Pins in Nitric Acid

[kamranashraf]

I have partial plated pins with the 70% silver coating i think its may be Ag or Nickel some test show Ag and some Show Nickel want to dip 500grams of partial plated pins into the nitric although can anyone give me full process and assure me that nitric wont attack my gold i dip about 10grams into few millimeter nitric after few minutes red fumes rise and i found there is white powder mix in gold foils it may be nickel or Ag but can any one clear me how much nitric acid we use for 500grmas pins and what is the step by step process to cement out all PGMS ,

 

[butcher]

nitric will dissolve silver, nickel, and other base metals, it will not dissolve any gold,
white powder sounds like you need heat, water or more nitric,
what is the concentration of nitric you are using? is it homade?
if alot of silver there is a chance that some platinum group may be dissolve with it,
(if high karat gold nitric may not be able to reach the other metals)
use as much nitric as needed to disolve all of the metals it can, when heat,additions disslove no more or no more reaction,try little more nitric.
1610 ml of nitric will dissolve 1 pound copper (laser steve has a post on this),
also Gold Silver Pro has several great posts on how much copper or base metals will dissolve in nitric. with instructions,use only as much as you need, so you don't have excess to eliminate later, but get all base metals it can dissolve, heat and (concentration) dilution can also help here, GSP has a classic post on this that you really need I am just not sure how to point you to it, minimum (but enough) use of nitric.

 

[qst42know]

If these are the pins you had in Hcl peroxide in another post, adding nitric at this point will dissolve gold.

 

[kamranashraf]

If these are the pins you had in Hcl peroxide in another post, adding nitric at this point will dissolve gold.

i am not using nitric for my peroxide its totally separate batch
,

what is the concentration of nitric you are using? is it homade?

the concentration of the nitric is 69% written i purchase one gallon of 5kg weight for 3 $USD the chemical sell in our country by weight i purchase it at a local chemical store the gallon is well packed.
Would anyone like to give me some links of GSP and Steve posts because i cant get through search, also how much i need H2O to dilute the acid as my acid concentration is 69% and is it distal water or tap water?

 

[Palladium]

also Gold Silver Pro has several great posts on how much copper or base metals will dissolve in nitric. with instructions.

:arrow: http://goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=534&hilit

I had a little problem following your math but it seems you came to the conclusion that it takes only a quart of 70% HNO3 to dissolve a pound of copper. The rest of the 1/2 gallon is made up with water. I don't understand why you said that I was correct. I guess you assumed that I meant 1/2 gallon of 50/50 nitric. I didn't.

I'm saying that it takes 1/2 gallon (2 quarts) of 70% HNO3 to dissolve 1 pound of copper. This is twice what you calculated and also twice the amount I see posted around the internet. I also add 1/2 gallon of water, making 1 gallon of 50/50 solution, to prevent crystallization of the copper. This is probably more water than needed but, it provides a good safety net.

The equation you gave is:

Cu + 2HNO3 = Cu(NO3)2 + H2

This is not the applicable equation. You didn't consider the NO or NO2 gas that is produced. The actual working equation for concentrated nitric is: (Call this equation #1)

Cu + 4HNO3 = Cu(NO3)2 + 2NO2 + 2H2O

For very dilute nitric, the equation is different: (Call this equation #2)

3Cu + 8HNO3 = 3Cu(NO3)2 + 2NO + 4H2O

Actually, in this last equation, the NO (colorless gas) immediately combines with oxygen from the air to form NO2 (red-brown gas). Here's the overall equation.

3Cu + 8HNO3 + O2 = 3Cu(NO3)2 + 2NO2 + 4H2O

Now for the math - first for equation #1:

One Mole of copper is 63.55 grams. Therefore, in one pound (454 grams) of copper, there are 454/63.55 = 7.14 Moles.

One liter of 70% nitric acid contains about 15.4 Moles. A gallon is 3.785 liters. One half gallon is 1.89 liters. Therefore, 1/2 gallon contains 1.89(15.4) = 29.1 Moles.

