electrolysis of (mainly) Cu bars

[scwiers]

In the past I've used electrolysis to remove copper from (dore) bars placed in copper sulphate solution (12v across a bucket of the solution). I guess, I'm wondering how much the sulphate solution 'degrades' after time. In particular, while copper dendrites readily continue to form at the cathode, the solution changes color. In any case, after running a 3-lb dore annode for a few hours, the solution turns from blue to blue green. It seems that the 'sulphate' part heads towards the annode bar, along with the slimes.

 

[Anonymous]

Do you know what other metals are in dore? Sounds like something may be forming an insoluble sulfate - silver sulfate or lead sulfate I believe both are considered insoluble or only slightly soluble, also is there nickel or iron?

 

[scwiers]

yes, pretty much every metal. In the past I've made sure there was *mainly* Cu in the bar before treating. But given the greenish look of the solution, over time, maybe sulphates of iron and nickel.

 

[Anonymous]

with all of the metals mixed in, you may need to evaporate the solution down to seperate by fractional crystalization. You would need to look up the solubility of the metals that are possible and then figure which would crystalize first.

Seems to be expsensive unless you use natural evap or solar.

I wanted to ask, why are you using such a high voltage? you should get better deposit at the cathode with lower voltage, much lower I had been researching this a while ago, I think the voltage should be like 1.5 or even less, search the net and you will get a lot of info on electrowinning copper.

 

[SilverNitrate]

I think the voltage should be about .3 volt for exact copper extraction, nickel would begin plate out above .5 volt.

Actually I wanted to know how to make a .3 volt power supply, from say a transformer from an old microwave oven?

 

[Anonymous]

multiple cells in series, ie, if you have 1.5 volt supply for example use
3 cells, each will drop .5 v.