Gold dust with HCL/CL method

[arsenic123]

Hello guys,
I have been on this forum from long time trying to grab the things on catalytic converters and other technique. Its going great till now.
I have been using AR to refine and recover gold from dust and other gold scrap from last 3 years. The material is basically sewer dust from an area where gold and silver work is done. It might be contaminated with other base metals too like copper, nickel, etc. I have fine powder which is burnt, sieved and made a very fine powder. The procedure I have been following from last 3 years is dip the dust in HCL and slowly add nitric acid with stirring for every 15 minutes till 4 hours. For 3-4 hours it’s just stirring and adding nitric acid in small quantity and then I leave the solution for 24 hours and next day I wash, siphon, filter and finally add SMB to drop the gold. It’s going great till now. Now I have been reading a lot on the forum is that hcl-cl method is actually better option for gold dust than AR. I am going to give it a try with HCL-CL now. Now I have some questions with it. As I said above that I use AR with nitric acid to dissolve the gold and I usually leave it for 1 day after stirring and adding nitric in small addition. So instead of nitric acid I will use HCL-CL in 4/1 parts as I read in general reaction list.
Now my question is should I use the same procedure and instead of nitric acid I will use HCL-CL method? I have been reading a lot on this forum and I found that if I heat the solution the chlorine gas will be driven off easily or I can just put in under sunlight for a day and that will drive off the chlorine gas slowly.
The questions are:
1) How much time should I heat the solution to drive the chlorine?
2) Should I use the same way CL the way I use nitric? i.e adding in small increment for 2 hours and stirring in every 10-15 minutes?
3) Heating would be better or just leaving in sunlight would be a better option for driving excess chlorine out and to ensure that I recover 100% gold. If heating how much time should I heat? Or how much days should I have to keep it in sunlight. (I know testing small sample in stannous chloride will tell me that but I am looking for approximate time depending on the user’s experience)
4) Should I use diluted HCL or 32% pure would be good?
5) For CL I have sodium hypochlorite 10%. Should this be diluted to make it 5%?
Any other tip you guys want me to follow in this process?
Also how to avoid adding more chlorox or bleach? Any special note or any way to know it if its enough? I know if I take proper measurement it should be 4 parts HCl and 1 part bleach. Still there is always a chance of adding excess bleach like nitric acid.
Thank you for everything.

 

[g_axelsson]

Hi Arsenic,

I think most of your questions would be very hard to answer unless someone is running the exact same material as you do.

Cl is is just a dissolved gas so it is easy lost to the atmosphere through the surface of your leaching vessel. The rate of loss is depending on the size of the vessel, temperature and if you have some sort of lid on top. (Warning! Don't add a tight lid as pressure can build up and you can get an explosion!) I usually add a piece of plastic film on top, it can't keep any dangerous pressure levels and it creates a Cl atmosphere that minimizes Cl loss.

Personally I think nitric acid is a better solution in most cases. I'm only using HCl Cl for redissolving small amounts of gold powder, nitric is my choise in all other cases.
If you want to test the method, take a well mixed batch of material and split it in half. Recover the gold with AR in one half and HCl-Cl for the other and compare the results. That way you know if you are losing gold with either method.

Good luck and let us know how it works out.

Göran

 

[Shark]

It has become my personal preference to use AR on things that might be a bit dirty and hydrochloric / Clorox once things are fairly clean. I haven't quite figured it out yet why, but for me, it seems easier to deal with silver (and other contaminants) from AR. It is very possible I just haven't learned the hydrochloric / Clorox method well enough also. Being able to use both properly can only be a benefit down the road so I keep using both at different times.

P.S.
I have been using 32% Hydrochloric and 10% Clorox. A cover seems to be a much needed thing, as the bleach gases seem to dissipate quicker than nitric. I do leave mine sitting in the sun in an open area as well.

 

[Palladium]

For this i would use ar also.

 

[eaglewings35]

Arsenic, I found that if I use my bubbler and add air, that it drives off the chlorine
really quick. Depending on the amount that you used, all the chlorine can be driven off in less than an hour.
This work really well, and the smb drops just as it is supposed to.

 

[Charles Connor]

I refine that kind of scrap too, also for me the AR process is the only one i use, because i think it is better to work with the CP grade acids... I have seen that method in a Youtube video but the gold was already refined so few impurities were in the gold, the guy used HCl and this pool chlorine flakes and a variety of lab instruments setup...

Here is the link: https://www.youtube.com/watch?v=Iwvt_QHeb7o