Hi Avled,
I’m doing very similar work and wanted to give me experience as being novice, reading hokes book and listening to the advice given here.
I start by going to a concentrate micron of under 40. It’s very very fine and what I’m looking for is the black sands/precious metals beginning to “clump” or move en masse as one in a sifting pan. I did much trial and error with sulfides and creek bed concentrates at over 40 micron and it just wasn’t concentrated enough for me personally to break the ratio possible in aqua regia.
After the concentrating I then roast the cons to help liberation (it appears sulfide rich ores tend to clump together or slime up) and from there I’ve noticed it’s actually better to not magnet these as it appeared to me that gold was being lost in the end.
Then I place about a pound of this material in a beaker and add HCL and boil it for 30 mins to an hour or more and pour off/rinse with water and toss the liquid
Then I add hcl to cover the material and add 5-10 mls of nitric and boil it to get a nice bubbling/reaction. I will then do this until the reaction calms down and add splashes of HCL to bring the temp down in the solution (it seems if you add straight nitric it will boil over) followed by a splash of nitric to start the reaction again.. continue till done..
Before doing this I was pre mixing or trying to at best run through 1-5 boiling reactions and then precipitating. Depending on the levels of precious metals or gold I was getting color changes and at best all the gold would go into colloidal/small amounts would begin to precipitate but never a full drop.
I can only venture to understand the high science of this but if you look at the different sol’s of gold concentrations in solution you can see different colors that go from red to orange to red to purple… these correlate to concentrations and SIZE of gold particles in solution. I’m sure a chemist or experienced worker can explain this much better than my limited understanding.
From here I tried various methods of expelling nitric and always found the sulfmaic acid method to be a bust for me. I’m not sure why but it didn’t work for me and so I went to the evaporation method. My methods follows hokes to the best I can..
I will evaporate down to approximately the amount of nitric milliliters I used (I’m not sure if you run into the same problem but when evaporating concentrate aqua regia you eventually come to a spot where all the lead salts and silver chloride prevent full evaporation to a syrup as a refiner of scrap or jewelry would encounter, so you either pour off the liquid and leave these solids behind and continue the evaporation or get as close as you can and add hcl) then add hcl. I’ll do this a minimum of 3 times.
An assay on the material you are working with is invaluable however I do believe it’s possible with keen observation and knowledge to perform this refining without the need of an assay; an assay would be invaluable not to warn you of the toxins potentially in the cons but as a benchmark for how to perform your refinement and expelling of nitric and precipitation of the precious metals
Have you had luck in your venture? What kind of material are you working with? How long have you been at this?
Did you notice these black sand concentrates having gold near invisible as I have as well? Under a microscope they are there but otherwise it’s extremely difficult to tell, I end up going by feel and weight and the sluggish look of the lighter material in a gold pan to give me an idea. when you roast so you notice brown specs appear that look like precipitated gold from solution as well? I have started using color as an indicator of particle size as well… the more dark brown and light brown/black the better… sulfides like I said tend to be much lighter and clump together but potentially could be of better yield …
Also.. when evaporating I started by taking the sulphuric acid out of a car battery and using it as the sulphuric acid to help drop the lead when evaporating.. while this worked if I used enough (it’s around 30%) you can buy a 32oz bottle of 95%+ sulphuric acid from your local ace hardware sold under the trade name “roto”… lol. follow hokes suggestion and add slowly to a hot evaporating aqua regia and you will be pleasantly surprised (around a ounce per liter).
If you can’t drop the gold out of your aqua regia save your liquids and eventually in theory you could have enough gold to do a drop.. but this could take time and you would still need to add a properly concentrated aqua regia to these other solutions to drop
