# Silver Solder refining tips?



## JonMiller (Oct 26, 2013)

i have approx 1,000 lbs or silver solder . It contains about %50 tungsten, %30 copper, %10 silver, %10 ZINC,NICKEL and iron . I know if i dissolve this material in 
nitric acid ( %54 concentrate ) i will totally dissolve in a few hours . My question is , after i filter the solution iam left with all the metals expect 
tungsten . Does the nitric acid need to be totally used up in order for me to cement out with copper or can i raise the PH with DI water and cement out with copper .

I tried a sample and used to much acid , i put a copper tube in the solution the silver cemented out nicely but redissolved because of too much free acid. Please help, Thanks.


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## goldsilverpro (Oct 26, 2013)

JonMiller said:


> i have approx 1,000 lbs or silver solder . It contains about %50 tungsten, %30 copper, %10 silver, %10 ZINC,NICKEL and iron . I know if i dissolve this material in
> nitric acid ( %54 concentrate ) i will totally dissolve in a few hours . My question is , after i filter the solution iam left with all the metals expect
> tungsten . Does the nitric acid need to be totally used up in order for me to cement out with copper or can i raise the PH with DI water and cement out with copper .
> 
> I tried a sample and used to much acid , i put a copper tube in the solution the silver cemented out nicely but redissolved because of too much free acid. Please help, Thanks.


The tungsten doesn't really dissolve in nitric. It produces this yellowish white slimy gunk that I never liked dealing with.

If I'm thinking right, to adjust the pH of 1 gallon, from, say, 1 to 4, you will have to add 1000 gallons of DI water. I may be way off on this. It may only take 100 gallons.


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## JonMiller (Oct 26, 2013)

goldsilverpro said:


> JonMiller said:
> 
> 
> > i have approx 1,000 lbs or silver solder . It contains about %50 tungsten, %30 copper, %10 silver, %10 ZINC,NICKEL and iron . I know if i dissolve this material in
> ...



The reason iam filtering the solution is to remove the tungsten. That way iam left with a solution that is just silver, zinc, nickel and iron . I need to get an idea of how much water to add in order for the copper to cement and also so the silver does not redissolve .

EDIT: are you saying yhe PH needs to be at 4 in order for me to cement the silver out with copper while also prevententing the silver from redissolving ? .


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## kkmonte (Oct 26, 2013)

I thought I read on here that you could start this process using AP (to save on the amount of nitric needed), to remove copper and other metals and just leave the silver and tungsten?


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## JonMiller (Oct 26, 2013)

Well then iam open to suggestions . There are 3 ways ( from my understanding ) to remove silver from nitrate . 
1) adding salt to percipitate silver into silver chloride 

2) adding pure copper to cement out 

And the third being to add hydroquinone to the solution , from what I understand when I add the hydroq 
It should knock the silver out like copper would however I would not have to worry about the redissolving of the silver . This 
Is a theory as far as I know. 


Iam also not sure if the salt direction is the right way to go because of the extra procedure needed to get pure silver.


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## goldsilverpro (Oct 26, 2013)

I'm saying it's an absurd idea to think you can practically adjust the pH to any level by dilution. It would take enormous amounts of water, even for small adjustments. Going from pH1 to pH4 was just an example to show how much water it would take for only 3 pH units. 

The silver will not cement and remain cemented until all the excess nitric has been consumed by the dissolving of copper. 

It's going to be difficult to rinse all of the silver-bearing solution out of tungsten sludge. With that much tungsten, you'll be lucky to get 2/3 or 3/4 of the silver.

The melting point of tungsten is 6200F. I can't believe that any silver solder would contain 54% tungsten. You couldn't melt it. I would bet it is 54% tin.

If I were offered 1/2 of the silver to process that lot, I would turn it down. I doubt if you could find a refiner that would process it.


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## JonMiller (Oct 26, 2013)

Maybe I explained the material incorrectly.. the material is granulated in almost a powder form. 
Ive sent out the filtered tungsten to be assayed and it came back at % o.5 silver content. So there is no substancial 
Amount of silver remaining in the filtered tungsten. 




Another question. 1 gallon of % 54 nitric acid will dissolve how much copper?


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## solar_plasma (Oct 27, 2013)

> Another question. 1 gallon of % 54 nitric acid will dissolve how much copper?



Now I am confused. You are handling tons of HNO3 and are asking such a question? Everybody in this forum can easily answer this question, though it depends a lot on the process. But now I would actually like to hear more about your setup.


