separating gold plating from iron/nickel alloy

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M

millgold

Member
Joined
May 7, 2020
Messages
12
Hi all, this is one of those experiments done for the sake of learning. I was given "grinding sludge" from a precision grinder that is no longer in business. Clean the machine for sale- get some sludge. There isn't much but hopefully enough to learn from.

Details: Gold plate was ground off from an iron nickel alloy. Sludge is Gold bonded to that alloy and abrasive grit.
no estimate possible on percentages of each metal, or grit.

Goal: Want to try leaching with HCl and Bleach, using SMB to precipitate.

Failure: root cause- ignorance. I took a half golf ball sized lump of the material, mixed 1oz ( 5%) Clorox with 2oz (35%?) HCl. very quickly I generated a very bright yellow liquid, in time it took a green cast (Nickel ions, no copper in alloy or plating) the next day, to this I added SMB... and more SMB... and yet more still. All I got was a dark brown liquid, no particular precipitate... and eventually a thick layer of white sludge.

From this brown liquid, I decanted the top layer, ran some of it through a coffee filter- just to see what it is like- think red clay mud. Ive made many errors... but its basically cost me time only. now I have a quart of brown liquid. I can start from scratch, but could use a bit of advice on how to proceed this time

I have done a fair bit of reading so far, I see more than a few mistakes, but as my material is somewhat limited I am hoping for a bit of guidance this time.

Thank you for both assistance and patience

MG
 
"Gold plate was ground off from an iron nickel alloy" I think what is meant is polishing hence minimize expectations
 
polishing, not quite. What I mean is the precision made parts for scientific purposes received a .001 inch thick plating of pure gold, and after plating, off of one side, .0012 to .002 inches was precision ground off, to provide access to the base metal and produce a perfectly flat surface. I don't expect a great quantity but am still wanting to try.
 
I would look at putting iron and nickel into solution in a recovery process.
You could use any of several different processes such as a ferric chloride leach or cupric chloride leach (or even a combination of those) to put iron and nickel into solution.

After parting gold from the base metals and recovering gold, then put the gold into the solution to refine it further...

At this point, you may have made putting iron into solution somewhat more difficult, the use of the highly oxidizing solution may have converted much of your iron to rust or oxides making separation a bit more difficult...

I would separate anything that did not dissolve or was still undissolved from the solution, and cement values from solution using copper, collect these for a recovery of the gold.
 
Information comes quickly here, thank you for your time and efforts.

Dissolving the iron nickel alloy was my original thought, filter the residue to gold and abrasive material, then work it down from there. The first attempt was a lunch break trial run. unsuccessful but I learned a bit. have a copy of Hokes book - good reading and a sincere thank you to whomever took the time to make it available.

My concern towards the dissolving of the iron nickel alloy comes from not knowing what would dissolve it but also how to neutralize the nickel solution afterwards
 
Very good, Ill read up on that. looking into the different processes, would the HCl/Peroxide be a viable option? The reason I ask that is because a bottle of peroxide runs about 55 cents and can be had on the next trip to the store and I have muriatic acid?

With regards to this reaction, is heat needed? Is it as simple as blend a solution 2 parts 35% muriatic to one part of 3% hydrogen peroxide

In a HCl/NaClO solution as I tried, does SMB only precipitate gold, or will the sulfur dioxide precipitate any metal in solution? Does it only works in a slightly acidic, chlorine free solution? I see that, by weight only a slight bit more is used than expected yield, is it a guessing game as to how much to use (with out having the needed chemicals to test for gold in solution)

(for what it is worth, I have printed off over 70 pages of threads that seem relevant, and have the copy of Hokes book- I intend to do some serious reading this weekend to get a better hold on things before proceeding further)

Thank you

MG
 
The cupric chloride leach uses CuCl2 to dissolve copper and most all of the base metals (including your iron and nickel), it will not put gold into solution (if you do not have oxidizers like H2O2 in solution).
You do not need heat necessarily but the solution works faster on warmer days and may slow to a crawl in freezing weather...


