The Stock Pot

[kurtak]

As a side note, why aren't you using calcium hydroxide for waste treatments? It's easy cheaper then sodium hydroxide and little easy to filter off. I can buy 25Kg locally at €3-€3.50.

Correct - calcium hydroxide (lime) is the better way to go for removing the iron after using iron to remove the metals below it in the reactive series - its cheaper & easier to filter - the down side is it takes longer to react & drop the iron out then NaOH --- if the solution is too dilute &/or temps too cool it can take a few days for calcium hydroxide to do its job - where as NaOH gets the job done in dilute solutions &/or cool temps.

So I use both - depending on conditions.

Kurt

 

[kurtak]

Keven - Jason

Agitation is key to the success of cementing (ether "constant" stirring or bubbling) especially if there is a high concentration of PGMs.

I was having trouble with this awhile back with solutions with high levels of PGMs that I posted about & 4metals helped to clear the problem up in this thread :arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=21218&hilit=cementing#p219231

My first couple post explain the problem then 4metals helps solve it - hope that helps you guys as well.

When you cement your copper (with iron) the more dilute the solution is & with bubbling agitation your copper will come down finer - then if you use the copper powder - in small additions - to your stock pot - with constant stirring - it should improve your stock pot recovery without ending up with a lot of copper contamination.

Kurt

 

[jason_recliner]

Thanks Kurt.
I've seen that thread before; it makes a bit more sense now, and different sense too.

 

[FrugalRefiner]

I too use a two bucket stock pot system, with copper in the first and iron in the second. All of the precious metals are below copper in the reactivity series, so given enough time and agitation, they should all cement out completely in the copper bucket. When I move the solution to the iron bucket, the copper will cement out on the iron.

I think it is important to remember that everything below iron will also cement out in this bucket, not just copper. This means you could have a mix of copper, antimony, arsenic, bismuth, lead, tin, nickel, cobalt, cadmium, etc. if any of those metals are in your waste stream.

I'm fortunate to have plenty of scrap copper available, so I prefer to use fresh copper in my first bucket rather than take the chance of adding any contaminants back into the first bucket. This keeps the cement in the first bucket pretty clean, since this is where I expect to find any precious metals.

Another thing to keep in mind is that Harold only used a single bucket with iron. Since he processed mass quantities of jewelers' waste, this made a lot of sense. He would use a magnet to remove all the iron from the waste he received and he added that to his stock pot. In this way, any precious metals that may have been mixed with the iron, e.g., bits of gold or platinum stuck to broken jewelers' saw blades, were not lost. As the iron blades were consumed in the stock pot, the values remained in the sludge.

I guess it depends on what type of scrap you process, and what processes you are able to use to treat the contents of your stock pot. Just keep in mind that it's not a clean, simple matter of PMs cementing on copper and copper cementing on iron.

Dave

 

[kadriver]

Great info here, thanks to all who responded.

About 10 days ago I had 5 rings, I concluded that all were 14k but one was platinum And unmarked.

I did a gold test with 14k acid and it LOOKED like 14k gold.

As I inquarted I began to stir and the one ring was not melting very well.

I pulled it up on the side of the melt dish and added heat and part of it went into solution/alloyed with the molten gold and silver.

I pulled the remaining part of the intact ring out of the melt and put it in with other scraps of Pt that I am saving for later on after I have gained some more experience with PGMs.

After making flakes from the melt, I treated with dilute nitric acid and then tested the silver nitrate with stannous.

Sure enough it was loaded with platinum. I added this to my silver jar for cementing later on.

I processed the gold in the normal manner with AR and the waste (I call the left over SMB liquid after the gold has been precipitated, waste) was tested and showed high level of Pt also.

I added this waste to my stock pot that is charged with at least 20 pieces of fresh copper metal from cut-open copper tubing.

Last Friday I added about 5ml nitric acid to see if that would help get the platinum to cement out - stirring manually several times a day.

I was going to siphon my stock pot liquid (settled overnight) to my iron bucket today but first did a stannous test and bang, still platinum clearly visible (see picture).

I am going to get several aquarium bubblers and use these to start agitating the buckets. This Pt has been in the stock pot for about 10 days and it refuses to cement out completely.

This stock pot info has all been very helpful. Thanks again to all who gave input.

kadriver

 

[kurtak]

I think it is important to remember that everything below iron will also cement out in this bucket, not just copper. This means you could have a mix of copper, antimony, arsenic, bismuth, lead, tin, nickel, cobalt, cadmium, etc. if any of those metals are in your waste stream.

Dave

Very good point Dave.

I'm fortunate to have plenty of scrap copper available, so I prefer to use fresh copper in my first bucket rather than take the chance of adding any contaminants back into the first bucket. This keeps the cement in the first bucket pretty clean, since this is where I expect to find any precious metals.

Due to the fact that most of my PMs come from dirty sources (electronics, contactor points etc.) I also use nothing but clean copper for cementing stock pot values & because I scrap metals in general I never have a shortage of clean copper on hand --- the copper I recover from cementing with iron gets melted & poured into 2 pound bars & sold as red brass to the scrap yard.

