# Zinc used for cementing too fine?



## toprow (Dec 3, 2013)

Hello.

Newbie here. I'm cementing silver from used photo fixer solution. I used some very fine zinc dust (5-8 micron). It appears that the replacement reaction went well, but the resulting solution is difficult to filter. Did I use too fine of zinc for a starting point? It either immediately plugs very fine filters, or it runs right through more course ones. Help? Ideas?

Much appreciated in advance.


----------



## Harold_V (Dec 3, 2013)

Why are you filtering?

Harold


----------



## toprow (Dec 3, 2013)

Cemented, then let it settle, but still ended up with a volume of sludgy solution. I thought I read where I should filter off the precipitate at this point. (To remove the last of the fixer and whatever it contains...salts, etc)


----------



## 9kuuby9 (Dec 3, 2013)

Here is your solution; http://goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=14920#p150486


----------



## goldsilverpro (Dec 3, 2013)

I always recommend 325 mesh "zinc dust". That's 44 microns. This zinc dust will tend to clump up in the container and I always run it through a fine sieve before use. If it doesn't clump, it probably contains a silica anti-clumping agent called Cab-O-Sil. This is an undesireable very fine white powder that ends up with the precipitated silver. It can cause filtering problems.


----------



## toprow (Dec 3, 2013)

This is interesting to me. So does the zinc particle size dictate the precipitate particle size? Learning....


----------



## toprow (Dec 3, 2013)

One more question regarding my superfine silver suspension/sludge - could I just dry it out, collect the dried material, dissolve in nitric, and then crash the silver with solid copper? In my mind this might be less fuss than trying to filter this mess....but I've never done it, obviously. Any thoughts?


----------

