# Aqua Regia process with nitric acid



## alexmaywood

Last summer I tried to refine some pounds of ceramic processors, fingers and pins. It was something like 80 F. I made AR by adding of 1 Part of 31% Nitric Acid to 3 parts of 40% HCl. After I added the procs it started to fizz actively, so actively, that soon it was boiling over the top. Lot of brown fumes. The gold on procs was all "eaten". So I decided it was in the AR which stopped finally to boil and turned green. I added urea till it fizzed no more, then plenty of SMB. There was too decent amount of mood if any on the filter. Looked like gold was diappeared.
I made it once more with 2 lbs of pins. The same.
It was sadly enough, because earlier I made the same process under the same conditions. Adding Sodium Nitrate instead, all was perfectly. I ended up with 1 oz of gold. 
I did not heat the solution. The first time it was active enough, so I did not see any need for heating. The second time it looked more like I needed to cool the whole process down.
Amazingly, because I read again and again the guys are using hotplate.
But what did I wrong on the second time?


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## Harold_V

Please understand I'm not trying to be rude-----

I'm doing my best to make sense of what you've told us, but I'm having no luck. Please read what you've posted and make corrections so there is some continuity to your comments. If you can't see what's wrong with what you've posted, please ask for someone to provide some assistance, then tell your story once again. I may be able to help you with what's going on, assuming I understand what it is you're trying to say. If it's a matter of losing your gold in the process, you're likely overlooking one very important detail. I'll know if that's the case if your next comments make sense. 

Harold


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## lazersteve

Harold, 

I have to agree it's hard to decipher what he is asking. I'm assuming English is not his native language (no offense Alex, just trying to help get you a good answer :wink: ).

From what I can make of it he has done two AR reactions, the first worked fine using Sodium Nitrate and 40% HCl, he got 1 oz. of gold yield.

The second reaction he used 1 part 30% Nitric and 3 parts 40% muriatic. This reaction was done at 80C and almost boiled over. He got mud which disappeared in the filter? This is where I get lost.

I hope this helps get you an good answer Alex, please correct me if I've missed your question. Harold will definitely be able to help you once we get your question worded correctly.

Steve


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## alexmaywood

This is not the question of language, this is the problem of beeing new in business. Thanks anywhere. Probably it will help me to be more professional.

There were two attempts to refine gold from ceramic processors and gold plated pins. The first one was pretty succesful, the second - totally lost. The only difference between these attempts was the way I made AR. 

I escaped from detailed description of the whole processes, because it was done in "classic" style: dissolving gold in AR, adding Urea and then precipitating gold with SMB. Filtering, washing the brown mud and finally melting it. And so on.

The problem which I was trying to figure, was that during the first reaction, when I was using HCl plus Sodium Nitrate, all was going well, gold dissolved quickly enough in AR. Then I filtered the green liquid, added Urea and SMB and got 1 oz of gold mud. So I was fully satisfied. 

Second time I used Nitric Acid and HCl, 1:3 ratio. The weather conditions were the same, app. 80 F, the amounts of gold and AR too.
The problem was that the reaction started very abrupt, it fizzed badly with lot of brown fumes and in a couple of minutes it was boiling and going over the top. So some amount of solution was lost, not too much.

After app. 15 min of boiling there was green liquid in the bucket, looked exactly like first time. But after adding Urea and SMB and filtering there was practically nothing left, no brown mud in bucket or filter. As I did hope to get the same amount of gold as it was before, I was disappointed.

Obviously during the second attempt the reaction of dissolving gold in AR was too active, too much energy was produced, solution boiled and spilled out. There was a lot of brown fumes, what I did not see during the first time (it was pretty uncomfortable). This was the only difference from the first attempt. All other reactions (with Urea and SMB) looked the same.

And there was no gold yield although all the gold from processors and all the pins were dissolved in AR. This is the main problem which bothers me. Was it because AR reacted too actively?

What is amazing me that most recommendations are to speed the process by heating the AR. And AR made from Nitric plus HCl suppose to be more powerful and therefore better as one made by adding SN to HCl. In my own experience I would rather have to slow the reaction down by cooling than heating it. To my opinion SN is more interesting than Nitric Acid.

So it comes to two questions - why did AR boil? And - was it the reason of loosing all the gold?

And why I mentioned the ratios of processors to AR - the guy wrote that all the gold will not precipitate, if one does not keep batches of 1# of processors to 1 quart of AR. It will redissolve back. May it be the reason why I lost my gold?

Thanks


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## Harold_V

I'm somewhat perplexed at what happened, although I think I may have a hunch what did. 

Let me give you some tips-----tips that may save you in the future. 

The first one is that AR is not a great way to strip gold----fact is, unless you're stripping from non-metallics, it should not be used at all. The sole exception I can think of right now would be if you're processing a lot of unidentified dental alloys---in which case there's a particular procedure you'd use to eliminate the base metals and retain the values. I think you did that, inadvertently, when you ran your pins. 

Stripping with AR when your gold is applied to base metals will generally gain you nothing but trouble-----and the gold that you may recover will not be as clean as if you'd used what I'd like to call a "proper" procedure. 

Here's the deal. When you strip with AR and there's any base metal present when the gold is stripped, as the acid level subsides, the metal that's present will start precipitating the gold as brown mud. Given enough base metal, your solution will end up barren, with all the gold sitting in the bottom as mud. Assuming you use enough acid to dissolve all the metal, so that doesn't happen, you'll have a solution that's heavily contaminated with base metals, which make it harder to precipitate clean gold, due to drag down. 

I would have suggested two things to you. First, run the non-metallics with AR, as you did, but DO NOT include any pins. That way you'll minimize the amount of base metal dissolved, and your results will tend to be much better. 

