Aqua Regia process with nitric acid

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?

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

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

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

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

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

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.

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?

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?

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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.

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

goldsilverpro said:

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

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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

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

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.

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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

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!!

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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

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

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.

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.

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

goldsilverpro said:

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

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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

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.