In Eq. #1, the Molar ratio of HNO3 to Cu is 4 to 1. Therefore, for 1# of copper, 7.14 Moles, it would take 7.14(4) = 28.6 Moles of nitric acid. Note that this is very close to the 29.1 Moles contained in 1/2 gallon of 70% nitric acid.

In Eq. #2, the ratio is only 8 to 3. This computes to 19 Moles of nitric for a pound of copper. This is about 1/3 gallon of 70% nitric. However, this equation is for very dilute nitric - maybe 1%. In practice, this very dilute nitric is not used because the reaction would be terribly slow. As I read somewhere on the net, the copper nitrate produced also acts as a solvent in very dilute nitric. This is similar to the copper chloride produced in the HCl system. This is probably one reason why the ratio is only 8 to 3 in dilute nitric. Evidently, this solvent effect doesn't apply in strong nitric.

In practice, a 50/50 solution of 70% nitric/water is usually used. This mix is considered the most efficient. It prevents crystallization of copper nitrate, improves a slight bit on the nitric required, and is still strong enough to give good reaction speed. The amount of nitric required is somewhere between Eq. #1 and Eq. #2 - between 1/3 and 1/2 gallon of 70% nitric per pound of copper. The figure is probably at least .45 gallons of 70% nitric per pound of copper, when using 50/50 nitric.

This is all theoretical. When the reaction produces fizzing, there is also some nitric loss into the air.

All in all, in practice, it takes very close to 1/2 gallon of 70% nitric acid (1 gallon of 50/50 nitric) to dissolve 1 pound of copper metal. I have proven this to myself 100's of times. It never fails, although it can be plus or minus a bit. This is the first time I've actually calculated it and I'm not surprised that the math worked out with my experiences. Try it out and see for yourselves.

The ratio figures for copper alloys and nickel will come out about the same as in pure copper above, when dissolving with nitric. For silver, one gallon of 70% nitric (2 gallons of 50/50 nitric) will dissolve about 7 pounds - 100 troy ounces.

The equations for aqua regia, being a two acid system, are much more complex. There are several different ones, all probably happening, to various extents, at the same time. It is almost impossible to predict what is exactly going on. There are too many variables involved: temperature, acids ratio, metals involved, etc. However, for most base metals, including iron, the approximate ratio is the same - about 1/2 gallon of aqua regia per pound of base metals. This is based on my experiences.

GSP

 

[butcher]

diluting the nitric concentration would reduce NOx fumes produced (and I figure wasted, (bubbling NO2 in H2O produce's dilute nitric), so in essence would be more to dissolve copper), sometime calculating this stuff on paper can be different from the real world reaction's, some physical expieriments can show a different result than we get on paper, or in our head.

Gold Silver Pro's real world experience with how much copper 70%nitric dissolves, involve's water, lowering concentration, my guess that is important to the amount of copper he was able to dissolve.

but diluting the nitric I believe would hold more copper, reaction may slow,producing somewhat less NOx fumes.than concentrated nitric will,

A Tip here be careful if you have powders, adding acids to these can get very reactive.
I can be wrong, that is not unusual.

dilute 70% nitric with about equal volumes water, and if no chlorine in water,distilled should not be nessasary

 

[goldsilverpro]

Damn, did I write all that stuff?

A Tip here be careful if you have powders, adding acids to these can get very reactive.
I can be wrong, that is not unusual.

I learned about 30 years ago not to pre-mix the nitric and water and then put it on the powder. Too many foam-overs. I first cover the powder with water. Then, I add a small increment of nitric. It should react immediately. If it doesn't, warm it up a bit. When the reaction slows down, stir and then add another increment of nitric. At some point, when an addition of nitric produces no reaction, you are finished. I do the same thing when dissolving silver contact points.

When dissolving gold powder in aqua regia, I follow a similar procedure. In this case, however, I cover the powder with HCl instead of water and maybe warm it up a bit before adding the increments of nitric.

In both cases, make sure the dissolving vessel is large enough to allow for the foam that will be produced.