Silver Nitrate and Nitric Acid Question

[PlainsScrapper]

Hello, everyone.
I hope this wasn't a question already answered, as I couldn't find anything on this topic using the search bar. If so, could you redirect me to a post regarding to this topic? If so, that would be great.
Anyway, I plan on doing a Chemistry experiment involving the dissolving of silver into a nitrate form(AgNO3). I plan on using silver mylars from around 40 keyboards to dissolve in a 1 to 1 ratio of concentrated nitric acid (70%) and Hydrogen peroxide, then rinsing each mylar with distilled or deionized water in a squeeze bottle. I plan on doing this experiment under a fume hood. Then, I want to produce silver crystals by using copper wire bent in various shapes, in order to see how the crystal growths change according to the orientation of the wire, and then wash the silver crystals and melt them into a bunch of pellets by pouring the molten silver into a heat- resistant glass bowl in cold water. I will have all proper safety equipment on, like gloves, safety goggles, and a lab apron.
Here is my problem. I know that when copper is added, and if the nitric acid hasn't been completely converted into silver nitrate, it will begin to react with the copper, causing it to redissolve into the solution, introducing copper nitrate into the solution. Is this a problem, or just something extra that doesn't contaminate the silver nitrate and foul the experiment? If it is an issue, how do I eliminate the excess unreacted nitric acid, as I don't want to deal with silver chloride? Or is it necessary to do so? If it is, how would I be able to produce crystals from them, or is this an impossible experiment to do, unless I have only silver nitrate in the solution, with no nitric acid present?

 

[FrugalRefiner]

When you use copper to cement silver from a silver nitrate solution, the copper dissolves into the solution to replace the silver. So even if you started with an absolutely pure silver nitrate solution, as soon as the first atoms of copper replace the first atoms of silver, you will have copper in your solution. So the simple answer is that copper in the solution will not materially affect the silver crystals.

Having said that, having a great excess of nitric in your solution when you start the cementation is just a waste of nitric acid and the copper it will consume. Use the smallest amount of solution you can, and try to use it to dissolve more mylars or other silver items until it is used up. Consider that when Harold would dissolve gold in aqua regia, once the material was dissolved he would add a gold button to use up any remaining nitric. You can use the same technique, but introduce an item made of silver to accomplish the same purpose.

Dave

 

[Anonymous]

Why not use 50/50 Nitric/distilled water? I'm not sure of the purpose of the Hydrogen Peroxide or was that a slip of the keyboard?

Jon

 

[FrugalRefiner]

A little peroxide will extend the use of the nitric by converting some of the NO_x byproducts back into nitric acid. I'm not sure about using that much, but that wasn't his question, so I didn't address it.

Dave

 

[Anonymous]

A little peroxide will extend the use of the nitric by converting some of the NO_x byproducts back into nitric acid. I'm not sure about using that much, but that wasn't his question, so I didn't address it.

Dave

Apologies did I do wrong by doing so?

 

[Barren Realms 007]

A little peroxide will extend the use of the nitric by converting some of the NO_x byproducts back into nitric acid. I'm not sure about using that much, but that wasn't his question, so I didn't address it.

Dave

Apologies did I do wrong by doing so?

Not IMHO you are fine.

 

[FrugalRefiner]

Apologies did I do wrong by doing so?

Not in my opinion. I assumed you asked the question because you weren't familiar with the use of peroxide with nitric. I just didn't address it in my response to the OP because it wasn't part of his question. He seemed confident in his process to dissolve the silver, but was concerned about the effect of dissolved copper on his silver cement.

I suppose I should have added that the greater the amount of copper in the solution, the more likely he'll have drag down in his cement. But that can be mostly avoided by dissolving more silver till the nitric is exhausted.

Dave

 

[PlainsScrapper]

Why not use 50/50 Nitric/distilled water? I'm not sure of the purpose of the Hydrogen Peroxide or was that a slip of the keyboard?