Pins. Why anyone would dissolve them with AR escapes me. There is no good reason to do so, particularly when you consider that you'll use the same amount of acid if you use accepted practice and dissolve the base metals with nitric acid, or even with the methods that Steve has developed so well. When you eliminate the base metals, the volume of gold involved will be quite small, and will later dissolve in AR for refining with no trouble. The rapid reaction you experienced was a result of dissolving a lot of zinc (yellow brass, of which pins are usually made). This material is very reactive with acids, plus it contains some lead, for free machining. It's always real smart to keep lead out of the process, which you'd have done nicely by dissolving the pins before dissolving the gold. 

When you follow proper procedures, and you expect to turn your work out in a timely fashion, you certainly don't want to run solutions cold. I'm not suggesting that they don't work, but when you work with heat, you learn how to introduce the acids such that you get a fast response, with few, if any, boil-overs. Don't let a bad experience poison your mind against a very useful process, the one of heating solutions. 

I'm of the opinion that you probably lost a good deal of your gold when you experienced the boil-over. Reason? All of the gold was likely in solution, and the acid level was too great for any of it to have precipitated as mud. Later, as the acid level diminished, and the amount of metal was being reduced, I'm of the opinion that the remaining gold self precipitated on the pins that remained. If you haven't tossed anything, you won't have lost any of it. You should learn to never throw out anything that has touched gold, recycling it instead. The exception is barren solutions, which have been well tested for values before discarding by your usual procedures. 

If I've missed something, or if you feel there's something more you can add to your comments such that I'd get a better feel for what happened, feel free to comment further. 

Also, where you had your boil-over-----if light has hit the area, it should have turned purple. Did you get that kind of reaction? Did you wipe up the spill with paper towels? It's easy enough to recover the values from them if you did. 

Harold


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## aflacglobal

Sounds exactly like one of my stories, lol

One of the few times i tried my hand at ( On hand refining ).
I was trying to sample some of that scrap i recovered from my mysteriuos new found scrap yard from space.

I'm new, I'm new . I didn't know. :lol: :lol: 

I took a hand full of some pins from some boards and proceeded to
Throw them in some A.R. 

I had limited knowledge ,and being like anyone new i had read to heat it.
Well i tend to over do things. You know just a little bit more won't hurt. :shock: :shock: :shock: ( i know you did't heat it )

Wrong !!!!!!

I'm dam lucky to still be able to breath right. Won't do that again. :lol: 

I had flash backs to my high school chemistry class and how important it is to do the proper math.

Now, If i do mess with it hands on. I use graduated cylinders and proper
weights and calculations. We all tend to run and jump into these processes without the proper tools and background. 

These procedures all follow a set of guidelines. These guidelines are set in place for not only for saftey reasons , but also to govern according to the laws of physics.

Back to the subject. Throw a hand full of pennies in some A.R. And see if you get the same reaction you got that day. Might tell you something ?

I would have to agree with Harold on this one.

Two quick things, off the subject.

Welcome paddles 2000. This gentlemen is the maker and i assume inventor of the gold bug device. Welcome.

Two. I haven't seen any ad's in about a week now. Somebody get a shot of ad be gone. lol I'm not complaining, Just trying to figure them out.

How about you GSP ? They gone on you again.

Thanks, 
Ralph


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## goldsilverpro

I'm still here, Ralph. There just hasn't been much that I could contribute to lately. Were I to start refining again, I would never use any acids on plated materials except for those that contain gold bearing brazes. I would use cyanide to strip the gold plate away from the copper. I know this is beyond the reader's capabilities and that is why I haven't mentioned it before. To me, the cyanide is cheaper, safer, faster, more efficient, and the waste is easier to treat. I used it daily for about 20 years.

I agree completely with Harold's last post. AR is not the way to go on pins.

However, if you do happen to use "real" aqua regia for pins, there is an easy way to prevent it from foaming over. First of all, never premix the aqua regia. Use the acids separately. Cover the pins with HCl and heat. When you get a little steam coming off, add a little nitric. You should get an immediate reaction and some foaming. When the action dies down and the foam subsides, give it a slight stir and add a little more nitric. Repeat until the pins are dissolved. The size and frequency of the nitric additions is determined by the amount of foam produced. It may take more HCl. It takes 1/2 gallon of either nitric or aqua regia to dissolve 1 pound of copper or brass.

You can do this at room temperature but, I prefer heating it, for this reason. At room temp., the reaction is somewhat slow in starting. This makes you think that not much is happening and you, therefore, add more nitric. The reaction generates heat. At some critical temperature and concentration, the reaction starts going at full speed and the solution foams over. By pre-heating the solution, the first addition of nitric goes full speed immediately and this will prevent you from adding too much nitric at one time.

If you don't pre-heat, put the pins in a 5 gallon plastic bucket and put the bucket in a plastic tray (a safety net for foam-overs). The bucket gives you plenty of room for the foam. I wouldn't run over 2# of pins per batch. Cover with HCl and add a little nitric. Be patient and wait for this first reaction. Stir well when the reaction slows down. Repeat as above.

You can also pre-heat the HCl to about 130 deg F before you put it into the bucket.

I learned this stuff the hard way. I've had my share of foam overs and have lost gold in the process. However, the vast majority of these foam overs occurred by starting with cold solutions.

Were I to use nitric acid only to dissolve the copper or copper alloys and leave the gold undissolved, I would put the pins in a bucket and cover them with very hot water. I would then start making nitric additions as above.

Live and learn. Patience is a virtue. Look before you leap.


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## alexmaywood

If I only would it know before! Now I know at least were to ask if I have any troubles next time.

