PGM's not cementing on copper

[markbones]

Hi, new here but not new to refining. We have a solution inn the shop of aqua regia which is loaded with platinum and palladium, about 2 oz Pt an 1.5 oz Pd per liter. It has had a copper buss bar and aeration for 2 weeks now and is still showing a stain on stannous chloride. Any suggestions to get it to drop?

BTW I was told about this site by a friend who is a consultant and it is an amazing site.

 

[publius]

Platinum will always show "staining" even in very dilute solutions. It is better to concentrate the solution then cement or precipitate. Why are you using aeration?

 

[markbones]

Thanks for the reply,

The solution is concentrated and it is being cemented; or trying to be. Aeration just keeps the solution moving and cements it quicker. Some sludge has come down, but there is a heavy and fast to develop Pt stain after 2 weeks with copper in the solution.

The same treatment on waste acid leaves the acid free of precious metals overnight.

 

[Barren Realms 007]

Thanks for the reply,

The solution is concentrated and it is being cemented; or trying to be. Aeration just keeps the solution moving and cements it quicker. Some sludge has come down, but there is a heavy and fast to develop Pt stain after 2 weeks with copper in the solution.

The same treatment on waste acid leaves the acid free of precious metals overnight.

Is your solution conentrated down to a syrup or down to where salts start to develope and settle to the bottom of your container?

How much surface area of copper to volume of solution do you have?

You might need to increase your surface area of the copper you are cementing with and slow down your areation of your solution.

And then of course there is patience involved as well. 8)

 

[4metals]

Welcome to the forum

Cementation never suffers from good agitation. Is it possible to filter the solution and see just how much of the expected yield dropped? Getting an idea of how much is left in solution is helpful.

Do you have any idea how much copper went into solution? 2 weeks is a long time.

 

[Westerngs]

Another possibility is that the pH of the solution may be too high. Above pH 4 the copper starts forming hydroxides on the buss bar and stops the reaction. I know you said the solution is aqua regia,but high pH is a possibility.

 

[markbones]

Thanks,

I will filter and weigh the precips that have come down and check the pH.

 

[markbones]

pH is .42 actually higher than I expected but still strong acid

Sludge was dried and melted and shows 62% Pt 31% Pd on the Xrayz bar weighs 65 ounces.

About 1/3 of the PGM's still are in solution from what we recovered and starting assays.

 

[markbones]

How much surface area of copper to volume of solution do you have?

You might need to increase your surface area of the copper you are cementing with

We have a 30 gallon tank with 10 4" wide buss bars hooked around the rim and hanging about 18" in solution. That is a lot of surface area of copper.

 

[Harold_V]

How much surface area of copper to volume of solution do you have?

You might need to increase your surface area of the copper you are cementing with

We have a 30 gallon tank with 10 4" wide buss bars hooked around the rim and hanging about 18" in solution. That is a lot of surface area of copper.

Inspect the bars to see if you are achieving a hard coating. If so, they are isolated from the solution. Might be helpful to lower the pH, assuming it's above 2.

In my worst examples of recovering traces of the platinum metals from silver solutions, I'd achieve full recovery in no more than two days. Something isn't making sense here.

Harold

 

[skippy]

Maybe it's palladium redissolving from the cemented values?

I never had much luck cementing on copper when dealing with large volumes of cat solutions, although I usually had excess nitrate in solution. I ended up using steel wool or wire, which works pretty rapidly. I liked the steel wool a lot, but it's expensive, I think thin gauge sheet would work too, roof flashing steel or something like that.
I found it important to not let the amount of unreacted steel to get too low, otherwise the solution would start to redissolve the cemented pgms. This was in SSN. The worst part of that was this produced a certain amount of nearly unsettleable values. However, if there was always lots of steel available for cementing, then the cemented metals maintained their easy settling properties. Maybe a back asswards way of proceeding (instead of denoxxing) but for me it wasn't practical due to the large volumes of solutions from cats, and the large quantities of dissolved salt in SSN.

 

[kurt]

I was having the same problem on a small test I was performing on some old telcom contactor points I have been working on. Most of them dissolve in nitric & are a Ag Pd alloy (DMG test drops Pd yellow & HCL test drops Ag chloride) but some of them go un-dissolved in the nitric --- so I put some of the un-dissolved points in AR & stannous test showed positive for PGMs.

I took a test tube sample & did a DMG drop for Pd (added DMG till no more Pd yellow precipitated) did a stannous test & got a Pt positive.

I took the rest of the solution & put in a copper bus bar & it started cementing but then it stopped. – Same thing – 2 weeks & it just was not cementing any more of the PGMs --- So I diluted it & warmed it – still would not cement any more of the PGMs.

So 2 days ago I decided to add some nitric & warmed it (set it out in the sun) & it finally cemented the remaining PGMs

My assumption is that in a PGM concentrated solution it starts to cement but then the PGMs form a tight bond on the copper preventing the acid from reacting with the copper & continue the cementing process --- so again my assumption is that by adding some free nitric (after the original cementing has stopped) to keep an acidic reaction going on the copper brakes the tight bond &/or prevents the PGMs from forming a tight bond that stops the cementing.

Kurt

 

[NoIdea]

Hi Kurt, Just a wee thought, instead of adding addition acid to your precipitation bath in order to reactivate your copper bar(s), could you not take the copper bar(s) out and have then form part of a electrowining cell with the bar(s) being the anode.

Small current should remove just enough copper underneath to be able to brush off any PM's, ...... maybe :?:

Deano

 

[kurt]

Interesting idea Deano - I actually considered trying that but had just burned up the power supply I was using to run my silver cell & I also had just sold 4 barrels of power supplies. I had held out three 3.3 V 28 amp supplies as back up's but it turned out none of them worked.

Seems like all the computers I have been getting in lately have a lower amp rating on the 3.3 volt out put (between 14 & 18 amp) & when I try to run those they only run for a short time then burn out.

I just got in another 8 computers yesterday & haven't checked out the power suppies yet - hopefully there is a working 3.3V 28 amp supply in 1or 2 of them.

Kurt