Jon

Spaceships, the reason for using a 50/50 combination of nitric acid and hydrogen peroxide was to limit the production of Nitrogen dioxide gases (NOx) in the reaction.
However, considering the fact that I will need additional scraps of silver, as well as my college's availability of a nitrogen dioxide fume scrubber and fume hood makes me reconsider not using H2O2 to suppress fumes.

 

[Barren Realms 007]

Why not use 50/50 Nitric/distilled water? I'm not sure of the purpose of the Hydrogen Peroxide or was that a slip of the keyboard?

Jon

Spaceships, the reason for using a 50/50 combination of nitric acid and hydrogen peroxide was to limit the production of Nitrogen dioxide gases (NOx) in the reaction.
However, considering the fact that I will need additional scraps of silver, as well as my college's availability of a nitrogen dioxide fume scrubber and fume hood makes me reconsider not using H2O2 to suppress fumes.

The best thing you could do is learn how not to use too much nitric when working with silver.

 

[Geo]

I have used sulfamic acid to rid silver nitrate of free nitric acid. It worked fine for me. You really can't add too much sulfamic acid. Well, technically you can but it would be hard to do. Heat the silver nitrate (higher temps generate a more vigorous reaction) and add a solution of sulfamic acid and water until it stops generating gas. The silver will cement out and stay out of solution much cleaner. Dilution of the solution also helps. It slows the reaction down but it saves the copper metal.

 

[butcher]

Concentrated mixtures of nitric acid and hydrogen peroxide can be dangerous, or can cause unwanted reactions.
http://hydrogen-peroxide.us/chemical-catalyst-decomposition/Solvay-Hydrogen-Peroxide-Nitric-Acid-Hazards-2005.pdf

Nitric acid 70% and water a 50:50% mixture will work well to dissolve silver , or even more dilute which can be somewhat beneficial to hold converted NOx gas in solution, the water itself helping to convert the NO2 gas in solution back to HNO3, more dilute can be somewhat slower, unless heating (which is normally needed anyway) is used towards later part of the reaction, that also helps drive the reaction and concentrates the solution so more silver dissolves, using up the free nitric.

Water with nitric is needed to effectively dissolve silver in nitric acid, beside holding dissolved salts of silver nitrate, the water can help to lower NOx fumes, converting some back to acids to react with more silver.
2NO2 + H2O --> HNO3 + HNO2

Very dilute hydrogen peroxide can also be beneficial to the process.
70% nitric acid contains some water in the acid, diluting it further can help when dissolving silver, a small amount of 3% H2O2 which is mostly water can also help to convert some of the NOx gas in solution back to acid. beside the water in the peroxide, the oxygen can help to convert other NOx gases.
2NO + O2 --> 2NO2
2NO2 + H2O2 --> HNO3
2NO + 3H2O2 --> 2HNO3 +2H2O
3NO2 + H2O --> 2HNO3 + NO

Of coarse this is really over simplifying the equations, and reactions, and the real world reactions produce many forms of the toxic and corrosive NOx gases in differing forms none of which we want to get complacent with, or underestimate their dangers, or effects.
We can convert some of the gases but not all.
For safety's sake learn to protect yourself, others, and the environment as much as possible when dissolving metals in acids.


Too concentrated of nitric and silver would waste nitric acid and not be beneficial, too concentrated of hydrogen peroxide would not be beneficial, too concentrated of both could just be down rite foolish or dangerous.

Depending on the concentration of the nitric acid used on metals, the reactions can form different types of NOx gases, some metals can form an oxide layer in too concentrated of nitric acid, making it harder to dissolve the metal into the acid, and build a layer of metal oxide Passivation, or it take longer for the acid to break down to the component of the acid which actually does the work to dissolve metal, like HNO2 decomposition with NO2 in the nitric to form to begin attacking the metals.