Thanks for help. Actually I remember the brown mud settled *before* I added Urea. Beeing profane I took it for some kind of stain. It was thrown away with filters. 

I did it outdoors and all the spills were lost. So I do not have any leftovers of solution or anything else. But I'm glad to have this valuable information. Everyone has to pay for the lessons. Let it be the price. Moreover, I have now some experience of myself.

But the problem still, that AR reacted too powerful with ceramic processors as well. The second attempt with "real" AR had two trials: one with processors and another with pins. Both showed the same boiling reaction. With ceramic processors all the gold was "eaten". Pins were not fully dissolved. They were partially left with "stain" on them.

As I see now it would be better to add NA to HCl partially. 

I must confess I put plenty of processors and pins. Probably too much. That's why I'm asking for ratios. Goldman on ebay says it should be kept 1lbs to 1 quart of AR. Shor International site that it must be given so much material, as AR could "eat". Where is the truth? 

As I understand, pins are to be processed with nitric acid first, whith would "eat" the base metals and leave gold flakes or dust. And this dust must be processed with AR to get pure gold. But will Nitric dissolve basic metals if I have to do with heavy plated pins? I have some pounds of military pins which are fully coated. Will the acid go through the plating?


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## goldsilverpro

To quote my own post, "It takes 1/2 gallon of either nitric or aqua regia to dissolve 1 pound of copper or brass." *This is the truth!!* Also, this ratio includes such things as Kovar (it's magnetic), which is the base metal of many gold plated pins on ICs.

If you're using AR, treat the processors the same way as pins in my post.



> I have some pounds of military pins which are fully coated. Will the acid go through the plating?



Probably, the nitric will penetrate the gold plating. Try a few to see what happens. Always experiment with samples first. Heat will help tremendously. Most all gold plating that is less than 100 millionths is porous. The nitric penetrates through the pores. The military parts are probably plated with less thickness than this.


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## catfish

Hi Alex:

Sorry about you misfortune on the AR boiling over thing. Sometimes experience is the best teachers.

Harold and Silverpro are very good on their advice on how to strip gold plated items and the use of nitric acid.

I only use Nitrate soda and hydrochloric acid for pins, Ceramic CPU chips and karat gold.

If you will send me your email address via PM, I will send you an excel spread sheet with all the formulas for making Aqua Regia (sic) using nitrate soda and hydrochloric acid.. The amounts of metal are very important if you want good balanced results on the dissolving of metals. I have included on the sheet the exact amount of metal to the amount of Aqua Regia.

Harold is correct in saying that if you use AR to dissolve pins, you will certainly get a lot of junk in your mix. This takes time, but it can be cleaned up to be good gold with a little effort though.

The biggest problem with dissolving pins is to make sure that you don’t put too many (Grams) of metal to the specified amount of solution...

You may also want to invest in a heat resistant flask of about 1000 to 2000 ml. Get your self a plastic tub or pan to put the flask in. Don’t put in more than about half solution to the size of the container. You will get some chemical reaction. You will always get more reaction with Nitric acid than you will get with nitrate soda.

Don’t give up; we all have made costly mistakes. You have come to the right place to get insider help from some of the very best in the business. You need to try and read the entire forum posts and most of your questions would have been already answered.

Just hit me with PM and I need your email address in order to send the file.

Catfish


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## Harold_V

goldsilverpro said:


> I would use cyanide to strip the gold plate away from the copper.



That works particularly well on pins that have a nickel barrier under the gold, but my experience in using cyanide for stripping early wave guide equipment that lacked the barrier was not a good one. In all cases, the material in question was brass, not copper. While I got a generous amount of the gold off, once it perforated, base metal started dissolving as well, leaving a portion of the gold behind. Total extraction was virtually impossible. 

Bottom line on recovering values is knowing each of the recovery systems, and being able to choose the appropriate one for the materials at hand. In the case of no nickel barrier on copper, or copper based alloys, a sulfuric cell would be the best of all worlds. One would expect total extraction without pulling any of the base metals. 

Harold


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## goldsilverpro

You're right. Waveguides wouldn't work too well in cyanide. I would probably design a rig that would have a wire or rod cathode down the center of them and then use the sulfuric stripper.

I was talking about common gold plated materials: pins, fingers, etc. Most everything gold plated in the last 30 years has nickel plate under the gold. There are exceptions, however, where the gold is plated directly on copper or a copper alloy. If the oxidizer in the cyanide is at a low level, the dissolved gold plates back onto the copper, in a black powder form. On these parts, I kept the oxidizer, H2O2, at a high level to avoid this problem


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## Harold_V

goldsilverpro said:


> I was talking about common gold plated materials: pins, fingers, etc. Most everything gold plated in the last 30 years has nickel plate under the gold. There are exceptions, however, where the gold is plated directly on copper or a copper alloy.



I can't help but wonder if the logic behind the heavy gold plating I found (no less than 2% was gold, but it was hard to know precisely because I couldn't achieve a full strip) was to circumvent the fact that gold migrates into the copper alloy. By plating enough, the migration surely must come to a stop at some point-----and with gold @ $35/ounce, it was likely as cheap to use too much gold as it was to use nickel-------or could it be that the nickel barrier was a later concept and it wasn't used because they weren't aware of the fact it became a barrier? I realize you have a plating background, so maybe you can shed some light on that idea. 

Harold


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## lazersteve

GSP said:


> To quote my own post, "It takes 1/2 gallon of either nitric or aqua regia to dissolve 1 pound of copper or brass." This is the truth!!



