Zn precipitating...

[dmarth10]

I just tried to precipitate some pgms with Zn. The Ph of the solution was a 4. Added Zn and there was fizzing and foaming. Instantly there was powdery stuff on the bottom. Is it possible for that to be Zn. There is quite a bit of it. Or is that the pgms. I kept adding and the grayish powder kept comming. I dont want this screwed up after 6 hrs. of denoxing. Anyone have an idea?

 

[Harold_V]

Gather the residue and place it in a beaker. Add some HCl slowly. Any zinc that is present will dissolve instantly (even violently)---thus the reason for adding the HCl slowly. What is left after the process will be of value unless you precipitated considerable copper along with the values. Even copper will dissolve with HCl given enough time.

I recommend a boil, then careful rinsing with tap water. Be certain to check the solution with stannous chloride in case there were nitrates present and you re-dissolved some of the values. Not likely, but not impossible.

In my experience, values cemented down by this process tend to be rather fluffy and very dark. A small amount of metal will produce a fairly large amount of residue.

Harold

 

[dmarth10]

Exactly, my precipitant was dark and fluffy. This is giving me some hope! When I was adding the Zn, it reacted and there was visibly stuff falling down through the solution. I guess thats the Zn cementing down the values? I love watching the Zn react with the solution, kinda like a crazy scatter of bubbles shooting every which direction in the solution!

 

[jsargent]

Gather the residue and place it in a beaker. Add some HCl slowly. Any zinc that is present will dissolve instantly (even violently)---thus the reason for adding the HCl slowly. What is left after the process will be of value unless you precipitated considerable copper along with the values. Even copper will dissolve with HCl given enough time.

I recommend a boil, then careful rinsing with tap water. Be certain to check the solution with stannous chloride in case there were nitrates present and you re-dissolved some of the values. Not likely, but not impossible.

In my experience, values cemented down by this process tend to be rather fluffy and very dark. A small amount of metal will produce a fairly large amount of residue.

Harold

I had a similar experience this morning experimenting with a Zn precipitation of a batch of gold-bearing sand I am leaching. A few tenths of a gram of powdered zinc in a 500ml beaker of pale yellow lixiviant yielded an instant drop of dark fluff. As a test I then used 500ml distilled water with enough HCL to drop the pH to 0.9 and I added same amount of zinc. Same result. Now I know pure water, HCL and lab grade zinc is not going to yield any valuable precipitate so what's going on do you think?

 

[Juan Manuel Arcos Frank]

dmarth 10:

Yeahhhh!!!!!...zinc reacts lovely with hydrocloric acid...BUT the bubbles you are looking at are... HYDROGEN!!!!! so be careful because you can blow up,Hydrogen is extremely explosive,so do it outside and do not use too much zinc.We want you healty and alive in this wonderful forum.

Manuel

 

[Harold_V]

Now I know pure water, HCL and lab grade zinc is not going to yield any valuable precipitate so what's going on do you think?

I would certainly question the quality of the zinc being used. Did you try boiling the material afterwards?

In my opinion, there should be no resulting solids. Perhaps Lou can offer an opinion.

Harold

 

[jsargent]

Now I know pure water, HCL and lab grade zinc is not going to yield any valuable precipitate so what's going on do you think?

I would certainly question the quality of the zinc being used. Did you try boiling the material afterwards?

In my opinion, there should be no resulting solids. Perhaps Lou can offer an opinion.

Harold

Thank you for your input Harold.
The zinc was lab grade right out of a sealed bottle so should be high quality. I'll get back to experimenting with it eventually but right now having excellent results with sodium bisulfite. Getting abundant quantities of precipitate of an even yellow color which under 40X magnification appears to be tiny spheres of consistent size. When I get some uninterrupted time I'll fire up the furnace and see how it melts.