Nitrate reduction using SMB

Hello Boy's and Girl's, as a newbie, i must say that i have enjoyed this forum immensely, great stuff.

I have searched this forum for something on using SMB to reduce NO3- in-situ with the reduction of PMG’s. As a bucket chemist, I have found this forum informative beyond and above expectation though challenging, lol. Having realised I had not gotten rid of the dreaded NO3- when trying SMB, I decided to reduce the volume via distillation condensation, and had notice mass precipitation upon heating. Having studied the REDOX of this reaction (4 Redox equations in total), the following became apparent:

5H2SO3- + 2NO3- + 5SO4- + 8H+ + N2(g) + H2O

The SO4- will ppt any Pb that may be present. My way of thinking is that this may aid in refining PMG’s from base metals and should reduce the number of sample reductions. Any waste goes into a bucket along with Al foil, and any SMB still around will help reduce my waste. I throw nothing away.

If I made a blunder somewhere here please let me know. Also does anyone know why my stannous chloride don’t work.

Cheers

NoIdea said:

Also does anyone know why my stannous chloride don’t work.

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Not enough information for anyone to venture a guess, but I'll start with asking why you expect it to work----what are you testing? How was it prepared? How old is the stannous chloride?

Harold

Edit: It's really a good idea for you to not try to reinvent the wheel. There are prescribed procedures that are known to work. I suggest you study them and become familiar with refining processes before you start thinking. That will keep you out of trouble and give you the necessary experience for you to venture forth with that new wheel you hope to invent.

Harold

Thanks Harold.

My stannous chloride was produced by boiling, under reflux, pure tin (anl grade) and HCl for about 1h.

Not trying to re-invent the wheel, just trying to reduce my process time. My aim is unlike some others in this group, in that my refined PMG's are bulked together and sold as-is. Refining costs here are a bit diff here in NZ, a straight fee for which metal you want them to analysis and a $ amount for each gram, sorry i can't be more specific, it's been awhile since i last sold.

Please, what part don't you like? For me it works well and reduces the number of times i need to reduce and refine. Granted i am using sintillated glass filters, which work well to digest and filter all in one go. To me using urea or HCl semi-dry reduction of the mother liquor to remove nitrate seems horibly time consuming and unnecessary. Prove me wrong lol or explain why this is not a good idea.

A true and tried method CAN exist in pairs.

NoIdea said:

Thanks Harold.

My stannous chloride was produced by boiling, under reflux, pure tin (anl grade) and HCl for about 1h.

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I made mine, always, from stannous chloride crystals. It was reliable and yielded the exact same results time and again. I followed the instructions in Hoke's book. I'm unable to comment on your procedure---but it leads me to wonder if there's anything in your solution that would respond. Do you have a standard solution of any description? If not, why not? How can you know if your stannous chloride solution is functional without one? Making a standard (gold) solution is covered in Hoke's book.

Not trying to re-invent the wheel, just trying to reduce my process time. My aim is unlike some others in this group, in that my refined PMG's are bulked together and sold as-is. Refining costs here are a bit diff here in NZ, a straight fee for which metal you want them to analysis and a $ amount for each gram, sorry i can't be more specific, it's been awhile since i last sold.

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I'm trying to wrap my mind around your comments, but I'm not sure I understand. If you combine all metals (I interpret PMG's to include gold, along with the platinum metals), you can avoid all of the evaporation and attempts at precipitating by simply cementing the values on copper. Am I missing something? With that process, you'd have no need to evaporate the nitrates---they could be eliminated by simply dissolving a little extra copper.

Please, what part don't you like?

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The use of SMB in the hopes of eliminating free nitric. I learned, much to my dismay, that it's not easy, and I certainly wouldn't rely on SMB to do so. I evaporated numerous times and still had residual nitric on several occasions. It was for that reason I took a different approach to evaporation, which I accomplished by consuming rather than evaporating. By adding a button of pure (gold, in my case), excess nitric was consumed in the process of concentrating (by evaporation) my solutions. That worked perfectly well, and saved a huge amount of time. By weighing the added gold before addition, and weighing after its removal, it was easy to determine how much was added, so I could still precisely track yields, which was important for my operation because I processed individual batches, and settled accordingly.

For me it works well and reduces the number of times i need to reduce and refine. Granted i am using sintillated glass filters, which work well to digest and filter all in one go. To me using urea or HCl semi-dry reduction of the mother liquor to remove nitrate seems horibly time consuming and unnecessary. Prove me wrong lol or explain why this is not a good idea.