I've worked out the *nitric acid* math to prove your point GSP :wink: , the variable is the concentration of the Nitric Acid, but you are pretty much right on the empirical values as demonstrated by my calculations shown below:

Here's the balanced equation which governs the reaction:

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


The molar atomic weights of the molecules involved are :

HNO3 = 63.01 g ( clear to pale yellow liquid ) Density = 1.4 grams per mL in 70% solution
Cu= 63.55 g (reddish brown metal)
Cu(NO3)2= 187.57 g ( deep blue water soluble crystals )
H2 = 2 g (flammable hydrogen gas)

The balanced equation atomic weights are as follows:

2 * 63.01 + 63.55 --> 187.57 + 2 ; 126.02 + 63.55 --> 187.57 + 2

Factoring in the 70% percent weight of the HNO3 :

126.02 / .7 = 180.03 g 70% HNO3

Using the density of 70% HNO3 to convert grams to mL:

180.03 / 1.4 = 128.6 mL 70% HNO3 = 2 Moles HNO3

Substituting into the equation:

128.6 mL 70% HNO3 + 63.55 g Cu ---> 187.57 g Cu(NO3)2 + 2 g H2

Converting the above data to pounds:

453.6 g = 1 lb

453.6 g / 63.55 g Cu = 7.14 Moles Cu per pound

128.6 mL * 7.14 = 918.2 mL 70% HNO3 = 14.28 Moles HNO3 required

Checking results:

918.2 mL * 1.4 g/mL = 1285.48 g * .7 = 899.836 g / 63.01 g /Mole = 14.28 Moles HNO3

Converting mL 70% HNO3 to Gallons:

918.2 mL / 3785.4 mL / Gallon = .24 Gallons ~= 1 US Quart

Checking Solubility of Copper Nitrate in Water at 20 C:

125 g Cu(NO3)2 per 100 mL H2O @ 20 C

7.14 * 187.57 = 1339.25 g Cu(NO3)2 for 7.14 Moles

1339.25 / 125 = 10.714 * 100 mL = 1071.4 mL H2O to dissolve 7.14 Moles Cu(NO3)2 @ 20 C

Checking water available in reaction from nitric acid:

1285.48 g * .3 = 385.64 g H2O = 385.64 mL H2O

Required additional water:

1071.4 mL - 385.64 mL = 685.76 mL additional water

685.76 mL / 3785.4 mL / Gallon = .18 Gallons = 2.88 cups ~= 3 cups

Conclusion:

1 pound of copper metal is dissolved by 1 quart of 70% Nitric Acid diluted with 3 cups of water @20 C

The above shows that GSP's 1/2 gallon of nitric (1.75 quarts= 0.4375 US gallons calculated) is pretty much right on the mark. 

I think I'll design a spreadsheet that will do the above math for each type of base metal automatically. I'll post the results of my work soon.

Excellent call GSP!!!  

Steve


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## Paige

I had the experience of putting in urea then going SMB. When I poured in the water & SMB, it boiled over and lost most of the gold. I had not killed the nitric like I thought I had.

I am with Harold; don't use urea. Boil away the nitric by heating it and adding distilled water and HCL alternately. You can use a pinch of urea to see of the nitric is gone, (if it fizzes, it's still there.)

Go SLOW. Take days instead of hours to complete the process. Boil for many hours, get rid of the nitric and then add SMB.

Do a search for Harold's posts and follow them.

Be sure and drop out Pt group metals as well as silver. Check for silver using ammonia on your mud. It turns blue if silver is present.

Be patient! Make this a week long project witn many washes with distilled water and HCL before you start thinking about melting.

You will have to go thru AR twice to get up to .99; but to get to higher purities, you may need to go with 3 AR treatments with filtering or use DMG.

Paige


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## Destroyer

Guilty of the same thing but I had secondary containment in place(The Oilfields were my life) So I did not lose anything. My problem was plain going to fast using the Shor directions. So I hit the hot AR with SMB in hot water not the add a little but dumped the whole thing at once. I now have a big glass jar like Steve.

I have more to do and I will be going a whole lot slower.

I mainly have memory and CPUs left to do how ever I have about 20 pounds of mother boards. One of them looks to have gold all over it. But I am not sure what to do with it so I think I will post some pictures.

I have half face MSA mask I use when it comes time to drop out the Gold.
I have an old Crock Pot I use it has a Ceramic Pot inside so I don't have to worry about anything getting knocked over. I bought some Pyrex 600 ml that I can heat smaller amounts in. I had been mixing a gallon at a time. I see that was a mistake.

I am vey happy to have found this Forum it is awesome...Thanks.


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## goldsilverpro

Steve,

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.

Alex,

Your solution didn't boil over, it foamed over. This was due to the large amount of gases, NO and NO2, produced in the above equations. Half of the nitric used is converted to gas bubbles.


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## lazersteve

Chris,

You are correct that I didn't consider the waste gases in my calculations. I noticed something interesting from your formulas that had not occured to me until I saw your formulas.. half of the nitiric acid added is wasted as off gases in the concentrated equation and a quarter of the acid is wasted in the diluted equation.

Thanks for setting things straight.

Steve


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## Harold_V

goldsilverpro said:


> For silver, one gallon of 70% nitric (2 gallons of 50/50 nitric) will dissolve about 7 pounds - 100 troy ounces.



That goes hand in hand with my experience. My silver cell was quite small----using only 30 troy ounces of silver for electrolyte. A liter of nitric (70%) was required to dissolve the 30 ounces. I used a 4,000 ml beaker, covered with a watch glass. A large portion of the vapors condensed and dripped back in the beaker instead of escaping to atmosphere. I expect my losses were minimal. 

Considering the large difference in acid consumption between digesting silver and copper, it's obvious why a person is far better served to use silver over copper or brass for inquartation. 

