gold and silver strippers

[future gold refiner]

future gold refiner

I believe what Nick & Deano are trying to tell you is that in order for the ferri or ferro cyanide complexes to work the iron (ferri or ferro) part of the complex needs to be disassociated (separated) from the CN part of the complex so that the CN becomes free CN in order to dissolve the gold --- in other words - once you are able to disassociate the iron in the complex from the CN in the complex - you in fact then have CN - which then allows the gold to dissolve

-> this is clear, since I wrote all the old posts about ferri and ferro

The iron can be disassociated from the CN with UV --- the problem is in getting "proper" exposure of the UV to the iron/CN complex to get "effective" disassociation of the iron from the CN - so that the CN can be effective in doing its work to dissolve the gold

As much as doing this in a small batch beaker can (or not) work (if you get everything right) it becomes "much" more complicated to get everything right on a LARGE scale in order to free the CN in order to get "effective" use of the CN to dissolve the gold

Though I may be wrong - I believe trying to use the ferri/ferro/CN complexes as a stripper on a "large" scale will do nothing but cause you frustration from one batch to the next

To put it another way --- what you are "in fact" trying to do is strip/leach gold/silver plating by way of CN stripping/leaching --- but you are also complicating the process because you first need to disassociate the iron from the CN for the CN to work --- so why not just go with actual CN in the first place ?
-> maybe somethig I have to hear, but i dont want to ....

I understand that you don't need permits to get the ferri/ferro/ CN complexes - whereas yes you will need to be properly permitted to set up for actual CN processing --- I would think that on the scale you are talking about the cost of getting properly permitted would "more" then pay for its self - then the frustrations you are likely to run into with a "work around" in order to avoid permits
-> you all can´t belive how difficult it is in germany to get permitions -> everthing that makes it safer, reduces time to get permitions or makes it possible at all >>> because they can just prohibit it or put the level of what you have to do so high that you don´t wanna start something ->>> german authorities become crazy over the last years



Also -keep in mind that once you disassociate the iron from the CN - you in fact have CN - so your waste is going to be CN waste - so you are going to need to deal with that waste the "same as" if you had started with actual CN in the first place

Also - as Nick pointed out in order to get FULL stripping - its not a matter of just putting the solution in motion - the material its self needs to be put in motion - other wise the solution will not get to the gold on parts that are touch each other

please look to the next post ->

That's why the "big boys" do this in open tanks (with proper ventilation on &/or over the tanks) the parts are then put in a barrel (that has holes & screens over the holes) the barrel is then submerged in the tank & turned so that the material moves in the barrel allowing the solution to come in contact with ALL surfaces of the plated parts - other wise part that are touching each other will not be completely stripped

Also you can not - under "normal" CN leaching conditions strip gold/silver plating if the plating is on aluminum - that's because CN leaches are normally run at (about) Ph 11 --- at that PH you will dissolve the aluminum instead of the plating --- so stripping gold or silver on aluminum is another story in & of it's self

Kurt

 

[future gold refiner]

Example of how the big boys do it - watch the second video of the video's on this page

:arrow: https://advchem.com/index.php/services/chemical-refining


I know this company and the video -> kind of this "galvanic sttreet" (barrel galvanic ) an offer is requested by a technical engineer I know.

But there is a reason wthy I wantto do it in such kind of vessel.


Kurt

 

[future gold refiner]

Using ferro or ferri cyanide complexes to generate cyanide is done only when you cannot access sodium, potassium or calcium cyanide as leaching material. As mentioned above in this thread the ferro or ferri complexes will give you exactly the same cyano complexes in solution as the straight commercial cyanide products.

You will have to work under the same safety and waste disposal protocols for both starting chemistries because you will have free cyanide complexes in solution no matter which method you use to generate these complexes.

