Silver and copper solubility

[theitalianhenchman]

Hi,
I remember that I've read the amount of nitric needed to dissolve silver and copper (if I recall was 4ml nitric for 1gram of copper) but I'm unable to find it. I don't remember the data about the silver. If someone knows or remember in which thread it could be found. Thanks.

 

[kurtak]

Hi,
I remember that I've read the amount of nitric needed to dissolve silver and copper (if I recall was 4ml nitric for 1gram of copper) but I'm unable to find it. I don't remember the data about the silver. If someone knows or remember in which thread it could be found. Thanks.

First off it is important to understand that there is no such thing as "it takes" - or - "you need" this much acid to dissolve this much metal - in other words there is no exact number(s)

That is because how much metal an acid will dissolve with the acid depends on the conditions under which the metal is being dissolved by the acid --- so depending on the conditions under which the metal is being dissolved by the acid it may take more - or less - acid to dissolve a given amount of metal

So - at best you can only figure "about" how much acid is going to dissolve a given amount of metal

If you try to calculate an exact amount of acid for a given amount of metal - more then likely you end up with -------

1) not enough acid to dissolve all the metal - or ------
2) dissolve all the metal but also still have acid remaining that can dissolve more metal
3) rarely - if ever - will you be able to calculate the exact amount of acid needed to dissolve a given amount of metal --- so you want to figure "about" how much acid you need - start with less then that - then make additions of the acid until all the metal is dissolved

This is especially true with nitric acid

Conditions that WILL change the amount of acid that will dissolve a given amount of metal are -----

1) the state that the metal you are dissolve is in --- is it foils - fine powder - poured to smaller shot/grains - or one solid piece

Examples; - it will take "much less" acid to dissolve a troy ounce of gold foils & "much more" acid to dissolve a solid troy ounce bar of gold --- & that is true with any/all metal

2) whether the vessel (beaker) you are dissolving the metal in is an open vessel or a closed vessel

Examples; - a beaker with no watch glass (or lid) on it will cause "acidic fumes" (NOx) to go out the top of the beaker - so you loose "some" of the acid as fumes so it will take more acid to dissolve the metal --- on the other hand if you put a watch glass on top of the beaker that allows most of the fume to be held in the beaker - "some" of those fume will the get re-absorbed back into the solution so it will take less acid to dissolve the metal

3) although not as much of a factor as the two above conditions temperature can also play a role in the amount of acid it will take to dissolve a given amount of metal --- because temp is not as important as the above two examples I am not going to try to explain it

So with all that said & to answer your question - copper (& other base metal) --- 4 ml of 67 -70% nitric (diluted with water) will dissolve "about" 1 grams of copper BUT depending on the conditions it may actually take more - or less then that

Gold & silver --- 1 ml of 67 -70% nitric (diluted with water) will dissolve "about" 1 grams of gold or silver BUT depending on the conditions it may actually take more - or less then that

In other words - it takes "about" 4 time more nitric to dissolve copper (& other base metals) then it takes to dissolve gold or silver

Kurt

 

[andu]

I'm not certain about silver, but to not waste nitric you can definetly get rid of the copper with vinegar and hydrogen peroxide.

 

[Yggdrasil]

I'm not certain about silver, but to not waste nitric you can definetly get rid of the copper with vinegar and hydrogen peroxide.

Separate before dissolving as always crap in crap out.
If it is practical the best is separation before dissolving, and this is what I consider one of the few constants in our world.
Whenever this is not possible then one have different approaches depending on starting materials.
Sterling for instance is not possible and gives you only one route (almost true).

As I can see Vinegar has absolutely NO purpose in recovery and refining of PMs.
Better use HCl and air bubbling aka Cupric Chloride leach aka AP.

 

[andu]

Vinegar is stronger than hcl on some metals like copper, i forgot i also added salt and the copper became a beautiful blue oxide, just as the solution.
I also just read that salt does help with silver corrossion, i have a bucket dissolving some silver plated cutlery, and i guess that if i added salt even more silver would dissolve than just with the hydrogen peroxide.

I know myself it sounds crazy but i'll prove it when i start uploading videos.
I found the mix of vinegar and salt and hydrogen peroxide works well when nitric is hard to get ahold. I haven't yet worked with an acid as dangerous as nitric.

 

[Yggdrasil]

Vinegar is stronger than hcl on some metals like copper, i forgot i also added salt and the copper became a beautiful blue oxide, just as the solution.
I also just read that salt does help with silver corrossion, i have a bucket dissolving some silver plated cutlery, and i guess that if i added salt even more silver would dissolve than just with the hydrogen peroxide.

I know myself it sounds crazy but i'll prove it when i start uploading videos.
I found the mix of vinegar and salt and hydrogen peroxide works well when nitric is hard to get ahold. I haven't yet worked with an acid as dangerous as nitric.

Vinegar and Salt forms a weak HCl, and HCl together with Oxygen forms Cupric Chloride which is an excellent etchant for Copper.
If you have a hard time getting Nitric some use poor mans Nitric.
Any Chloride based leach will not handle Silver since it firms Silver Chloride.

 

[Anil]

Between 3 to 4 L of Nitric acid having 70% strength is enough to dissolve both gold and silver if the alloy is in granule form allowing the reaction to happen much faster due to more surface area available when an alloy is in granular form. Also, make sure that the Nitric Acid used is free of any halides which otherwise form Silver Halides which are not soluble in Nitric Acids. In short, check your nitric acid quality for the presence of halides before you use it.

 

[Yggdrasil]

Between 3 to 4 L of Nitric acid having 70% strength is enough to dissolve both gold and silver if the alloy is in granule form allowing the reaction to happen much faster due to more surface area available when an alloy is in granular form. Also, make sure that the Nitric Acid used is free of any halides which otherwise form Silver Halides which are not soluble in Nitric Acids. In short, check your nitric acid quality for the presence of halides before you use it.

Excuse me?
The volume of chemicals are totally dependent on the amount of metals to dissolve.
And Nitric do not dissolve Gold, it is however, well suited for Silver, Copper takes about 4 times the amount of Nitric as Silver.
And to my knowledge the only Halide of concern is Chlorides, depending on the next step this do not necessarily make much of a difference.

 

[Anil]

Excuse me?
The volume of chemicals are totally dependent on the amount of metals to dissolve.
And Nitric do not dissolve Gold, it is however, well suited for Silver, Copper takes about 4 times the amount of Nitric as Silver.
And to my knowledge the only Halide of concern is Chlorides, depending on the next step this do not necessarily make much of a difference.

Hi, I am sorry. I meant HNO3 will dissolve silver and copper and any other base metals but not Gold. My apologies and many thanks for drawing my attention.