A newby starting the learning curve

I took Kadriver's Tutorial and transcribed his calculations to an Excel spread sheet.

It can be found here: http://www.mikeinkaty.com/GoldRefining2.xls

I put it in the old Excel format for people not having the Excel in Office 10.

I did this as a means to help me begin the process of understanding this stuff. I would appreciate any comments from anyone having Excel that could take the time to validate the calculations. If the calcualtions are basically correct I will leave the spread sheet here else I will delete it and start over! I didn't bother to search for a spreadsheet already existing as I wanted to run out the calculations myself as part of my process.

Thanks
Mike
Katy TX

I thought the spreadsheet was quite good. I do have a couple of comments on the math. I know I am being somewhat picky on this, especially the first part, so please forgive me.

The standard amount of silver to add is 3 times the gold content minus the base metal (BM) content. That would make the Au one quarter (25%) of the total of the Au + Ag + BM. Thus, the term, inQUARTation. This would be:
Silver to add = (3 x Au) - (BM)
For example, with 10g of 18K, there is 7.5g of Au and 2.5g of BM. This would be:
Silver to add = (3 x 7.5) - 2.5 = 20g
Using these same numbers in the spreadsheet, you get 22g of silver. Working backwards, that would mean that, in the final alloy, gold would be 23.4%, instead of 25%.
(7.5)/(7.5 + 22 + 2.5) = .234
In practice, either would work. In fact, a little extra silver might help in the dissolving, in case the alloy weren't mixed thoroughly.

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Actually, the term BM, or base metals, as used in the spreadsheet, isn't all base metals. There is silver in there also. I only mention this because it takes about 1.22ml of 67% nitric to dissolve a gram of silver. With the base metals in there, usually copper and zinc, it takes about 4.15ml/g. However, you really couldn't accurately consider this since the silver content can vary considerably.

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The nitric needed is a different story. In the spreadsheet, you assumed that the nitric percentage is linear, as to the amount of nitric it contains. This is not true. In the above example, for 70% nitric, you say it takes 34ml. For 35%, you say it takes twice as much, or 69ml, rounded off.

Using the calculator in this link, you find that the specific gravity of 70% HNO3 at 20 degrees C is 1.413g/ml and that of 35% is 1.214g/ml
http://www.handymath.com/cgi-bin/nitrictble2.cgi?submit=Entry
The amount of nitric in 1 ml of 70% is therefore 1.413 x .70 = .989g. For 35%, it would be 1.214 x .35 = .425. Therefore, the strength of 35% is only .425/.989 = 43% (not 50%) as strong as 70%. Therefore, in the above example of 10g of 18K, if you used 35%, it would take 34/.43 = 79ml and not 69ml - that's a 15% error. I assumed you based everything on 70%. The error for nitric percentages that are closer together, like 68% vs 65%, would be less, but there would still be an error. To take this to extremes, if you used 5% nitric, it would take 838ml, and not 480ml as given in your spreadsheet.

Since it's not linear, it would be much more difficult to set up an accurate spreadsheet for the nitric. Actually, if you were to plot this out, from say 1% to 70%, you would see that it forms a very complicated curve, the equation of which would not be simple to establish. Since most available nitric seems to be 50%, 67%, 68%, 69%, or 70%, maybe you could set up the spreadsheet just for these definite values, using the specific gravity method of calculation I outlined above to determine the proper values.

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Like I said, some of this is pretty picky, but some isn't.

Goldsilverpro -

Thank you for the review!

I did modify the spreadsheet and recopied to that web page. Note that I say less than 34% Nitric shouldn't be used. Technically I guess that isn't true but holding the minumum to 34% keeps the spreadsheet simplier.

I did change the formulas for amount of fluids to add. I had those wrong. You can now enter the strength at the top in the range of 34% to 100%. I highly doubt anyone would be dealing with anything > 70% or < 34%.

I did chart the data in the Specific Gravity data sheet you provided. In the range of 34% to 80% at 20°C the data is fairly linear but does have a slight upward curve. The slope of a line fitted through that part of the curve is essentially the same as what I used. I used the linear formula of Y = acid%/34 -1 to establish the endpoints in my calculations. i.e. - Distilled Water = 1.44 * TotalWt Base metal * Y. This was derived solely from kadrivers tutorials. Can you provide another linear formula that would be better?

So, what do you think? Is this close enough? Should I leave the spreadsheet where it is now or should I not?

SIncerely
Mike
Katy TX

Our new forum firebug just wants to burn all kinds of stuff.

Pretty soon he will be telling everyone the benefits of incineration.


If the nitric acid does not have enough water the reaction slows, or when the acid is too strong.