Personally, I would not use sulfamic acid with a silver nitrate solution, thinking I may form some only slightly soluble silver sulfate, from a sulfuric acid byproduct in solution.
Using less nitric and heat to use up the nitric with some silver remaining, then adding increments of nitric as needed to finish completely dissolving the metal would be my choice.

1 gram of copper will cement about 3.4 grams of silver.
Approximately 1.2ml of 70% HNO3 and 1.2ml of distilled water will dissolve a gram of silver.
Approximately 4.15ml of 70% nitric acid and 4.15ml of distilled water will dissolve a gram of copper.
Sterling silver 92.5% Ag 7.5% copper takes approximately 1.5ml 68% HNO3 and 1,5 ml H2O to dissolve a gram of sterling silver.
A little bit of free acid can actually help to cement metals from solution.
Unless you use way too much acid (a very common problem with those new to this chemistry of metals), you should not lose to much copper in the normal cementing process, as most of the nitric is consumed or diluted in the reactions.
Considering how much nitric acid the copper consumes, (or to say it another way), how much nitric it takes to dissolve copper, the little bit of copper that is used in a slight excess use of nitric will not amount to much, and how little copper to replace the silver from solution, the copper is not wasted in my thinking, besides I have several uses for the copper nitrate anyway.

 

[PlainsScrapper]

Why not use 50/50 Nitric/distilled water? I'm not sure of the purpose of the Hydrogen Peroxide or was that a slip of the keyboard?

Jon

Spaceships, the reason for using a 50/50 combination of nitric acid and hydrogen peroxide was to limit the production of Nitrogen dioxide gases (NOx) in the reaction.
However, considering the fact that I will need additional scraps of silver, as well as my college's availability of a nitrogen dioxide fume scrubber and fume hood makes me reconsider not using H2O2 to suppress fumes.

The best thing you could do is learn how not to use too much nitric when working with silver.

That is true. Frugality is very important, and as I am still reading and getting more information, I find it increasingly important to save money and resources, as well as reduce waste output as much as possible, so yes, I will definitely be only using the bare minimum that I need.

 

[PlainsScrapper]

Concentrated mixtures of nitric acid and hydrogen peroxide can be dangerous, or can cause unwanted reactions.
http://hydrogen-peroxide.us/chemical-catalyst-decomposition/Solvay-Hydrogen-Peroxide-Nitric-Acid-Hazards-2005.pdf

Nitric acid 70% and water a 50:50% mixture will work well to dissolve silver , or even more dilute which can be somewhat beneficial to hold converted NOx gas in solution, the water itself helping to convert the NO2 gas in solution back to HNO3, more dilute can be somewhat slower, unless heating (which is normally needed anyway) is used towards later part of the reaction, that also helps drive the reaction and concentrates the solution so more silver dissolves, using up the free nitric.

Water with nitric is needed to effectively dissolve silver in nitric acid, beside holding dissolved salts of silver nitrate, the water can help to lower NOx fumes, converting some back to acids to react with more silver.
2NO2 + H2O --> HNO3 + HNO2

Very dilute hydrogen peroxide can also be beneficial to the process.
70% nitric acid contains some water in the acid, diluting it further can help when dissolving silver, a small amount of 3% H2O2 which is mostly water can also help to convert some of the NOx gas in solution back to acid. beside the water in the peroxide, the oxygen can help to convert other NOx gases.
2NO + O2 --> 2NO2
2NO2 + H2O2 --> HNO3
2NO + 3H2O2 --> 2HNO3 +2H2O
3NO2 + H2O --> 2HNO3 + NO

Of coarse this is really over simplifying the equations, and reactions, and the real world reactions produce many forms of the toxic and corrosive NOx gases in differing forms none of which we want to get complacent with, or underestimate their dangers, or effects.
We can convert some of the gases but not all.
For safety's sake learn to protect yourself, others, and the environment as much as possible when dissolving metals in acids.


