# Some advice on removing base metals?



## zorba (Apr 2, 2010)

I have all these old CPU:s, pins e.t.c laying around in my basement. 
I am familiar with most of the precipitation methods, separations and so forth.
Now my question is what is the best method when removing the base metals, primarly copper ? Would it be soaking them in some nitric? 
I appreciate some advice on this. And is it possible to have the collection of gold and copper sand together when burning it into a dot and during the process heating it over the coppers evaporation degree so that the copper evaporates leaving the gold behind?


----------



## Anonymous (Apr 2, 2010)

Suggested reading, Hokes, Refining Precious Metals Wastes - you will find it on the forum.


----------



## zorba (Apr 2, 2010)

gustavus said:


> Suggested reading, Hokes, Refining Precious Metals Wastes - you will find it on the forum.



Thanks for the reply, i have read a bit of her master piece but i cant find her instructions on separatating the copper from the gold. 
What page was it if you recall?


----------



## goldsilverpro (Apr 2, 2010)

The Hoke book is mainly involved with jewelry scrap and wastes. The reason it is recommended is that she provides the best basic (but, detailed) information on the reactions of the various chemicals on various metals. If you are doing jewelry scrap, the info is step-by-step, in detail. The Hoke book is written very simply and she writes in such a way that is very easy for the layman to understand. 

You will find that there is almost no information on electronic scrap (after all, the book was written in 1940). The best info on the planet in dealing with electronic scrap is found on this forum. However, the Hoke book will give you a better understanding of most all the processes on the forum. No matter what you want to do, the Hoke book is the best place to start.

As far as separating gold from copper goes, you basically have 3 options:

*(1) Selectively dissolve the copper without dissolving the gold.* This can be done with nitric acid or by using the muriatic acid/hydrogen peroxide method as developed by Lazersteve. There are tons of very detailed information on the forum for both processes.

*(2) Selectively remove the gold without dissolving the copper.* This can be done by using the electrolytic sulfuric acid stripper. Here again, there is tons of information on the forum about this.

*(3) Dissolve everything and selectively precipitate the gold.* This can be done with aqua regia (a combination of muriatic and nitric acids) but, unless the gold makes up a major portion of the material, this is not the way to go, for a number of reasons. With most gold plated electronic materials, such as fingers, this is almost never the way to go. With certain types of old CPUs that contain gold brazes, however, this may be the best method.

Read Hoke, search and read the forum, and watch the videos on Lazersteve's website.
http://goldrecovery.us/


----------



## glorycloud (Apr 2, 2010)

Excellent post GSP!! Concise and to the point!


----------



## zorba (Apr 3, 2010)

goldsilverpro said:


> The Hoke book is mainly involved with jewelry scrap and wastes. The reason it is recommended is that she provides the best basic (but, detailed) information on the reactions of the various chemicals on various metals. If you are doing jewelry scrap, the info is step-by-step, in detail. The Hoke book is written very simply and she writes in such a way that is very easy for the layman to understand.
> 
> You will find that there is almost no information on electronic scrap (after all, the book was written in 1940). The best info on the planet in dealing with electronic scrap is found on this forum. However, the Hoke book will give you a better understanding of most all the processes on the forum. No matter what you want to do, the Hoke book is the best place to start.
> 
> ...




Very well put goldsilverpro, i am actually acquainted with many of the above mentioned processes. I have been reading a lot on this and have tried some myself, but i have not yet reached the meaningful points and because of the fact that i am a newbie to this i have done many faults while working.
If it werent for this excellent forum and books by Hoke and Ammen i would have given up on the refining business a long time ago. 

So just one quick question, if i have my gold and copper assay (containing some other base metals aswell) in the form of sand, were i have precipitated it through electrolysis, is it possible that i could now treat it with some nitric to dissolve the base metals and the gold will then be left as a brown powder? (And later on maybe dissolve the gold itself in AR to purify the gold). 

