Excess H2SO4 in AR

[kernels]

Hi guys,

I have recently recovered my first plated gold using a Sulfuric Cell, I ended up with the expected settled black mud (after days), syphoned off the bulk of the Sulfuric Acid and diluted the remaining black mud mixture. I let it settle again for a day or so, then syphoned off the water + Sulfuric acid mix into the waste.

I then went straight for AR, dissolving the mud. Denoxxed with Sulfamic acid and filtered the solution into a clean beaker.

I am relatively sure all the Nitric was neutralized.

I tried dropping the gold with SMB as per usual, but only got a very very small amount of gold dropped.

I then added a copper bar to the solution and over the next day or so, quite a lot more brown powder (assumed to be gold) cemented on the copper.

Is it possible that because I didn't was all the H2SO4 out properly, it was somehow preventing gold from dropping with SMB ? Any guidance appreciated.

 

[4metals]

The sulfuric is not a problem, sulfamic converts to sulfuric while it gets rid of your excess nitric, and the sulfur dioxide (from the gas or metabisulfite) also makes the spent acid a sulfuric solution. So I don't see an excess from incomplete rinsing affecting your reaction.

Did you test the solution with stannous after the gold was dropped? Was the solution mixed well when you tested it? I have seen solutions dropped with SMB, tested to assure a complete drop, but never mixed thoroughly and the result was the waste was holding metal (substantial). I suspect that you did not completely kill the nitric and after you dropped the solution, gold redissolved.

Fortunately the copper caught it for you!

 

[kernels]

Thanks 4metals, I have become a bit lax in my testing of solutions. I usually see the gold going into solution, then see it again coming out of solution, then have some copper in the solution for a few days. I also have built up a bit of an idea of how much gold I expect, so am certainly not testing anywhere near as much as my early days.

I suspect you are likely correct that I may not have 100% neutralized the excess Nitric. Always appreciate your wisdom.

 

[Shark]

Although this is using Hydrochloric and bleach here is a poor quality video of what happens when you don't have the oxidizer neutralized. I done this to show that if it is a small excess you could over power the oxidizer and get the drop to produce anyway, although it isn't a good way to do it.

Please don't use food type glassware for refining and ever use it for food again. I bought this glass just for testing some things.

[youtube]http://www.youtube.com/watch?v=V6DPbGiccNc&t=31s[/youtube]

 

[4metals]

I have become a bit lax in my testing of solutions.

Sooner or later this practice will bite you in the "arse" as you New Zelander's would say.

I have been looking at solutions dropped with SMB or SO₂ for more years than I care to remember. And yes there is a discernable color shift which can be used to indicate the reaction is complete. But I always preferred to use the color shift to tell me it is time to test with stannous. Waste acid with gold always seems to look just like waste acid without gold, and I always preferred to err on the side of caution. It is never fun chasing unrealized yields through the refinery, I have had to do that for clients too many times, it is better to perform a simple test and know you have recovered all the recoverable values when necessary.