Too concentrated of nitric and silver would waste nitric acid and not be beneficial, too concentrated of hydrogen peroxide would not be beneficial, too concentrated of both could just be down rite foolish or dangerous.

Depending on the concentration of the nitric acid used on metals, the reactions can form different types of NOx gases, some metals can form an oxide layer in too concentrated of nitric acid, making it harder to dissolve the metal into the acid, and build a layer of metal oxide Passivation, or it take longer for the acid to break down to the component of the acid which actually does the work to dissolve metal, like HNO2 decomposition with NO2 in the nitric to form to begin attacking the metals.


Personally, I would not use sulfamic acid with a silver nitrate solution, thinking I may form some only slightly soluble silver sulfate, from a sulfuric acid byproduct in solution.
Using less nitric and heat to use up the nitric with some silver remaining, then adding increments of nitric as needed to finish completely dissolving the metal would be my choice.

1 gram of copper will cement about 3.4 grams of silver.
Approximately 1.2ml of 70% HNO3 and 1.2ml of distilled water will dissolve a gram of silver.
Approximately 4.15ml of 70% nitric acid and 4.15ml of distilled water will dissolve a gram of copper.
Sterling silver 92.5% Ag 7.5% copper takes approximately 1.5ml 68% HNO3 and 1,5 ml H2O to dissolve a gram of sterling silver.
A little bit of free acid can actually help to cement metals from solution.
Unless you use way too much acid (a very common problem with those new to this chemistry of metals), you should not lose to much copper in the normal cementing process, as most of the nitric is consumed or diluted in the reactions.
Considering how much nitric acid the copper consumes, (or to say it another way), how much nitric it takes to dissolve copper, the little bit of copper that is used in a slight excess use of nitric will not amount to much, and how little copper to replace the silver from solution, the copper is not wasted in my thinking, besides I have several uses for the copper nitrate anyway.

butcher, I will decide to use distilled water instead of hydrogen peroxide, as that seems to be the more straightforward route. I was just trying to follow samuel-a's method on the forum and his channel. Thanks for all of the advice, as I don't want there to be more trouble than necessary. All of that additional information will be put into my mind for future use.

 

[Anonymous]

butcher, I will decide to use distilled water instead of hydrogen peroxide, as that seems to be the more straightforward route. I was just trying to follow samuel-a's method on the forum and his channel. Thanks for all of the advice, as I don't want there to be more trouble than necessary. All of that additional information will be put into my mind for future use.

Great news plains. It's never a problem to ask a question 8) 8)

Jon

 

[kurtak]

I have used sulfamic acid to rid silver nitrate of free nitric acid. It worked fine for me. You really can't add too much sulfamic acid. Well, technically you can but it would be hard to do. Heat the silver nitrate (higher temps generate a more vigorous reaction) and add a solution of sulfamic acid and water until it stops generating gas. The silver will cement out and stay out of solution much cleaner. Dilution of the solution also helps. It slows the reaction down but it saves the copper metal.

Geo

using sulfamic to kill the free nitric when cementing silver is totally un-necessary --- I am not saying that doesn't &/or wont work - just that is not necessary

I believe you posted on the RPM web site that "excess" free nitric will cause copper to oxidize during the cementing & thereby cause a greater copper contamination in your silver cement ( I had meant to comment on that when I read it but didn't have time at that time --- & please correct me if I am wrong)

It is not the free nitric in silver nitrate that causes the copper oxide contamination problem when cementing silver --- a fully silver saturated solution can end up with this problem just as well as a solution with free nitric can

The all to common mistakes that people make when cementing their silver are

(1) they don't fully submerge their copper in the solution - this cause's the exposed copper to form a copper oxide that then falls into the cemented silver & or washes off into the silver cement when washing the bar off

(2) they don't "hang" their copper in such a manner that room is left at the bottom of the vessel for the cement to fall & collect in a copper free zone - in other words if the copper hangs to low & silver cement builds up around the copper - what happens is the build up of silver around the copper prevents fresh silver nitrate solution from contacting the copper hence the nitrate that is contacting the copper becomes weaker & weaker thereby loosing its ability to fully react with the copper & thereby causing copper to oxidize rather then dissolve