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## JonMiller (Oct 27, 2013)

solar_plasma said:


> > Another question. 1 gallon of % 54 nitric acid will dissolve how much copper?
> 
> 
> 
> Now I am confused. You are handling tons of HNO3 and are asking such a question? Everybody in this forum can easily answer this question, though it depends a lot on the process. But now I would actually like to hear more about your setup.




Sorry for the misunderstanding its hard to understand my goal without knowing more about my process. 

My setup is industrial , the material will be placed into a 150 gal tank then the nitric acid will be pumped into the tank
With a parastaltic pump . The tank is fully enclosed and also connected to a scrubber . The material is then mixed until the 
Metals are dissolved ( minus the tungsten of course ) where it will then be discharged into a filter that captures the tungsten . Leaving me with a solution that is described above. 

The problem I have run into is the cemented silver redissolving. Obviously this is not something iam doing in small quantities
So aquiring certain materials for percipitation or cementing is not the problem . 

Question is , do I keep adding copper until the acid will discontinue the reaction and start cementing the silver or will it be an ongoing process where the silver and copper exchange places continuously ? . 

This is a side project in my company I plan to further expand however the learning curve has its setbacks.


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## butcher (Oct 27, 2013)

Copper is higher in the reactivity series of metals than silver.
silver dissolved in solution this case nitric acid forms silver nitrate AgNO3, the silver is in solution as silver ions (missing electrons), copper being lower in the reactivity series will donate electrons to the silver, in this the silver ion gain electrons and are reduced to silver metal atoms (to reduce means to gain electrons), also in this chemical reaction copper which now gave up its electrons to the silver is oxidized to copper ions in the solution (oxidation lose of electrons), basically copper replaces the silver from solution.
This is a replacement reaction, the metal higher in the reactivity series of metals replaces the metal lower in series from solution.
2AgNO3 + Cu --> Cu(NO3)2 + 2Ag

A little free acid in the solution helps to keep the reaction in progress, to much excess HNO3 in solution would just consume more copper.

Dilute nitric works better than concentrate nitric acid, metals can oxidize in too concentrated of a solution this oxidation can form a passivated layer which slows the reaction, the water also helps the reaction to go further as gases that will form can stay in solution and do more work, 50:50 ratio of 70% HNO3:H2O is a good ratio, heat helps especially at the later stages of dissolving silver, as towards the end point the reaction slows, adding heat will put a lot more silver into the solution.

How much acid is fairly dependent on conditions, generally 1.2 ml of 70% HNO3 and 1.2Ml of H2O will dissolve a gram of pure silver metal, copper can take about 3.4 time this volume.

1gram of copper will cement about 3.4 grams of silver from solution.

If the cemented silver is redissolving I suspect you still have a lot of un-reacted free nitric acid in solution.


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## solar_plasma (Oct 27, 2013)

In this link Lou gives the explaination, why dilluted HNO3 is more cost effective:

Lou:


> Less than 4.9 M:
> 
> 3 Ag + 4 HNO3 --> 3 AgNO3 + 4 NO + 2 H2O
> 
> ...


http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=50&t=18598#p187350


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## goldsilverpro (Oct 27, 2013)

Is it tungsten or is it tungsten carbide?

It takes 5.73ml of 54% nitric to dissolve 1g of copper. That assumes an open top container with all the fumes escaping.


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## JonMiller (Oct 28, 2013)

Sorry for the late replies guys 




goldsilverpro said:


> Is it tungsten or is it tungsten carbide?
> 
> 1 ml of 54% nitric will dissolve 5.73g of copper. That assumes an open top container with all the fumes escaping.





Its a tungsten powder that has not been sintered . All of the metals will be dissolved in an enclosed SS tank and mixed with an internal
impeller. 

So basically depending how much air the solution is exposed to varies the amount it can dissolve? 







butcher said:


> Copper is higher in the reactivity series of metals than silver.
> silver dissolved in solution this case nitric acid forms silver nitrate AgNO3, the silver is in solution as silver ions (missing electrons), copper being lower in the reactivity series will donate electrons to the silver, in this the silver ion gain electrons and are reduced to silver metal atoms (to reduce means to gain electrons), also in this chemical reaction copper which now gave up its electrons to the silver is oxidized to copper ions in the solution (oxidation lose of electrons), basically copper replaces the silver from solution.
> This is a replacement reaction, the metal higher in the reactivity series of metals replaces the metal lower in series from solution.
> 2AgNO3 + Cu --> Cu(NO3)2 + 2Ag
> ...




Thanks alot for this post it cleared up a few things for me. I was under the impression that i would need to raise the PH in order to start the cementing process with copper. However
is seems its just a matter of diluting the solution to a point where it would be able to cement without redissolving the silver .


