# silver melts



## eek257 (Oct 31, 2013)

I am processing silver from scrap rods, etc using nitric to dissolve, then hydrochloric to drop out of solution. I then use a vacuum filter to clean it until water coming from it is clear. From there I add water then Sodium Hydroxide and finally dextrose. Then I again filter till it is clear. 

My first question is from what I am seeing on this forum that many people melt after originally dropping it out using copper, am I taking more steps than I need, with the cost of copper the hydrochloric is cheaper to use for me, also could I melt it after just dropping it out with the hydrochloric or would the purity be substantially less than the additional steps I am taking?

My second question is that I am just destroying crucibles. I use a fire clay crucible that I have been getting at legend and I get about one melt per crucible. The crucibles will have several colors from blue, green, and black sludge/slag. It is just eating them away. Most of my pours are around 10 pounds so the crucible is in the furnace for a while and I pour off quite a bit of liquid slag during the melt that is grey in color when it hardens. Because I am adding material as it melts down I have not been using much flux as I would just be pouring it off with the rest of the liquid slag during the melt. Not sure what I am doing incorrectly here. After my final step with washing it out, the liquid is basically clear so I just don't know if there is still contaminates in the silver. Am I not adding enough of the sodium hydroxide or dextrose to fully convert the material?

I have been doing this for about 10 months so am still very much a newbie at it. Any input would be greatly appreciated.


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## Lou (Oct 31, 2013)

It's probably excess sodium hydroxide (check the pH of your filtrate) that is tearing up those silica crucibles.

Silicon carbide is very enduring and you'll get many dozens of melts.

You can find them at mifco.com.


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## eek257 (Oct 31, 2013)

So do you think I may not be rinsing the final enough then? Will test the pH on the next batch I have not done that.


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## Lou (Oct 31, 2013)

Is the slag very fluid?


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## MysticColby (Oct 31, 2013)

what is in the flux you are using?


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## niteliteone (Oct 31, 2013)

I've always worked under the premise of the best process is the one that achieves the desired result I want in the simplest manor.
What is your end goal for your silver :?: 

If you want ultra pure (999+)Your dirty melting dishes shows you're not getting it :shock: 
If you want regular purity (99+) just cement the silver nitrate with copper and wash the powders well 8) 

The cemented silver can then be melted into bars and run through a silver cell to boost the purity to 999+ much easier than the process you are currently using. 
This will also increase the recovered silver since you will not have the loss of silver chloride that didn't convert, that evaporates from your melting dish causing the damage you see with your dishes.


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## eek257 (Oct 31, 2013)

Lou - The slag is a reddish liquid when hot then cools to hard gray material.

niteliteone - My end goal for my silver is to sell it which I have been doing. At this point it is a hobby more than anything but it is already paying off very well and I want to correct my errors to do more as currently I have a good constant supply of material.

Several places I have read that cementing out with copper does not get all the silver which is one reason why I have gone this other route, also the costs for the copper were a big reason as well. Is the ratio of copper to silver the same...meaning if I know I should have roughly 3 pounds of silver in my liquid, do I need to use 3 pounds of copper to cement it out? Also where would be a good place to purchase the bar stock of copper? I live in Colorado.

I will have to look up how to build a silver cell as I have no idea how. I have seen it mentioned in a lot of places on this forum but since I was not currently processing that way, did not look into it too much.

Mysticcolby - honestly I am not sure what type flux it is, I purchased it through a mining supply shop. Again, I am a newbie at this. I have processed over 50 pounds in the past 5 months and per the assessor reports that I have had test it, it has been 95-99%. Just want to get more consistent and as pure as I can possibly make it.

Thank you for your information so far!


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## butcher (Oct 31, 2013)

copper works really well to cement silver, it will also convert the silver to metal, all in all I would say it will do a better job than trying to convert the silver chloride to metal. From solution to melted metal, I say you will get more silver easier by using copper to cement.

I do not understand why anyone would make silver chloride when they do not have to.

Also I say copper is economical to use, about 31 grams of copper will cement about 3.4 troy ounces of silver, (and if you wished you can recover the copper for reuse), copper at a couple of dollars a pound and silver in the twenty of dollars for a troy ounce, copper is a cheap way to go, you can get clean copper scrap cheap (if you do not buy it new, or from the scrap dealer, you may find a source of free copper if you look around you.


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## Lou (Nov 1, 2013)

Copper will get all the silver out. You can pick up large copper buss or thick plate or sheeting from the scrap yard. You'll probably pay a bit over spot copper for it but it will reduce quite a bit of silver, as Butcher noted above.

If your material contains no copper (sounds like it does, amongst other things) then you can alternatively use iron to cement it out rapidly. If the solution is clean, it is very unlikely for your silver to be below 999 fine if properly fluxed.


You can also use iron to cement out your copper solution. When you can take that iron solution, add ammonia and get no blue from Cu(II)-ammonia complex, you can raise the pH up to 5 and be left with rust and a salt solution that may contain more reactive metals than iron. The logic there is that the Cu(NH3)4+2 is a very potent indicator of copper, so if it shows no copper, your solution must be free of more noble metals as well. Of course, a quick test for whether or not you're done cementing the copper is to simple take a small drop of it and add a grain of table salt. I prefer doing it on a black stone.


