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Electrochemistry Clearing a pregnant leach
- Thread starter rusty
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- Feb 25, 2007
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No opinion. Not something I ever tried.
I'd still be inclined to cement with zinc, however, assuming you have a source of zinc. It's much easier than dealing with a deposit that may or may not release easily from stainless.
I think I'd be inclined to do a small test batch before committing to electrical recovery. Might save you a lot of grief.
Harold
I'd still be inclined to cement with zinc, however, assuming you have a source of zinc. It's much easier than dealing with a deposit that may or may not release easily from stainless.
I think I'd be inclined to do a small test batch before committing to electrical recovery. Might save you a lot of grief.
Harold
A big problem with trying to plate everything out is that, as the metal decreases in the solution, the cathode efficiency decreases and, at some point, all or most all of the current will be splitting water (or, kicking off chlorine gas, if HCl is present) instead of plating metal. If the metal is low to start with, this might start immediately. In other words, it is unlikely that all of the metal will plate out. Also, if there are a lot of base metals, as compared to the PMs, the base metals will generally tend to plate out first. Also, the success of this can depend on the acidity (or, alkalinity) and/or the type and quantity of the anions in the solution. The current density can also make a difference.
After saying all of this, try a liter sample and see what happens. When trying to plate from a non-perfect solution, there are a jillion parameters and things can be difficult to predict. You'll never know until you try it. If you get it to the point where the solution tests negative for PMs, I guess this would be a success. Of course, then you would have to deal with the separation of whatever deposits on the cathode. If you can rig up a loose cloth bag that surrounds the cathode but does not touch it, that would help confine the loosely or non-adhering deposit that will probably fall off. If the bag does touch the cathode, the deposit will grow through the bag. Been there, done that. Maybe some sort of plastic frame with a lot of hole area could be put between the bag and cathode. Or, maybe you could just filter the solution ever so often. Just thinking out loud.
After saying all of this, try a liter sample and see what happens. When trying to plate from a non-perfect solution, there are a jillion parameters and things can be difficult to predict. You'll never know until you try it. If you get it to the point where the solution tests negative for PMs, I guess this would be a success. Of course, then you would have to deal with the separation of whatever deposits on the cathode. If you can rig up a loose cloth bag that surrounds the cathode but does not touch it, that would help confine the loosely or non-adhering deposit that will probably fall off. If the bag does touch the cathode, the deposit will grow through the bag. Been there, done that. Maybe some sort of plastic frame with a lot of hole area could be put between the bag and cathode. Or, maybe you could just filter the solution ever so often. Just thinking out loud.
freechemist
In Remembrance
Hi Gill,
If the 30 liters of pregnant solution are based on HCl primarily, I would not even give it a try, to recover the values by electrical current. 1.) Pd, and especially Pt from HCl-solutions are not reduced easily by electrolysis to the metals. 2.) Stainless steel in HCl-medium will not last a long time without heavy corrosion, even if connected as a cathode. 3.) The "corrosion-activated" stainless steel itself will cement values out of your solution, thus making an electrolysis an out of control process.
If the pregnant leach is based on HNO3 (H2SO4) exclusively and does not contain halides, not even in traces, it may be, that cathodical reduction works, but even then I would use graphite, or better, glassy carbon as cathode material, not knowing if a metallic deposit will release easily from the cathode-base.
Regards, freechemist
If the 30 liters of pregnant solution are based on HCl primarily, I would not even give it a try, to recover the values by electrical current. 1.) Pd, and especially Pt from HCl-solutions are not reduced easily by electrolysis to the metals. 2.) Stainless steel in HCl-medium will not last a long time without heavy corrosion, even if connected as a cathode. 3.) The "corrosion-activated" stainless steel itself will cement values out of your solution, thus making an electrolysis an out of control process.
If the pregnant leach is based on HNO3 (H2SO4) exclusively and does not contain halides, not even in traces, it may be, that cathodical reduction works, but even then I would use graphite, or better, glassy carbon as cathode material, not knowing if a metallic deposit will release easily from the cathode-base.
Regards, freechemist
