I need an advice for impurity handling in cement silver smelting

[conglioa]

Hi everybody.
Today I want to ask everyone about my silver bar issues.
First I will describe a bit about the origin of silver as well as how I do it:
- This silver is recovered by me from the anode sludge of copper electrolysis.
- I use the method of separating silver with concentrated sulfuric acid and then silver cement from silver sulfate solution with clean copper rods.
The cement silver is then heated with 1: 1 hydrochloric acid and all is washed off with hot water.
Then I proceed to melt and cast into silver bars as the image I attached.
My problem now is that after casting my silver bars are covered with an impurity layer, a purple bar and an opaque white bar.
I boiled them with 1: 1 sulfuric acid but it was not nearly as clean. So I have to polish them.
After polishing it I sent them for testing at a gold and silver store and the result was about 99.7% silver and some impurities as shown.
So I would like to ask you for advice so that my silver bar after casting it is the correct color of silver, not covered with impurities as before.
Another information is that when I melted, I removed the slag from the surface with a stainless steel spoon, all the slag was picked up by me, but on the surface of the molten silver water there was always a thin film and I could not remove it.
After removing the slag I put the smashed charcoal into a cooking pot and mixed well to remove oxygen while hoping it could stick the impurity film on the molten silver water but it seemed when pouring it in. in the mold, the film still follows and sticks to the surface of the silver bar.
Hope among the experienced members of the forum can have useful advice for me and I will be very grateful for that.
I wish you a good day.

 

[goldenchild]

The techniques you're using are only good for recovery of silver. If you would like to further refine your silver to higher purity you will have to use an actual refining technique. Many use electrolysis via a silver cell. Some use the "sugar and lye" method. Search around the forum for these 2 subjects and prepare to do much studying.

 

[nickvc]

If you quench your bars while still hot it should shatter the flux from your bars, let the silver solidify and drop into cold water that should remove most of the flux with ease.

 

[conglioa]

Thank you. I am probably the best result of this work and for better silver than I have to refine with electrolysis.

 

[goldenchild]

At .997 purity you're extremely close to fine silver so what you're doing to get these bars to their current state is very good. Electrolysis will take your bars to the next level. Being that your bars are already high purity, electrolysis will leave you with very little contamination in the electrolyte (this is a good thing). Also, if you need to remove flux off of an already melted and cast bar you can simply boil the bar(s) in very dilute sulfuric acid. It only takes a few minutes of boiling.

 

[conglioa]

At .997 purity you're extremely close to fine silver so what you're doing to get these bars to their current state is very good. Electrolysis will take your bars to the next level. Being that your bars are already high purity, electrolysis will leave you with very little contamination in the electrolyte (this is a good thing). Also, if you need to remove flux off of an already melted and cast bar you can simply boil the bar(s) in very dilute sulfuric acid. It only takes a few minutes of boiling.

I boiled the silver bar after casting with sulfuric acid but it doesn't seem to work. The color of the silver bars still cannot return to the correct color of silver, it is still almost original. I was wondering if I could use an extra amount of borax when I melted because these 2 bars when casting I only use a very small amount of borax (I add the borax after scraping off the slag on the molten silver surface ). The problem with the ugly color of the silver bar I think was due to the thin film of impurity floating on top of the molten silver that I was unable to remove it. Is there any way to make those impurities stick together that I can easily remove them like slag.

 

[conglioa]

At .997 purity you're extremely close to fine silver so what you're doing to get these bars to their current state is very good. Electrolysis will take your bars to the next level.

I'm just trying to get its purity to .999 so I'm looking for a way other than electrolysis. If there was no way, I would consider electrolysis because I had done a little experiment to electrolyze one of my silver bars before. The result is a purity of .9999. But I just need to go to .999 because it is enough for the needs of the school where I live.

 

[kurtak]

to get to a purity greater then 99 you have two options

(1) run it in a silver cell - that should give you 9999 silver

(2) or the salt - lye - sugar method - which should also give you 9999 silver

you will NOT get a purity higher then you already have with a smelting process (smelting being melting what you have along with a flux)

that is because there is so little copper in the silver - as it is (997) - melting with flux will NOT remove that little bit of copper - that "little bit" of copper is just going to melt along with the silver & stay with the silver - flux will not remove that small amount of copper

Kurt

 

[conglioa]

to get to a purity greater then 99 you have two options

(1) run it in a silver cell - that should give you 9999 silver

(2) or the salt - lye - sugar method - which should also give you 9999 silver

you will NOT get a purity higher then you already have with a smelting process (smelting being melting what you have along with a flux)

that is because there is so little copper in the silver - as it is (997) - melting with flux will NOT remove that little bit of copper - that "little bit" of copper is just going to melt along with the silver & stay with the silver - flux will not remove that small amount of copper

Kurt

I am also trying electrolysis to refine silver.
But the crystalline silver particles on my cathode are usually small or spongy.
Maybe it's because I chose the parameters that are not right.
Currently I am electrolysis with a silver content of 60g / l in solution. And the anode current density is about 230A / m2.
With such current density my electrolysis tank reaches I = 3A and U = 3V.
The volume of crystallized silver on the cathode is 12 g / h.
Because of the urgent time, the equipment for the experiment is not good, so perhaps everything is not good. The silver appearance on the cathode may not look good, but I know it is still at 9999 because I have also conducted electrolysis in smaller amounts before now.
I am planning to build a silver electrolyte that can handle 2-4kg / day.
Thank you and would love to receive more but helpful advice so that I can take it to improve my work.

 

[ION 47]

you can try smelting with saltpeter, borax, and soda ash. Then boil the ingot in a solution of citric or sulfamic acid. It will not reach 999.9, but the appearance will get better.

 

[sena]

Shaping machine would do better job by removing thin layer on all sides of the block.