Why won't my gold precipitate?

[Oz]

I am not a chemist so I can not give you an exacting solubility curve but the solubility of Cl2 gas (chlorine gas) is increased with lower temperatures and decreased with higher temperatures. This is why heating your solution drives out the free chlorine.

It may also be of interest to you that the solubility of the SO2 that is generated from your SMB will behave the same way as to how much of the gas is able to be held within your chloride solution at a given temperature. This is why Harold used to ice his highly concentrated solutions of auric chloride in order to counteract the heat that was generated from the reaction.

Cold temperatures can be your friend for some reactions.

 

[lazersteve]

Just wanted to say the last 2 small drops I did got harder and harder to drop.
I will try heating the solution now, the weather here got colder and I can see the effect it has on dropping the gold.
It appears the chlorine can't dissipate very quick at all.

The speed at which the chlorine dissipates is temperature dependent. Other factors would be the volume of water in the solution and if there is still a chlorine producing reaction going on in the solution. If the reaction keeps producing chlorine at a rate greater than it is dissipated, then the chlorine levels would no decrease.

Working with HCl-Cl is like working with nitric acid in the sense that if you use excessive amounts of oxidizers (nitric= NOx or bleach=Cl) to get a fast dissolution, you end up with the problem of removing them to get the gold to precipitate. Matter can not be created or destroyed, it merely changes forms. For this reason if you add too much of a reagent to your reaction during the dissolution stage, it will have to be removed before precipitation can occur.

Steve

 

[adam_mizer]

The heat/warmer drove the chlorine out pretty much right away. Several minutes of low/warmer.
Well I've been eyeballing this pretty good lately.
Decide on a measured amount of HCl, on a small amout its just a hair too much maybe, been trying less and less.
Then drop in a tiny amount of clorox, and again just until a reaction is working which amounts to about 25% or less of the HCl poured in.
Just to use barely enough to take all the gold into solution over a few minutes time.
My ambient temp may be 40 or below, and above 45 worked better. There's a difference.

Now I havn't seen the other end of this spectrum when its actually too hot of an ambient temperature.

 

[lazersteve]

You'll also find that actively stirring the mix will promote a faster dissolution of your gold and also produce the maximum amount of chlorine from each Clorox addition.

Steve

 

[dtectr]

Do I have this right??

Not to get side-tracked - i believe this is relevant ...

According to info re: Plattner's Process:
"Chlorine gas will react with gold.

Typically the reaction is done at elevated temperatures or in the presence of aqueous HCl at lower temperature." [from lazersteve] http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=5815&p=50167&hilit=plattner#p50167
Using a minimum of HCl minimizes the dissolution of base metals (acc. to Ammen). Using HCl:Clorox at a ratio of 1:1.5 in a sealed vessel, rolled to effect maximum exposure of Gold to chlorine gas.
At lower temps only as much HCl to initiate the reaction & time to allow chlorine gas to develop, accumulate, & dissolve gold. So extra Clorox is better than extra HCl, as long as it is expelled sufficiently before precipitation is attempted.

Is this a correct interpretation??

any feedback appreciated.
thanks

 

[lazersteve]

My observations using HCl and Clorox is that it works better in the cold and faster with more diluted HCl. This also requires less zinc to precipitate PGMs when processing cats.

The quote you posted of mine concerning chlorine at high temperatures is a reference to gas phase extractions, not aqueous ones.

I would not read too much into the quotes you have posted. It seems as though you are headed in the direction of selective extraction of gold using HCl-Cl and I can tell you from experience with this idea, it has hidden problems. The biggest problem with attempting to use HCl-Cl selectively for gold is the fact that the other base metals work against you by cementing your gold out of the solution.

Steve

 

[dtectr]

that's what i was wondering - butcher always adds the comment, regardless of process, e-scrap or ore, that if base metals are still present, they WILL cement out some values & if the ratio is high enough, the process may slow or stop altogether.

what about the amounts of Clorox added? I know the more I add the more I have to worry about dissipating, but that aside - is having too much chlorine an issue, as to effective dissolution of gold?

I'm sure this has been covered elsewhere - problem-solving as in this post help me to see these procedures in real-life scenarios, which, because of my ADD, is how I learn & retain. You can imagine which of my instructors in school thought I wa a genius/moron ! :lol:
thanks again

 

[lazersteve]

Once the solution is saturated with chlorine, which depends on the temperature of the solution and it's acidity, any additional chlorine produced goes up in smoke as a greenish-yellow chlorine vapor. If you are seeing chlorine vapors rise out of your solution, it is saturated and you are wasting Clorox by adding more.

At this point you need to stir and apply low-medium heat until all of the chlorine reacts with the gold or is driven out by the heat.

Once the chlorine is either used up or driven out of solution, either add more Clorox ( if there is still undissolved gold) with stirring or stop the reaction and allow to cool, then filter, if the gold is all dissolved.

Steve

 

[dtectr]

thats exactly what i was wondering - thanks.