Maybe the too strong of an acid is somewhat oxidizing the silver building a passivated layer, and somewhat slowing down the progress as most of the acid fumes off in a big red cloud, I am not sure why exactly.

When the nitric acid is up to 68% the much of the acid is wasted as NOx gas fumes, from the reaction on metals and also from heating,

I would bet trying to use concentrated acid would actually use more acid than dilute 50% (68%) HNO3 :50% H2O to dissolve the same amount of silver.

I also add a little more water to this or hydrogen peroxide to help my acid go a little further (diluting helps keep gases from escaping but let them mix into water to reform nitric, and allows heating to increase acids strength on attacking metals but only drive off mostly water fumes instead of NOx fumes.

mikeinkaty,

Check this thread,
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=48&t=10457&p=131207&hilit=nitric+acid+graph#p131207

In it, I came up with a simple formula for the S.G. of nitric solutions:
S.G. = (0.006 x Nitric%, by weight) + 1

I tested it for 35% and 70% and it's very close (1.21 and 1.42 as opposed to the actual values of 1.214 and 1.413 from the chart. However, the S.G. alone is not a good indication of the strength of the nitric. To get the strength, you must multiply the S.G. times the decimal equivalent of the percentage. For 35% and 70%, this would be 1.21 x .35 = .424g/ml and 1.42 x .70 = .994g/ml. I haven't plotted these figures, but I doubt if the curve will be as linear as that of the S.G.

It is interesting to note (at least to me) that for 70% and 35%, the ratio of the approximate S.G.s, minus 1, is .42/.21 = 2, whereas, the ratio of their actual strengths is 994/424 = 2.35

Were I you, I would keep the spreadsheet between 35% and 70%, for 2 reasons. (1) these are the strengths that most are likely to possess, Actually, most commercial nitric is 68%, which is the azeotrope. Reagent grade can be purchased at 70%. Anything higher starts getting fumey and is more dangerous. For this reason, the use of stronger nitric would probably not be allowed for discussion on this forum. (2) I think the curve starts failing at both extremes, especially on the high side.

Unless you can derive an equation for the strength of nitric between 35% and 70%, I would think you would have to use a different calculated strength number for each percentage. I have shown that the difference in 35% and 70% in your spreadsheet is 15% in error and that hasn't changed it your new version. I know I'm picky but, practically, that wouldn't be acceptable to me. I might also note that it's the nitric that dissolves the silver and not the water. The main reasons for dilution are that it speeds up the dissolving and it prevents the crystallization of silver nitrate and copper nitrate when the solution cools.

This is slightly off the subject but, in several other threads, I have shown that, if you have 70% nitric and dilute it with an equal volume of water, you end up with 41% nitric, and not 35%

Picky is good. Especially in science.

I asked GoldsilverPro this question off line.

What is the best concentration of Nitric Acid to use with 6k gold scrap and inquarted 999 silver? Kadriver says to mix equal parts of distilled water and 68% Nitric which apparently results in a 41% concentration. Others say to use a 35% concentration which would need about 20% more water.

After reading Hoke it looks to me like one should first cover the karat gold with the recommended amount of water then slowly add in, say, half the recommended amount of 68% Nitric Acid. After the reaction has subsided then start adding in small amounts of acid until such time that a reaction no longer occures. Doing it this way you might have wound up with 41% or 35% or maybe even 20% concentration. It seems to me that this way would insure that one would use only as much acid as was needed for the particular batch of scrap at hand. This way might be slower but sounds like it may be a more precise way to go about it. After seeing all the various base metals that can be in scrap gold at a wide varying concentration I can see that trying to calculate a 'precise' amount of acid needed is probably futile.

I was first thinking that one would mix the water and acid to the recommended concentration then dump it all in with the gold scrap. After reading all the warnings about "Boiling over" what Hoke is saying now makes sense to me.

Any other thoughts out there on this?

Mike

I think your doing one heck of a good job of understanding !
I like that.

mikeinkaty said:

I asked GoldsilverPro this question off line.

What is the best concentration of Nitric Acid to use with 6k gold scrap and inquarted 999 silver? Kadriver says to mix equal parts of distilled water and 68% Nitric which apparently results in a 41% concentration. Others say to use a 35% concentration which would need about 20% more water.

After reading Hoke it looks to me like one should first cover the karat gold with the recommended amount of water then slowly add in, say, half the recommended amount of 68% Nitric Acid. After the reaction has subsided then start adding in small amounts of acid until such time that a reaction no longer occures. Doing it this way you might have wound up with 41% or 35% or maybe even 20% concentration. It seems to me that this way would insure that one would use only as much acid as was needed for the particular batch of scrap at hand. This way might be slower but sounds like it may be a more precise way to go about it. After seeing all the various base metals that can be in scrap gold at a wide varying concentration I can see that trying to calculate a 'precise' amount of acid needed is probably futile.

