brown false positive, no smb

[ericrm]

does someone know what cause the brown false positive that we often got in aR. im not talking about smb false positive just plain green aqua regia than when you add sncl it come dark(brown) then if you add more sncl it come back clear. it is very frequent on dirty solution, at least for me it is. it often looklike a gold positive that disapear for no reason (but it is brown no blue).it got no stinky smell.

 

[butcher]

stannous chloride will reduce other metals besides gold, to reduce means to get back an electron, and convert back to metal, so if your solution has other metals, if you have a lot of these metals in solution it would not take an overuse of stannous chloride to reduce some of these metals back to metal to show a dark color in your test, on the other hand if you had very little base metals dissolved with your gold in solution in the test the violet color may be seen better as gold is the predominant metal reduced in solution giving the solution the recognizable purple color, then again if you only had a little metal in solution and gold was precipitated out of solution and you did not overuse the SMB the stannous would not have much metals to reduce, and you also did not reduce some of these metals with using too much SMB. so the test may show a yellow color from just normal acids and base metals, but the use of too much SMB reducing some base metals, plus the stannous chloride reducing them no wonder you get a brown reaction of reduced metals in the false positive test.

The stannous test works great when used properly, but just like our recovery and refining process we need to be able to do them properly, the name of the game seems to be the less base metals in solution, not overusing acids and chemicals, and proper procedures help to make everything work smoother.

SnCl2 + CuCl2 --> Cu + SnCl4
I am not sure but for copper chloride, and sodium metabisulfite I suspect something like this:
CuCl2 + Na2S2O5 --> 2NaCl + 2 SO2 +SO3 +Cu

 

[ericrm]

i have tryed to make a video to show what im talking about... the first drop is the ar than stannous chloride than ar than stanous chloride... there is no smb in there. could it be copper like with AP and H2O2, but rather than going from brown to green now it is green to brown?

http://www.youtube.com/watch?v=jy07ByOHb7Y&feature=youtu.be

 

[Lino1406]

A brown that disappears can be, among others, Ni.

 

[ericrm]

thank you Lino1406 that could realy be a possibility as theyr is nickel in mostly everything i dissolve with AR

 

[Lino1406]

Theory behind Stannous chloride assessment:
http://www.goldnscrap.com

 

[Emporio]

I got this brown spot when I did the SnCl test on a solution using maybe to much SMB. I ended up with some salts and gold on the bottom. But how do I see if there is more gold in the solution?

I used HCl and NaNO3 on five intel pentium 80502/80503 and then dropped with SMB.

 

[Charles Connor]

Im having the same problem in a disol. i have, i`ve done the same process for the same scrap, but this is not from my shop, this is from the polishing machine but instead i got a metal that reacts the same as copper when tested with the karat acids, I use the AR with SMB, it also ends up with a salt that looked exactly like AgCl, but it was the SMB. Does anybody knows whats this all about... Thanks!!