Au/Cu, it seems that my best option is to use heated Nitric acid with agitation at high or full concentration to get the Cu into solution. I found references that suggest to me that commonly stated inquartation ratios often exceed the required level at least in some circumstances. In the reference, a button was used and there was no indication it was reformed to increase surface area before parting. Taken together these two points suggest this is at least worth a test. To the extent that it doesn't work, it will fail only for the 50/50 alloy.

?? Assuming I can actually get the Nitric acid at or to the necessary strength, is this worth attempting? Should I attempt an alternate method -inquartation with Cu? Since Nitric acid will be needed from what I can see in every case, It would seem to best to get the 'good stuff' and dilute as needed. Am I ok so far?

I have looked into electrolytic methods a little. Were I to use this method, most approaches start out melting down metal into anodes. Melting means I loose the possibly optimal state the alloy is in now. Would a stainless steel basket to hold the material as-is work? Another metal? This would seem to be an opportunity to contaminate the system with metals not otherwise present. In any event, I still end up needing Nitric acid for this process along with a donor Au anode cathode for (of less purity?) for the second electrolytic step. and I am not sure what more I will have to do with the first stage slimes which should be pure Au. I would hope wash, melt and make electrodes for purification would be all that is needed since the starting alloy had no other metals - only Au/Cu.

Another problem with electrolytic process is that I would have to cast (for parting) alloy around a pure copper core. This I can probably do. It would help prevent contamination by other metals (fasteners) while permitting complete dissolution of the alloy portion of the electrode. Not at all sure how reliably I can make a 'popsicle' that will have good fusion of alloy so the last bits of alloy won't fall off as the end of separation approaches. This is braze metal though so probably that will take care of itself.

Summing up, It appears that the electrolytic process is more complex and will leave me with an electrolyte solution and possibly sacrificial electrode pieces that will contain more than trace Au that will still need to be recovered. Since my goal is not absolute highest purity or an ongoing process, the electrolytic process may not be warranted. The acid precipitation and electrolytic methods both involve Nitric Acid at some level. So, at the limited scope and scale of this effort, my best option is probably acid precipitation. The worst case for the acid parting will leave the 50/50 alloy intact which I can then inquart to a lower concentration and proceed as before.


Thanks for your time and I look forward to any insights you all can offer.

 

[snoman701]

You won't get a better price processing that amount yourself than you can from a competitive buyer. You should be able to get 80% on the Ag and 98% on the Au without looking too hard for a buyer.

 

[nickvc]

I agree with Sno here, all you need to do is melt the scrap into bars keeping the alloys separate and assay or get an xrf reading on them then you know what you have and what to expect in regards to payment.

 

[ItsASecret]

sno and vic

Thanks for your input. I will run some more numbers and find a place I can get the XRF done.

I know I should know this but what are the percentages based on? I assume the weight of the PM - but at what purity?

So long as I have a precise weight and independent XRF, what would be the need to melt down? Is this down to the narrowness of the sample window on the device? Is it just - to put it bluntly - to keep everyone honest or maybe better said, avoid temptation?

IAS

 

[nickvc]

Unless you have a product that can be easily identified by melting you have one piece of material that can be weighed and valued by both parties.
With an xrf reading you will get a percentage of precious metals in the whole bar.

 

[ItsASecret]

Nickvc.

I wasn't thinking about ID. Just the fact that the stuff isn't homogenous. Some proportion is 50/50. So, 'seeing' more or less of it could skew the reading. There is definite merit in homogenizing the material if I don't refine myself.

Anyone
Comments on the electrolytic separation and having the material held in a basket? I seem to recall seeing plating operations where AG or AU nodules were held in baskets. My memory may be faulty. It may have been PM buttons suspended by wire. They are almost the same thing but only the basket would work for my material. Current density and proportions of surface area being the main differences.

As I think about this further, an initial step with the scrap material in tray (or even laying on a copper screen or grid on the bottom of the cell might work. There would possibly need to be several screenings and or concentrations to separate out all the copper but getting rid of a significant fraction of the Cu this way seems at least worthy of a little more thought.

IAS

 

[Martijn]

From what I've learned so far: For electrolytic separation you need the target metal that you want to plate out in a relative high purity as anode bars. Over 98%.
A too high content of non target metal will pollute your electrolyte really fast or your anode bars will get covered in a passivated layer the current can't get to, stopping the ionization process.

The silver nitrate cell needs almost pure silver anodes.
The copper sulphate cell is good for almost pure copper anodes.
The sulfuric stripping cell is used for stripping pure gold plating from copper or brass items.
The first two capture the values in an anode basket, the latter collects the liberated gold dust on the bottom of the cell.

Using a copper basket will only work in concentrated H2SO4, otherwise the copper basket will dissolve.
An anode bag to catch the values or the impurities is used in stead of a basket with the other electrolytic processes.

If you separate the 2 different alloyed wires and plates, and have them XRF analyzed, it will be easier to sell. Or at least get an offer on to make a decision.

You can take a bit and inquart that to get some experience and to see if it's worth it for you to refine the lot.
In your case with a pure Au/Cu alloy, inquarting with copper in stead of silver may be best to keep silver out. Nitric consumption will be higher with copper.

Martijn.

 

[etack]

The gold strait to AR no need to inquart it will just make another step to filter. you will need to refine the powder again. The Ag, Au, Cu mix will need XRFed to know what it is. this could be mixed with some of the silver braze to then digest in nitric and recoup the gold; drop out the Ag with Cu.
The silver brazing is low grade trash sell it to a refiner or a person that would use it in another process.

Eric