The very weak peroxide is only needed to get the reaction started and is not needed after that (oxygen from atmospheric air a fish tank air pump will keep the solution active and help to regenerate the solution.

You are not dissolving metals with HCl acid and hydrogen peroxide, the goal is to make a starter solution of copper II chloride, which then the Cupric chloride dissolves metals being changed to cuprous chloride which can be regenerated back into cupric chloride to dissolve even more base metals...

The SMB can precipitate gold from a solution of HCl and NClO, once you eliminate the chlorine gas (oxidizer) that was generated by the reaction, the reaction does need some free HCl or acid for the SMB to form SO2 gas in solution...

Why work blind, you can make your own gold testing solutions, with either dilute sulfuric and iron, or tin solder (pewter) and HCl...

It may be better to work in some small experiments before recovering or refining in bulk, get an idea of what happens in small lots before putting the whole lot in solution...
 
You could use sulfuric and H2O2 to dissolve the Ni and Fe. This is another form of AP however your gold wont dissolve.

https://www.sciencedirect.com/science/article/abs/pii/S0304386X1730511X

Eric
 
etack said:
You could use sulfuric and H2O2 to dissolve the Ni and Fe. This is another form of AP however your gold wont dissolve.

https://www.sciencedirect.com/science/article/abs/pii/S0304386X1730511X

Eric
Click to expand...
How about the Ag, Pt, Pd or other PM. Will those go into solution?

Sent from my SM-G950U using Tapatalk

 
Hey all. , Ive done a bit of reading on my end, some questions have been generated, some displaced.

Ive set the residue of the first "lesson in how not to proceed" aside for disposal processing later- learning what doesn't work, and why can be valuable- even if the end result isn't. The section on dealing with waste ties a lot together and so does the formula list.

Now I have tried a couple more experiments- on a single small lump of grindings. I have not yet made the ferric chloride- I do intend to. As it is- I tried the sulfuric acid (battery electrolyte) with 3% hydrogen peroxide, and a small aquarium pump bubbling air through the solution... after a day or so, much of the solids had gone into solution. I decanted the solution off (perhaps unnecessary- I probably should check the PH to see if it is still effective? use pool test strips?) after decanting, I repeated as before, H2SO4/H2O2- this time the solution did not dissolve as much material, I am thinking the nickel was not significantly affected by the sulfuric acid and remained solid. So, I decanted, added water, decanted, added water... to basically wash the solids of most sulfuric. Then switched to hydrochloric and peroxide with air bubbling through. The grey sludge has gone into solution, leaving white abrasive and particles of gold.

now then, It is a safe bet that I have over used materials, over processed and over complicated the procedure and generated more waste than necessary for later. But I did learn the H2SO4/H2O2 will dissolve much, but not all the undesirable material quickly... and, I probably did dissolve some gold when I used HCl and H2O2.... education rarely comes without cost. I'm still reading and wanting to listen.

Before proceeding further with this experiment- please direct me if I am wrong in my thinking. I have a mixture of abrasive, some gold and HCl/H2O2. The bulk of undesirable material is gone in solution. I think I should decant and dilute and repeat a couple times to wash the solids, then try the HCl/NaClo to put the gold into solution, then filter this to remove abrasive and add SMB to precipitate Au? It is a couple steps off but I am still not clear on weather SMB only drop gold or will it drop all metals from a HCl/NaClO solution?

I'm sure there is much to be said about all Ive said- please share your thoughts.

Thank you

MG
 
Pool test strips won't help much, as they only work in a narrow range near pH 7. Search eBay for pH strips. Look for something with a wide range like 1 to 14 or 0 to 14. You should be able to find some for a dollar or so.

As you mentioned, HCl and H2O2 will put gold into solution. Check your solutions with stannous chloride to make sure you don't throw away your gold.

SMB is pretty selective when used properly. If you overdose, it can also start to precipitate other metals. Again, testing with stannous will tell you when you've reached the end point.

Dave
 
with respect to butchers suggestion of using either one or a combination of ferric chloride and cupric chloride leach, Is the Ferric Chloride the same as the chemical used for etching metals and making computer boards? If I understand correctly it is made by dissolving iron into HCl and then adding a surplus of HCl? it should attack the iron/nickel alloy?