I was first thinking that one would mix the water and acid to the recommended concentration then dump it all in with the gold scrap. After reading all the warnings about "Boiling over" what Hoke is saying now makes sense to me.

Any other thoughts out there on this?

Mike

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I sent you a long PM. I could copy the PM to the forum if you don't mind.

You could inquart with scrap sterling instead of pure silver. It would probably be cheaper. Make sure there is no solder on it, though. Most plain scrap sterling spoons or forks would be good.

When these people say 35%, they are assuming that when you dilute 70% nitric 50/50, you end up with 35%. Actually, it's 41%. Kadriver is right about the mix.

Are you sure the process is in Hoke? I don't recall it being in there, as you outlined it. After doing essentially what you suggested, to make sure all the silver is dissolved, I often let the gold settle well, pour off the solution carefully, cover the gold with some fresh 50/50 nitric, and then heat it a little below the boiling point for about 30 minutes. After pouring off the solution, rinsing isn't necessary in this case. If I accidentally pour off some fine gold particles, I can get it later after the solution I poured off has completely settled. Or, you can just filter all of the nitric solution plus the gold and then heat it in some fresh nitric.

goldsilverpro said:

When these people say 35%, they are assuming that when you dilute 70% nitric 50/50, you end up with 35%. Actually, it's 41%. Kadriver is right about the mix.

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That is why I'm so thankful my supplier has 42%! No need to mix unless I want it to be just a bit weaker!

GoldsilverPro -

I found it kind of difficult to follow Hoke to the letter. I sorta read between the lines a little. It somewhere up close to the top of chapter V.

I also thought that decanting and adding some more 50/50 and stiring well wouldn't hurt any and might get the last bit into solution.

Like I said earlier it will be a while before I get to the acid steps. My first several months will be collecting the inquarted scrap in the form of shot. It was only an afterthought that I added the fluid amounts to that spreadsheet. Maybe I should have stopped while I was ahead!

Mike

mikeinkaty wrote:

Thought I'd take this to a PM.

I guess one critical question is - What is the best strength of Nitric Acid to use for inquartation?

Based on your last paragraph in the previous message, I increased the H20 amount by 20%. This would get the concentration close to 35%. But, is 35% the ideal concentration?

I added a drop-down list for Acid % that restricts it to one of these values - 35%, 40%, 45%, 50%, 55%, 60%, 65%, 68%, 70%.

Given this finite number of values allowed, how much H20 and acid should be added per gram of BM to get the desired reaction for typical karat scrap? I could just put that in a table then just multiply by the wt of BM. The table would have 2 columns - ml h2o per gram, ml hno3 per gram, and 9 rows.

Mike

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Mike,

Have you ever actually done this?

There are no absolutes in this. The nitric is what actually dissolves the silver. The only purposes of the water are: (1) To speed up the dissolving. Nitric alone will dissolve silver but it is quite slow. The addition of water makes it go much faster. (2) When dissolving, the solution gets hot. If nitric were used alone and was used until it could hold no more silver or copper (called saturation), silver nitrate and copper nitrate would crystallize when the solution cools. This is undesirable. The addition of water prevents this, if enough water is used. Distilled water must be used. Tap water contains chlorine and this will precipitate some of the silver as silver chloride. This is also undesirable.

Any combination of nitric and water will dissolve silver. The common mix is to use equal volumes of water and 68% or 70% nitric - called 50/50 nitric on the forum. This is about the right amount of water to both prevent crystallization and to maximize the speed. I would base the other strengths on this.

Do you understand the mathematical concepts of the specific gravity (SG) vs the strength? In the handymath.com link I gave you, you can see that, at 20C, the SG of 70% nitric is 1.4134. One ml of 70% weighs 1.4134 grams. However, this is only 70% nitric by weight. Therefore, one ml of 70% would contain 1.4134 X .70 = .989 grams of nitric acid (HNO3). The remaining 1.4134 - .989 = .4244 grams of water. Since 1 ml of water weighs 1g, 1 ml of 70% is made up of .4244ml of water and 1 - .4244 = .5756ml of 100% nitric. This has nothing to do with the amount of water needed to make up a 50/50 solution. I just added this to help you understand what nitric actually is composed of.