I may be wrong, but I think I've read that the large refiners digest in closed systems, to prevent losses by gassing. 

Harold


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## goldsilverpro

Harold,

Sounds like about a 5 gallon silver cell. Your figures come out to about 113 tr.ozs. per gallon of nitric, which is in the same ballpark. Were you using reagent grade nitric? I was using technical grade, which is weaker. That could have made a little difference. Were you using any water to dilute the nitric? 

I may be completely wrong but, I can't really see how the fume condensation would make much difference. I don't think the reaction in the equation is reversible. But, something gave you a better yield than I was getting, so maybe the condensation helped. I'll have to think about that. Also, you probably lost more fumes than you realized, since they eventually leaked out through the spout area of the beaker. I think some of the big guys collect the fumes and separately convert them back to nitric acid.


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## Harold_V

goldsilverpro said:


> Harold,
> 
> Sounds like about a 5 gallon silver cell.



It wasn't that large, although I don't recall exactly how large it was. Were it not for notes I provided to the buyer of the refining business, I'd not even have the information at hand that determined the acid consumption. My guess would be that the cell held about 2½ gallons, total. I was never very interested in silver----it was a necessary evil, so I ran it. 



> Your figures come out to about 113 tr.ozs. per gallon of nitric, which is in the same ballpark.



Fact is, the amount I'd start with would consume almost the entire amount of silver, but not quite. I'd heat until there was no more action, then add a tiny amount of acid until I was satisfied with the traces of silver remaining, and the pH was acceptable. All of it went in the cell, including the undissolved bits of silver, which was just crystal from a previous refining. I think the 100 ounces/gallon is actually quite accurate. 



> Were you using reagent grade nitric? I was using technical grade, which is weaker. That could have made a little difference.



When I first started refining, I purchased some reagent grade nitric, but ended up using it almost expressly for making critical solutions. The nitric I was purchasing appeared to be of high quality, so I, like you, used tech grade with excellent results. I watched for the formation of silver chloride when making electrolyte, but that was never an issue. I, of course, used distilled water. 



> Were you using any water to dilute the nitric?



Absolutely! While I'm not a chemist, one of the things I've read about is the hydronium ion. When you introduce nitric to silver, you find that it does very little work. Even when heated, it doesn't attack the silver with gusto. Add the slightest amount of water and all of that changes. My total volume of silver nitrate/water was held to about a half gallon while being produced, but, of course, was diluted for the cell. If I allowed my solution to cool, it immediately grew silver nitrate crystals. 



> I may be completely wrong but, I can't really see how the fume condensation would make much difference. I don't think the reaction in the equation is reversible. But, something gave you a better yield than I was getting, so maybe the condensation helped.



It's been so long now that I don't have a clear memory of the things I'd experience, but one thing I seem to recall is that what little fuming I got was slow to leave the beaker. Fact is, I used the presence, or lack thereof, of brown fumes in the beaker to help identify when there was no further action. Like you, I have no clue if what I did was helpful, or not, but it did help keep the solution from getting contaminated from outside sources. I even kept my silver cell covered to exclude any dust that might settle. 



> Also, you probably lost more fumes than you realized, since they eventually leaked out through the spout area of the beaker.



I fully agree. Considering I was the only person to use my equipment, I was all too aware of the losses one experiences in refining. It's the reason my fume hood had a filter, which, for the most part, collected the majority of values that were lost from the vessels. While the amount of gold recovered from the hood wasn't large, as compared to the volume of gold that was processed, I recovered no less than eight ounces about every other year, and that was strictly from cleaning out the hood, that did not include the filters that were changed on a regular basis. You'd have to see how the hood was built to have this make sense. I had built a chamber for such material to accumulate, secure in the knowledge that there were losses. I should also comment that my hood was built entirely of asbestos, and was used for incinerating polishing wastes and filters from jeweler's benches. I have no doubt that some of the losses were from dusting in incineration, not just vapors. 



> I think some of the big guys collect the fumes and separately convert them back to nitric acid.



Yeah, that's what I was alluding to. Somewhere in my library, all of which is in boxes aside from the odd book, I have something that discusses that very thing. Given enough time, I'll finish the house I'm building and unload the boxes. 

I did a search a while ago to see if I could find books and other information pertaining to refining, but came up only with the loose-leaf you and I discussed some time ago, the one about the seminar in California. Couldn't even find my two copies of Hoke's book! We have a huge amount in storage----and I'm not up to spending enough time to sort through all of it at this point. 

Harold


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## aflacglobal

You know it's funny, but i was just reading about a machine that covers some of what GSP and Harold are both saying. I think Harold will like the recovery system on this one. Take a look.

Some good process info to.


Thanks,
Ralph.


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## goldsilverpro

Hey Ralph,

I first saw that machine on the net 4 or 5 years ago. There's much less info available on it today, so I assume that it wasn't a success.

The process it uses is simple and most people on this forum could set it up cheaply, without the use of a high dollar machine. It simply involves inquarting with copper or silver, shotting, and parting with nitric. Some of you are using this process already. The parting is done with several fresh applications of nitric and the purity of the gold is said to increase with each parting. It is said that after 3 partings, the purity may reach 99.99%. However, in the pdf, this third parting wasn't tested.

The first two partings are said to be similar to those used in fire assaying. The first is weak to prevent the gold from breaking up. The second is stronger. In fire assaying, the first nitric is about 1 part nitric and 7 parts distilled water. The second is 2 parts nitric and 1 part distilled water. In the pdf, the first acid is boiled for 2 hours and, since the total cycle time is 6 hours, I assume the second acid is boiled for 4 hours. The purity after two partings is said to produce 99.9% gold. The details on the third parting aren't given.

