AP process questions

[pslyde]

I'm using the AP process.
After removing gold foils, I pulverize the material, add HCL, and drip (high-concentration) H2O2 over time to oxidize the remaining metals. When the reaction stops, I add a bit more of each and let it sit for 24 hours. After filtering, I heat to just below boiling for 24 hours (adding distilled water as needed) to remove oxidants. Then I use SMB to precipitate gold over 24 hours. After filtering, I do another round of SMB, just in case I missed any. I've gotten a fair amount of gold precipitate, and I believe I know how to process it out and refine the gold. But I'm a little shaky on the other metals.

Silver: precipitate from AP mix with salt (non-iodine). Then what?

Am I correct to assume that copper will cement all ions higher in the reactivity series, ie: gold, silver, platinum, mercury?
Would the rest of the platinum group cement with copper?

Am I correct to assume that iron will cement out copper, along with the lesser amounts of bismuth, antimony, lead, tin, nickle, cobalt, and cadmium that may be present?
Is there a way to remove all metal ions from the solution?

Basically, what I want is pure gold, pure silver, an amalgam of remaining PM's, and an amalgam of the remaining metals.

P.S. First post!
Been lurking for a while under a friend's username. There is a great deal of information on this site, and I'd like to particularly thank harold_v, lasersteve, and palladium for their contributions.

 

[FrugalRefiner]

pslyde,

Welcome to the forum under your own identity. I'm a relative noob myself, but it looks like there are a few things you don't understand yet.

Once you've precipitated your gold, you should finish all of your washes and drying in the same vessel. It avoids having any of your gold tied up on the filter.

You don't need to precipitate silver out of an AP solution. Silver will not go into solution to any detectable degree in AP. Any silver in your feedstock will be in the form of silver chloride (AgCl) precipitated in the bottom of your AP.

Copper will cement ions lower in the electromotive series. Most tables will show the most highly electromotive ions higher on the table, and those with lower values lower on the chart. It's easier to remember that way. Yes, copper will cement these metals out.

Once you've used iron to cement out the remaining heavy metals, you can neutralize the pH and the iron will drop out leaving salt water and iron oxides / hydroxides (I believe that's right, please correct me if not).

I'm sure you've read this during your lurking, but everything you want to know is on this forum, but you have to do the work by reading it. Hear are the standard links I provide to new members.

Safety
Guided Tour
Refining Precious Metal Wastes
Forum Handbook Vol 1
Forum Handbook Vol 2

Dave

 

[pslyde]

Thanks for the thorough reply. I wanted to do a bit of reading and thinking before I responded.

Though I usually use the same vessel I drop in, sometimes I have to filter. I understand that some gold will be left behind in the filters. I can rinse them and recover a portion. Later I plan to incinerate them and process the ashes. But that's a thread for another time...

Based on your comment, when I do an initial filter on my AP bath, part of my solids will be silver chloride? So maybe if I get a small amount of nitric acid to dissolve the AgCl, then cement that out? I really didn't want to deal with nitric acid quite yet.

I did not know that even high-concentration AP would not dissolve much silver. How do you recover what little silver would be in solution without cementing it along with the other PM's?

What about the other platinum group metals?
With the price of platinum these days, perhaps I should separate that, too. I believe I read that platinum salts will precipitate with ammonium (something), which can be made from ammonium hydroxide and sulfuric acid. Is this correct?

What do you use to neutralize the liquid's PH to drop the remaining metal ions? I must have overlooked that part. Maybe pool or aquarium PH chemicals? Please forgive my laziness on this aspect, I'm no where near the PH neutralizing step, just curious.

 

[butcher]

pslyde,
My friend, from your questions and thoughts,It definitely sounds like you have a lot to learn before you are ready to put acids and metals together.

Silver in acidic chloride solutions will not dissolve, if you put a solid piece of silver in HCl the outer layer would oxidize and quickly build up a layer of silver chloride which would stop the attack of the acid on the silver this white crust of passivated silver protects the rest of the silver from further oxidation, if this is some thin powders or something like thin solder it may break down to silver chloride, a milky insoluble or clumping to fluffy lumps of insoluble silver chloride which if let settle will settle to the bottom of the vessel, the silver chloride if stirred can stay in solution for a while as they float around easily but will settle again given a little time, in the Copper II Chloride leach (acid peroxide), silver will settle to the bottoms as white powders, but silver is not the only insoluble chloride salt, lead chloride or copper I Chloride are also insoluble, and your white powder will be a mixture of these.

What about the other platinum group metals?
With the price of platinum these days, perhaps I should separate that, too. I believe I read that platinum salts will precipitate with ammonium (something), which can be made from ammonium hydroxide and sulfuric acid. Is this correct?


