# KI/I.2 Precipitation Questions - Colors - Time sensitive



## DNIndustry (Nov 13, 2008)

Brand new to the board..
F*IN AWESOME!!!
Finishing.com is to ....Focused.


I have been researching and testing for a while now. 
I have initial test 3500g of gold plated contacts and center pins from high end Comm equipment. I checked their specs and its gold plate.

Id did several variations of AR and tryed to precipitate with SMB. I calculated out how much metal was actually consumed by the acid. Its not dropping. The liquid is still black. I neutralized the nitric with urea, but its still extremely acidic.. around 1pH. What should the pH be at to drop properly,


My main questions are about KI / I2. I used 4:1:10(h20) ratio. I am following the attached patent. 

I will disolve some gold plating til i see the white nickel sublayer.
when I precipitate I use Hydroxylanime-HCL neutralized.
My solution even prior to stripping is 4.25 pH.
I use Pure Iodine crystals.
Once I start the pH drops to 1.5
I calibrated my meter just to be sure.


I used NH4CL/NH4OH buffer 1:1
When I precipitate I get a white/purple sediment with a small amount of gold yellow sediment. The solution goes blue and is about an 8pH

Is the Yellow Gold oxide? or Gold Hydroxide?
What is the purple? Is it KAuI4 or a nickel base>
Time is important...Any help would be fantastic....
thanks
-DNI


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## Shecker (Nov 13, 2008)

I recently discovered that if you add some potassium ferricyanide to an iodine solution it will make a very green precipitates. This can be be one of two things -- gold or palladium. They both form the same green colored precipitate from an iodine solution. You might consider using ascorbic acid has a potential reducing agent for gold from an iodine solution.

Randy in Gunnison


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## Shecker (Nov 13, 2008)

I have a report out of Japan involving the use of I3 for leaching precious metals and recovering the gold with ascorbic acid. If someone will pm me I will get the pdf document to them for inclusion on the forum.

Randy in Gunnison


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## Harold_V (Nov 13, 2008)

DNIndustry said:


> Id did several variations of AR and tryed to precipitate with SMB. I calculated out how much metal was actually consumed by the acid. Its not dropping. The liquid is still black.


Let me get a clear understanding. 

You are using AR to strip gold, with the idea that you can selectively remove the gold, stopping when you hit the nickel barrier level? 

Now you can't make a recovery? Do I understand your question properly?

Harold


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## Lou (Nov 13, 2008)

It would've been a good idea to cyanide strip the gold off the pins, if they are indeed struck with a nickel baseplate over (I assume) copper. That would've worked a treat.


Lou


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## lazersteve (Nov 13, 2008)

Since I don't have any cyanide, I would use the sulfuric cell and a copper mesh basket.

Steve


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## DNIndustry (Nov 14, 2008)

Sorry I was confusing.

I am using the Iodate -3 ion to strip. Very fast. 
I pull it out be fore I hit the nickel.

I use hydroylamine-hcl to drop. Its neutralize with NaOh.
If I dont use a buffer it drops KAuI4-(Purple)
If I add excess NaOH it goes yellow. I think it is gold hydroxide
I put it in some aluminum containers to dry...
the aluminium actually started to reduce it....

I used the NH4CL/NH4OH buffer i fear I have some Gold Fulminate in my garage...Whats the best way to get rid of the ammonia or check with out dying? 

Any info on colors or better directions would be helpful.!!


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## Harold_V (Nov 14, 2008)

I'll spell this issue out as easily as I can, but be aware that I am not a chemist, just a guy that refined gold for many years. 

No one in their right mind uses AR to remove gold from base metals. The problem you have is one of not being able to stop the dissolution of other metals, which, in turn, precipitate the values in the process. If you feel you can pull the items out in time to avoid that happening, you're going to lose gold, either by not removing it entirely, or by precipitation of values on the base metal as the acid is depleted. It's a no-win situation. 

I have a completely different attitude towards the process under different circumstances. The use of AR for recovery of values when they are applied to non-reactive substances is a whole different issue. It works fine for gold recovery from chips, for example. 

You have a few options. One of them is to use a buffered stripper (cyanide), which is selective and will recover the values without precipitating on the base metal(s). 

Another is to use a sulfuric cell, as has been advised. A sulfuric cell strips by persulfuric acid, which is created in the proximity of the anode (the parts being stripped), but only there. As the dissolved gold migrates towards the cathode, it self precipitates as a black powder, which is recovered and further processed for purification. Base metals are not dissolved. 

You can dissolve all of the base metals, eliminating them entirely, leaving behind the gold. 

Do not involve aluminum in your recovery process. It creates horrible problems with filtration. If you dissolve gold with AR, it must never come in contact with other metallic elements, most of which will precipitate the values. You should not be surprised that you are achieving reduction by storing in aluminum. That's the nature of the beast. 

You would be well advised to read more about refining----starting with Hoke's book. If for no other reason, it would be to help you understand the refining process, and what you can expect from the chemicals that are used. 

Harold


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