I have seen the ferri and ferro cyanides used in small commercial setups and at the time I wondered why they were used when permitting for straight cyanides was possible. I assumed that they were being used because the operators presumed, incorrectly, that they were safer than straight cyanide, at least that was the explanation I was given.
-> In my case it is only because of permitions. of corse once in solution as "free CN" it is the same "risk potential"

this is the reason why the glycine thing was so interessting.

These operations used a separate tank for the dissolution step so that they could get the CN concentration to the right level before leaching started.

Nick is totally correct when he says that CN leaching of e-waste is a learned art, the variations in substrate types and plating thickness mean that substantial experience is needed to even get your product sorted properly before leaching.

Assuming that you can get an aluminium free waste source you have two options.

Firstly you can use high cyanide levels with strong oxidisers to quickly strip the gold but, as pointed out by Nick and Kurt, you will solubilise a lot of base metals as well as the gold. This is not the cheap option you might have been expecting for processing.

do you have a not "straigt CN" recipe (concentrations) for that ?


Secondly you can use a lower cyanide level with oxygen from the air as the oxidiser. This will lessen the base metal dissolution but will require a longer gold leaching time.
do you have a not "straigt CN" recipe (concentrations) for that ?

do you have a not "straigt CN" recipe (concentrations) for that ?
I would prefer that way - time is not so critical

Everything is a trade-off, if you want a rapid leaching system you will have much higher reagent costs, if you want cleaner leaching you will have a slower processing system.

as always - it is a trade-off

Deano

 

[future gold refiner]

Is there any other way to strip with thiourea (I know carcinogen) or thiosulfate or something else to leach gold / silver? + oxidizer to speed up.
(except of iodine, bromine or chlorine)

Reagent costs are no big problem because I have acsess to big chemical companys - so chemicals are "cheap" to me.

Adsorbtion on Resin is preferred.

 

[nickvc]

If you are looking to strip e scrap you need decent volumes even though it has a higher gold content than many mine products, if time isn’t a problem you are then looking at huge plant with very large volumes of solution at a very low level of cyanide and still have to move that product to effectively strip it, not just the solutions as that will leave gold on product.
To run at low levels, I think Dean has specified what level, you need to monitor your solutions to maintain those levels adding more reagents to keep the stripping going and at low levels it could be days if not weeks before your product is stripped to an acceptable degree.
I know nothing of the other stripping chemicals as I have always found cyanide a good way to strip reasonably cost effectively, efficiently and within acceptable time scales so have never bothered to research those processes, if that is the way you want to go you may well have to develop your own processes through trial and error, all those clever chemists working for the large mines and refiners haven’t bothered or abandoned the idea so unless you are very clever or lucky I guess you may well find the same result.

 

[Deano]

Always look at what the mining industry uses in their processing, despite many myths about secret process methods the industry will always use the most cost effective method and there are a lot of papers available regarding these methods.

In the case of e-waste any acid system will cause attack on the substrates preferentially to the gold plate. This rules out thiourea and thiocyanide leaches.

Thiosulfate leaches are run alkaline but the balance of copper in the leach solution is easily upset by the copper solubilised from the substrates.

The biggest problem with thiourea and thiosulfate leaches is that, despite the claims of ion exchange representatives, gold complexes from these leaches load very poorly both on resins and carbon.

This means that gold recovery from these liquors has to be done by zinc or electrowinning, neither of these is an attractive option when you have low tenor solutions.

Typical cyanide concentrations w/w for sodium, potassium or calcium cyanide are;
High cyanide concentration. 1-2 % per litre
Mining industry usual level. 0.1% per litre
High base metal leaching. 0.01% per litre

Keep in mind that hydrogen peroxide in the presence of oxidisable materials such as cyanide and many base metals will very rapidly disassociate and evolve oxygen unless kept under pressure. This is difficult to do if you are trying to keep visual control of the processing and makes glycine leaching not terribly cost effective. It is also the reason this processing is only used in the mining industry for very high grade concentrates.

Deano