I have grave doubts that three partings will produce 99.99% gold. Maybe that's why this machine seems to have fallen by the wayside.

The Refining Machine Police


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## Harold_V

goldsilverpro said:


> I have grave doubts that three partings will produce 99.99% gold. Maybe that's why this machine seems to have fallen by the wayside.
> 
> The Refining Machine Police



I've said that right along. Achieving 4 9's is not accomplished easily----although one must keep in mind that the industry standard is only 9995, which, in my opinion, is achieved with diligence. 

Aside from the nice stainless reaction vessel(s), I see no particular advantage to buying a machine when the processes involved are identical to that which I have espoused. Think Hoke, and you have the entire process covered in fine detail. 

Harold


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## lazersteve

GSP said:


> The Refining Machine Police


 8) 

I love the fact that we have such an experienced membership here, it makes me feel all warm and fuzzy inside!!!

Thanks for looking out for all of us GSP.



Harold said:


> Think Hoke, and you have the entire process covered in fine detail.



Well said Harold! Hoke has documented the pioneer work for all us in great detail. 

Steve


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## aflacglobal

The man enjoyed it so much. He said it twice.

   

I wasn't impressed by the machine much. It was the way it captured the fumes and converted them into usable products. Plus with this it seems the losses from evaporation's would be nearly impossible. I know Harold
is a vocal supporter of this issue. I like things that go from a to b , and are both automated and environmentally friendly. The company still makes the product i think. I will email them for a pdf. I like to collect info anyway.  

Thanks,

Ralph.


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## lazersteve

Ralph,

I found this same document about a year ago. I put a copy into my refining documents folder back then.

Steve


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## aflacglobal

Hey, Harold got you an avatar.
Does it have a underlying meaning Harold ? I notice it's a crest.


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## Harold_V

That's a picture of the stained glass window we had made for the castle. We removed it and brought it with us when we moved to Washington, where it now resides in our stereo room, on the front of the house. 

It's a compilation of my wife's maternal coat-of-arms, and the coat-of-arms of the country of Greece (I'm American born, but of Greek heritage). Where the two lions stand, there would be two cavemen had we not altered it. We created our own design to reflect our heritage. 

The crown is the logo I used in my refining business. You can see it here in the picture of the ingots I posted some time ago. 

Harold


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## lazersteve

Harold,

The window is magnificent. I love the design of the crest, it's very medieval. I'm into making my own armour from the medieval period. Every few years at Halloween I'll suit up in my armour and hand out treats for the kids in full garb. They enjoy it and we get a kick out of there reactions to the suit.


Steve


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## Harold_V

lazersteve said:


> Every few years at Halloween I'll suit up in my armour and hand out treats for the kids in full garb. They enjoy it and we get a kick out of there reactions to the suit.
> Steve



You'd have fit right in with us, Steve. 

The window in question used to live in the round opening you see above the front door of the castle. The plywood you see was removed and a back lighting provided (fluorescent). There was a sheet of white acrylic plastic between the light and window to diffuse and make the light uniform. It looked really pretty at night. We left the light on at all times.

Harold


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## aflacglobal

That is just so cool.


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## austexjwlry

alexmaywood
I skimmed through a couple times looking to see if anyone mentioned always using stannous testing solution before throwing away solutions. If not look in the testing part of this forum!

Wayne


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## scavenger

I'm trying to dissolve a impure 14 gram button in AR. I've flattened it and cut it up as small as I can get it. I started with 100mls of 1 part 70% nitric and 3 parts 38% HCL. When it stopped bubbling I assumed it was done. Most of my gold was still in the bottom. I precipitated and got maybe 1 or 2 grams of black gold powder. I put the remainder of the gold to 200mls of AR and it has stopped bubbling but still lots of gold undissolved. Am I not using enough AR? If I heat it will it start again? Do I have to break the gold up more? Any help on this would be greatly appreciated. Thanks, Dave.


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## lazersteve

Is it possible the gold is alloyed with a large portion (30-80%) of silver? If so it may not be dissolving due to silver chloride formation. Do you see a crust forming on the gold? If a crust has formed and it darkens on exposure to light it is most likely silver chloride. Inquarting will free the gold from the silver. 

Steve


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## Noxx

Do your gold turned black ? If it's the case, you probably have silver alloyed. If not, I would recommend to try to heat it.


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## scavenger

The gold pieces have blackened. How can I inquart it? Will nitric alone dissolve the gold like in your video?


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## Noxx

No nitric can't dissolve gold. Melt silver with gold until your gold is about 30% of the total weight. Then put the nugget (if you flatter it, it will dissolve faster) in nitric acid. Very weak nitric acid won't work good. Use 35% Nitric acid or more. You can heat it if you want to speed up things. But be careful with fumes and hot nitric !


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## goldsilverpro

Most all karat gold contains silver. You have to heat the AR to even have a chance of dissolving the gold. If you don't have a fume hood, this will be very fumey.


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## Noxx

Yup, you most likely have to do it outside


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## lazersteve

Scavenger,

Inquarting, or inquartation , involves alloying the gold with a base metal, preferably silver, to 25% gold content. So if the undissolved nugget weighs 5 grams simply melt it together with 15 grams of silver (stir with a carbon rod when molten), slowly pour the molten alloy into a deep stainless steel dish of cold water, and dissolve the resulting 'cornflakes' in a diluted solution of 1 part 70% nitric to 1 part distilled water. 

My video on separating silver from gold shows the dissolving in detail. I have since learned from Harold and GSP that it's better to drop the silver from the Silver Nitrate solution using metallic copper once the gold powder is separated out. I have a new video demonstrating this 'cementing' process. I'll post it to my site soon. It is in the editing stage now.