Note: For accuracy, each nitric percentage in your drop down list will have to be computed separately, due to the non-linearity of the strengths. You asked if 35% was ideal. No, because 70% diluted 50/50 is not 35%. It calculates out to 41%, using the method given in the paragraph above. Like I said, it's not linear.

Here's a problem. Read my posts on this thread.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=53&t=16374
In it, you will find the equation for dissolving silver with nitric:
2HNO3 + Ag = AgNO3 + NO2 + H2O
Note that, on the left side of the equation, it takes 2 molecules of nitric to dissolve 1 molecule of silver. However, on the right side, the ratio of Ag to the NO3 is one to one. The second N in the nitric on the left comes off as NO2 on the right. In other words, half of the nitric is wasted, as far as dissolving silver is concerned.

If you assume the use of common commercial 68% nitric, it takes 1.22ml to dissolve 1 gram of silver. However, this figure assumes an open top dissolving container where all of the NO2 produced in the equation goes off in the air and is lost. If you were able to collect all of the NO2 in a condenser and return it to the solution (called refluxing), it would combine with water to produce more HNO3 and you might be able to reduce the nitric usage to half or, 0.61ml/g of silver. There are other ways of refluxing that are mentioned in the thread link I gave above. In some cases, people are doing things to improve the efficiency that they're not even aware of. Were I you, in your calculator, I would use the 1.22ml/g figure, based on 68%, and make the following disclaimer:
"The nitric figures given are accurate assuming the dissolving is done in an open-top container, where all the gases given off are lost. With perfect refluxing of these gases, the nitric usage could be only one-half of these figures. In practice, the nitric usage might be somewhere in between these two extremes."

For copper, nickel, and zinc, which are the most common base metals in karat golds, it takes about 3.4 times as much nitric as with silver or, 4.15ml/g of 68% in an open container.

In the literature, you'll find that some people inquart with copper instead of silver. This works fine but it takes 3.4 times more nitric. Since the members of the forum buy nitric in small quantities, it is extremely expensive. Their average cost is probably $75 to $100 per gallon, whereas, in 55 gallon drum quantities, it's only $3 - $4/gallon, excluding the $750 returnable drum deposit. Using copper, therefore, is undesirable for most people. Also, with copper, you end up with 3.4 times more waste to deal with. The silver is much more expensive than copper to start with but it can be used over and over.

Chris

More to come later but what about the CU in the karat scrap? There is one video on Youtube where this guy melted like 10 lbs of scrap jewlery of all kinds and stuck the resulting bar in the analyzer. It showed 58% gold, 27% CU, and 8% silver. You do say that it takes more nitric for copper. Could that be where the 1.44 factor came in?

Your example makes more sense to me than when my chemestry teachers made us calculate everything in Moles!

Mike

ive only been doing the chemistry part of PM recovery in earnest for the last two years but from personal experience i can tell you that hardly anything actually turns out in practice the way it does on paper.when im dissolving metals, i start on the low side and add as needed. i know theres ways to calculate the exact amount of each component for a reaction and i wish i had the same kind of analytically knowledge GSP has but im stuck with an 8th grade education and no chemistry background what so ever. its easier for me to estimate the weight of base metal and start with the lowest amount of acid i think i may need and if its not enough,add a little more at intervals until its complete.

i must sound like a caveman in a room full of real humans. :lol:

Geo said:

ive only been doing the chemistry part of PM recovery in earnest for the last two years but from personal experience i can tell you that hardly anything actually turns out in practice the way it does on paper.when im dissolving metals, i start on the low side and add as needed. i know theres ways to calculate the exact amount of each component for a reaction and i wish i had the same kind of analytically knowledge GSP has but im stuck with an 8th grade education and no chemistry background what so ever. its easier for me to estimate the weight of base metal and start with the lowest amount of acid i think i may need and if its not enough,add a little more at intervals until its complete.

i must sound like a caveman in a room full of real humans. :lol:

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You're right. Nothing ever comes out exactly as predicted but, as a guide, it's good to have at least a ball park idea of what is needed. When I use nitric for dissolving silver or copper or for use in aqua regia, I often calculate what I need and measure it out. I'm good at this adding nitric in increments method and don't need to do this, but I do it because it's easy to do and it keeps me from adding too much in case my mind is wandering (this can happen when I'm doing a dozen things at the same time). Usually, though, it takes a little more or a little less than what I have calculated. The important thing is to master, by eye, how to use only that exact amount of nitric necessary to dissolve something, with no extra. In many cases, you have no idea how much metal you have, so you can't calculate it. An example would be gold foils mixed with plastic.

