# Heatsinks



## jeffdanyelle1234 (Dec 4, 2016)

Hello,
I have a question, I have been just recycling my heatsinks for copper prices. Is that gold colored patch on inside of the CPU heatsink really gold? If so is there an easy way to remove it, before I sell the copper? I have about 30 pounds of heatsinks. Your help would be greatly appreciated.
Thank you


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## Barren Realms 007 (Dec 4, 2016)

Depends on what type of CPU you are talking about. There are many kinds of CPU's with heat sinks. You might want to post a picture of what you have to get a better answer.


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## patnor1011 (Dec 4, 2016)

He meant these, and yes that is a gold plating. They can be easily stripped in cyanide or sulfuric cell (I did not tried cell but I guess it should work fine on these).


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## FrugalRefiner (Dec 4, 2016)

Welcome to the forum jeffdanyelle1234. We ask members not to double post their questions here. Most of the folks who will be able to help you read all the new posts, so they'll find your question. I've deleted your other post.

Dave


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## Chrisr7688 (Apr 14, 2017)

Will the sulfuric cell work for these? What about the Solder in the middle?


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## g_axelsson (Apr 14, 2017)

Chrisr7688 said:


> Will the sulfuric cell work for these? What about the Solder in the middle?





patnor1011 said:


> He meant these, and yes that is a gold plating. They can be easily stripped in cyanide or sulfuric cell (I did not tried cell but I guess it should work fine on these).



Maybe you should take some more time for searches... :wink: 

Göran


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## solar_plasma (Apr 14, 2017)

The solder is indium. It has dissolved some of the gold. I think until now there is no thread about how to part indium and gold.

On the other hand it is said to be a very thin layer.


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## g_axelsson (Apr 14, 2017)

Indium is dissolved in HCl and the gold alloyed within collects in the sludge at the bottom.

Göran


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## solar_plasma (Apr 14, 2017)

But how do we get indium in elemental form again? Electrowinning, cementation or by hot reduction?


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## g_axelsson (Apr 14, 2017)

solar_plasma said:


> But how do we get indium in elemental form again? Electrowinning, cementation or by hot reduction?


That is an interesting question... let me know if you find out how.  

A quick googling found "Preparation of high purity indium by electrorefining" (pdf) where different electrolytes are discussed. Sounds like sulfuric acid at 20-40% actually is faster to dissolve and easier to recover the indium from. I have to test this... by a pure coincidence I have 20 CPU:s with heat spreader sitting beside me. :shock: 
The article talks about electrolysis but it should be applicable for electrowinning too. 

Some other links in no specific order...
* Patent : https://www.google.com/patents/US3268426
* LLX from etching solutions http://www.sciencedirect.com/science/article/pii/S0304386X11002039
* Electrolytic recovery of indium from concentrated sulfate solution https://www.researchgate.net/publication/286231736_Electrolytic_recovery_of_indium_from_concentrated_sulfate_solution_J
* Indium recovery from secondary sources by electrowinning http://www.4980.timewarp.at/sat/reclaim/Reclaim%20Pr%C3%A4sentationen%20HP/ISE%20-%20electrowinning.pdf (good one)
* Comparison of indium purification between vacuum refining and electrowinning http://link.springer.com/article/10.1023/B:JMSC.0000004403.01132.b3 (good one)
* Patent : Method for recovering indium by electrowinning and apparatus therefor http://www.google.com/patents/US5543031

The last one states that indium is a lot more soluble in HCL than H2SO4.

I have some links and info on http://goldrefiningwiki.com/mediawiki/index.php/Indium too.

... more research is needed.

Göran


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## 4metals (Apr 14, 2017)

As the heat sinks are primarily copper and the small quantity of gold (and indium?) they would be a perfect candidate to melt into anodes and part in a copper refining cell. The copper will be high purity and the slimes will accumulate the PM's. The beauty of this is the simplicity because the copper content is so high, it is good to go as is for melting into anode material.


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## solar_plasma (Apr 14, 2017)

Nice infos!

I just saw that indium is at a scrap price close to silver. With a density of over 7g/cm³, I would guess there is up to 1g or 0.40€ per piece on those heatsinks. So the highest value is there, followed by maybe 0.03€ copper, a little gold as a byproduct and a little annoying nickel.

So, I think the focus should lie on the indium.