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I prefer to not think of my method as being right (or wrong), but well documented and known to yield the desired results. That was my point. When you are more familiar with processing, you may choose to alter many of the approaches with which you are familiar, but I don't encourage people to get creative until they understand what they're doing. If you have a chemical education and understand the reactions and can predict the results of your endeavors, fine---have a great day, and carry on. However, if you're new to refining, and lack a chemical education, you are well served to "follow the book" until such time that you can make meaningful changes that are of benefit. Like it or not, you risk more than financial loss when you screw around with metals, many of which are known to become highly unstable in the wrong circumstances. I'm not suggesting that you're putting yourself in that position, but you'd be well served to not experiment until you have a firm understanding, both for your wellbeing and for financial reasons.

A true and tried method CAN exist in pairs.

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Yes, they can. Even more than in pairs. Clever people often insist that they have many approaches to a given problem---but wise people know which one is to their advantage and use it instead of putting their head down and forging ahead with what they want to believe instead of using a process that has been proven in time, regardless of sound advice from others. I have no way of knowing if you're one of them, or not. I simply stated that unless you are a seasoned refiner, you'd be best served by following prescribed processes until you have enough knowledge to make advantageous decisions. That may keep you from chasing your tail.

May I suggest to you that there are no *real* shortcuts* to refining? You can do it right, or you can settle for the results you achieve, good or bad.

Have you been reading Hoke's book?

Harold

Thanks Harold, well put. I should have been a liiitttle bit more clear on what i am doing. I process the whole board, i remove basic base metals(large elec caps, tantalum caps, etc, for later classification and processing), pyrolyze to safely dispose of most of the Cl, F, etc; high temp melt/ashing, grinding, sieving to removing the visible metal fraction(usually in beads from 1mm up to 5mm), with this i melt under flux producing a alloy bar for electrolysis, the mud is filtered then refluxed with Conc HCl, dilute then filter, repeat till liquid clear. Then it is fluxed, melted, cast and sent to the refinery for sale.

Now, the rest of that which was left over after removing the metal beads, you may ask. Well it contains a high silica content, water insoluble (after washing) powder. This i reflux with conc HCl, dilute and filter, repeat till(never really gets 100%) clear. Then reflux in Poor Mans AR, dilute and filter, drop/reflux with hot SMB, filter, reflux HCl and filter, fluxed, melted, cast and sold. I Know that I am not recovering everthing thats why i keep everything. Still need to recover AgCl from the residue.

Yes I am a qualified retired poorly paid research chemist, with a life time(since 8yro) interest in recycling of all sorts, plastic, batteries, organics etc, and have many a years in the field.

Obtaining a more pure separation of PGM's, and others, for a more profitable sale will come, but a quick return is of the utmost priority for present works, i need supplies. Hence the post on nitrate reduction using SBM, this worked for me and i wished to share, just another wheel i guess. Still a bucket chemist at heart.

Yes i have been reading, been doing it the recomended way, good results, just a bit tooo time consuming at the moment, need better equipment, got all the glassware, very little machines.

As for the stannous chloride, tested on a diluted Poor M. AR gold finger leaf digest.


Alot of Kiwi ingenuity involved, lol, Cheers

From one chemist to another, you might consider writing a proper redox equation.

Ooops, what did i do wrong, things seem to balance, and i took my time. :lol:

Ok, my bad, see the problem, my arrow is missing, Try this:

5H2SO3- + 2NO3- ===> 5SO4- + 8H+ + N2 + H2O

It balances :lol:

You can try the new and improved forum method;
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=62&t=10706

Jim

Mass balance aside, are you so sure that nitrogen is produced?

Very few things give nitrogen gas. Nitric acid and nitrates in general are not among them.

For me, the best way to avoid the free nitric problem is not to use an excess of nitric to start with. If you do have a slight excess, though, the SMB (I use sodium sulfite) will take care of it before the gold starts precipitating. With a great excess, however, it takes way too much sulfite to neutralize it. Also, the precipitated gold will likely be contaminated with other metals, a lot of SO₂ will be generated, and salts can precipitate.

Sulfamic Acid - H₃NSO₃

I recently had a solution that contained 50% HNO₃ and some HCl and dissolved gold. I needed to get rid of the HNO₃ first in order to drop the gold. 4metals suggested (and Lou seconded this) that I try sulfamic acid. It worked great. It was quite cheap - $.58/pound in 50# bag quantities from Univar. On eBay, I saw 10# lots at about $4/pound. Here are the equations that 4metals gave:

4metals said:

With HNO₂, sulfamic acid reacts to give N₂, while with HNO₃, it gives N₂O.
HNO₂ + H₃NSO₃ → H₂SO₄ + N₂ + H₂O
HNO₃ + H₃NSO₃ → H₂SO₄ + N₂O + H₂O

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As you can see, the nitric is replaced by sulfuric acid, which causes no gold precipitation problems (I also used the sulfamic successfully with platinum). The N₂O is nitrous oxide (laughing gas). No crystals are formed, unlike the crappy urea.