The reason why i am asking and not trying it myself is the knowledge which i do not have on this subject and you surely have. And also the fact that i must think cheap and not waste the little nitric i make for myself.. Moreover, Hoke only indicates how to treat the assay when it is in the form of a button, so i doubt it myself but is there any difference when it is not in that form?


----------



## goldsilverpro (Apr 3, 2010)

> So just one quick question, if i have my gold and copper assay (containing some other base metals aswell) in the form of sand, were i have precipitated it through electrolysis, is it possible that i could now treat it with some nitric to dissolve the base metals and the gold will then be left as a brown powder? (And later on maybe dissolve the gold itself in AR to purify the gold).


Sure. Just make sure that all the chlorides (if that's what you used in the electrolysis) have been rinsed out very well before using the nitric. Otherwise, you could form some aqua regia and dissolve some of the gold. I would probably use hot distilled water for the final rinse or two.

What do you mean when you use the term "assay"?


----------



## zorba (Apr 3, 2010)

> What do you mean when you use the term "assay"?



Ok thanks for the answer, i meant the collection of copper and gold.


----------



## Harold_V (Apr 3, 2010)

zorba said:


> And is it possible to have the collection of gold and copper sand together when burning it into a dot and during the process heating it over the coppers evaporation degree so that the copper evaporates leaving the gold behind?


What you propose is not viable. When you heat gold to the point of melting, any base metals contained within tend to oxidize. While you may drive some, at least partially, from the gold, the net result is gold of poor quality due to entrapped oxidized base metals. An exception to that concept is if chlorine is introduced to the molten mass, which systematically expels elements. The process is well documented (Miller chlorine process) and beyond the scope of the home refiner. 

Harold


----------



## zorba (Apr 3, 2010)

Maybe a bit off the topic, i just wonder if there is anything wrong with my concentrated sulphuric acid which has a yellowish almoust orange colour? 
I took the acid from a car battery and boiled the water in 150-200 celsius for about 30 minutes. Now it has taken this colour, is that normal ?


----------



## zorba (Apr 3, 2010)

Harold_V said:


> zorba said:
> 
> 
> > And is it possible to have the collection of gold and copper sand together when burning it into a dot and during the process heating it over the coppers evaporation degree so that the copper evaporates leaving the gold behind?
> ...




Right, as i thought it is almoust impossible for a home refiner to do such. 
Great explanation thanks.


----------



## qst42know (Apr 3, 2010)

zorba said:


> Maybe a bit off the topic, i just wonder if there is anything wrong with my concentrated sulphuric acid which has a yellowish almoust orange colour?
> I took the acid from a car battery and boiled the water in 150-200 celsius for about 30 minutes. Now it has taken this colour, is that normal ?



Crystal clear new battery acid can turn an amber color when concentrated.


----------



## zorba (Apr 3, 2010)

Good, so there is nothing wrong with mine, thanks for the reply.


----------



## zorba (Apr 7, 2010)

When removing base metals with nitric acid, is it essential for the nitric to be diluted with one part water (according to Steves recipe in the GRF Handbook) if the nitric is approximately ~50 % due to being homemade ? Or should it only be diluted when having the 70 % nitric?


----------



## lazersteve (Apr 7, 2010)

Diluting 70% nitric plus an equal volume of water makes twice the volume of 35% nitric.

Considering the expense of store bought nitric acid, and the time required to make your own, be sure to dilute the acid to 35% (or even less will work, but slower). The water acts as a medium for the metal nitrates to dissolve into. This is also another reason to add your nitric in controlled doses, and to know how much nitric to use in advance of performing the reaction.

Imagine it like 70% HNO3 is a room nearly packed full with 70 people in it, while 70% HNO3 with an equal volume of water added to it is the same number of people, but the room is now twice the size of the first room. The first room will hold only a few more people, but the second room will hold more than 70 additional people. Of course, those people must be soluble in water to fit in the additional space provided by the added water! :mrgreen: 

Steve


----------



## Oz (Apr 8, 2010)

Unless you get nitric very cheaply it is also of benefit diluting it to 35% because some of the red nitric gases are re-absorbed into the water to perform a repeat performance in digesting your metals.