Nope not correct ammonium hydroxide with sulfuric acid would give ammonium sulfate salt and water.
NH4OH + H2SO4 --> (NH4)2SO4 + H2O
Platinum can be precipitated from solution using ammonium chloride, but you will not have to worry about that here there is no way you are going to put platinum into solution with the Copper II Chloride leach (incorrectly called acid peroxide), platinum would not dissolve in this solution.

Nitric acid will not dissolve silver chloride, HCl will not dissolve silver chloride, and sulfuric acid can convert it to a fairly insoluble silver sulfate salt.

Why are wanting to adjust pH of the solution to precipitate other metals, the leach solution is re-useable until contaminated or you wish to dispose of, then you treat it as waste, if for some reason you screwed up and dissolve gold by adding too much peroxide you can cement it out using copper metal to replace the gold from solution, copper in solution can be replaced using iron metal, although some other metals will also cement out of solution with your copper, read dealing with waste for further discussion of the process and to learn how to treat your waste responsibly, so you are not poisoning people with it.

Please forgive my laziness on this aspect, I'm no where near the PH neutralizing step, just curious.

I can overlook not understanding something, but I do not overlook laziness, put up those dangerous acids and toxic metals, and stop fooling with something you are too lazy to study about, get off your lazy duff and pick up the books, do not pick up the chemicals until you study enough to use them safely, stop making deadly toxic waste until you understand how to make it safe, I do not want you to poison the drinking water in your area hurting or killing others because of your ignorance in dealing with waste, and laziness to learn about pH neutralizing step, for your own safety you should have learned about neutralizing acid before you even bought the acid.

This swift kick in the hind end is meant to get you up off your duff and your face into the books, it is not meant to insult you, I will help you learn but you have to work for it, seriously put up those acids you will only lose your gold and hurt someone, unless you educate yourself first, there is too much to this too many dangers, to take it lightly mixing up acids and metals, making toxic metal solutions and salts you do not know how to deal with.

Start with reading the safety section and dealing with waste.

I say this above in friendship, trying to help you understand how dangerous the road you are on is, and to hopefully get you off the dangerous road on to the road that will get you where you wish to go, to the gold safely.

 

[pslyde]

No insult taken. I appreciate the input.

I know some of what I'm doing, but obviously, not all. I constantly read, but sometimes it's difficult to get the straight scoop. There is a lot of great info on this site, but a there is also information that is inaccurate (hard for the mods to catch everything) or worded in a confusing manner. Not to mention that there are many sites with half-truths and outright lies that I looked at before finding this forum. Sometimes I get sidetracked and forget where I found the information before I took notes, so I get a mistaken impression of how something works.

I do follow safety principles very carefully (I only have two eyes and lungs). I know how to kill the acids quickly and effectively; I just didn't know how to balance ph in the solution. But I do now.

I am approaching this right now from an experimental aspect. I've had success recovering gold, but the rest will take time to learn. If I can't get this figured out (to a reasonable degree) soon, I may have to get a consultant. I intend to scale up massively once I have the process down.

I have more questions, but I'll compose them (and research first) a bit more carefully than I have time for at the moment.

Again, thank you.

 

[butcher]

pslyde,
You will do great, it takes a little time to learn, when we first begin to learn a complicated field of science at first many things are confusing, but if we stick with it many things begin to clear up, and it makes learning easier, not that we would ever be able to learn it all, and that too is OK because if there is always something to learn about it, then the fun never ends.we do need to focus on understanding something before we jump in with both feet, especially when there are dangers involved.

P.S, I also know some of what I am doing, not all, I will continue to work to learn more, in many ways I see I still know very little, seems the more I learn, the more I find out I do not Know.

Too I know your not a lazy man, and you will do what you need to do to learn, I have to admit I was hard on you, but laziness as you know can get someone hurt when it comes to safety, I also have a thing about laziness I cannot stand it(it has never helped anyone).

 

[solar_plasma]

I use AP on my Cu-contaminated Ag anode sludge from copper refining method and H2SO4 on my low grade sludge, - mostly Ag-containing kathode copper. Last one in order to make fresh CuSO4 electrolyte.

Now I wonder, if the HCl/H2O2 also will form some traces of AgCl from the silver, when all Cu is dissolved? Ok, it will not make the great difference, since it has to be refined thereafter, but if there was a bigger amount to be expected, this would have influence on my weight calculations.

 

[butcher]

Silver dissolves in dilute nitric acid.

Silver can also be dissolved into hot concentrated sulfuric acid, but will not be attack much by the dilute cooler sulfuric acid.

