fools gold foils!?

[Bernie Foley]

Hi all,
I just made nitric acid from sulfuric acid and sodium nitrate same as i always do. took some of my prime or high yield gold plated boards and
put them in the nitric acid.....soon the solution turned pea-green and a white precip. stated to build up in the bottom of the flask....at the end of the reaction there was only a white precip.on the bottom and the liquid was pea green....It tests with stannou chloride as negative for gold!??
Was i fooled by nickel plated boards colored to look like gold!??
I've looked at enough boards so i think i would not be fooled...Bernie

 

[Lino1406]

Gives SnO2 with nitric, a very durable precipitate

 

[Bernie Foley]

I'm shure some tin oxide and probly lead nitrate...but i can't find any gold foil at all..no gold dust,or a trce of gold...the solution is very bright pea grean!! nickel probly some of course.....??...Thanks Bernie

 

[Lino1406]

Did you miss 2nd stage (dissolving gold
with aqua regia)?

 

[Lino1406]

inside the white precipitate

 

[Platdigger]

Nitric acid made from sodium nitrate that contains chlorides could.
Randy

 

[Harold_V]

Nitric acid made from sodium nitrate that contains chlorides could.
Randy

In such a case, the values (gold) would be precipitated as minute particles that likely would not be recognized when mixed in the white residues. If the solution tests barren, and gold was known to exist previously, it has to be somewhere. I'd begin by insuring that my stannous chloride was active.

Harold

 

[Lino1406]

The ammount of gold is negligible

 

[Bernie Foley]

Hi all,
Good answer Harold...stannous worked ok on a test solution that is weak.
I filtered the solution very well and took the filter and residue and dried
it then in a melting dish brought it up to about 2,000F..lead and tin left
leaving flux and a little copper. No signs of gold. I took the remaining solution and added to each quart SMB concentrate . total additions of SMB
was 1/4 lb of SMB to the 1/2 gallon of solution. It turned from green to olive brown and no precip gold showing..the solution is clear and no precip. on the bottom of the coffee pot....It got hot when SMB added but did not precip...These boards were my prime boards....can't believe that not one showed gold...I have been around gold since 1976 and can judge
gold by sight..I never rely on that testing is the only way....testing usually confirms what i see..I have been fooled before! but not very many times!
HELP.........Thanks to all..hope we figure this one out...baffling to me!...!

 

[lazersteve]

Bernie,

If you still have some of the boards untouched try this simple test.

Cut a small sample of the foils off of the board surface using a sharp Xacto knife or razor blade.

Place the sample foil into a test tube and add a few drops of HCl.

Add a drop of Clorox and heat until no more fizzing occurs.

Repeat Clorox additions with heat until the sample foil is fully dissolved.

Test the resulting solution with known good stannous to determine if gold is present.

A negative test means no gold.

Remember when working with unknown scrap to begin with very small tests to determine what you are dealing with. This will save you headaches, time, and chemicals. If you can prove your stannous is good on a known sample of gold, you can trust it for testing unknowns.

Steve

 

[Lino1406]

Show a photo, you may have a surprising answer

 

[Bernie Foley]

Hi All,
The gold finally did come down (precipitated). It is very fine and settled overnight...Thanks for all the help..most of the boards in that batch i had tested with 70% nitric acid using a glass rod to put a small drop of it on the foil. I had one board that tested bad..green color immediatly appearing. that board was not put in this batch. It was very lightly sorta gold color which could be seen very easy.
In the future i will test each board and be carefull about copper when using SMB. I'm going to make a test gold solution to have for testing.
I usually test solutions (stannous chloride) buy Steves method and also
I retest with 3-4 drops of solution and the same amount of stannous in a test tube..adding more stannous to the test tube I would think would prove
gold/no gold. THANK YOU ALL!!.....Bernie

 

[Bernie Foley]

Hi all,
It looks like the brown phenolic boards which delaminated reacted with the
nitric acid. fiberglass boards were ok. One of our best chemists probly can figure it out. For now don't put the brown phenolic boards in nitric!
Next post i should be able to get some photos up when needed..
Thanks.......Bernie

 

[eagle2]

I would not even put fiberglass boards in Nitric. They all react with Nitric acid and fall apart. I think there is some sort of glue that holds the laminates and/or threads together. The fine gold particles would stick to the Silicon particles and glue mess and be difficult to completely separate. Also I have seen fine Gold particles stick to the main body of the board itself and not wash off. Rubbing or scrubbing just welds the particle to the board.

Ceramic chips will not, but thats the exception. The AP method for boards works very well.

Also if your solution is too acid when precipitating with SMB, the gold will be very fine, slow in forming and the reaction not complete.

 

[Platdigger]

Hi Eagle, what ph do you suggest is best?
Randy

 

[GeeDub]

took some of my prime or high yield gold plated boards and put them in the nitric acid.....soon the solution turned pea-green and a white precip. stated to build up in the bottom of the flask....at the end of the reaction there was only a white precip.on the bottom and the liquid was pea green....It tests with stannou chloride as negative for gold!??

I'm thinking... "Metastannic acid". Was your nitric dilute or concentrated? If you put the boards in strong nitric, the tin in the solder will oxidize to that state. Stannous chloride was probably instantly converted to more of the same. I would try a more dilute solution of the nitric next time.

 

[jamthe3]

OK, I'm gonna give this a try...chapter V11, pg. 72 ??

Possibly gold & tin paste. 50/50 sulfuric/water over filtered residue, pour off into large amount of water, then move on with the now washed residue in AR.

Might want to wait for someone more knowledgeable's advice though.

 

[butcher]

Hokes method sounds great to me. thanks

 

[Bernie Foley]

Hi all,
I think the gold & tin paste(tin oxide) is close. What threw it off mostly was brown phenolic board caused a reaction. I have not had a reaction with the green board(fiberglass). The nitric was about 50%.
I also think some of the boards had a thick nickel underplate also.
Too cold here in N.H. to be out in the lab so i have not done anything
most of the winter. Thanks to everyone!...Bernie