Steve


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## scavenger

I have a jar of what I assume is dropped silver. It is a grey powder and it was filtered from acid peroxide after stripping foils and cpus. Do I use the same technique to melt into a button as in the video?


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## lazersteve

Scavenger,

I assume you are using a torch. 

You won't need borax. Just perform the melt in a shallow metling dish and be sure everything is good and molten. Be careful of any smoke that this may produce as silver gases are very dangerous. Silver will volatize very easily so use the torch on the lowest possible setting to get the metals melted together. The standard circular motion of the torch will work well for this. I like to preheat the metals to redness with a MAPP gas bottle torch to conserve my OXY/ACT rig gas. 

I am not sure that the gray powder you mentioned from the AP process is a silver compound. I know what you are talking about, but I'm not convinced it's silver at all. If you don't have any known silver or sterling silver on hand many other base metals will work. Choose one that has a low melting point and dissolves easily in nitric acid. Try to avoid anything with tin or lead in it as these can interfere with the inquarting process. Copper works but has a higher melting point and will require more heat as well as consuming more nitric acid than silver.

Harold and GSP should have some good tips here as well.

Steve


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## Palladium




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## butcher

bumping an oldy but goody


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## butcher

While doing some research on the reaction of copper and nitric acid, I was searching for the concentration of nitric acid that the dilute nitric was used to react with copper in this popular formula:

3Cu + 8HNO3 --> Cu(NO3)2 + 2NO(g) + 4H2O

I found the concentration in a chemistry book to be 20% HNO3:
http://books.google.com/books?id=svv_AgAAQBAJ&pg=PA163&lpg=PA163&dq=3Cu+%2B+8HNO3,+nitric+concentration,+amount+of+nitric+needed&source=bl&ots=cLt8CiRXV6&sig=U7iFf1kAeT2y_Ir_J8vNDsTux6g&hl=en&sa=X&ei=noRYU5K0HoOayASflIGYBA&ved=0CFIQ6AEwBA#v=onepage&q=3Cu%20%2B%208HNO3%2C%20nitric%20concentration%2C%20amount%20of%20nitric%20needed&f=false

With this in mind and the fact the density of 20% HNO3 is about 1.11g/ml

If my math is correct this is what I get:

3Cu (190g of copper for 3 moles) + 8HNO3 (504g of HNO3 for 8moles{20%HNO3 sp.gr 1.11g/ml}) --> yields
Cu(NO3)2 (one mole of copper nitrate 187.5g/mol) +2NO(g) (30 grams or 2moles of nitrogen monoxide gas) + 4H2O (72g of water or 4moles)

If my math is correct we need 559 ml of 20% HNO3 to dissolve 190grams of copper metal or about 0.41 pound of copper in this reaction with dilute HNO3.


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## solar_plasma

Somewhere you have lost 2 moles Cu in your equation


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## solar_plasma

butcher said:


> While doing some research on the reaction of copper and nitric acid, I was searching for the concentration of nitric acid that the dilute nitric was used to react with copper in this popular formula:
> 
> 3Cu + 8HNO3 --> 3Cu(NO3)2 + 2NO(g) + 4H2O
> 
> I found the concentration in a chemistry book to be 20% HNO3:
> http://books.google.com/books?id=svv_AgAAQBAJ&pg=PA163&lpg=PA163&dq=3Cu+%2B+8HNO3,+nitric+concentration,+amount+of+nitric+needed&source=bl&ots=cLt8CiRXV6&sig=U7iFf1kAeT2y_Ir_J8vNDsTux6g&hl=en&sa=X&ei=noRYU5K0HoOayASflIGYBA&ved=0CFIQ6AEwBA#v=onepage&q=3Cu%20%2B%208HNO3%2C%20nitric%20concentration%2C%20amount%20of%20nitric%20needed&f=false
> 
> With this in mind and the fact the density of 20% HNO3 is about 1.11g/ml
> 
> If my math is correct this is what I get:
> 
> 3Cu (190g of copper for 3 moles) + 8HNO3 (504g of HNO3 for 8moles{20%HNO3 sp.gr 1.11g/ml}) --> yields
> Cu(NO3)2 (one mole of copper nitrate 187.5g/mol x 3= 562,5g ) +2NO(g) (30 grams or 2moles of nitrogen monoxide gas) + 4H2O (72g of water or 4moles)
> 
> If my math is correct we need 559 ml of 20% HNO3 to dissolve 190grams of copper metal or about 0.41 pound of copper in this reaction with dilute HNO3.


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## butcher

Thanks I have been tired, and missed that 3 in front of the copper salt in my writing of the original formula, which I used for calculation, I am still unsure if I done the math right.
thanks for catching the mistake.

Them doggone moles, just like in my garden always giving me troubles.


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## solar_plasma

60g NO and 2520,4g 20wt% HNO3
the other values are correct

*I love it, when I can give some help back to my mentors*


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## solar_plasma

not to forget:

2NO+O2-->2NO2
and
4NO2+O2+2H2O-->4HNO3

...so under ideal conditions you gain 126,02g HNO3 or you need less HNO3 depending on the setup


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## solar_plasma

but if I remember right, this one is better (please double check):

Cu+H2O2-->CuO+H2O
CuO+2HNO3-->Cu(NO3)2+H2O

63gCu+34gH2O2 (102g at 33%, 283g at 12%, 1133g at 3%) + 127g HNO3 --> 187g Cu(NO3)2 + 36g H2O (theoretically!!)

so instead of using max. 2520g 20wt% HNO3 you would use at least 1905g 20wt% HNO3 and 306g 33wt% H2O2 to dissolve 189g Cu, don't know,if this is cheaper for you, at least less fumes to handle

by using HNO3 AND H2O2 in small increments to dissolve the copper


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## goldsilverpro

Although others may disagree, I think this is the most straight-forward way of looking at this problem.