I guess it depends on what type of scrap you process, and what processes you are able to use to treat the contents of your stock pot. Just keep in mind that it's not a clean, simple matter of PMs cementing on copper and copper cementing on iron.

Correct - if I was processing more - or nothing but sterling &/or coin silver & karat/dental scrap & didn't scrap other metals (which provides a cheap source of copper) I would then likely use my copper recovered from the iron cementing process --- but only then.

kadriver,

If there was a relatively high concentration of PGMs in your AR stock pot it may have already formed the passivation layer of PGMs on your copper that was giving me troubles which 4metals helped with (agitation) in the thread I provided a link to in my other post --- this passivation layer maybe somewhat of a problem if you try to re-use it in your AR stock pot - even with agitation now added.

At least it was for me when I tried re-using it in my AR stock pot after I got my bubbler --- so what I have been doing is adding my copper with the passivation layer to my silver nitrate solutions when cementing my silver - the silver nitrate seems to get under the passivation layer better then in an AR solution & the PGMs are then being recovered in the anode slime from the silver cell.

In fact if the AR stock pot has a "high" concentration of PGMs the passivation problem can still be "somewhat" of a problem - even with the bubbler - though certainly not as bad as without the bubbler.

I have found (since the discussion with 4metals) that when higher levels of PGMs are involved "fine" copper powder on the magnetic stirrer works better - you want to do it with small additions of copper powder - with time given to each addition to insure that all the copper has had time to dissolve & go into solution - more time needs to be given between additions as it nears the end - so there is a bit of a learning as you go curve - & of course stannous testing as you go near the end.

Here is a pic of a bus bar (right) used with a bubbler in AR high in PGMs - compared to one used to cement silver (left) first day in the bubbler most of the PGMs came down but still had a PGM positive stannous test --- 3 days later it was still testing PGM positive so stopped it & went to copper powder on the magnetic stirrer - a few hours later I had the rest of my PGMs with a negative stannous test.

Kurt

 

[kadriver]

Excellent Kurt, I got two aquarium bubblers today at WalMart, about $7 each.

I have 5/16 clear tubing with a 12 inch length of rigid tubing at the end to keep it directed at the bottom of the buckets.

Copper powder, magnetic stirrer treatment for stubborn PGMs - that is very good to know.

Also withdrawing copper with passive layer from the stock pot and using it to cement silver, I never would have done that. Thanks for that tip.

I concluded that after the PGMs are cemented with the stir and copper powder that the solids are returned to the stock pot.

Great info - thank you!

kadriver

 

[nickvc]

As has been said it really does depend on the quantities and sort of materials you refine and recover as to what the best route is with stockpots. I always had a settlement tank to allow any fines to settle to the bottom with added precipitant then two stockpots the first loaded with copper the second with a little steel added fresh every time it was full. The last stockpot contents were added back into the first every now and then depending on how much material I had in my system, the last stockpot I worked on the theory if I could cement copper out all the values especially any PGMs should have also been cemented out and could be recovered later from the first stockpot.

 

[jason_recliner]

As a side note, why aren't you using calcium hydroxide for waste treatments? It's easy cheaper then sodium hydroxide and little easy to filter off. I can buy 25Kg locally at €3-€3.50.

Correct - calcium hydroxide (lime) is the better way to go for removing the iron after using iron to remove the metals below it in the reactive series - it's cheaper & easier to filter - the down side is it takes longer to react & drop the iron out then NaOH --- if the solution is too dilute &/or temps too cool it can take a few days for calcium hydroxide to do its job - where as NaOH gets the job done in dilute solutions &/or cool temps.

So I use both - depending on conditions.

Kurt

I've just exhausted my NaOH on my waste so I'm going to buy some calcium hydroxide as per your excellent suggestion. Here's a follow up for anyone else playing at home.
It's a bit hard to buy "calcium hydroxide". As I researched bulk limes, you might find the right one in your local Bunnings / Mitre 10 / Lowes as "builder's lime" or "hydrated lime". On the other hand, "lime" from the garden centre may well be calcium magnesium carbonate. Just keep an eye on the fine print or MSDS.

 

[MarcoP]

I was finally able to find the english product's name of what I'm using: lime wash paint, basically slaked like (calcium hydroxide) in water.

 

[kurtak]

Calcium carbonate works just fine - it's what I use - I buy what is called "barn lime" (used by dairy farmers to spread on their barn floors) any feed/farm supply store should have it & it is dirt cheap - it takes 2 - 3 days with stirring it a few times a day to complete the reaction.

Kurt

 

[4metals]

The moderators would like to thank all of the members that contributed to the original thread upon which this thread was based, as well as those that asked questions showing what was missing. Because of the extra length and interest in this thread we have created the above consolidated version making for an easier read. We encourage all members to read, comment, and ask questions in the original thread, The Stock Pot

The Library threads should not be considered to constitute a complete education. Instead, they're more like reading a single book on the subject of recovery and refining. There is so much more information on the forum, and it is impossible to include it all in these condensed threads. Members are strongly encouraged to read the rest of the forum to round out their education.

For those who prefer a printed copy, a pdf file of this thread is provided below.