Question concerning the History of the AP process,..

[eagle2]

Nopyrite
Looks like your Gold went into solution.
The way I recover small amounts of Gold mixed in with large amounts of base metals is with a Zinc precip.

First the solution needs to be brought as close as you can to neutral Ph, without precipitating a lot of base metals. Heat the solution to about 50-80c. Add about 1-2 grams of dissolved and filtered Sodium or Ammonium Thiosulfate per liter.
Then add small amounts of Zinc powder with stirring. Keep stirring 5-10 minutes. Add just enough Zinc to precip the antisipated amount of Gold in solution.

This will give you close to 100% recovery.

Al

 

[Harold_V]

In a case where one decides to recover values with zinc, you should consider the idea of leaving the solution acidic, perhaps down around 2 pH. Introduce a tiny amount of zinc, which will reduce some of the base metals, which, in turn, will precipitate the values. By using precious little zinc, you should be able to achieve a 100% recovery of values by this method, without including the base metals. They go back into solution when the values are precipitated. I get the idea that's what's going on with your method. Could be wrong, however.

Flirting with pH can be troublesome in that when you lean towards basic, pretty much anything that's in solution has the tendency to precipitate. Have you had any experiences that are in keeping with that thought?

Harold

 

[eagle2]

Hi Harold
Yes that depends on the base metals in solution and very importantly, their concentration. Tin starts to precip around Ph 3. Iron soon after. You absolutely don`t want to precip the base compounds here. But if the solution is too acidic the Zinc will dissolve without doing any work of reduction.

AP processes are way acid, well below Ph. 0.1 i`m sure. Its necessary not to be that acid for a Zinc precip.

I gradually raise the Ph, until the soultion starts to get cloudy, then back off some with HCl. Adding Zinc always has the effect of raising the Ph. anyway. So the precip of Gold is well contaminated with base metals. But at least you have recovered most all the Gold from a very large amount of base metals.

It used to be the recommened method of using Zinc, was to add 5-10 fold excess Zinc, with much stirring, hoping to cement the Gold on the Zinc particles.The Gold covered the Zinc particle and most of the Zinc was unused and wasted. Then they only claimed about 70% recovery!!

The important discovery that made Zinc so much more useful was the addition of the Thiosulfate. This chemical has an effect which uses all of the Zinc particle and allows close to 100% precip.

I dont have the document that describes this effect, handy with a link, but if anyone requests it, I will find it.

I have used this method many times and it works.

Al