Would it be a good idea to feed the acid as much as possible until it literally cannot dissolve anymore and then cement out with copper?






Iam in no way a chemist ( obviously ) , Just looking for some helpful tips. Honestly if it comes down to it i will have a spot open for a job. Looks like 
iall be headed to the nearest college for some help . Unless somebody here is interested.


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## Lou (Oct 28, 2013)

Silver solder isn't made with tungsten. Lowest Ag/W contacts or Ag/Mo contacts I've personally run were 12% weight silver.


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## kadriver (Oct 29, 2013)

JonMiller said:


> The problem I have run into is the cemented silver redissolving. Obviously this is not something iam doing in small quantities
> So aquiring certain materials for percipitation or cementing is not the problem .
> 
> Question is , do I keep adding copper until the acid will discontinue the reaction and start cementing the silver or will it be an ongoing process where the silver and copper exchange places continuously ? .
> ...



Jon

I had this problem when I first started working with silver. When I added the copper (I used 4 to 12 gauge clean copper wire coiled) to the filtered solution to cement out the silver, the solution would heat up considerably, emit brown fumes and the silver would redissolve as fast as it cemented. The cemented silver would become bloated with NOXX gas and tend to float instead of sinking to the bottom of the container. When cementing finally did take place, the silver was very fine (like pluff mud) and very hard to clean (rinse).

This was due to excess nitric acid being present in my silver nitrate solution. It caused my copper to be consumed needlessly, and wasted nitric acid.

To solve the problem, I now add nitric acid in small doses rather than using a predetermined amount based on the weight of the material i am trying to dissolve.

For example, if I am going to dissolve 1000 grams of 80% silver I would first add the annealed silver (annealing burns off external oils and other impurities) to my reaction vessel and cover it with 1 liter of distilled water. Then add low heat.

Then I would begin adding nitric acid in 100 ml doses. As the reaction calms down from the first acid addition, I add another 100 ml dose and continue these additions, waiting between additions for the reaction to decrease, until nearly all the material is dissolved.

I want to have just a little undissolved material left in the reaction vessel and all reactions ceased (as indicated by lack of brown fume production). The undissolved material ensures that all my nitric acid has been consumed and I can dissolve it with my next batch.

I then siphon off the SETTLED liquid and filter it. It is now ready to be cemented with copper.

To cement, I fill a four liter beaker about half full of distilled water, then insert about a 400 gram coil of copper wire into the distilled water.

I then carefully, slowly, while stirring, add about 250ml of the filtered silver nitrate solution to the 4 liter beaker that contains the distilled water and 400 gram coil of copper wire. If you put the copper directly into the concentrated silver nitrate solution, it may form a passive layer of hard silver on the copper and cementing will not take place until you dilute the silver nitrate and mechanically scrape off the passive layer - a huge pain.

Once the silver begins to cement, I slowly add more silver nitrate to the 4 liter beaker, then wait for the silver to cement. When the cementing action slows down I add another small dosage of the silver nitrate solution the the beaker and continue until all the silver is cemented out.

Sometimes after adding the the silver nitrate to the distilled water and copper coil, nothing happens, the copper coil just sits there in the solution and no silver cements. This happens when the nitric has been used up so completely in the reaction vessel as described above. To get the cementing going just add a tiny (few drops) of nitric acid and stir. Some free nitric is required in order to get the cementing reaction going.

I have never worked with silver solder, and I don't think I have encountered tungsten yet. I work with small amounts of sterling and some 80% silver. But this method should scale up to the amounts you are working with.

This method will definitely take longer because you must wait for reactions to cease and for the solids to settle. But it will produce some nice results and conserve your copper and nitric acid, at least that has been my experience.

kadriver


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## kadriver (Oct 29, 2013)

JonMiller said:


> Sorry for the late replies guys
> 
> 
> Would it be a good idea to feed the acid as much as possible until it literally cannot dissolve anymore and then cement out with copper?



Yes, but add the acid in small doses and wait for the reaction to slow, then add a little more acid. You want to end up with just a little undissolved material in the reaction vessel with no more brown fumes being produced. If you over-shoot and ALL the material dissolves, then just add some more material and heat until any remaining free nitric is used up. 

You can tell when the nitric is used up by the lack of brown fume production while heating. I actually boil the solution and wait for the atmosphere in the reaction vessel to become clear with no evidence of color. This ensures that there will be very little, if any, nitric left in the solution. Then the silver will cement out nicely.

kadriver


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