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## Shark (Apr 15, 2017)

4metals is right. I have been doing mine this way for while now. I used to drop them in my stockpot until 4metals made his post on using a copper cell and smelting. That annoying nickle can be greatly reduced with a soak in a weak sulfuric bath first.


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## Topher_osAUrus (Apr 15, 2017)

Shark said:


> 4metals is right. I have been doing mine this way for while now. I used to drop them in my stockpot until 4metals made his post on using a copper cell and smelting. That annoying nickle can be greatly reduced with a soak in a weak sulfuric bath first.



Did any of the indium go in solution after the sulfuric treatment?


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## Shark (Apr 15, 2017)

> Did any of the indium go in solution after the sulfuric treatment?



That I am not sure of. I Have only been targeting the copper and gold. I have around 15 pounds melted and ready to run, just been having a few health issues again lately that slows me down at times.


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## Topher_osAUrus (Apr 15, 2017)

Shark said:


> That I am not sure of. I Have only been targeting the copper and gold. I have around 15 pounds melted and ready to run, just been having a few health issues again lately that slows me down at times.



That's no good, hope you're well soon.

I only asked because I grew curious if a dilute sulfuric bath with heat alone, could remove the indium and nickel. Leaving a gold sludge on the bottom and a copper block. I will have to search some on the links Göran posted as well as some scholarly articles, and maybe run a couple tests here. Think I still have a few of those heatsinks in a bucket somewhere.


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## Chrisr7688 (Apr 15, 2017)

4metals said:


> As the heat sinks are primarily copper and the small quantity of gold (and indium?) they would be a perfect candidate to melt into anodes and part in a copper refining cell. The copper will be high purity and the slimes will accumulate the PM's. The beauty of this is the simplicity because the copper content is so high, it is good to go as is for melting into anode material.



I have at least 30 lbs of these, I will save these for melting, I've kinda tried to avoid these when they come around maybe not so much anymore. Thanks for the good information everyone!


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## g_axelsson (Apr 16, 2017)

My line of attack will be two stages.
1. Dissolve the solder (indium) in HCl or H2SO4
2. Recover the gold in a sulfuric cell and from the sludge after dissolving the indium.

This leaves the copper heat sinks as copper scrap and I can sell them as is and it is probably faster than melting and a copper cell. It is a bit more handling but I can do it without the need of a furnace and a copper cell. Those are on the planning stage so sometime in the future I'll test the copper cell thread.

Indium can later be recovered from the indium solutions when we have cracked that nut.

Göran


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## Shark (Apr 16, 2017)

When running them in my stock pot, I had an air pump go out on me and didn't catch it for several days. When I cleaned that bucket out the gold layer's were thick enough to hold together. I have a coffee can full of heatsinks that I still haven't melted, I may try doing a few in AP or HCl and see how that comes out. Warm Sulfuric will eat the nickle layer off pretty fast and if left will attack the copper pretty quick as well. I just can't recall how it acted on the solder. I have kept the cell solutions separate from from everything else but what I need is a way to test it for indium.


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## Topher_osAUrus (Apr 16, 2017)

Shark said:


> ..what I need is a way to test it for indium.



I have only had a chance to download and skim over this so far, but it seems it may give some good qualitative testing methods.

https://books.google.com/books?id=vJ46AAAAMAAJ&pg=PA380&lpg=PA380&dq=qualitative+indium+testing&source=bl&ots=ko9fa-xnvC&sig=kCY-MhFVByyp5aEXKbM3GYVi2iA&hl=en&sa=X&ved=0ahUKEwjpgq7eq6rTAhVL2oMKHW4-DS4Q6AEIMDAD#v=onepage&q=qualitative%20indium%20testing&f=true

My word thats a huge link

Edit: nevermind, the forum fixed its length for me. Thank you again, grf!


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## g_axelsson (Apr 17, 2017)

Two ways of testing for indium is using spectroscopic methods and voltammetry. Both are a bit tricky but should be possible for a crafty amateur. As I'm working a lot with electronics I have looked into voltammetry as an interesting way of analyzing liquids.
https://en.wikipedia.org/wiki/Voltammetry

Göran


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## g_axelsson (Apr 26, 2017)

Adding to the indium recovery... interesting article from 1944 about indium and extraction.

Written at a time when the total accumulated indium production was... 1 pound. :mrgreen: 

Göran


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## solar_plasma (Apr 28, 2017)

Excellent!


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