A bit more bang for your buck.


----------



## Harold_V (Apr 8, 2010)

I've never tried to hide my lack of education, especially where chemistry is concerned, but one of the things I did when I refined is take a quarter of chemistry at the community college, near my home at the time. In it there was discussion of the hydronium ion-----which raises my question. How much does it enter in to the equation where nitric acid is concerned? I was lead to believe that the addition of water provided an extended amount of work by a given lot of acid. It's clear that water should be added to concentrated nitric when silver is dissolved----the question is, does it actually do more work? If so, what, exactly, is the mechanism by which the additional work is provided. Regenerating from the fumes sounds like part of the process. Is there more?

Harold


----------



## Oz (Apr 8, 2010)

As you know Harold, I am no chemist. What I speak of is predominately empirical in nature. One thing going for dilution with water is also the solubility curve of some base metals we are trying to remove. Most have witnessed driving a reaction with heat to get the most out of an acid only to find a crystalline mass upon cooling. How do we fix that? We add water, and perhaps some heat to speed things along. When was the last time anyone found that the best way to solve that problem was to add more acid instead of water.

When I am digesting platinum I usually use an erlenmeyer flask with a glass funnel in the mouth. Due to the long digestion times with platinum I find it advantageous to reduce evaporation while under heat as well as the added benefit of condensing the NOX fumes back into solution.


----------



## zorba (Apr 8, 2010)

lazersteve said:


> Considering the expense of store bought nitric acid, and the time required to make your own, be sure to dilute the acid to 35% (or even less will work, but slower). The water acts as a medium for the metal nitrates to dissolve into. This is also another reason to add your nitric in controlled doses, and to know how much nitric to use in advance of performing the reaction.



Alright, that cleared my foggy mind up a bit... Apparently, the water also helps as a solvent to the base metals. 
So lats say that i have a ~50% nitric which i dilute one part down to 25%, will it still have an effect when dissolving 
copper and silver from the already precipitated brown gold sand?



> Imagine it like 70% HNO3 is a room nearly packed full with 70 people in it, while 70% HNO3 with an equal volume of water added to it is the same number of people, but the room is now twice the size of the first room. The first room will hold only a few more people, but the second room will hold more than 70 additional people. Of course, those people must be soluble in water to fit in the additional space provided by the added water! :mrgreen:
> 
> Steve



Nice metaphor when explaining. :lol: 
Thanks Steve !


----------



## butcher (Apr 9, 2010)

Harold, I have read a little bit on H20 and acids or bases, and how water is such a strange chemical, can be acidic or basic easily, and about the Hydronium ion, Hydrogen positive, and hydroxide negative.

reading this has confused me also, but I think you have a point about its effect on the acids ability to consume metals into solution.




I would also be interested to learn more about this subject.


----------



## Platdigger (Apr 9, 2010)

"water soluable people"...hmmmm

lol


----------



## zorba (Apr 12, 2010)

Harold_V said:


> How much does it enter in to the equation where nitric acid is concerned? I was lead to believe that the addition of water provided an extended amount of work by a given lot of acid. It's clear that water should be added to concentrated nitric when silver is dissolved----the question is, does it actually do more work? If so, what, exactly, is the mechanism by which the additional work is provided. Regenerating from the fumes sounds like part of the process. Is there more?
> 
> Harold




Harold, im not an expert on these fields. But i am pretty sure that you guys are referring to the passivation process
which mainly occurs when you add really pure nitric to base metals. Therefore, water is added to lower the concentrated value?


