AR - another first for me

mikeinkaty · Apr 9, 2013

Had some time to kill so decided to process my filter papers.

I incenerated them in a SS bucket and got out most of the ash. Washed with water, let it settle out, decanted the murky liquid, repeated that process again, filtered it, dried it, then added Nitric & dh2o to disolve out the silver.

Filtered again and kept the AgNO3 for dropping. I rinced the solids, dried, and weighed. Wt was 4.2 grams.

Mixed up 12ml of HCL (Muriatic acid 35%) and 3 ml of 68% nitric and added it to the solid material. In 2 minutes the solution was a yellow green color or maybe gold-ish. (I'm red green color blind).

(side note) I dropped more silver than expected. The little beaker was half full of the percipitate from the copper drop.

I'm going to let the AR go all night. Will rince, filter, and weigh the silver cement tomorrow. I figure to add water to the AR, let everything settle out, then decant off to another beaker and save that aside for the SMB once half or more has evaporated off. (should I add the water?) The rest of the solids I'm figuring on doing the AR thing again (depending on how much is left) with a hot solution.

The solids left behind after filtering the AgNO3 solution were real grainey - almost like sand???

How is this so far?
Mike

butcher · Apr 9, 2013

You will want to be sure you have no free nitric before diluting the aqua regia.

mikeinkaty · Apr 9, 2013

butcher said:
You will want to be sure you have no free nitric before diluting the aqua regia.

Thanks Butcher. I don't have any Urea so guess I'll have to let it evaporate, without heat. That's kind of slow here in the high-humidity Houston area. Unless there is some other way to neutralize the acid?? What about KOH? Would that work? I have a pound of potassium hydroxide. I think it's 90% pure.

The AR calculated out to be 16 & 4 ml of the two acids (4.2 gms of solids). I backed it off to 12 & 3 ml cause I didn't figure all the solids was gold. But, I really didn't know what volume to use as I had no idea how much might (or might not) be gold. What does one do in that event??

This morning I did notice that most of the grainey black stuff has apparently disappeared into solution. Since AR disolved it and not the nitric, does that mean it was gold? Lazersteve says in his list of reactions that AR must be heated for platinum to dissolve.

Since this is such a small amount I don't figure on filtering anything. I'll just dilute and decant (several times) after the SMB. What is it then? 3 boiling water washes, then 3 dilute HCL, the three more hot water washes, then dry and melt?

Mike

butcher · Apr 9, 2013

mikeinkaty,
We have discussed this in detail many times, you can read several post on this topic, I will not go into detail here, but just give highlight of it you can read more about it on the forum.

If you do not use too much acids, and you use heating in your process, the gold reacts with the acids consuming them, we do figure a little excess HCl in this already, but not that much, with heat while you are dissolving your gold you are removing water (the acid already contains), we also remove the water formed from the reaction, so when done right we will not have much free acid to remove through evaporation or by chemical means, after we dissolve our gold, we consume the acid used reacting it with our gold, also heating while you are working to dissolve your gold you are concentrating the solution for the first time, if done while dissolving your gold you will already have it evaporated down fairly well by the time the gold is dissolved, and then you will not have much liquid to do the following two evaporation's, but also note this, when we do it this way, we do not want to heat the solution too fast or too much to evaporate our acid too fast and drive it off before it has a chance to dissolve the gold.

3.8 ml HCl and 0.95 ml HNO3 will dissolve a gram of gold.

If you do not know how much gold you can guess and add HCl to your guess, add nitric by drops, with heat till the gold is dissolved, leaving a little gold, or adding a gold button when done can help to use up any remaining nitric acid or be sure the nitric is consumed, sulfamic acid will also eliminate nitric acid (making sulfuric acid in the reaction).

Using these figures as a guide and only adding nitric in small amount just enough to dissolve the gold.
With using heat this will help to dissolve the gold and can be concentrating solution while the gold is dissolving, you may not use all of the nitric in the formula above, and when almost all of the gold is dissolved the solution will already be fairly concentrated, not taking much to concentrate it the rest of the way to the first evaporation, after gold is dissolved adding a few drops of H2SO4 which will assist in keeping the solution from forming salts if evaporated too far by mistake, and completing the first evaporation to a orange solution , the added H2SO4 will also help with lead removal later, after the first evaporation, adding a few ml of HCl, to wet and evaporate again to an orange concentrated solution, will not take long the second time, and will help to drive off any excess HNO3, doing this one more time insures most all of the nitric is consumed, As stated above we can leave some gold undissolved to remove excess, or add a gold button and heat to use up any excess if needed, and we can also use sulfamic acid, or a combination of these procedures.

Urea can form amines, which could be dangerous, urea does not do a good job, it is useless to remove nitric acid from aqua regia in my opinion, and if working with any PGM would give problems in recovery.

After denoxing your gold solution, let it settle to decant solution from the insoluble material, to a clean vessel, you want to dilute it with 3 to 4 parts of water, the silver in the form of AgCl2 will precipitate as AgCl, (if H2SO4 or sulfamic acid was used as described above) lead will precipitate as PbCl2, both a white powder with any other insoluble material, letting this settle over night the solution can then be filtered before we precipitate our gold, working with clean glassware and tools is important, the gold precipitant can be left to settle, liquid decanted, and then washed per Harold's procedure, and then re-refined again, and washed again, before drying and melting.

mikeinkaty · Apr 11, 2013

Well, I gut a slight dusting of brown powder on the bottom of the solution beaker plus about an equal amount of white powder. Probably not enough to even register on my scale. But the solution is still yellow. What does that mean?

Mike