# NFG here



## usernameguy (Mar 4, 2009)

Hi Guys,
I'm the NFG. I've been into prospecting for years, and am new to refining. I'm a geologist by education and electical engineer by trade. I work in a clean room, and recently found out that they are disposing of the Au etchant Halide based (I) as waste. I've found that KOH can be used to turn the solution basic enough to drop out the Au, and have done this to end up with a grey precipitate. Not sure what all/how pure this is, but I wouldn't think there's enough PT in it to cause the greyness, any ideas would be nice. 

The other topic I'm intersted in learning about is Au plating solution. We use a product from Enthone(??) I believe it's called BDT 510, however for uniformity purposes, it's again thrown out as waste once the resistivity drips below a certain value. I'll look into that if that number is helpful, but his solution I have no idea what I can use to precipitate Au from. I'm being as cautious as I can as not to create an dangerous/unstable compounds by doing basement chemistry with just enough info to be dangerous. I know certain I compounds are contact sensitive. This actually brings up a 3rd interest that I've retired due to safety and being a daddy now, but in my younger days I made fireworks, big fireworks (not cherry bombs or stupid stuff that just gets people hurt, but mostly aerial displays, etc.) Thusly, worth mentioning I probably still have quite a few leftover chemicals the average person would not just have lying around. 

Glad I found the site. Haven't read too much yet, but looks like a very knowledgeable site. Look forward to talking with some of you and am curious on your ideas regarding my precipitate from the I solution and what I can do with my plating solution. I also know the plating solution is slightly basic and is CN free.

Thanks alot! 
guy


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## SilverFox (Mar 4, 2009)

:? 

1. What are you Etching that has Gold on it? Lets begin there.

2. Why would your gold etching solution have pt as a precip? is there any reason you would suspect there to be?


Silverfox


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## goldsilverpro (Mar 4, 2009)

If nothing has changed since I worked with it, the BDT gold bath is made from sodium gold sulfite and has a pH between 8 and 10. With the old BDT 100 and 200 baths, the gold could be dropped out by simply acidifying the bath with 10% sulfuric acid - I think as brown gold powder. It will probably work the same on your bath. I don't remember how much acid to use - probably not much. Play with it using small samples. The bath also contains sodium sulfite and will generate sulfur dioxide when the acid is added. Use a fume hood. Keep us posted.

How large is the gold bath? How often do they change it? What type of parts are being plated and what is the plating criteria? In a little more detail, how is the gold deposit affected when the resistivity is beyond its limits? 

Also, the bright yellow dried crusty material that forms from drips around the plating tank is a gold compound.



> however for uniformity purposes, it's again thrown out as waste once the resistivity drips below a certain value


Do you mean "resistivity" or "conductivity"? In normal operation, the resistivity will increase and the conductivity will decrease. The conductivity is built back up by adding "conducting salts", which are (or, used to be) sodium sulfite. If the BDT bath is kept clean, uncontaminated, analyzed weekly, operated at the right temp, current density, and pH, and if all the ingredients in the bath are kept within an acceptable range, a BDT bath should last for at least a year, or two. The only thing that would limit this would be contaminants and the build up of sodium, from many additions of conducting salts.

BTW, I'm deleting the duplicate post you made on a different thread. You don't need to post the same thing twice. Everything gets read.


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## usernameguy (Mar 5, 2009)

cool, Thanks guys.
I dont actually do the plating, so I don't know all the details. I could talk to the guy who deals with it. I just found out they were throwing it out without "recycling" it. 

As far as the etch solution. I work in a semiconductor research environment, so we deposit, pattern, etch all kinds of metals. Pt being one. Likely there would not be much PT in this solution since it's most often etched with a plasma. The Au gets wet etched alot in this I solution, and 95% of the time the Au is held on the substrate with Cr as an adhesion layer, but since that's not a Pt group metal, it doesn't get etched. 

Thanks for the info on the plating solution. I'll try the H2SO4 and see what happens. Do you know what the brown precipitate will be? I'm curious about purity and it it can be smelted. I'm really curious to find out how much Au is in the plating solution. That's the newest discovery. I've already played with the I solution a bit. THey even throw away wafers that get damaged/broken, so I usually "prospect through that waste bin, and the ones that have Au depostied get time in the I etch before I drop out the gold. They throw it all out well before depletion just cause it's a smaller research operation and it's not in their cost interests to do otherwise. We're not talking about mass quantities here either. I probably get a gallon of etch solution every other month and the plating solution, maybe a couple gallons a year. nothing big time here, but it all helps especially with the way things are these days. 

Thanks again. If anyone else has any ideas about the grey precipitate I'm dropping out of the I etch, I'd be much appreciative. I take it's not true that Au always drops out of basic solutions, huh? Dropping out the Au from the I solution using KOH I read from a patent on how to recycle and reuse the etch solution, but my small facility isn't interested in this due to the small volume we use.


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## usernameguy (Mar 5, 2009)

How nasty is SO2? Is it really corrosive? I'm more familiar with H2S which is REALLY nasty. My fume hood isn't ideal, so I need to know how safe I should be.

Thanks again.


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## Harold_V (Mar 6, 2009)

If you work with HS2 in your hood, you should be fine with SO2. I used it for years, working in a home built hood that moved roughly 1,000 cfm. No problems with smelling the SO2, which is hard to miss. Very suffocating smell----and likely damaging to lung tissue. 

Harold


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