Non-Chemical Why focus so much on the gold?

[amishfighterpilot]

I've been wondering for some time now about why so many seem obsessed with using chemicals and mechanical stripping to get directly at the gold on electronics and jewelry. Since gold only really reacts with a select few things, why not use various acids to remove all the other metals and reduce things down to where it's just gold? In my old thrift store job, we did this thing called "negative sorting", where we would focus on getting rid of all the trash, and then it was almost all good stuff left. Seems like this would make a lot of sense in gold recovery. I even watched a video about a company in England that was doing something sort of like this where they melted it all down and then rolled it into a sheet. Then they used various acids to remove all the other metals, leaving the sheet just gold. I'm still trying to figure out why even bother doing that..... why take the gold off the boards at all until all the other metals are washed away?

 

[butcher]

amishfighterpilot, read more about what we do, it sounds a lot like what you just described. we get rid of trash then refine pure gold.

 

[amishfighterpilot]

Sorry to be unclear. I meant the net in general, not this site in particular.

So if I am to understand this correctly, the following method should be able to produce gold and other metals:

Scrap heated to around 1000 degrees Fahrenheit to melt out the solder and other low-temp metals. From an environmental safety standpoint this should be done in a sealed electric furnace yes?

Then the remaining material would be washed in a series of acid baths to remove copper, silver, nickel, and other reactive metals that won't melt at lower temperatures.

Then the scrap could be ground into a fine powder and subjected to enough heat to melt out the gold, filtering out the PCB material that still remains.

Would this method work? What is the problem with it if not?

 

[butcher]

Well there is alot more to it.

melting solder with gold can dissolve some of your gold into the solder, some metals become problems with some acids, acids cost money so you would not want to waste them creating solutions that will take you money or time and labor to prepare to safely dispose of, the list of problems of your Idea are many, but your general idea of getting rid of trash and concentrating the values and purifying them is correct.

 

[patnor1011]

Also, there is not that much of gold in electronics to warrant dissolving all unwanted metals. Most of gold in electronics came from very thin plating. While this method is preferred with karat gold it is unsuitable for electronics. (I mean to acid bath whole motherboards for example)

 

[amishfighterpilot]

Thanks for the replies. Are you saying that the solder will act as a flux and melt away the gold? Is there no way to melt the lower temp metals off the boards without affecting the gold plate?

Also, when using an acid to remove a metal, if that acid is then used in electrolysis to remove said metal, does it not revert the acid back to an active state? That is to say; if I use nitric acid to remove copper, and then use electrolysis to remove the copper from the nitric acid, does that not leave me with copper on one hand and nitric acid on the other? Since most copper is electrolytic, I would suspect there must be some way to reuse the acids involved yes?

 

[jimdoc]

Thanks for the replies. Are you saying that the solder will act as a flux and melt away the gold? Is there no way to melt the lower temp metals off the boards without affecting the gold plate?

The solder will act like a solvent, it will alloy with the gold at a much lower temperature than gold's melting point. And basically no there is no way to melt lower temp metals off the boards without making a mess, and more problems than it is worth. You don't want to burn the boards because the fire department or the cops will get a call.

You should study the forum and read Hoke's book, Ammen's book is another good one.
You will get the answers to your questions and more. If there was an easier way, without any drawbacks to create problems, and without high dollar equipment being needed, then all on the forum would be doing it. This is a hobby for most here, and a business to some others. So something you think may work in theory may work for the big companies, but not for the little guy.

Jim

 

[amishfighterpilot]

I will look up those things. Thanks for the info. My stubborn side says that there's usually a way for the little guy to do whatever the big guys are doing though. I've seen it happen too many times to say "never". I definitely wont' burn any boards though, wouldn't dream of it.

 

[jimdoc]

Here is the forum page with Ammen's book link;
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=54&t=11096&hilit=Ammen

And Hoke's book is in forum member Palladium's signature as well as the forum handbooks and other info.

Jim

 

[butcher]

amishfighterpilot
"I will look up those things. Thanks for the info. My stubborn side says that there's usually a way for the little guy to do whatever the big guys are doing"

Put your stubborn side to studying the materials available through this forum, you will find what you need to acomplish your goals, you will see us little guys are doing it.

 

[amishfighterpilot]

Thanks again!

 

[Harold_V]

Sorry to be unclear. I meant the net in general, not this site in particular.

The net, "in general", is filled with people that should be asking questions instead of giving directions. They know nothing about refining, but don't know that. Here, you have the benefit of several individuals that have refined, commercially, with, likely, a grand total of nearly 100 years of experience.

(snip of previous comments)------Then the scrap could be ground into a fine powder and subjected to enough heat to melt out the gold, filtering out the PCB material that still remains.

Would this method work? What is the problem with it if not?

No, it would not. Please read Hoke's book, so you gain a basic understanding of what is required to separate metals from one another. It is not accomplished by heat---it is accomplished chemically.

Molten metals are solvents of other metals. Few of them will separate from one another when melted. Those that do melt tend to solder to (and digest) those that do not.

Harold

 

[amishfighterpilot]

A chemist friend of mine wants to do an experiment on this issue. We plan to actually melt all the metals together on purpose. Main obstacle to this would be the coatings on the boards. We plan to shear off all the surface mounted components(with a machine, not by hand), but we would really like to remove the coatings before actually melting off the metal. Is there a solvent anyone here would recommend that would remove coatings but not the metals? Please bear in mind this is an experiment and does not need to be profitable. I did a forum search but I can't seem to find a clear answer on this...

 

[qst42know]

Incineration will remove all coatings. It is how it's done on an industrial scale.

It is very hazardous and irresponsible without a proper incinerator though.

 

[NoIdea]

A chemist friend of mine wants to do an experiment on this issue. We plan to actually melt all the metals together on purpose. Main obstacle to this would be the coatings on the boards. We plan to shear off all the surface mounted components(with a machine, not by hand), but we would really like to remove the coatings before actually melting off the metal. Is there a solvent anyone here would recommend that would remove coatings but not the metals? Please bear in mind this is an experiment and does not need to be profitable. I did a forum search but I can't seem to find a clear answer on this...

Evening – amishfighterpilot

Pyrolysis is the answer, check out this link for a quick peek at what products are produced using this approach.

http://www.sciencedirect.com/science/article/pii/S0165237008000375

Instead of collecting the gas/liquid product, just introduce it back into the burner, reduces fuel and really ramps up the heat which destroys PCB's and Dioxins if present. And the nitrogen is not necessary, just put a wee bit of water, the steam produced will be enough to diplace any air that may be present after charging the reactor.

If you would like to know more, just ask. 8)

Cheers

Deano

 

[Geo]

which coating? are you talking about solder mask? a soak in warm caustic soda solution will remove it. are you talking about solder? a soak in warm hcl acid will remove it. same with tin.

 

[patnor1011]

I wonder why to go in that... Under solder mask is just copper. Very occasionally you may find some gold plating but that is so thin that even if extracted it will never be profitable and will cost you several times more than real value in terms of machinery, electricity, chemicals and work. It is done but on industrial sizes with batches of several tons. Main product however is copper they go after and all the rest is cream on top of profit made from copper.