In the link that butcher gave, there is a typo on the left side of the equation for strong (68%) nitric. Instead of Cu + HNO3, it should read Cu + 4HNO3. Also, for very weak (1%) nitric, it is assumed that the left side would be Cu + 2HNO3, although that equation isn't given in the link. For 20%, it is assumed to be, as stated, 3Cu + 8HNO3.

Notes: 
(1) For this particular problem, the left sides of the equations, assuming they are correct, is all we need worry about. The left side shows what goes into the reaction and the right side shows the end products. In this case, we are only interested in what goes into the reaction and not what comes out.
(2) The left side of the equation for 68% nitric is Cu + 4HNO3. The number before these 2 items indicates the Mole relationship of each that are required for this particular reaction. Therefore, 1 Mole of Cu reacts with 4 Moles of nitric acid. Therefore, the Mole ratio of Cu/4HNO3 is 1:4 or 1/4.
(3) Very simply put, one Mole of a substance is the addition of all the atomic weights of the elements in the substance, expressed in grams. These atomic weights are found in most any chemistry text or handbook. If you have a copy of CRC or Lange's, you can simply look up the total atomic weight of most compounds without having to add up all the individual atomic weights of the elements involved.
(4) The molecular atomic weight of HNO3 is 63.02. Therefore, one mole of HNO3 weighs 63.02g. One Mole of copper is 63.54g. Therefore, when using 68% and the left side of the equation is Cu + 4HNO3, it takes 4 X 63.02 = 252.08g of HNO3 to dissolve 63.54g of copper.
(5) For those interested, here's the chemistry definition of a Mole: "a chemical mass unit, defined to be 6.022 x 1023 (called Avogadro's number) of molecules, atoms, or some other unit. The mass of a mole is the gram formula mass of a substance." In other words, 63.54g of Cu contains 6.022 X 1023 atoms and 63.02g of HNO3 contains 6.022 X 1023 molecules. That's 602,200,000,000,000,000,000,000 or, .602 billion billion.

According to the left sides of these equations, the Mole ratios of Cu/HNO3:
@1%, it is 1/2
@20%, it is 3/8 
@68%, it is 1/4

According to the nitric chart on handymath.com
http://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry
The specific gravities (g/cc or ml), at 20C, of these nitric solutions:
@1%, it is 1.00364
@20%, it is 1.115
@68%, it is 1.4048

Therefore, the weight of HNO3 and the number of Moles of nitric (1 Mole of HNO3 weighs 63.02g) contained in one liter of these solutions:
@1%, it is 1.00364 X 1000 X .01 = 10.0g. This is 10.0/63.02 = 0.158 Moles/liter
@20%, it is 1.115 X 1000 X .20 = 223g. This is 223/63.02 = 3.54 Moles/liter
@68%, it is 1.4048 X 1000 X .68 = 955g. This is 955/63.02 = 15.15 Moles/liter

One Mole of copper weighs 63.54g. Therefore, based on the Mole ratios given above, 1 liter of these 3 solutions would dissolve these weights of copper:
@1% = 0.158 x 1/2 X 63.54 = 5.02g
@20% = 3.54 X 3/8 X 63.54 = 84.3g
@68% = 15.15 X 1/4 X 63.54 = 241g

The 241g/l for 68% figures out almost exactly to 2 pounds of copper/gallon [(241 X 3.785)/454], the figure I have always promoted. Easy to memorize. For silver, it comes out a little under 7 pounds/gallon (actually 6.8#/gal) or 100 tr.oz./gallon (actually, 99 TO/gal), again easy to memorize.

In my experience, when using hot 68% nitric, cut 50/50 with water, in an open top container, the ratio of the copper dissolved to the amount of 68% nitric used conforms very closely to the 68% numbers above. 

Besides using weaker nitric, there are several things that will swing the ratio closer to the other strengths: The use of hydrogen peroxide, ethylene glycol, etc., in the solution; Keeping the solution cool; Covering the vessel; Refluxing the off gases; etc.

Edited and added to several times.


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## solar_plasma

@GSP

do those 20% mean vol% ? I have never seen vol% used other than for drinking alcohol :shock:


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## goldsilverpro

solar_plasma said:


> @GSP
> 
> do those 20% mean vol% ? I have never seen vol% used other than for drinking alcohol :shock:



Surely not. They are all w/w. In any scientific literature I have seen, it is assumed to be by weight unless declared otherwise.

I might mention that, at 20C, 68% nitric, by weight, cut 50%, by volume, with water, ends up as about 38.5%, by weight.


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## solar_plasma

I first thought I did make a mistake in my calculation, but my calculation was based on dissolving 3 mole Cu.




> I might mention that, at 20C, 68% nitric, by weight, cut 50%, by volume, with water, ends up as about 38.5%, by weight.



welll, yesss....this can easily get lost by mistake. That's why I never think in volume but in weight, if possible.


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## butcher

Thanks goldsilverpro, and solar_plasma, I have always had problems with math, and numbers, and it looks like the post above is no exception to that. I really messed that calculation up, not taking time to check my work.

I was up about 20 hours yesterday working on that problem, after spending most of the day and about half the night, to get the wrong answer, I think I will just enjoy my coffee and study gold silver pro's solution to this problem.

I was going to try to redo that calculation, but I had better not post more mistakes, at this time.

GSP I really envy your skills with those numbers, and really appreciate you doing the math with explanations above, hopefully with reading and studying it, maybe some of that skill with the numbers will rub off on me, although for now it looks like I have a lot more studying to do.

Thanks again


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