Pulling precious and noble metals for iron ore.

[187penguin]

I work at an iron mine that has been dormant for about 30 years. Once at this mine they ran across a vain of silver ore. They sent off about 250 tons of ore and yielded 60 Tons of silver. The company is more interested in the money from the iron ore, but I have the owners permission to hound all the rocks I like. I have rock hounded out there a bit and found a few dozen pounds of softball size chunks of this ore. Most of the metal in the ore is silver (about 50-60%), then Iron (40-50%), then gold (5-10%) and then a bit of copper(1-5%), and occasionally trace amounts of platinum group metals. I have a bit of nitric acid and was able to make detectable amounts of silver from a 1.5 oz sample by classifying it to about 40 mesh, bathing it in nitric acid, then using copper to displace the silver. The remaining sludge shows no trace of copper or silver, just iron and gold. I would like to get rid of the iron and copper, pull the silver and gold, and if I could collect the platinum metals to send off to a commercial refiner that would be gravy. I have access to a 2000 degree F electric furnace that can handle about 6 lbs. and a small ball mill that can handle a 6 lb sample.

What I am thinking I could do is crush and ball mill 6 lbs at a time, then electrically smelt it at 2000 degrees in 3lb portions with the flux explained here (poorman's smelting) http://www.nuggethunters.org/Poormans-Smelting.html
# 1, anhydrous Borax, 5 parts. [regular Borax from the supermarket will do the same]
# 2, #70 silica sand, 40 parts. [get it at any home depot]
# 3, soda ash, 10 parts.
# 4, sodium nitrate, 20 parts [oxidizer].

Then I think I can toss the flux that hopefully will just contain iron and copper. I should be left with a button containing silver, gold, and maybe platinum.

Then after I collect a few buttons from this I could bathe them in 70% nitric to pull the silver, then precipitate it either with copper or with salt then heat at 2000F with soda ash and pour it. If I could figure it out, I would really like to use electrolysis. I do have a 3.5vdc 20amp power supply. I think that's about what silver needs.

Then hopefully I would be left with gold and maybe trace amounts of platinum. I would like to pull the gold out, maybe with aqua-regia, or figure out a gold flux and smelt it, but I dont know if 2000F is hot enough.

Any Ideas or input? Thanks.

 

[Barren Realms 007]

Sounds like you have a game plan laid out there. You might consider melting your uttons together and pouring the material into a cold water bath slowly to cornflake the material so your acids can work on it easier.

Welcome to the forum.

 

[187penguin]

Thank you for the welcome!
I have a follow up... could I use a sodium nitrate bath to get rid of the iron and copper in lieu if using a smelter ? I read this:
SODIUM NITRATE (NITROGEN) BATH(FOR DESOLVING IRON,COPPER,AND UNWANTED METALS)
1 CUP SN + 1 CUP WATER(DISTILLED WATER IF YOU WANT).
I would rather use chemical solutions than acids to get rid of the iron, copper and other impurities since I can get most all of the chemicals for ~50-90 cents a pound delivered, but not the acids. Nitric costs me $160 for a case of 6x 2.2l bottles delivered.

Also, is there a way to dissolve all the ore in aqua-regia and selectively precipitate the metals straight from ore? Or would that need too much acid? I believe I can precipitate platinum group metals with ammonium chloride, the filter and let it set unheated for a day to see if any rhodium falls, then can I use plain salt to precipitate silver and smelt with soda ash, then heat the solution and use urea to neutralize the nitric acid, then use a warm sodium metabisulfite solution to precipitate gold, then filter and wash the gold mud with ammonia then distilled water, and smelt with borax flux.

Does this sound right, or can I not use salt in the aqua regia solution before precipitating gold?

 

[Harold_V]

Also, is there a way to dissolve all the ore in aqua-regia and selectively precipitate the metals straight from ore? Or would that need too much acid?

Bingo!
Rarely will you find an ore that can be treated with acid directly. All too much of the acid is consumed on the gangue--so it's just not a viable solution to your problem.

I believe I can precipitate platinum group metals with ammonium chloride, the filter and let it set unheated for a day to see if any rhodium falls, then can I use plain salt to precipitate silver and smelt with soda ash,

Nope! You don't dissolve silver in AR, although miniscule traces are known to go in to solution. When you expose silver to AR, it either remains as elemental silver, or is converted to silver chloride. The addition of salt to a chloride solution won't make any difference. The fact that gold and silver can not be in an acid solution at the same time is the reason it's so easy to part silver from gold.

then heat the solution and use urea to neutralize the nitric acid, then use a warm sodium metabisulfite solution to precipitate gold,

Not sure why you'd heat the solution---and urea is an option, not a requirement. Evaporation was my choice of method of eliminating nitric, or the addition of a button of gold, where it was consumed by dissolving the added gold.

The act of precipitating gold from solution with SO2 (that's what you'd be doing) is an exothermic reaction. If the solution is too hot, gold fails to precipitate---so you're better off working with cold solutions than you are with warm or hot solutions. Very low levels of concentration likely won't make a difference, however (because very little heat would be liberated in precipitation), so that may or may not be an issue.

then filter and wash the gold mud with ammonia then distilled water, and smelt with borax flux.

One does not "smelt" recovered gold. It is simply melted. Smelting is the act of recovering values from ores via furnace. That isn't what you'd be doing.
Ammonia alone is not an adequate washing procedure. Precipitated gold should be well washed with acid (HCl), and should include an ammonia wash, too.

Harold