# Removing Gold with Leach...PH Level?



## Ferrell (Jul 4, 2011)

We're using saturated salt and nitric as a leach on crushed ore (100 minus) that's not a complex ore. We were directed to do so by a lab that leached and extracted gold from our ore. They told us the ore was very easy to extract from with no complex metals that got in the way of extraction, but we're concerned about the PH level as we have a lot of red clay in our material. We have microscopic gold that can't be removed by panning, only via a chemical process. The lab told us we could leach it with the clay intact or wash it, but that the clay (also taken down to 100 minus) could easily contain microscopic gold as well. We've heard (we're new at this) that the PH level is important, and we forgot to ask the lab about it (& can't reach them for several more days). We tested our soil with a simple gardening kit and it shows as a dark green or 8+. Does anyone know if we should be lower than that, and if so, how we bring the level to a 7 (if that's where it should be)?

Also, some of our leach/ore mixes have foamed and been very strong (as to fumes) and others have had no foam at all and only a very mild smell/fumes, with exactly the same mix. We are aware (now) that we need to be above 80 degrees and preferably 88-100 degrees for the 24 hr leaching period, and it's possible that was a variable. We're going to start keeping records of each test run now, but are there other things we need to be concerned about besides the temp and PH? We're doing a 7-1 leach mix, recommended by the lab and what we've read. 

After the leaching we're extracting using butyl and oxalic. Any input/help appreciated.


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## samuel-a (Jul 4, 2011)

Your solution should be acidic to hold the chloride of gold.
You can provide those H+ , either by adding some HCl or sulfuric acid, say 40-50ml per liter.

I'm not sure, but i don't think the caly should bother the reaction.

You might consider also diluting by half the saturated salt water.


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## Reno Chris (Jul 4, 2011)

Really you need to ask the lab to tell you what the pH should be. - even if you have to wait.

As Samuel-a said - the pH needs to be acidic to hold the gold in solution - 6 or even less.


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## Ferrell (Jul 4, 2011)

Yes, we've sent an email to the guy who owns the lab, but he does a lot of field work and is often away for a wk or two at a time. 

Does either the hydrochloric acid (I assume that was the HCl designation?) or Sulfuric acid get mixed into the ore sample first, or straight in with the leach/ore mix? Can either be mixed with nitric acid/saturated salt? 

At this point we're trying to learn and just Googling the individual chemicals doesn't answer specific questions.

The reason we wondered about the clay is it's the only dirt, and we assumed that's where the strongest PH factor would enter in....that if the clay was washed off it could change the PH balance of the remaining ore. We haven't tried that, but just wondered if you have an opinion.


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## Reno Chris (Jul 4, 2011)

The problem is that the lab guy has worked with your ore - none of us have. He's tested your ore and knows all about it - none of us do. 

I can tell you that the method you are using is not a normal commercial method for processing gold ore. I can't tell you about the experience of someone else using that method commercially, because I've never heard of anyone doing it that way except on a lab scale testing arrangement. 

So asking us to explain and define the method the lab developed for your ore is like asking someone to explain the characters and ending of a book he has never seen or read and knows nothing about.


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## samuel-a (Jul 4, 2011)

Ferrell 

I'm no expert on ore leaching or ore composition. Just tossing ideas around based on the limited info you provided.
The pH shifting to above 7 may very well result from the salt water reaction to some alkline cations in the ore, but i might be way off on that one.

Anyways, a solution of a salt is neutral in pH, that's what defines it as salt in the first place.
Once you acid the salt solution, provide it with free H2O and an oxidizer (nitric/clorox/Cl), you facilitate the dissolution of gold (and other metals) and its remaining in the solution as chloroauric acid.

You'd probably be better mixing the salt water with the acid before you put your ore in it... you can even use only dilute HCl (yes, hydrochloric) if you get it cheap enough.
The oxidizer, you should add after the ore is in the leach and put small addition at a time as you do not want an excess of oxidizer in you leach (especially nitric).

You should really get a hold of stannous chloride test solution even before you start the endeavor, look here.

It seems you know you way around enough to get started, stick around, you have a ton of reading ahead...
before moving forward, i'd suggest you to read more posts here of some of our resident experts (GSP, Harold, The rock man, 4Metals and more)
Get a copy of hoke book if you haven't already

Once you understand the basics and the dynamics of the reactions that are discussed here on the forum, you won't need any lab to tell you what to do. You could just figure out for your self.

I'm sorry in advance if there is some mistake in my explanation. I really think you should experiment on a small scale until you get the hang of it.

Good luck and happy 4th of july to you and all.


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## Harold_V (Jul 6, 2011)

I'll comment on one thing, and history pretty much supports the assertion. 

Recovering values by the use of acids, when the source is ore, is rarely successful. You may find that the cost of chemicals far exceeds the values recovered. That's because much of the feed reacts with the acid, not dissolving the values intended. 

Harold


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## Ferrell (Jul 6, 2011)

So you're saying it can't be done to recover microscopic gold from ore, or just that it can't be done profitably using chemicals? I'm not clear....


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## Harold_V (Jul 7, 2011)

My assertion is that it is most likely going to not be cost effective. That, of course, depends on many variables. Typically, the products of ores consume acids at an alarming rate, which is the very reason cyanide, when it's applicable, has been used for the recovery of gold and silver. Given proper circumstances, it can be used for cents on the ton of ore, where acids may cost in the hundreds of dollars. You can verify this information by doing a search on mining and smelting and other extraction practices for precious metals, in aged technical manuals. They were the source of what I learned, albeit many years ago. 

I am not a chemist, nor am I a geologist, so I am unable to determine if your ore lends itself to any particular extraction process, nor do I even know if the method you chose to use is even successful. I highly recommend you go back to the source of your information and seek guidance. If they have been successful in achieving an extraction, they may be willing to provide data to support their findings. 

Harold


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## dtectr (Jul 7, 2011)

What was the result of your assay report? XY oz., g., etc.Gold/ton of ore?
That is the most logical place to start, before spending $100s or even $1000s on chemicals/equipment/etc.

For instance, water has been called the universal solvent. EVENTUALLY it can break down most elements, with the help of other processes. The problem is - It may take millions of years, but it eventually gets the job done. It would WORK, but I wouldn't want to invest my time & materials in that project.

Not trying to be cocky, just trying to help you with analysis reasoning.


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