----------



## Anonymous (Apr 14, 2010)

zorba said:


> lazersteve said:
> 
> 
> > Considering the expense of store bought nitric acid, and the time required to make your own, be sure to dilute the acid to 35% (or even less will work, but slower). The water acts as a medium for the metal nitrates to dissolve into. This is also another reason to add your nitric in controlled doses, and to know how much nitric to use in advance of performing the reaction.
> ...




My first post. I have about 9 years industrial experience with gold and base metal refineries.

Seems to be a few gaps in general chemistry here. Let me try to settle the muddy waters a bit.
Some basic chemistry concepts:
*1) Inorganic reactions go to equilibrium not completion.*
Le Chatelier's principle states that when a system in chemical equilibrium is disturbed by a change of temperature, pressure, or a concentration, the system shifts in equilibrium composition in a way that tends to counteract this change of variable. 

For example:
Copper + sulfuric Acid + hydrogen peroxide <----> dissolved Copper + dissolved sulfates + Water 
Cu + H2SO4 + H2O2 <-----> Cu+2 + SO4-2 + 2H2O
Basically the reaction will continue until every thing on the left side of <-----> equals the right side. (Equilibrium)
Lets apply Le Chatelier's Principle. If I have a reaction that is in equilibrium then I have copper dissolving and copper precipitating equally. Now if I added more sulfuric acid and hydrogen peroxide, the reaction will be forced to form copper sulfate and water. On the other hand, if I added water or copper sulfate to mixture, the reaction would reverse direction generating solid copper, sulfur acid, and hydrogen peroxide. The reaction is reversible.

My point is, you can't say arbitrarily water will do this or that. It is dependent on the chemical reaction.


*2) Solubility Limits*
From my experience in industry, the total metals concentration (Copper, Iron, Nickel) in a h2so4-ammonia solution is limited to about 100 g/l at 100F. This an approximate number that is highly dependent on temperature and the metal salt. (ie, Solubility Limits) Water, for the most part, does not dissolve the metals, the acid does. The amount of metal dissolved can limited by the solubility limit. Adding water dilutes the metals concentration, thereby, allowing more metal to dissolve. On the other hand, adding water also dilutes the acid, which will slow the reaction; so, it would be a good idea to monitor acid concentration. 
*3) Solubility is temperature dependent*
The solubility of a metal salt is very dependent on the temperature of the solution. For most reactions, the metals become more soluble with higher temperatures. (This is not always the case however)
I hope this helps.


----------



## Anonymous (Apr 14, 2010)

goldsilverpro said:


> As far as separating gold from copper goes, you basically have 3 options:
> 
> *(1) Selectively dissolve the copper without dissolving the gold.* This can be done with nitric acid or by using the muriatic acid/hydrogen peroxide method as developed by Lazersteve. There are tons of very detailed information on the forum for both processes.
> 
> ...




Depends on what you are working with, but sulfuric acid and hydrogen peroxide will dissolve copper, not the gold. Another alternative is dissolve everything in aqua regia and use sulfur dioxide to precipitate the copper from solution. Adding HCL will precipitate the silver. Gold can then be electroplated.


----------



## Rhodium (Apr 14, 2010)

PonyExpress said:


> Another alternative is dissolve everything in aqua regia and use sulfur dioxide to precipitate the copper from solution. Adding HCL will precipitate the silver. Gold can then be electroplated.



So2 will drop gold from ar.


----------



## Anonymous (Apr 14, 2010)

Rhodium said:


> So2 will drop gold from ar.




Oops, add urea to eliminate nitric acids, need to add the HCl to drop the silver first...then SO2


----------



## Oz (Apr 14, 2010)

PonyExpress said:


> Another alternative is dissolve everything in aqua regia and use sulfur dioxide to precipitate the copper from solution



I think the point Rhodium may have been making is that SO2 will precipitate gold from a chloride solution preferentially over the copper you stated. Yes it will also precipitate copper if used in excess, but what little copper is there is what proper washing technique is for.


