Alkaline NaOCl leach

[solar_plasma]

http://www.zndxzk.com.cn/down/upfile/soft/20101108/1997-2-5.pdf

Since I couldn't find that anything about this already has been written in the forum, I'd like to share this with you.

It is about leaching gold from iron-/arsenic sulfide ore concentrate by ball milling in a NaOCl/NaOH leach at high pH. The gold will form soluble sodium-gold-complexes while iron stays insoluable in the form of hydroxides. The nano-particles were dissolved within an hour with an efficiency of far over 90%.

I do not believe this can be used for leaching pins since the involved metals might form soluble compounds at that high pH'es, but it is an interesting reading!

 

[butcher]

This looks just like the old barrel process an hypochlorite leach of ore, it has been discussed many times on the forum.

Traveler I believe was one of the members who discussed it fairly thoroughly, and made a lot of post on this old mining process.
http://goldrefiningforum.com/phpBB3/search.php?author_id=1379&sr=posts

 

[Gratilla]

NaOCl and Ca(OCl)2 (sodium and calcium hypochlorite, respectively) are interesting strong oxidizers in that they can leach gold over the whole pH range - although different dominant species come into play over different pH ranges; OCl^- at high, Cl₂ at low and HOCl at mid pH. (See diag, below)



Traveller11 posted a lot of interesting info using hypochlorites to leach high-Fe ores at different pHs. Pity he doesn't seem to visit much these days.

 

[solar_plasma]

Thank you both! I searched all his threads now and only found this topic to be about the high pH leach.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=17336&p=176084&hilit=naocl#p175553

I think I will revisit this topic again after easter vacation, when I can prove some small experiments beside the work. I guess this will not work with kovar, but if it would work, it would be a shame not to have checked this.

 

[solar_plasma]

But wait, according to table 6 of the chinese paper, gold can be leached as H₃AuO₃(_aq) also at pH 9-10 where Ni, Co, Cu as well as Fe form insoluble hydroxides! It could be light at the end of the tunnel. On the other hand, to prevent any cementation all base metal have to be oxidized, as far as I understand. This would take years for whole pins. :mrgreen:

Maybe it could work with the fine e-scrap powders Kevin is working with...oxidizing and removing base metals, leaching gold and treating base metal waste in only one step might be an advantage and a comparably less dangerous alternative to other alkaline methods.

edit: this seems to have good relevance too http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=44&t=16292&start=20#p174537