Silver will not dissolve into a chloride solution to much of any extent.

In the dilute and weaker copper II chloride solution, (or HCl / 3% H2O2) no silver would go into solution, although the acid can form silver chloride as it would oxidize the silver (at least at its surface), below I will discuss what may happen depending on the alloy or other conditions of the silver.

Silver will passivate in aqua regia forming a crust.

In strong acidic chloride solutions, and highly concentrated like aqua regia a very small amount of silver will go into solution as AgCl2 (A higher oxidation state than silver chloride AgCl, but the solution will not hold much of the silver in this higher oxidation state), when this solution is diluted the AgCL2 will precipitate from the solution as the insoluble AgCl as white powder.

Silver metal will passivate in an acidic chloride solution, with the HCl, copper II chloride or aqua regia, the outside layer of silver is oxidized by the acid and forms a crust of silver chloride, since this will not dissolve into solution this passivated layer or crust will protect the silver or other metals below this crust from being attacked (unless this crust was removed to expose new metal).

Powders can be a bit different as the particle size is very small, basically the same thing happens, but much more of the silver can be exposed to the acids and form silver chloride, in this case you could have most or all of the silver converted to silver chloride, if all of the silver is exposed to the acidic chloride solution, but here again there may be instances where not all of the silver is exposed, or forms the crust to protect some of the silver.

If a metal was treated in an acid chloride solution and this metal would dissolve in the acid chloride solution and silver was part of the alloy but the silver was in low enough concentration of this alloy, the metal would dissolve, the silver would also form a silver chloride as it is oxidized by the acid, but since the silver is so dispersed in this original alloy, the silver not be in a large enough concentration to form the protective crust, in this case as the metal under the silver chloride dissolved the silver chloride would just form insoluble chloride powders flake off and settle as the other metal was oxidized into solution.

Silver chloride is insoluble in acids, so nitric acid, HCl, and even aqua regia will not dissolve it, silver chloride is also insoluble in a dilute sulfuric acid solution.

If the silver chloride was boiled in the sulfuric acid the chloride can be driven off as gases on concentration, HCl gas is more volatile and will leave solution on concentration, and the silver can be made into silver sulfate, silver sulfate is soluble in the concentrated acid but not that soluble in dilute solution or water, basically silver sulfate is only slightly soluble.

If we have insoluble silver chloride in a solution of dilute sulfuric acid and add an elemental metal higher in the reactivity series, we can convert the silver chloride back to silver metal as powders, the other metal donates electrons to the silver and this other metal itself is oxidized and goes into solution.

Silver chloride will dissolve as an ammonium complex, if treated with ammonium hydroxide, or strong ammonia solutions, the silver chloride will dissolve as an amine in solution, note this solution can be very dangerous if dried, so it is always acidified afterwards to precipitated the silver from solution as silver chloride, and to make the solution and powders safe again, also you should keep ammonium solution out of your normal stock posts or waste solutions, keeping them separate and dealing with this waste solution separately from your other waste.

So I guess if I understand the question, the answer is yes you can form silver chloride with the HCl,
But the silver chloride is insoluble, and copper II chloride is soluble.

 

[solar_plasma]

So I guess if I understand the question, the answer is yes you can form silver chloride with the HCl,
But the silver chloride is insoluble, and copper II chloride is soluble.

Thanks again for the compressed information! I hope you know, that I was conscious of most of it, so that you don't believe, i am a totally noob but your consciencious explainations will as always be very valuable for all other students of refining, who will read this thread. You are quite a born teacher!

Well, your answer explains, why my medium grey silver powder has got the violett-reddish-brown teint of UV-exposed silver chloride. So, when I dissolve it in HNO3, I will treat the filter solids as impure silver chloride.

Then (we talk about 500g Ag from plated flatware, ca. 1850-1980)

a) From the filtrate I will drop pure AgCl, wash in HCL, wash in H2O and check all solutions for Au and PGMs. The AgCl will be converted with NaOH/glucose. Then it will be pure enough to be melted for the thum cell.

or

b) It will be cemented from the filtrate together with other PMs ( I tested some black particles with AR/SnCl2 - got tea brown solution, very slightly yellowish with dmg, though I am still not believing blindly in my testing skills. Could be dirt, Mn02, Ag-oxides, sulfides or thousands of others). Then the cement will be processed in a Thum cell and other PMs, if they exist, be collected from the anode sludge and processed equal to high grade dental scrap.

Have to sleep some nights about it, before I can decide, which one would be better.

If I have missed something, I'll be glad to get corrected.

It's amazing how even the fairly simple processing of silver shows it's difficulties in the small details.