----------



## Anonymous (Apr 15, 2010)

Oz said:


> PonyExpress said:
> 
> 
> > Another alternative is dissolve everything in aqua regia and use sulfur dioxide to precipitate the copper from solution
> ...




I stand corrected, was 15 years ago, sorry I a little flamboyant. The gold drops. We used to wash then dissolve the gold at that point and then plate. Gives very high quality gold.


----------



## Oz (Apr 15, 2010)

After you precipitated your gold with SO2 and you had finishing washing it you mention you re-dissolved it and then plate. I am assuming you were making a plating solution from your refined gold. Do you care to walk through the steps you followed to make your plating solution?


----------



## Anonymous (Apr 15, 2010)

For example:
Copper + sulfuric Acid + hydrogen peroxide <----> dissolved Copper + dissolved sulfates + Water 
Cu + H2SO4 + H2O2 <-----> Cu+2 + SO4-2 + 2H2O
Basically the reaction will continue until every thing on the left side of <-----> equals the right side. (Equilibrium)
Lets apply Le Chatelier's Principle. If I have a reaction that is in equilibrium then I have copper dissolving and copper precipitating equally. Now if I added more sulfuric acid and hydrogen peroxide, the reaction will be forced to form copper sulfate and water. On the other hand, if I added water or copper sulfate to mixture, the reaction would reverse direction generating solid copper, sulfur acid, and hydrogen peroxide. The reaction is reversible.

My point is, you can't say arbitrarily water will do this or that. It is dependent on the chemical reaction.


Hi,
Are you sure about the above? Adding water to a copper sulfate solution has never forced copper out of solution for me, nor has adding copper sulfate forced out elemental copper.

From my understanding all of the components, copper, sulfuric acid, and hydrogen peroxide are in a higher energy state before the reaction than they are after the reaction because there is heat energy generated by the reaction that is transferred to the environment.

I also think regeneration of H2O2 is also a limiting factor as it is hard to form and breaks down in the presence of metal ions.

Jim


----------



## Anonymous (Apr 22, 2010)

Oz said:


> After you precipitated your gold with SO2 and you had finishing washing it you mention you re-dissolved it and then plate. I am assuming you were making a plating solution from your refined gold. Do you care to walk through the steps you followed to make your plating solution?




I am getting some backlash from the establishment in this forum, probably deserved. Guess I was a bit vague, not 100% technically correct. Anyway, there are many ways to skin a cat. 

The replating process I was referring to is called electrorefining and if this topic is of interest look up the Wohlwill process. I am aware of at least one gold refinery using it. Basically you make the powdered gold the anode and replate the gold to the cathode. Impurities will tend to remain at the anode or under it as slimes. The electrowinning solution can be a weak acid (HCL) or cyanide/caustic solution. Basically run the cell at about 2-3 volts. Amps will depend on the amount of surface area (number of cathodes/anodes) you are working with, the electrolyte, and the amount of gold plated. 

Depending on gold content and impurities present at start, you can get 99.999% pure.
Design thoughts
1)Use cathodes/anodes with large surface area. This makes the process quicker, but will increase amp usage. (follows Faraday's law of electrolysis) 
2)There are different ways to create the anode. You can melt the gold and cast it into shape, melt the gold and place a stainless steel hook into it, or make a basket to hold the gold powder.
3)Use of HCL prevents silver from plating since it forms AgCl and falls to bottom of cell; not sure about other PGM's though. You may be able to optimize voltage to lower pgm content if you have it.

Hope this helps


----------



## Harold_V (Apr 23, 2010)

PonyExpress said:


> The electrowinning solution can be a weak acid (HCL) or cyanide/caustic solution.


Depending on your objective, cyanide may not work. It is not selective, and will transfer silver as well as gold. I expect it would also co-deposit copper. It is beyond reason to expect fine gold using it as an electrolyte unless you start with fine gold, and have no contaminants in the electrolyte. It can be an excellent recovery process, but not worth a damn for refining. 

