# About Silver Cement



## juxtaposedsoul (Jul 7, 2011)

Hello Everyone, 

I'm very new at refining and have chosen silver to work with until I fully understand it and feel I have mastered it. That will take some time, but I do not want to rush into refining any gold and botching it. Please forgive my admitted ignorance as I am by trade a laboratory manager/technician who specializes in the testing and analysis of construction materials and geotechnical lab work. I am not by any means an expert chemist or precious metals expert, but I am trying to learn. I am certain that nearly everyone on this forum has experienced the blend of fascination, intrigue and desire for refining that I am experiencing. And so I come to a point where I must ask this question of the forum, as I have been unable to locate sufficient answers in prior postings: what EXACTLY is the silver cement? More specifically, the cementitous silver precipitated from the nitric solution by means of addition of copper.

How toxic is it? 

What precautions must I observe when handling it?

Can it air dry inside my house, or should I leave it outside?

What is the best type of container to store it in, and what materials should it not have contact with?

Is a thorough rinsing of it really all that is necessary before allowing it to dry?

Please, if someone would spell it all out for me I would be so very, very grateful. I have, of course, done my research and only ask because the information I have found thus far is incomplete and unsatisfactory. I like to know what I am dealing with.

Thank you in advance to whomever will come to my aid.


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## goldsilverpro (Jul 7, 2011)

The silver cement is finely divided, nearly pure, silver metal powder. It's called cement because it looks like cement. A simple way to look at it is that the copper and and silver trade places - the solid copper dissolves and, at the same time, the dissolved silver becomes a solid. Assuming everything is done right, after thorough rinsing to remove all traces of acids, it is essentially safe. I wouldn't eat it though. I also wouldn't do any of this work in my house.


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## juxtaposedsoul (Jul 8, 2011)

GSP,

Thank you! Naturally I have been treating the silver cement as if it were lethal (go on everyone- have a good laugh) because I did not know for sure. None of the work has taken place indoors except for the washing/cleaning of some glassware that I rinse outside first. I am so concerned with safety that I wear goggles, butyl rubber gloves and a full respirator when washing my glassware. But, if the silver powder is essentially inert or non-toxic as far as fumes, vapors, corrosiveness, etc. could I allow it to air dry indoors so long as it is in a safe place? I only ask because recent rains have interfered with the drying process outdoors. I do not mean to make you repeat yourself GSP, your advice is greatly appreciated.


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## goldsilverpro (Jul 8, 2011)

> But, if the silver powder is essentially inert or non-toxic as far as fumes, vapors, corrosiveness, etc. could I allow it to air dry indoors so long as it is in a safe place?


Sure.


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## goldenchild (Jul 8, 2011)

juxtaposedsoul said:


> GSP,
> 
> Thank you! Naturally I have been treating the silver cement as if it were lethal (go on everyone- have a good laugh) because I did not know for sure.



Not funny at all. Better safe than sorry. I think I can speak for most when I say that we enjoy helping those that ask relevent questions and also read and study before going and trying things haphazardly.


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## juxtaposedsoul (Jul 8, 2011)

Thank you, Goldenchild. "Better safe than sorry" should become my tag line at the bottom of each post. I live by those words (no pun intended). Maybe I overdo it a bit but I plan on being around to do it again tomorrow. I am glad that you guys don't mind, and even enjoy, giving advice and helping me navigate this treacherous road. I know I will have more questions and the only way I can thank you for the answers is to assure you that I am taking every possible safety measure to not harm any person, animal or the environment. And to let you know that when I have enough knowledge I will answer questions and help others, too. Thanks!


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## element47 (Jul 8, 2011)

http://www.youtube.com/watch?v=kq1W-QdMsWQ

Here is a very schematic, rapid video as to what cementing silver is. Cementing produces somewhat pure but not ideally pure silver. It's necessary to electrorefine the cemented silver further to get to .999 (silver) That typically involves melting the silver crystals into an ingot. The purer your ingot, the longer your electrolyte will last. 

Once you are done with the nitric acid, you're pretty much done with the bulk of the nasty (and they are indeed nasty and you are 100% right to respect their toxicity) fumes. It is good that you are careful, and the more of this you do outdoors (or under a proper fume hood) the better. Obviously, any melting should be done outdoors, as it can liberate some amount of fumes and for fire-hazard reasons. 

One of the things the gurus on this forum advocate strongly in silver operations is to assiduously avoid introducing chlorides or chlorine into your silver. Specifically, that includes the use of tap water. Always use distilled water with silver. Tap water or careless washes with HCl produces silver chloride, which is quite annoying to deal with and entirely avoidable.


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## seawolf (Jul 9, 2011)

I agree you can never be too safe. As to distilled water I learned the hard way some bottlers add chlorine to the water and I have had to boil the water to remove it.
Mark


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## Harold_V (Jul 9, 2011)

goldsilverpro said:


> > But, if the silver powder is essentially inert or non-toxic as far as fumes, vapors, corrosiveness, etc. could I allow it to air dry indoors so long as it is in a safe place?
> 
> 
> Sure.


I'm not so sure!