My mentor in this method did a lot of karat gold (usually shotted - no inquarting) and he never calculated or measured anything. He had the HCl and HNO3 in plastic gallon jugs. He watched the reaction closely and added a splash of this or a splash of that until the stuff was dissolved. He ran 12, 4 liter beakers full, often twice a day. He ran them a little less than boiling and pushed them hard with the acids. If some gold didn't dissolve (usually not much) because of the silver, it was all gathered together and it was either inquarted (rarely) or melted with other jewelry (usually). Green gold (often about 35% silver) was initially separated out and inquarted. He never evaporated the solution down or used urea. The gold dropped almost immediately with sodium sulfite and 9 out of 10 times it ended up 999.5 or better, usually with a little furnace cleaning. If he couldn't clean that 10th one in the crucible furnace with pinches of flux, he cast it into a bar, rolled it quite thin in a huge power roll, dissolved it, dropped it, and melted it, all in about an hour, or so.

I used this same method in my refineries, but I usually inquarted what wouldn't dissolve. My only improvement to this was to make sure I started with an excess of HCl, which requires a calculation for best results. That way, when an addition of nitric produces no reaction, I know it's finished. Without a calculation, when an addition of nitric produces no reaction, it might be because you need more HCl. Therefore, without a calculation, you often end up having to go back and forth with the 2 acids.

I apologize for getting off the subject but the dissolving of gold or silver is related, in that, at least in my mind, both require the mastery of incremental additions of nitric.

I apologize for getting off the subject but the dissolving of gold or silver is related, in that, at least in my mind, both require the mastery of incremental additions of nitric.

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Chris! I, for one, don't care if you're on topic or not. It's always interesting and informative when you, Harold and some of the other pro's enlighten us with your experiences. Ah! The stuff you guys have seen!!!!

In the spirit of accuracy, I would like to add a side note to the 'theoretical calculations' verses the 'real world results'.

If you keep your reaction temperatures moderate (ie: not wildly boiling or on high heat) and you cover your reaction reactor with a lid that can breath (ie: watch glass) you will find you use much less nitric than the numbers quoted above.

For those wondering why, the reason for this can be seen quite clearly by examining the chemical equation for dissolving silver and base metals with nitric acid.

You can read about the equations here and many other places on the forum Nitric Acid Equations

You may notice that on the right side of the equation we see one of the by products is NO2. This NO2 reacts with water via :

Wiki Nitric Acid Production said:

Wiki Nitric Acid Equations

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This means if we trap the NO2 (and NO) from the dissolving metals via reflux (eq: with a lid, watch glass, or reflux condenser) and have some available O2, and water, we will form more nitric acid from the off gasses of the reaction. It is for this reason you will find that your calculated amount of nitric acid is more than required when you perform your reactions at low to moderate heat and with a cover on the reactor. With optimal reaction conditions one can get theoretically twice, or more, of the work from your nitric acid.

Steve

Good to see you post Steve. Hope the shoulder is doing well.

Dave

lazersteve said:

This means if we trap the NO2 (and NO) from the dissolving metals via reflux (eq: with a lid, watch glass, or reflux condenser) and have some available O2, and water, we will form more nitric acid from the off gasses of the reaction. It is for this reason you will find that your calculated amount of nitric acid is more than required when you perform your reactions at low to moderate heat and with a cover on the reactor. With optimal reaction conditions one can get theoretically twice, or more, of the work from your nitric acid.

Steve

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Steve - in the above you say "and have some available O2, and water". Would using 3% H2o2 instead of distilled water put more O2 into the reaction?

Mike

mikeinkaty said:

lazersteve said:

This means if we trap the NO2 (and NO) from the dissolving metals via reflux (eq: with a lid, watch glass, or reflux condenser) and have some available O2, and water, we will form more nitric acid from the off gasses of the reaction. It is for this reason you will find that your calculated amount of nitric acid is more than required when you perform your reactions at low to moderate heat and with a cover on the reactor. With optimal reaction conditions one can get theoretically twice, or more, of the work from your nitric acid.

Steve

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Steve - in the above you say "and have some available O2, and water". Would using 3% H2o2 instead of distilled water put more O2 into the reaction?

Mike

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im sorry, im not Steve. in refluxing, your returning nitric to the reaction that would have escaped into the air. putting H2O2 into the reaction may not effect the reflux process. refluxing is when you are processing with nitric acid to dissolve a base metal (like inquarting with silver or digesting copper, freeing foils). NO and NO2 is formed when dissolving metal with nitric acid. a reflux apparatus is basically a distilling rig fixed vertical so the escaping fumes have to pass through the condenser.water vapor condensing will trap the NOx fumes and as it drips back into the reaction, return the NOx back to the reaction in the form of nitric acid.