# stumbled upon something at work.. any merit to it?



## AuMINIMayhem (Aug 13, 2009)

:idea: 

Before I push the "eureka button", thought I'd tell ya the story and see if anyone has considered this.

We had an interesting thing happen at work. We were bonding/soldering some electrical components that had gold contacts. Shortly thereafter we started having all kinds of failures and after some long nights and watching engineers scratch their heads for a bit, our senior chemist took a look at the problem and said "well, hell.. there's you problem right there"..

Turns out, the solder we used contained Indium.. apparently Indium has the capability to "leach" gold off of the contacts and create a short/electrical gap.. :idea: 

Now.. anyone see where I'm going with this?.. 

I'm curious how much gold indium can leach out proportionately.. is this a viable leach in recovery?.. what process could be used to try this as a potential way to absorb gold off of contacts/foils/etc?..

Just throwing this out there as a fun theoretical problem to work out.. I'm not planning on chasing it myself.. Indium, itself, can be pricey.. :roll: 

well, unless the "eureka button" gets pushed.. :mrgreen:


----------



## AuMINIMayhem (Aug 13, 2009)

ps. Mods.. wasn't quite sure where to put that post.. my apologies if it's in the wrong spot. 8)


----------



## AuMINIMayhem (Aug 13, 2009)

ok.. I'm thinking "scratch that thought"

http://www.aimsolder.com/techarticles/Indium_article.pdf

*sigh* :roll:


----------



## 4metals (Aug 13, 2009)

It was many years ago but I worked for a connector manufacturer and they did a lot of dipping gold plated pins into solder pots. Tin lead if I remember correctly. Anyway the molten solder leached some gold off of each plated contact it was applied to and the levels of gold built up as a contaminate in the solder. It got to the point where the solder joints became brittle from the gold stannate alloy which formed. The pots had to be periodically emptied and the gold recovered. I don't even know if solder pots are used in that fashion anymore, but if they are that may be a source of gold for recovery.


----------



## goldsilverpro (Aug 13, 2009)

Large facilities use wave soldering machines to solder the components from the bottom of the board. The boards ride over the crest of the wave of the molten solder. The "wave" is created on a metal drum. I think the component leads are trimmed after soldering.
http://video.google.com/videosearch?q=wave%20solder%20&sourceid=navclient-ff&rlz=1B3GGGL_enUS259US259&um=1&ie=UTF-8&sa=N&hl=en&tab=wv#

Here's a good video
http://www.youtube.com/watch?v=WXLv7MNjGL0

Some of the gold, silver, and copper from the component leads dissolve in the solder, especially if it contains lead. I seem to remember that the limit of contamination for these metals is about 2%, total, before they start getting poor solder joints. The Bureau of Mines once published a Report of Investigation (RI) of stirring aluminum into the molten solder to extract these metals. The Al (containing the Au, Ag, and Cu) floated on top and was skimmed off.

This is similar to the Parkes process for removing silver (and, gold) from lead. It used zinc instead of aluminum.
http://www.google.com/search?q=parkes+process&sourceid=navclient-ff&ie=UTF-8&rlz=1B3GGGL_enUS259US259


----------



## AuMINIMayhem (Aug 13, 2009)

yeah.. we had wave soldering machines at my old job, but here we do very specialized "one-off" stuff for space applications.. LOTS of gold in the space industry, btw..

so, in theory alone, not for practical purposes (seriously... this is more than likely best left to the LARGE conglomerate refiner groups) ...you could leach gold in something such as Indium or tin/lead.. would you then digest the alloy in something like HCL, then nitric, then AR, etc?. :?: I used to be able to get my hands on MASSIVE quantities of used solder from my old job that were loaded like you described.. I could have taken as much as I wanted.. if only I had known.. I could have sold it to the local refiner for a decent pinch I bet  

anywho.. what I'm actually trying to understand now is the difference between an "alloy" and an "amalgam" and when gold is "leached" is it just "in solution" or is it part of the matrix, etc..


----------



## 4metals (Aug 13, 2009)

An amalgam is a compound formed with mercury, when I spent time in Equador recovering placer gold and refining it the gold was micro small particles which we concentrated and processed with mercury. What is neat is the gold "flour" is collected in the mercury pool which becomes lumpy and you place it in a chamois cloth (the kind like you clean your car with) and squeeze it and the mercury squeezes out leaving what was collected in the chamois. The gold is further separated from the remaining mercury by distilling it in a mercury retort, and finally the remainder is acid refined. 

Mercury pollution is well documented and really something you don't want to mess with unless properly equipped. It fumes off in nitric acid so make sure it's been collected (by retort) before any acid processing.


----------



## Oz (Aug 13, 2009)

4metals said:


> It fumes off in nitric acid so make sure it's been collected (by retort) before any acid processing.



Not that I mess with amalgams much, but this is very important to those that handle dental scrap. While retorting has been covered on the forum, so has the cementation of mercury on copper. However I do not recall anyone mentioning it fuming off in nitric. 

While mercury can be handled safely, it is best avoided with better alternatives available.


----------



## AuMINIMayhem (Aug 14, 2009)

yeah.. I would *never* deal with mercury, personally.. if anything I'm interested in trying that "amalgamite" stuff I've read about.. it's some alloy of bismuth (I suspect there's some tin or other bits in there as well)..


----------

