Identification of material from paper storage

[sylvesta]

I was wondering if someone could clarify what I might be dealing with. I decided to scrape some of the material off a few filters I had saved in the storage paper bin thinking that it was gold. I placed 2.5 grams into a beaker and decided to boil the material in hydrochloric acid and then nitric acid to dissolve out any impurities that were present. I thought that by using both acids I could eliminate everything except gold and pm's.

The material was very dark brown/black and after boiling in hydrochloric acid I added water and let it stand before syphoning off mixture. The color had lightened slightly so I went ahead and added nitric acid and brought to a boil and left it for 5 minutes. When I returned to check it the material remained but had changed color to cream/white flakes.

The nitric acid I used wasn't 70% as I had made my own by adding 500 grams of sodium nitrate to 4 liters of water and 1 liter of 96% sulfuric acid which has been left to stand and is now a browny yellow color. I'm not sure if this nitric is the problem and if I am dealing with gold.

Any thoughts?

 

[martyn111]

By using both hydrochloric and nitric acid you are in danger of dissolving values as,however much you wash the resulting sediment after the hydrochloric wash, you will never remove all of the acid unless of course you take Harolds advice and perform an incineration step between the two acid stages.

I would have probably gone with the nitric stage first, that would have dissolved any silver and base metals which may have been present, Incinerated the remaining sediment after washing with distilled water until no colour was noted in the wash water, then dissolved the sediment with either AR or HCl-Cl and test to indentify if gold was present before going onto filtering, dropping and washing before melting.

Anyone have any comments on my proposed process?

As to what you may or may not have remaining in your beaker, I will leave that to someone with more experience to speculate on as I have never used "homebrew" chemicals.

 

[jimdoc]

Any thoughts?

Did you test with stannous?
That would answer questions.

Jim

 

[sylvesta]

That's a fair point Martyn111 and thanks for replying to my post. The nitric acid was an afterthought which in retrospect I know I shouldn't have done, especially with a self made concoction of nitric acid and without doing my best to rid the hydrochloric.
I can see now the benefit of incineration and will certainly work that into my processes in future.

Yes I tested Jim but only after bringing the solution to a boil and adding sodium nitrate to dissolve any gold and the liquid did turn yellow but the test showed negative. I spoke with Harold who explained that iron can also turn solutions yellow but as to what the cream/white flakes are I've still no idea.

My only concern at this point is to discount that I have any material of value. The stannous test showed no color change and I made a fresh batch to be sure of my findings. I have now disposed of it and kept the flakes but if they are have no known value I will discard those too.

 

[qst42know]

Have you tried sun light?

 

[Oz]

If you have an excess of nitrates or other oxidizing compounds in your HCl solution it is easy to get a false negative with stannous as to the gold or PGM content that may be in the solution.

If you follow proper waste disposal you will still recapture those values but will have shorted your customer. Never a good thing under any circumstance.

 

[sylvesta]

I did leave the flakes outside but there's not been much sunlight and no change to the material. I know silver darkens as a chloride or at least I think it's silver chloride. I'll have to re-read Hoke's silver section again.

It's very possible then that I've thrown values away by having a false negative with too much nitric in solution. Well that's annoying but thanks for the tip.