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## galenrog (Nov 1, 2013)

You have gotten a lot of good advice from people who know a lot more than I do on the subject. That said, I have only one bit of advice: Do NOT use a basic gold smelting flux in attempting to refine silver. Smelting is part of many recovery processes, but not yours. If you had concentrated ore that would be another matter. Your end product in using a smelting flux in the manner you stated can easily be less pure than what you had prior to using the smelting flux. A little bone dry borax when melting is ok, but your flux, if my assumptions are correct, contains silica, borax, soda ash, and manganese dioxide (the source of your grey slag).

Keeping the number of processes, in both recovery and refining, to a minimum, tends to give a greater weight of greater purity. 

Keep plugging away. If you have not yet studied both Hoke's "Refining Precious Metal Wastes" and Ammen's "Recovery and Refining of Precious Metals", you should do so. Hoke is easier for me to understand and is available as a free download on many member signature lines.

I wish you well.

Galen


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## Lou (Nov 1, 2013)

Especially don't use manganese dioxide or Chapman's of any flavor.

Borax and sodium carbonate to adjust the viscosity to prevent prill hold up.


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## eek257 (Nov 1, 2013)

It sounds as if I am doing it the more difficult way and need to go by the scrap dealer for some copper, will do that today. 

I have purchased Hokes book several weeks ago and am reading it but do not have Ammen's, that one is pretty expensive but will look online.

Lou - what does "prill hold up" mean? And do you mean I should just use a combination of borax and soda ash? How much of each would be a good starting point and about how much should I start out with when melting? The reason I ask this is that the few refiners in the area are very difficult to get anything out, I understand it is their livelihood so have not pushed them on it.
Thank you,
Erik


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## Lou (Nov 1, 2013)

Prill hold up is when you get small, fine BBs of precious metal or PM-containing alloy that gets stuck in the slag which decreases your yield. Fluxes are generally case-by-case and should be formulated empirically to get the desired properties. 

If you use just borax alone, there's enough viscosity to suspend some of these small particles in the melt. As a rule, use only enough carbonate to get a fluid slag (you might try 1 part borax to 0.5 parts carbonate, thoroughly mixing it into the crude silver powder). We typically pour cones first, de-slag, XRF the slag and mill it if it shows values and re-smelt with a thinning flux. 99% of the time we get that right the first time. Usually it's more of a problem with dirty material. You can make a simple cone mold out of carbon steel, but you must coat it with soot or graphite powder to prevent sticking or brazing. That's not so much an issue with pure silver, but can be with gold or when other elements are present.

When you're melting pure gold, your slag should have a slight purple tint from finely divided Au that vaporizes during the melting process. The borax isn't really required save as a crucible release agent to help the gold flow out of the crucible and not stick.

If you're melting pure silver, your slag will have a very light creme color, if even you use a flux.

Wouldn't spend the money on Ammen's. Everything in that book is here on the forum for free, and much higher quality information (his is more recovery-related).


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## eek257 (Nov 1, 2013)

Yes, I have seen the little bb's of silver in my crucibles. As they have been eaten up with the past melts I break them to them back into the nitric to recover the silver.

Thank you all for your help. I am going to try the copper tomorrow and have am researching how to build the silver cell. Will let you know how my next attempt turns out.


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## niteliteone (Nov 2, 2013)

eek257 said:


> Yes, I have seen the little bb's of silver in my crucibles. As they have been eaten up with the past melts I break them to them back into the nitric to recover the silver.
> 
> Thank you all for your help. I am going to try the copper tomorrow and have am researching how to build the silver cell. Will let you know how my next attempt turns out.


eek257,
For good ideas on building a silver cell read the many posts from " Kadriver " and his many successes with them.
Here is one thread, search his name for all the rest.
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=50&t=17233


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## kadriver (Nov 3, 2013)

eek257 said:


> So do you think I may not be rinsing the final enough then? Will test the pH on the next batch I have not done that.



The first time a did the NaOH and sugar conversion on a large batch (about 1 kilo is a large batch for me) I failed to test the rinse water for pH. The water looked clear and the silver looked clean.

When I put the "rinsed" silver in the Corning ware casserole dish to dry, there was still some sodium hydroxide present and it ruined my Corning ware drying dish.

I now rinse until the pH is neutral, then rinse it one more time.

kadriver


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## eek257 (Nov 3, 2013)

I have not been testing the pH but will do that now. It makes sense, just doesn't enter your head until it is mentioned though. 

Will be trying the copper this week, picked some up at the scrap yard and will have some material in nitric hopefully tomorrow. 
Thanks for the help.


