silver refining problem

[joheleh]

hi guys, i've decided to refine some scarp silver, i've worked it with a proper amount of nitric 1:1 with water ( 2,5ml for grams), well dissolved heating a little the solution, filtered, diluted a bit with water and then i tried to put in a copper bar and suddendly i noticed cementation of silver, but as the silver cement out it redissolve into solution...no settle. so i putted out immediatly my copper bar...i think it's because the solution were still warm...right? so, what's the cause, i'll wait untill tomorrow and i re-try when the solution cool down. any advices?

just like that:
http://www.youtube.com/watch?v=DR1E1M0eoEQ

 

[joheleh]

uhmmm...probably there's to much free nitric...i suppose i've to increase pH from 1 to 4...how?...urea?

 

[goldsilverpro]

Never adjust the pH and never add urea or anything else to this solution.

Sounds like you used too much nitric and the extra is re-dissolving the cemented silver. If that's the case, the silver won't permanently cement until the extra nitric is used up by the dissolving of copper. If you used too much, just put the copper bars in and, eventually, the extra nitric will be consumed and the silver will cement. Test for completion of the cementation by removing a drop of solution and combining it with a drop of HCl or salt water. If a white cloud forms, it is incomplete and you should leave the copper bars in until the test shows no cloud. If, for the test, a drop of HCL is used and it turns yellowish, don't worry about it. Whether or not a white cloud appears is the issue.

At most, a gram of pure silver takes 1.22ml of 70% nitric. Copper takes 4.15ml of nitric/g and sterling silver takes about 1.5ml/g. These figures assume an open top container when dissolving. If covered, it will probably take less.

In the other thread, I told you how to add the nitric in increments and then stop when an increment produces no reaction. Did you do that?

 

[joheleh]

In the other thread, I told you how to add the nitric in increments and then stop when an increment produces no reaction. Did you do that?

Thank you so much goldsilverpro, yes, i've done as you said but...i noticed a specimen of silver scrap i used weren't dissolving, so i had the bad idea to add nitric... :roll: for me that's a great lesson in the fine art of refining.

 

[goldsilverpro]

In the other thread, I told you how to add the nitric in increments and then stop when an increment produces no reaction. Did you do that?

Thank you so much goldsilverpro, yes, i've done as you said but...i noticed a specimen of silver scrap i used weren't dissolving, so i had the bad idea to add nitric... :roll: for me that's a great lesson in the fine art of refining.

When a chunk of silver doesn't dissolve well at the end, try heating the solution a little below boiling for 5 or 10 minutes. If it still doesn't dissolve, carefully pour the solution off into another container and dissolve that final bit with a little fresh nitric and distilled water. Then, combine the solutions.

Before cementing, I usually add more distilled water, about enough to double the volume. Then I filter the solution to remove any dirt that was on the silver or anything else that will contaminate the silver. The cementation seems to work a little better with a more dilute solution. Also, this dilution will absolutely prevent any crystallization of the copper nitrate.

The final cemented silver will never be perfectly pure, but the purity will mainly depend on how well you rinsed it. Several hot water rinses is best. If you are absolutely sure that all of the silver was cemented and none remains in the solution, you can use hot tap water.

 

[joheleh]

understood, now the copper bar it's fizzling, i think the process will be very long, i'll let it there untill it stops.

 

[joheleh]

the reaction still going, the color of the solution changed from royal blue to green, i'll wait the finish of the reaction( the eventual full dissolution of the copper bar) and then i'll test it with HCl.


EDIT:
thank you so much, everything gone well, this is the result after a first filtering and water wash...approx 60g of (almost) pure silver :lol:
i'll proceed with decanting and hot washes

 

[joheleh]

Aaaaand......here what you get when u don't know what you're doing after the washes, i've dried the silver powder and melt it, with borax, and i've got this...a nugget with reddish-pink plating...what happened? i've done a light hand of sandpaper to expose the metal.


by the way the borax in the crucible is dark green and i think i've ruinated it, is there a method to clean it?

 

[butcher]

Looks like copper is involved.
How thick was the copper bar you used?
How well did you wash the powders?

 

[joheleh]

Looks like copper is involved.
How thick was the copper bar you used?
How well did you wash the powders?

my mistake, i've used a copper pipe, in the starting solution there were a nitric excess, so i putted 2 copper pipes into the solution, when reaction was over, all the silver were cemented and i found on the bottom the pipes...heavily consumed

anyway, how can i clean the crucible?

 

[butcher]

Search for Harold's posts describing how to clean your melting dish.
You can try different key words than I used here:
https://www.google.com/search?hl=en&as_q=clean+the+melting+dish+&num=1000&ft=i&as_sitesearch=goldrefiningforum.com&as_qdr=all&as_occt=any

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=582

I would not worry about the copper in the silver bar, I would just use it to in-quarter the next batch of karat gold.

And go and find a thick copper buss bar.
Going easier on the nitric next time.

 

[joheleh]

ty so much, i've putted it in controlled nitric solution with this silver bar.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=19665

 

[joheleh]

the second refining gone perfectly! With the right amount of nitric and the properly dilution with distilled water, the silver cement without problems of re-dissolution.
here's a pic of the solution, you can see a lil precipitation, i've run a fast test with copper pipe to see if everything was ok, i'll proceed cementing as soon as i find a nice thick copper bar. thanks for everything guys.

 

[9kuuby9]

I think we should create/rename a new chemical called "increment, Nitric Acid" ;It's a more controlled form of nitric acid but it still exhibits all it's dangerous chemical properties to an certain extent when used "incrementally" And It entails a great deal of wisdom and escapes the loop of "additional unnecessary work".

So all the new members will ditch nitric acid and use "increment, Nitric Acid" in its place, And also as a reminder for the rest of us. :mrgreen:

 

[butcher]

If that was the color of solution after dissolving the silver bars, it shows there was a fair amount of copper involved.

Did you dilute solution any to see if crystals dissolve, it may be too concentrated, dilution will help in cementing also, you also want it slightly acidic for the process, but normally it is plenty acidic.

 

[joheleh]

here there is 38.8g of pure silver, 39.8g of contaminated(copper) silver, 100ml of nitric acid, 300ml of distilled water. should i dilute it more?

 

[joheleh]

those cristals are not AgNO3. It's a little cementation of silver. i've run a test with some copper just to be sure to have not a nitric excess that redissolve the silver. It's stable.

 

[pattt]

hi,

Who says that the "cuban" silver bar was pure silver?
marked with 74, that could mean its 74/100 silver ,that is less than sterling silver.
If it was cuban , it could be russian hallmarks.

"quote: Converting the Russian marks to sterling values, we obtain the following comparisons in silver purity degree:
84 zol. = 875/1000
88 zol. = 916,6/1000
91 zol. = 947,9/1000
unquote"

Pat

 

[joheleh]

hi,

Who says that the "cuban" silver bar was pure silver?
marked with 74, that could mean its 74/100 silver ,that is less than sterling silver.
If it was cuban , it could be russian hallmarks.

"quote: Converting the Russian marks to sterling values, we obtain the following comparisons in silver purity degree:
84 zol. = 875/1000
88 zol. = 916,6/1000
91 zol. = 947,9/1000
unquote"

Pat

the weight of the bar is 39.8, and it's signed P(plata=silver) 38.88g...so i guess it's 976/1000 silver...ok not pure but a lil amount of base metal.

by the way there's a sign that seem japanese

 

[pattt]

hi ,

P could also mean plated.

U could have bought a 1 ounce 9999 silver maple leaf for 18,50 euros this week :roll:

Pat