Traveller11 wrote:Any idea by how much the fire assays under report micron gold ? Would anything else affect a fire assay, say, perhaps, a high salt content in the concentrates?
The most accurate answer is probably, "It depends". And unfortunately I'm not the best person to ask what the various reasons it depends on are, although for one, size does matter. There are occasional reports both here and on MicronGold Yahoo Group of fire Assay under-reporting though and it's generally accepted as normal.
It also depends to which school of thought (David Hudson, Walter Lashley, Paul Welk, etc) on "unreported gold" you belong to. Until recently belief in the existence of undetectable gold (and PMs) was regarded as the "howlings of mad dogs" by the mainstream. But more recently with the findings of researchers such as Al Johnson it is believed that there are significant values (undetectable by traditional means) in certain ores encapsulated and tied up in amorphous silicon (and IMO chelation bonds). It's not high on my list of things to look into (before I die) though.
<Where are we on Salt Cells, BTW? I'm disappointed that the Brazilians weren't very forthcoming; perhaps a search for the right person to talk to would be in order???>
Still toying with the salt cell idea. At the moment, I am more interested in the actual solution produced by the salt cell and the ph of that solution. As you know, a 100 year old version of the electrolytic salt cell actually produces the chlorine solution in the cell, transports it to a revolving leaching chamber filled with ore and then brings the pregnant solution back to the electrolytic salt cell. There, gold is stripped from the chloride, deposited on the cathode and the liberated chlorine is recycled as fresh chlorine solution and sent back to leach more gold.
As far as I can tell, this saltwater electrolytic cell is producing either sodium hypochlorite (NaClO), sodium chlorate (NaClO-3) or both. NaClO in water becomes hypochlorous acid (HOCl) and NaClO-3 in water becomes chloric acid (HClO-3). Both are powerful oxidizers.
Seawater has a ph of about 8. Barring anything else taking place, I cannot see how the ph of this chlorine solution could be anything below 7-8. This is in direct contradiction to the HCl/Clorox leaching method where we are told copious amounts of HCl must be added to lower the ph to 1-2.
Sodium hypochlorite bleach exists only because sodium hydroxide (a base - NaOH) is added to bleach to raise the ph to over 12, preserving the NaClO and preventing it from becoming hypochlorous acid. When you add hydrochloric acid (HCl) to bleach, you get: HCl + NaOH = NaCl + H20. Acid neutralizes base and, once the ph falls below 11.86, sodium hypochlorite becomes hypochlorous acid and sodium hydroxide. NaClO + H20 = HOCl + NaOH, requiring more HCl to neutralize the additional NaOH and continue to lower the ph. In the interests of economy, it would probably be better to use dry calcium hypochlorite and mix it with water. This would start our solution at a ph of 8, requiring less acid, as this bleach solution would not have sodium hydroxide (NaOH) added to it as a preservative.
So, eventually, our HCl/Clorox arrives at the same place as the saltwater electrolytical cell; namely, a solution of hypochlorous acid at a ph of 7-8. If it was possible to put gold into solution using the chlorine solution from the saltwater electrolytic cell, is there any reason to continue lowering the ph of the HCl/Clorox solution, and risk making it so acidic that it begins to put base metals (iron) into solution, as well?
I am now building a unit that resembles a rock tumbler (ore agitator) and am awaiting mail delivery of a ph meter. First experiment, HCl/Clorox solution of 7.5 and black sand concentrate.
Here is some more interesting reading from the "Prospector's Paradise":
"Remember chlorine is very slow. You will have to maintain this system for several hours to a day or more.
Like all of the halides, if you allow the solution to go acid, the chlorine will rapidly boil off and if you are close by will be extremely uncomfortable. Bromine and iodine are not so bad. They are not nearly so volatile and will give you a little more time to rectify the situation by addition of a little lye water.
If you are extracting with halides, in particular, chlorine where you have no visual reference as to what is happening, you should have some hydrochloric (muriatic) or sulfuric acid at hand. If your reaction should start to slow down and you are sure you have an excess of halide in solution you might have to add a little acid in order to liberate the halide from it’s salt form in order to keep sufficient free halide to ensure a good extraction. If you can keep the pH at say 8.5 you will be about right.
If chlorine production should get out of hand, you probably should have some solution of sodium thiosulfate on hand. It can be bought from any chemical supply. This is the stuff that tropical fish freaks use to treat tap water to destroy chlorine. You will need much more than they use however. This is a good way to neutralize any solution you wish to dump. Your neighbors will probably appreciate your thoughtfulness."
"He was always cold, but the land of gold seemed to hold him like a spell....Though he'd often say, in his homely way, that he'd "sooner live in Hell"....." ~~Robert W. Service~~
"When you live beside the graveyard, you can't cry for every funeral." - Russian Proverb
"Good judgement comes from experience, and a lot of that comes from bad judgement." ~~Will Rogers~~