(3) (& this is the "biggest" problem) they don't dilute their silver nitrate enough before they start cementing - what happens here is that if the solution is to concentrated & not diluted enough - the silver will not slough off of the copper but will instead start building up & adhering to the copper --- this causes the same problem as problem (2) above --- the build up of the silver on the copper prevents "fresh" silver nitrate from contacting the copper & again the nitric near the copper becomes weaker & weaker until it is no longer effective in fully dissolving the copper - thereby causing the copper to oxidize instead --- this will happen whether you have free nitric or not - if the silver nitrate is not dilute enough so that the silver cement readily "sloughs off" the copper thereby keeping the copper "exposed" to fresh silver nitrate - copper oxide will form

Diluting the silver nitrate causes the silver to cement out a bit finer so you have to be careful that you don't over dilute or your cement will come down so fine that it causes washing &/or filtering problems --- you want it diluted enough so that the silver sloughs off the copper but not so dilute that the silver cements out "ultra" fine

Three key points to cementing silver & ending up with a "clean" cement are (1) suspend the copper so it is "completely" submerged (2) also suspend it so there is room at the bottom of the vessel for the cement to deposit without covering up to much of the copper (3) & most important - dilute the solution enough that the silver "sloughs" off the copper as the cementing takes place

The only (some what) problems with "to much" free nitric is that in the first place it is a waste of nitric & second is that besides reacting with the copper it will also react with the silver "as it is cementing out" & because the silver particles are already small in size they will be reduced in size thereby causing at least some ultra fine cement - how much ultra fine will depend on how much free nitric

One way to deal with the free nitric (& IMO better then using sulfamic) is to put your copper in - let it cement only "some silver" - pull the copper out & let the free nitric re-dissolve the cemented silver so the silver uses up the free nitric --- you may need to put the copper in & take it out a few times to reduce the free nitric to a point it is not a problem - but free nitric is really only a problem if there is a LOT of it

Of course the best is to not over do the nitric in the first place

pics show the silver sloughing off the copper as it cements out of solution

Kurt

 

[butcher]

Very good information Kurtak well done ,
To add a little to your great post.
Some other things which may cause problems, is using too thin or too small of a copper bar, dirty or oxidized copper to begin with, using dirty or oxidized copper, or copper with oils or other surface contamination.

Heating the copper buss bar to burn off oils or other contamination, and cleaning it of surface contamination, or its patina, to expose a bright clean copper surface, copper can oxidize over time in the environment, to form a patina (of oxides, or of various copper salts), much faster if it has been exposed to air after it has seen acids, (oxides or salts some of which can even be hard to dissolve in acids), oils, patina or copper salts which can passivate the surface of the copper with salts which do not have that extra ion to give to your silver nitrate to cement the silver metal from solution.

Storing your copper buss bar under water, or in a solution of copper nitrate can help it from forming a salt patina between uses, or at least after brushing it, cleaning it by rinsing in water, drying it (with heat from your torch) and storing the cooled bar in a air free zip-lock plastic bag.

Movement of the solution, or the copper buss bar can help during the cementing process, insuring the silver ions in solution come into contact with the clean copper metal.
Where the ion exchange can take place.
Note: that each atom of copper gives up its free electron to the silver ion, (each copper atom is oxidized),and goes into solution as a copper ion (copper nitrate salt), the silver ion gaining the electron is (reduced) back to a silver atom with a full shell of electrons the silver atoms joining together in solution to form a metal silver powder.
Using an air bubblier or pump to circulate the solution, or shaking the copper buss bar now and then can be helpful during the cementing process...

