Advice needed on pfm/ white dental.

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Hova19

Active member
Joined
Jul 21, 2019
Messages
36
Hello, I have 4 bars of melted together pfms and white dental weighs around 1.8kg . Some of the bars are not completely homogeneous but they average around 20% AU and PD (between them) about 10-15% copper and loads of base metals on XRF, I added 10% copper to each melt in the hope of a more homogeneous melt. I have done the yellow crowns seperate.

What would be the best way to recover AU and PD (I am only interested in their values) . I am seeing mixed things in Hoke's it says to go straight to AR but then some posts on here say a nitric boil and I should be able to recover the PD out of the solution. If the gold or palladium has contaminants that is fine, I just want to be able to put a value on my material.

I am already aware of the dangers of handling this material and i am in the process of purchasing the correct safety equipment. I just need a point in the right direction how is best to handle this material for when I am ready.
 
If the bars are not homogenous then you cannot assume anything.

Send one into Sheffield assay office and pay them for a melt and assay. Stick a picture of the assay up here for us to look at.

They won't take long and you'll know exactly what you've got.
 
I don't think Sheffield is doing melt and assay at the moment? . It is a assumption but some of my material is homogeanus and over the past 2 years it's been from 15%-30% gold and palladium content.

Rest of the metal silver 10%-15% and small percentages of titanium cobalt hafnium manganese and others I can't think from the top of my head.
 
I can understand why you wish to do this after your last experience but f you want to refine or should I say recover the values melting is not perhaps the way forward.
My suggestion would be to make sure you have a good fume hood as you will at some point be dealing with PGMs in solution, also proper chemical gauntlets and protective aprons, those salts are highly toxic.
Then I’d try individual pieces in a variety of acids starting with Hcl to see if you get any reaction, if no reaction rinse well and then try dilute nitric which may well dissolve some of the base metals plus any silver and palladium and with enough silver possibly platinum leaving the gold and some of the base metals. If this is the case then dissolve what is left in AR which should allow the recovery of the gold and possibly platinum if present.
The mix of metals could well cause some problems if you were going after pure metals but I believe that is not your purpose but simply a way to produce a bar or bars of easier to assay materials, that been the case then total dissolution of all the material in AR may be the way to go which would leave the silver as a chloride but all the other values in solution which would need filtering before cementation to recover the values, the recovered powders could then be melted but I would suggest perhaps using Sheffield to do this as melting PGMs is not easy to get a good homogeneous bar to sell.
The other point to remember along the way is that you are going to create toxic solutions that will need treating properly or been disposed of to a licensed waste disposal company, that can be expensive but provides you with cover in these litigious times.
 
Thanks Nick that was exactly the information I needed, that's all I want at the moment to produce bars of easier to assay and sell bars . Down the line I would certainly like to have some fine AU and PD, but right now i just need the materials separated so i can sell. It's easy with the yellow crowns as I can just add copper and the melt comes out fine.

I am looking into a fume hood and I won't be starting until I have one. I have a friend in hazardous waste who can dispose of the solution correctly.

I have another 800g removed from root but still can't get all porcelain removed would it be wise to melt them with silver instead of the copper I have been using ( trying for homogeneous bar) now that in the future I want to dissolve them. Would the best way to deal with the PD is to cement with copper and let Sheffield deal with it?

I should add In the dental around 2-2.5 kg of dental I have had in last few years have only had a couple gram of pt in one assay.
 
Thanks Nick

One thing I would add is that you need to look at the commercials. How much more money would you make by processing it yourself?

On the one hand an assayed bar will sell at a certain price with the paperwork to back it up. Refining it further will still have the same amount of metals. How much does it cost in time and equipment and how much more would you realise?

Try it by all means however I think you'll find that your time is worth far more than the uplift you may or may not get.
 
Normally I would just send for a full melt and assay. there is two companies called king refining and simple (they don't actually refine anything) can witness the melt but they are shut. they are different companies but they sort of work together they buy dental around UK melt together in a homogeanus bar and sell on, they can actually get a good homogeneous melt for assay. They claim ( I know they would say this to help there business) that Sheffield and guardian can not get a good sample from dental work and it is best letting people who deal with it all the time because of its specific blend.

At this point in time I don't trust anyone enough to send them my material to do a melt and assay if they wanted to buy it( wouldn't mind Sheffield as they have no gain from a false assay) . If I could get fully homogeanus and get a good sample myself yes but I wont be giving money away again by sending material to sell blindly.
 
I do not know how well it would work, an assayer may able to answer, can you take several drill samples and have them assayed similarly to sampling a claim to get at least a general Idea...
 
I don't actually know of anyone offering a melt and assay at the moment with the lockdown and don't know when I they will be doing them again.

Nothing is local either most places that do analytical test is about 150 miles even jewellers and gold buyers local don't have XRF.
 
Even if Sheffield did the melt and assay I can almost guarantee the top and bottom samples will be different and the assay will be the mean of the two.
I’m not too sure that with PGMs and gold mixed you will ever get a true homogeneous melt depending on the quantity of PGMs, bars melted that have PGMs in them tend to be brittle and shatter if hit with a hammer or even dropped on a hard floor, I’m not sure but I suspect the Pd is the problem, perhaps Lou could give some advice as he deals with PGMs on a regular basis.
 
Would there be companies willing to pay on their assay ? Or would they want to do there own. Wouldn't want to pay for one and then companies not want to accept it anyway because its dental.

Seems dental is a tricky material do deal with from melting to assay, I was hoping with the correct melt and icp you could get very accurate results of what exactly was in the bar.
 
Most buyers accept Sheffield’s assays as they are normally very good and the bars are stamped and as they are independent they favour no one.
A quick phone call to your buyer or potential buyer should answer that question very quickly.
 
I am waiting on a reply from Sheffield assay office to see if they will do it for me at the moment, they have just reopened two days a week on Wednesday and Thursday so fingers crossed they are not just doing specific types of work. If they can I will find someone who will accept their assay. I just want paying for all the PM and right now I can't see places offering them, gold traders UK are still buying PM but not on a melt and assay basis.
 
Just had a look, they pay £8 more per gramme as a trade customer than what I would get.
Hopefully I can get assay sometime soon from Sheffield and maybe get more than the 80% spot price on PD that I get now.
 
Will post the assay results next week, hoping for 20% of it to be split between au and pd
 
Got the results back today, looks like they had to double the weight in copper to get good results.

PD 265 6 gramme
AU 75
AG 52.8
PT 2.9

Delighted with the results and the turnaround time especially during current times.

Now to find the best place to get paid, I wouldn't mind sacrificing AG and PT if it means I can get a higher price per gramme on PD, up to now have found 45.09 on PD that will accept Sheffield assay
 
You are been offered 88% of spot for the Pd, I’m guessing they are offering 94% for the gold, that’s about the best you can get unless you supply more metal more often or go to someone like Inco as was, I believe they were purchased by Vale some years ago, who will pay more but you had to wait I believe 90 days for settlement.
 
So it's a good deal i suppose since payment is same day as they receive your material.
Thank you nick for all your help, was my best move going to Sheffield for a independant assay.
 

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