# Selective leach?



## Traveller11 (May 13, 2012)

Outside of cyanide, are there any leaches that will leach only gold and not touch base metals?


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## butcher (May 13, 2012)

Search sodium thiosulfate (hypo) used in photography.

Other methods are to leach base metals and concentrate the values, like dilute sulfuric acid.

Much depends on the type of ore; it is not all alike and so not all treated alike.


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## Traveller11 (May 14, 2012)

Thanks, butcher.

I've been reading about the sodium thiosulphate leach and, from what I've read, it is a very touchy leach with limited success. It will put gold into solution, it seems, but only under very precisely controlled conditions. If only cyanide wasn't so dangerous to use; it seems such a simple process.

You say base metals can be removed with dilute sulphuric acid? What percentage would that be?

The only base metals I have in any appreciable volume are iron oxides in the form of magnetite and hematite. Although some thought they were too tightly bonded with oxygen to be affected, the iron was definitely going into solution from these oxides when I attempted to remove gold from my black sand concentrates with the acid/clorox leach.

I have decided the only way to make the acid/clorox leach work on my concentrates is to remove the iron from them first. If you believe dilute sulphuric acid is the answer, I'm all ears. Someone suggested hot HCl would do the same thing. Is that possible, too?

As to the type of ore, this is strictly beach sand, black sand and micron sized particles of free gold.


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## butcher (May 18, 2012)

magnetite can be roasted crushed and re-roasted making it into hemitite (which is also roasted), hemitite will react with acid's, where magnetite will not very well, sulfuric strong will not work, but dilute it will work, and it will dissolve the iron (or iron oxide) making ferrous sulfate FeSO4 from hemitite Fe2O3 in dilute sulfuric acid H2SO4:

Fe2O3 + 2H2SO4 = 2FeSO4 +1/2 O2 +2H2O

this reaction can go both ways, in mining sometimes they will add SO2 or other additives, to help the process, some time because iron will quickly deplete the acid they will remove the iron from the acid, (making Iron hydroxide with high heating and sometimes under pressure, and reuse the acid to collect more metals, regenerate sulfuric and the SO2 gas, in this process, they also can make the sulfuric acid from the process of roasting the ore, bubbling SO2gas generated from the roast into water and sulfuric to make oleum and then diluting the oleum into more volume of sulfuric acid, you could do some research into heap leaching and get some Idea's, sulfuric acid is not the only acid, HCl, with other oxidizers are also used, citric acid and others are also used depending on ore and what they are after, or cost in recovery or type of ore they are working with.

trouble with leaching ore for the small guy is the costs of acids, and disposal of waste, (not to mention the price of fuel), so unless you concentrate the gold in your ore (floatation for sulfides), or pan your placer gold I feel acid leaching large volumes of rock is going to cost more than you could gain in value.

I do not think there is anything easy when it comes to mining.


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## Traveller11 (May 19, 2012)

butcher said:


> magnetite can be roasted crushed and re-roasted making it into hemitite (which is also roasted), hemitite will react with acid's, where magnetite will not very well, sulfuric strong will not work, but dilute it will work, and it will dissolve the iron (or iron oxide) making ferrous sulfate FeSO4 from hemitite Fe2O3 in dilute sulfuric acid H2SO4:
> 
> Fe2O3 + 2H2SO4 = 2FeSO4 +1/2 O2 +2H2O
> 
> ...




If magnetite does not react with acids very well, perhaps it is the haematite, and not the magnetite, that is giving me problems with the acid/clorox leach? 

As to concentrating this material, this work has been done already, in large part, by the ocean. I further concentrate but not by gravity methods. This material is far too fine to be caught by gravity methods. The best way to concentrate it is to take advantage of the gold's minute particle size and classify it by screens. This way, very little gets lost but the volume is still reduced.


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