I used to rinse my cement silver well with (tap) water, then pull the residual water off with an aspirator and a Buchner funnel. I'd tamp down the silver quite well, and then wash it one more time by adding a considerable amount of water. When fluid stopped running from the funnel, it was then emptied to a large Coors evaporating dish, so the silver could be force dried (in the fume hood). Always, when water had been evaporated and temperature went up, brown fumes emanated from the heated silver. 

The residual nitric is VERY difficult to eliminate---which is the very reason I always talk about incineration when going from one acid to another, when doing washes when working with materials that contain values. Incineration results in total loss of residual acid(s), assuming it is carried out properly. 

My point here is that if you dry silver without added heat, when it is dry, it will still contain traces of nitric. Storing such material indoors will result in corrosion of metallic objects, albeit in a very subtle way. Store the silver indoors only if you force dry. Best scenario is that it gets melted as soon as possible. That way, should it be dropped, no harm done. Dropping silver powder can have drawbacks, as I'm sure you see. 

Harold


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## butcher (Jul 9, 2011)

I made the wife very mad, had some dry silver I thought was neutralized, had it in a jar in the house and added some water to wet it, well to make a long story short She doe's not like red clouds in the house.


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## Barren Realms 007 (Jul 9, 2011)

butcher said:


> I made the wife very mad, had some dry silver I thought was neutralized, had it in a jar in the house and added some water to wet it, well to make a long story short She doe's not like red clouds in the house.



Hide the check book so she can't pay the lawyer. :twisted:


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## 4metals (Jul 9, 2011)

One of the silver producers I work for upgrades the 40% silver 60% copper in 50% nitric / water and cements the silver, rinses in a Buchner until it runs clear. 

Every time he melts the cement silver it blows a red cloud for a few seconds when it gets hot.

Still, keeping the damp cement silver in a zip lock bag would be no safety issue. IMHO


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## samuel-a (Jul 10, 2011)

4metals said:


> Every time he melts the cement silver it blows a red cloud for a few seconds when it gets hot.



Yup... no way to get around this with just water wash...
Though i never tried rinsing with dilute NaOH solution...


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## juxtaposedsoul (Jul 10, 2011)

Wow, thanks for all of the replies! I take all of your advice seriously and appreciate it beyond measure. Being new at this I am probably doing something that many beginners do- trying to improve (not re-invent) the wheel, so to speak. I have been doing my silver cement washes outside, with a large fan and respirator, using very hot distilled water. I flush the filter 10 times and I have not noticed any fumes whatsoever when I melt. That is not to say there are no fumes, just not visible fumes. Maybe I am wasting some time and distilled water but I swear my semi-refined silver looks every bit as good and pure as the many coins and bars I have bought over the years. Also, during experimentation I noticed that after I have precipitated all the silver cement and decanted the solution, I can heat the solution for a few minutes and get some more cement from it.


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## goldsilverpro (Jul 10, 2011)

After rinsing the cemented silver many times with water, a leach or two with household ammonia and several water rinses after that would pretty much insure that the acid is neutralized and most of the copper is gone. Any traces of blue color in the ammonia indicates copper.

It's easy to test the solution to see if you got all the silver out. Put about a ml of solution in a small beaker or test tube. Add a drop or two of dilute HCl or non-iodide table salt solution. If you get a white cloud, silver is still present in the solution. In that case, you should continue the cementation until the solution tests negative for silver. It can speed the cementation reaction to stir the solution occasionally and also to scrape the silver off of the copper a couple of times.


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## goldenchild (Jul 10, 2011)

element47 said:


> It's necessary to electrorefine the cemented silver further to get to .999 (silver) .



You can also achieve .999 and higher using the silver chloride method.

About the red fumes... I find that if you try to filter your silver in a buchner or conical funnel right away it never gets out all of the nitric. Or whatever liquid you are trying to get out. No matter how much water you pour down the funnel I notice some residual liquid is still caught up in the filter which means the silver isn’t totally washed either. This is very apparent when you are trying to eliminate copper chloride using white filters.

I always pour off the bulk of whichever liquid I'm working with into a filter. The filter being there only to catch any silver that makes it out of the vessel. Then add water to the vessel and stir vigorously making sure to really kick up all the silver. Let it settle and decant. Do this until no more color is left in your water additions. Then perform one more water addition and boil before decanting. You could boil each water addition if desired. I bet you will have no more nitric on your silver after this procedure.


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## 4metals (Jul 10, 2011)

I guess it all comes down to what you want to do with your cement silver. The guys I get involved with are cleaning up low grade silver to run it in a silver cell, a little red NOx when it melts is not a big deal but treating volumes of waste-water produced to prevent the little red puff is a big deal. 

The silver coming out of the silver cells at.999+ is where you have to worry about rinsing well. Most of the impurities in fine silver from a cell (providing the cell is operating within parameters) come from electrolyte being dried on the crystal and melted in. This is where rinsing is most important.