Harold


----------



## Oz (Apr 23, 2010)

PonyExpress said:


> I am getting some backlash from the establishment in this forum, probably deserved. Guess I was a bit vague, not 100% technically correct. Anyway, there are many ways to skin a cat.



I appreciate you taking the time to reply to my inquiry. I had the impression from your profile that you were are metallurgical engineer for some years predominately in precious metals. I had hoped that you could have outlined an exact procedure that you used to follow in your course of work, it had the potential of being a variation that had not been discussed on the forum prior given your background. As you stated, there is more than one way to accomplish the same thing, and I am always willing to hear of a method that is different from others. 

No one here is trying to give you grief, but there are members here with considerable knowledge and they strive for accuracy. If someone posts something it will be scrutinized and corrected if necessary. If it is new, novel, or not understood, clarification will be asked for. This is what sets this forum apart from others. It is a great place to be if one wishes to learn refining.


----------



## goldsilverpro (Apr 23, 2010)

Pony Express,

Harold is right in that the other coinage metals, silver and copper, will co-deposit with the gold in a cyanide system.

Search for Wohlwill cell on this forum and you will find it's been discussed quite a few times. The usage of the cell originally patented by Emil Wohlwill is quite well known. However, due to the tremendous costs of setting it up properly (about an oz of Au/liter), I doubt if anyone on the forum is using it except, perhaps, those members who are presently dealing with very large quantities. Also, the best thing to use for bussing is pure silver and the best cathodes to use are pure gold sheet. I'm sure it could be jury-rigged a bit, but one shouldn't stray too far from the basic setup. I am also curious how you would efficiently set up an anode basket to hold gold powder. Instead of providing us with a technical analysis through such things as Le Chatelier's Principle, perhaps you could give us a more practical step-by-step on exactly how you set things up. It would be much more valuable. Like plating, when you get down to the nitty-gritty of it, refining is almost totally a practical endeavor.

There's about half a dozen of us on the forum I could name that have a combined total of about 200 years of professional refining experience. Three are moderators. Interestingly enough, I'm sure that all of us would admit to having learned many things since being on the forum. I certainly have and I spent 40 years in the refining business. One of the most enticing things about precious metals is that one never knows it all. When I first came on the forum, I thought I knew it all. It didn't take long to get my comeuppance.

Chris


----------



## Anonymous (Apr 23, 2010)

More great comments. I really hope I am not upsetting anyone. I realize there is a lot of expertise here, and I came to the forum looking for expertise since I was think of doing a start up. Sorry this post is sliding from Advice on Removing Base metals. 

When I first posted, I had not read Hoke's book, but I have read or skimmed most of it now. I understand the background of the forum better.

Now to address some issues brought up. Cyanide vs HCL. It comes back to selecting the correct method from your starting point. You will be disappointed with the Wohlwill process if you are not at least 95% gold to start with. As mentioned before, platinum group metals may not separate either. Yes, plating onto purified gold and casting the anodes totally with gold will give a higher end product, but it will also increase inventory. Comes back to objectives, what is the starting point? What is the desired end point? If you want the ultra pure, you need gold cathode/anode; otherwise, save some bucks plating on SS cathodes. 

I agree, the cyanide method will transfer silver, and I have seen copper. I brought up the cyanide method since the original post was about base metals. The scenario I had used cyanide, we had a lot of base metals, ie, gold plated on steel wool. Starting with a product that was probably 50% iron, replating in this instance replaced the retorting step (oxidizing the steel), and eliminated a whole bunch of smelting. Difference in purity went from 87% (retort/smelted) to 90-92% (replate/smelted) of gold. If you want more documentation, look up the Mesquite Mine, CA. The process has been documented. 

Some interest in Le Chatelier's principle in above comments. I do not have time at the moment to add more comments; however, since this is a fundamental chemistry concept that anyone in the refining business should understand, I will make separate post at a later date.

Cheers


----------

