I want the silver going into my silver electrolysis cell as pure as possible. The more copper I elminate the longer the electrolyte will last. I see blue color at the beginning of the sulfuric acid wash and even the ammonia wash. This is even after the previous step had been washed colorless.
The filtrate has a lot of silver nitrate. I am not sure what you are really asking here.
Hello James
Sorry for the delay in getting back to this but have not been feeling so good & in fact had to take the last couple days off work & spending those days in bed
First of all let me say nice time laps video of cementing silver with copper - when I was full time refining for a living silver was my "bread & butter" so I cemented a lot of silver & I always enjoyed watching the cement silver slough off the copper during the cementing process (not that I stood there & watched it but checked on it from time to time to see how it was going
Now to the reasons for my question
Have you tested the filtrate (the solution after filtering) for silver ?
To which you replied
The filtrate has a lot of silver nitrate. I am not sure what you are really asking here.
Per the bold print that is what I thought (& the reason for my question)
The reason I figured there is/was still a lot of silver nitrate in your solution after cementation came to a stop (&/or slowed WAY down) was that nowhere in the video did it show you stirring the silver cement that was sloughing off the copper - but rather that you simply put the copper in & let the cementing do its thing until the cementation slowed WAY down &/or stopped --- so you did not get complete cementation of the silver & here is why
In order to get complete cementation of the silver - ALL of the silver ions in the solution MUST come in contact with the copper -in other words - if dissolved silver ions don't make direct contact with the copper the ion exchange of copper going into solution & thereby cause the silver to cement (drop out) of solution can not take place
So what happens if you simply put the copper in the solution & "let it do its thing" is that as the silver is sloughing off the copper & starts pilling up in the beaker & dissolved silver nitrate ions start getting "trapped" in the silver cement that is piling up in the beaker preventing those "trapped" silver ions from making direct contact with the copper which in turn prevents those silver ions from make the ion exchange with the copper (copper going into solution & actual silver coming out of solution) Which in turn prevents you from getting complete cementation of the silver from your solution
So in order to get complete cementation of all the silver you have in solution you MUST from time to time "stir up" the silver cement that is building up in the beaker in order to bring the silver ions getting trapped in the cement up & out of the cement so that they can make direct contact with the copper & make that copper/silver ion exchange
In other words - you MUST stir the silver cement up OFTEN in order to bring the silver ions trapped in the silver cement up & out of the cement silver so they can make contact with the copper or you will NOT get complete cementation of the silver
As you get closer & closer to the completion of the cementing process you need to do this stirring more often & more continuously (longer) & that is because the closer you get to the end of the process you have less & less silver ions spread out more & more not only in the solution but in the cement silver as well - so those few & few ions being more & more spread out in the solution & cement needs more stirring to bring those fewer ions in contact with the copper to complete the ion exchange
I am not saying that as you near the end of the process you need to stir without stopping - just that you need to do it more often & "a bit" longer
Something like this
In the beginning - after about 15 - 20 minutes of cement building up in your beaker you want to give the cement a good "quick" stir (stir for a few seconds) to bring trapped silver ions up out of the cement to make contact with the copper --- you want to be careful here because if you over stir you can cause a runaway reaction that will cause the reaction to foam up & out the top of your beaker (taking cement silver with it) so let it settle until the reaction slows back down (10 - 15 maybe 20 minutes)
As the reaction (foaming) starts to die down after each time you stir the cement you want to start to stir the cement "a bit" more often & "a bit" longer (this is somewhat determined by the amount of reaction you see when stirring) - example - stir "about every 10 minutes for "about" 1 or 2 minutes & again allowing some time for settling (this settling time also allows for the time needed to make the exchange of the silver ions with the copper)
Again - how often & how long you want to stir as well as how long you want to let settle depends on the reaction you see taking place between each stirring
One way to tell that is by how the silver is sloughing off the copper
As you get closer & closer to the end of the cementation process the time it takes for the silver to sough (fall) off the copper slows down --- this is in part because fewer silver ions are making contact with the copper so it starts taking more time for the silver to build up on the copper before becoming heavy enough to fall off
Also - as silver ions become fewer & few the silver cement particles become smaller & more light weight so the sloughing off slows down - this is the "mossy" buildup of the silver you start to see on the copper as you get closer to the end of the cementation process & this mossy build is the result of the acid becoming more loaded with copper ions & less silver ions --- so the acid is becoming less & less effective (weaker) at making the ion exchange
As I said the silver ions MUST make contact with the copper for the ion exchange to take place - so - as you get closer to the end of the cementing process you need to stir more often not only to bring silver ions up out of the cement to make contact with the copper but also to knock the cement that is not sloughing off the copper as fast so the fewer & fewer silver ions can come in contact with the copper
So - if you don't stir more often as you get closer to the end of the process - to keep that mossy silver knocked off the copper & because the acid is becoming weaker & less effective at making the ion exchange - if you allow that mossy silver to build up on the copper for to long the weaker acid starts creating copper oxides - instead of fully dissolving the copper - which ends up in your cement silver --- so stirring more often closer to the end of cementing process to reduce large amount of copper oxides ending up in your silver cement
You know you have come to a point of very near complete (if not complete) cementation when you see little or no mossy silver collecting on the surface of the copper after letting the silver settle for a couple minutes after stirring --- you can test to make sure all the silver is cemented by taking a few ml of the solution (after settling) & adding a few drops of HCl to that few ml test sample of the solution to see if a silver chloride cloud happens
Bottom line here - cementing silver with copper is not as simple as simply putting some copper in the solution & letting it do its thing (just letting the copper sit in the solution until you see little or no more reaction) --- cementation is a "process" that
requires stirring (or some other type of agitation) so that ALL the silver ions make direct contact with the copper
Like anything else in refining - there is a bit of a learning curve to cementation
And for what it is worth - you can in fact turn out cement silver that is between 99 -995 with absolutely NO need for any kind of chem washing (sulfuric/ammonia etc.) just water washing
I will talk about that if/when I get a chance to post again
Kurt