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## juxtaposedsoul (Jul 10, 2011)

Again, thanks. I will test the spent solution with ammonia since I bought a bottle of it a few months ago as I was gathering supplies for refining (I did this at many different stores, never buying enough supplies in one place to make my intent clear. I'm not paranoid, I just didn't want to explain myself or answer unwanted questions!) Anyway, it's good to see that I do need the ammonia, although I had forgotten why I needed it in the first place. Checking will prevent me from having to do the re-heat procedure I mentioned earlier. Question: is my silver nitrate solution too strong if it really chews up my copper? Cementing seems fine so I had not given it much thought, just wondering. Also, if the solution was too strong would the precipitated silver re-dissolve and possibly bond with the copper? I only ask because the batch I processed today annihilated about 3 inches of copper piping and yielded a silver cement with a slightly pinkish hue.


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## Harold_V (Jul 10, 2011)

goldsilverpro said:


> After rinsing the cemented silver many times with water, a leach or two with household ammonia and several water rinses after that would pretty much insure that the acid is neutralized and most of the copper is gone. Any traces of blue color in the ammonia indicates copper.
> 
> After cementing, it's easy to test the solution to see if you got all the silver out. Put about a ml of solution in a small beaker or test tube. Add a drop or two of dilute HCl or non-iodide table salt solution. If you get a white cloud in the solution, silver is still present. In that case, you should continue the cementation until the solution tests negative for silver. It can speed the cementation reaction to stir the solution occasionally and also to scrape the silver off of the copper a couple of times.


In addition, stir the cemented silver. It commonly traps some silver nitrate (dragged down). It won't cement if it doesn't make intimate contact with the solid pieces of copper. There's an electron exchange between the two, which happens only upon contact. Simply having copper in solution does NOT cement silver. 

Harold


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## goldsilverpro (Jul 10, 2011)

Sounds like you're using way too much nitric to start with. If so, you're wasting both nitric and copper. I don't know what you're dissolving to start with but, if it's something like sterling silver, it's easy to control the nitric you're using and not use an excess. If you do have an excess of free (unused) nitric in the solution, it will first attack the copper. When the free nitric has been consumed, silver starts cementing, although there is some overlap. A liter of free 70% nitric will dissolve about 240 g of copper. If there was no free nitric, only 0.3 g of copper would dissolve for each gram of silver that cements.


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## juxtaposedsoul (Jul 11, 2011)

I think I did overdo the nitric on my last batch. It was not a good thing. I started (on my very first batch, that is) using 1.2ml nitric for each gram of sterling, plus 1.2ml of distilled water. This did not work well as 24 hrs. later (with no heating) the sterling was mostly intact. I added the equivalent of 0.3ml nitric p/gram of silver add heated on medium-low setting of my hot plate. This worked pretty well but the solution inevitably began to evaporate. I stopped heating after about one hour and let cool. Still a fair amount of solid pieces. Doubled the solution with distilled water and filtered old-school style. I dropped the silver with copper piping and retained and THOROUGHLY washed the undissolved silver for later refining (meaning the large chunks caught in the filters). So I ended up using 1.5ml nitric to 1.2ml H20 per gram of metal on my first batch. It worked well as far as the quality of the silver but left a lot undigested. I need help here. I have tried it by the book (Hoke's book) and I have tried slight variations from 1.1ml nitric/1.1ml H2O up to 1.6ml nitric/1.6ml H20 at each tenth of a ml in between. All ratios have worked pretty good but I still have undigested silver. Why is that? Shouldn't "soaking" for 24 hrs. or heating for several hours be long enough? I am using Lazersteve's recipe for 50% nitric and using 99.9% pure sodium nitrate crystals and Liquid Fire sulfuric. I am certain my portions and procedure are exact when making the nitric, including the freeze time. What am I doing wrong that my silver should be so difficult to digest? Please- I know it's the oldest question on the forum and has been addressed numerous times, but none of the previous posts are helping. As always, thank you very, very much for the help.


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## juxtaposedsoul (Jul 11, 2011)

Thanks GSP,

As always your advice is sound and much appreciated. I tried an experiment just now cutting back the nitric to 1.3ml per gram of silver alloy and 1.1ml distilled water. The smaller increment of H2O is to account for the nitric being 50% as opposed to 70%. This worked great! I did not even need heat. Is it safe to assume that the "50/50 nitric and water solution" is based on 70% nitric acid? If so that would explain why my solution seemed weak and left a fair amount of metal undissolved.


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## Barren Realms 007 (Jul 11, 2011)

I don't guess you are not starting with pure silver so are you taking into account that it takes 3 times the nitric to dissolve a gram or copper as it does to dissolve a gram of silver?


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## philddreamer (Aug 5, 2011)

Thank you all for the great information. 
I've used the silver chloride method for refining my silver recovered from inquartation, which is usually 2 or 3 ounces.
I got used to it, & liked "playing" doing it so I could kill some time. I tried cementing once, but, by not following the proper steps, I had a very soft sediment.

Now that I have several hundred ounces to refine & wanting to speed things up; after reading in this series of posts, an hour ago I gave cementing another shot following the steps here, & ended up with great results. In less than 30 min's I had my 4.7 ounces cemented. I'll let it settle for a while, then follow with the filtering & rinsing.


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