Still reading and trying to piece things together (and waiting on PH test strips).

Thank you.

MG
 
I just received word, the original alloy the plating was put on is "Carpenter 42", it is alloyed as follows: " 0.05 max. C, 0.40 Mn, 0.25 Si, 41.0 Ni, Bal. Fe"

perhaps this provides some insight as to what im up against

MG
 
One more tonight, I'm afraid.

I have given up finding much information online beyond this site- the technical knowledge is impressive, and everything outside of here seems to be "Turn miscellaneous scrap to solid gold in four hours or less".

With the (incorrectly named?) AP process, using either HCl or H2SO4- how long does it take to dissolve base metals (I know there are many variables but is it typically in terms of hours, days, weeks?) and how do you know if the solution has become saturated with base metals to the point it is no longer effective (simple as PH approaches zero?)

I am sure all of this has been covered before but I have not yet found it. Thank you for your patience in advance.

MG
 
The leaching processes are not as aggressive as dissolving metals in the highly oxidizing acids...
So the leaches are much slower, instead of seconds or minutes, it may take hours or days, along with the environment which can speed or slow a reaction with other factors such as temperature, as well as the oxidation or reduction potential of the leach or solution...

The more reactive a metal the easier it dissolves, some metals are so reactive like sodium, it will basically explode when in contact with water or an acidic solution.

On the other end of the reactivity series of metals, we have metals like gold silver and the platinum group that resists being dissolved into solution as ions, and can only be attacked under extreme conditions with highly oxidizing solutions.

The physical size, thickness, surface area, type of alloy or combination of metals, temperatures, concentration, type of acid or oxidizer, and how much, these and many other factors come into play of how fast a metal will oxidize...

In some of our leaching processes like cupric chloride solution, the color of the solution can give us an indication of how effective it may be at its ability to attack iron copper and other base metals, as the cupric chloride attacks these metals it itself becomes cuprous chloride, changing the bright green solution dark brown...

As you study more, you will understand more...
Hoke's getting acquainted with experiments and doing the same kind of similar experiments on your own to gain a better understanding of what you are studying.
Doing as she suggests in her book, with other leaches or reactions your learning about here on the forum, is a great learning tool and should be very helpful in answering many of these and many more questions you have not even thought of to ask...
 
Still reading... I have had a batch of grindings soaking in the hcl/h2o2 solution and hadn't given a thought to it for a few days now... well I took a look and it appears the iron/nickle has dissolved out... so that does seem to be an option. I also have a batch of ferric chloride stewing.

Questions develop from every angle as I read more... Would electroplating of some form be an option to separate the gold residue from the remaining abrasive media? Or is disolving and precipitation the best option?

Thank you

MG
 
It is hard to picture what you have, without seeing it, it would be easier to see if you posted some pictures...

leaching base metals should leave you with gold in foils or gold in some powdered form, which should be fairly easy to dissolve using HCl and bleach.

From the picture of the material that I vision in my head, electrolysis would not be an option.

in an electrolytic circuit, you need some type of physical connection with the anode material, or have the metal already in solution as ions for oxidation or reduction to occur, in the electrochemical circuit...
 
Hey all, I'm back. Ive had some success, and some failures... and a whole lot of distractions between.
The victory: one batch of grindings reduced to gold and abrasive, then dissolved with HCl/Bleach. some time later smb, time, coffee filters, a potato and a torch... I have a .5 gram pellet!

the failure: I have about a liter more of gold dissolved in HCl/Bleach. it has sat around for a while, was heated in a double boiler arrangement to drive off any residual chlorine and smb was added once cool. no gold has precipitated- it is still a very yellow solution. I diluted a portion with water and tried again to no particular effect. I must be missing something? the first solution I did dropped gold quickly and left colorless liquid.

Please ask questions, I'm positive the problem lies in details left out.
Thank you for any and all help and also for helping me get far enough to produce a pellet of gold

Mg
 

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