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## saadat68 (Oct 22, 2018)

Hi
I read this from hoke book: some fluxes remove oxygen by reacting chemically with oxides.
-------
In silver melting:
we know green color in crucible and fire means there are copper contamination in melt and we must add some soda ash or baking soda 
1- Does Copper oxide produces green color? Or copper nitrate?
2- What happen when we add soda ash to melt?
It converts copper oxide to copper and copper backs to the melt? In fact we don't remove copper!!!
Or maybe they are copper nitrate and react with soda ash and produce copper oxide which goes to slag :?: 

Thanks


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## butcher (Oct 22, 2018)

Carbon is a great reducing agent in your flux mix.


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## saadat68 (Oct 23, 2018)

Thanks
My question is:
If we see green flame in silver melting ( specially silver cement ) so we have copper contamination. What is this compound that makes green flame?
Copper nitrate? Or copper metal ?

And what happen when we add flux to this melt (for example soda ash)? What's the chemical reaction?

I think the contamination is copper nitrate and when we add soda ash they reduce to copper oxide and go to slag.Right?

Thanks


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## butcher (Oct 23, 2018)

Burning copper oxide will produce the green fumes and flames...
Carbon in the melt flux can reduce the copper oxide to metal...

The flux can be oxidizing or reducing depending on its recipe, it can make metal, or slag oxides glass borates, silicates ...

Cu(NO3)2 + heat --> CuO
Copper(II) nitrates in the heat of the melt oxidize, Cu(NO3)2. At 80 °C, then convert to "basic copper nitrate" (Cu2(NO3)(OH)3), which converts to CuO at 180 °C

(Note: without flux, we basically have copper oxides even before we begin the chemistry of the melt)

2 Cu(NO3)2 → 2 CuO + 4 NO2 + O2

Borax (glass) and copper nitrate
4 Cu(NO3)2 + 6 Na2B4O7 = 4 Cu(BO2)3 + 12 NaBO2 + 8 NO2 + O2

Borax (glass) and copper oxide
Na2B4O7 + CuO → Na2[Cu(BO2)4]

Sodium carbonate (soda ash) and copper nitrate
Na2CO3 + Cu(NO3)2 --> CuCO3 + 2 NaNO3
(Note above: that the product of sodium nitrate is an oxidizing agent which can oxidize copper or other metals...)

Sodium carbonate (soda ash) and copper oxide
CuO + Na2CO3 = CuCO3 + Na2O

Copper oxide and carbon (flour) (charcoal) (paper- wood)...
C + CuO → Cu + CO2

Sand, Glass form silicates which hold oxidized metals, and metal silicates in the slag glass formed, Note also that SiO2 is oxidizing in nature.


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## saadat68 (Oct 23, 2018)

I think I read before in this forum when see green flame in silver melting add some soda ash to remove copper 
I am confused
Sounds like contamination is copper nitrate and copper oxide. Copper nitrate converts to oxide with heat. And copper oxides go to slag with some borax so why we must add soda ash?!
Heat in the melt and some borax do the job!!!

Edit:
It is for oxdizing probable copper metal in the melt with sodium nitrate form soda ash. Right?


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## butcher (Oct 24, 2018)

You're confused?
I am the one who is confused here, I am not sure what the question is or what your asking.
I am not sure what it is I am trying to answer.

Soda ash, sodium carbonate, is a powerful basic flux it reacts with silica-based (acidic) minerals to form a fusible sodium silicate (slag). CO2 produced from the reaction can cause frothing of the melt with high temperatures. Soda ash is a good desulfurizing agent and an oxidizing agent. soda ash is also corrosive to the crucible.

If you are trying to remove copper contamination from your silver it should be done before the melting process, in recovery-refining or washing procedure processes.

Using flux to reduce copper or oxidize the copper in the silver melt, at this stage would not be helpful.
Although the flux can help to improve the silver melt.

Sodium carbonate works great as a desulfurizing agent, for example where silver was reduced with H2SO4 and Iron. it also is very helpful in forming the slag silicates...

As far as removing or reducing copper it would not be that helpful, silver can hold oxygen in the melt, the soda ash can aid here in helping to remove some oxygen from the melt but not as well carbon would for this purpose.

Silver and copper will alloy easily, using a flux melt to separate these metals would not work very well.

I still am unsure of what the question or the goal is here.


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## saadat68 (Oct 24, 2018)

Thanks Butcher and I am sorry for my bad English 
I thought when we saw green flame we must add some soda ash to the silver melt but sounds like it is wrong 
I was confused because as you said adding soda ash for removing copper don't have any benefit

Thanks again


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## butcher (Oct 24, 2018)

Soda ash is a good flux for silver chloride conversion.

Where silver (I) chloride reacts in a fusion with soda ash (sodium carbonate) at around 850 -900 degrees C reduction of silver:

4AgCl + 2Na2CO3 
--900C-->
4Ag + 4NaCl + 2CO2 + O2


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## snoman701 (Oct 24, 2018)

butcher said:


> Soda ash is a good flux for silver chloride conversion.
> 
> Where silver (I) chloride reacts in a fusion with soda ash (sodium carbonate) at around 850 -900 degrees C reduction of silver:
> 
> ...



Use a covered crucible, heat it very slowly, and still expect high losses. It will also carry other precious metals like au up with the smoke. 



Sent from my iPhone using Tapatalk


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