 

[Geo]

Thanks Kurt. The problem is that most beginners do not saturate the solution with silver. When dissolving silver, if 100 mL works good, then 200 mL will work better seems to be the status quo to many. Perhaps they do not know exactly how much nitric acid was used. Perhaps it's a nitric acid leach or wash for some other process that contains silver. Destroying or depleting the excess nitric acid with sulfamic is better than using solid copper. I agree that sulfamic is not needed if the leach has absorbed as much silver as the solution can hold but that's not really the situation I am talking about.
By way of example, you have incinerated a large lot of IC chips. You have washed the ash away and are left with the heavy material. For a cleaner gold solution, you would first leach using hot nitric acid. The largest percentage of metal in the leach should be copper with some iron and silver. You would like to reclaim the silver but the wash is still loaded with free nitric. Because you don't know the exact weight of the base metal you are leaching, you make sure to add an excess of nitric acid to be sure you get it all. You can re-use it on the next batch but that will leave you unsure that all the base metal has been removed from that batch meaning you must add more to be sure. Either way, it will have an excess of nitric acid. This is just one small example.
When you add solid copper to a solution with silver and excess nitric acid, silver will cement out. As soon as it does, it redissolves. The copper and silver dissolving at the same rate makes the cemented silver look black instead of the bright shiny crystals you would like to see. I think it is tiny particles of copper metal that gets trapped within the cemented silver and doesn't dissolve or it's copper oxide that does not dissolve for the same reason.

 

[PlainsScrapper]

All of you guys have been so helpful on the forum, helping others including myself with the processes, so thank you for that. I have another question regarding mylars. In the case involving the processing of laptop keyboards, the mylars are all glued together, and when they are separated, there is a sticky adhesive that remains. Should I incinerate the mylar and just obtain the silver that way, attack the adhesive with a solvent or compound, or does the nitric acid remain untouched? I don't want to foul the solution and have more losses than necessary. All feedback is appreciated.

 

[g_axelsson]

Geo, wouldn't adding sulfamic acid added to nitric acid and silver nitrate form weakly soluble silver sulfate?

When I use nitric acid for dissolving metals I usually add less than needed, when it stops reacting I pour off the metal nitrate salts, then add new acid and water. The last acid digestion contains a concentrate of precious metals as silver and palladium while the first couple of cycles usually contains very little, it cements back on the remaining metal.
The last batch is either used for recovery of the precious metals it contain or saving it for dissolving base metals next time I need it.
The smaller volume I work with also keeps the concentration up so it's easier to judge when the acid is used up and it works faster. For me who have to save nitric as it is hard to find, this is a great way to make it last as long as possible.

Göran

 

[Geo]

Geo, wouldn't adding sulfamic acid added to nitric acid and silver nitrate form weakly soluble silver sulfate?

When I use nitric acid for dissolving metals I usually add less than needed, when it stops reacting I pour off the metal nitrate salts, then add new acid and water. The last acid digestion contains a concentrate of precious metals as silver and palladium while the first couple of cycles usually contains very little, it cements back on the remaining metal.
The last batch is either used for recovery of the precious metals it contain or saving it for dissolving base metals next time I need it.
The smaller volume I work with also keeps the concentration up so it's easier to judge when the acid is used up and it works faster. For me who have to save nitric as it is hard to find, this is a great way to make it last as long as possible.

Göran

This is from my understanding of this particular situation, The sulfamic acid only creates a minute amount of sulfuric acid in solution. You would have to heat the solution and evaporate to the point that the concentration of metal exceeds the solutions ability to hold it in solution. The small amount of sulfuric would then react to the highest reactive metal and precipitate that metal as a sulfate. Silver sulfate is prepared by adding sulfuric acid to silver nitrate and heating the solution. The sulfuric acid created when adding the sulfamic acid is negligible at best. besides, the very tiny amount, if any, is well worth it when weighed against the prospect of costly copper metal consumption and contaminated cemented silver. I will have to leave the chemistry behind it to someone else and all I have to go by is what I've observed. Given the choice, I will use the sulfamic acid.