The sulfamic works stoichemetrically and it takes about 3.35 pounds to react with a liter of 70% nitric (15.8 molar) or, 1.5g/ml of 70% nitric. I dissolved it in water before use but it would probably work as a solid. The solubility at 20C is about 150g/l. However, the dissolution reaction is very endothermic so, by using warm or hot water, you'll get a lot more in solution.

I'm not suggesting it's use for large excesses of HNO₃. However, for small (or, large) excesses of free nitric, it runs rings around such things as crappy urea (as you can probably tell, I hate that stuff).

Safety. It is an acid and it should be treated as such. It will burn you and it is corrosive. It's a powder and you should use a dust mask to keep it out of your nose. Also, since you don't want everyone to get stoned on the nitrous oxide, the fumes should be exhausted. That's about it.

A problem is to determine when all the nitric is gone. In some of my work with the sulfamic, I most probably used at least a small excess but it didn't seem to cause problems and I still got at least 999.5 Fine gold. 4metals suggested I put a single prill of urea in the solution. If it fizzed and floated, there was still free nitric. Something I've used in the past to test for nitrates is the brown ring test. It's simple and instructions are on the internet. Another method is to pull out a small sample and see if the gold will readily drop (with no brown fumes) with a little SMB or sodium sulfite.

Everyone should give the sulfamic a try to kill the excess nitric before dropping the gold from aqua regia. I guarantee that you'll never go back to crappy urea.

Lou said:

Mass balance aside, are you so sure that nitrogen is produced?

Very few things give nitrogen gas. Nitric acid and nitrates in general are not among them.

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Thanks Lou, No im not sure, theoretically and what ive seen visually it seems plausable. Basically I used ISI redox data, using 4 potential reaction:

Oxidation H2SO3- + H2O ==> SO4- + 4H+ + 2e- (-0.17)
Reduction NO3- + 4H+ + 3e- ==> NO + 2H2O (0.96)
Reduction 2NO + 2H+ + 2e- ==> N2O + H2O (1.59)
Reduction N2O + 2H+ + 2e- ==> N2 + H2O (1.77)

I guess that any insoluble gas will expell upon heating so maybe not all, or even any, of the nitrate will leave as N2, some may leave as N2O or NO though the last two are slight soluble in H2O, not sure how soluble they may be in my working stew. Grated using SO2 is the way i want to go.

All said and done, it works well.

I must add that chemicals here in New Zealand are difficult to obtain due to our large Meth problem, HCl is OK, sodium/potassium nitrate i make myself, and i try and keep all the nitric acid produced when liquid reduction requires HCl evapouration, not much but it all adds up. Nitric acid is not available to the public. Sulphuric acid from batteries, basically i use what i can, make what i aint got. Improvisation. :lol:

Hi

Do you believe that sulphamic acid might be effective in removal of HNO3 in other processes involving PGM?
Like for instance palladium from monolith capacitors(instead of fuming NO2 out at least 3 x)?
Anyone try that?

Yes but the solution must be hot to have favorable kinetics (that is, rapid rdxn)

you mean heated to gain better movement of the molecules(internal energy of the molecules itself ,so that they can step faster into reaction).
hmm, I'll try that, when done I'll post some detailed review and maybe some pictures or movie too...

thanks for answer

I thought this may a good place to place something I noticed.
Ridding nitric acid from aqua regia and precipitating gold with sodium sulfite or SMB.

Sodium sulfite and nitric acid (alone) yield sodium nitrate and sulfurous acid:
Na2SO3 + HNO3 ---> NaNO3 + H2SO3
The sulfurous acid decomposes to water and sulfur dioxide gas:
H2SO3 ---> H2O + SO2 (g)

Now if we had an acid (aqua regia) and gold in solution like hydrochloric acid, then the HCl and NaNO3 would form poormans aqua regia and re-dissolve the gold we were trying to precipitate using the sulfite from the aqua regia we did not properly eliminate the nitric first.

What happens is actually more complex.


If you have a nitric acid rich aqua regia, containing Au + 3 as chloroauric acid, what will first happen is that you will get a coarse precipitate of high quality gold upon the addition of the sulfite or SO2. Sulfites are acid instable and will immediately form sulfurous acid (which has an equilibrium with water and sulfur dioxide).
The gold is a very strong oxidant and will oxidize the SO2 or sulfito anion to sulfate, SO4 2- while being reduced to Au(0). This will get perhaps 90% of the gold from solution. Then, as you continue to add the sulfite or SO2 and the reaction heats up, you notice a more prominent display of the competing side reaction: instead of more gold precipitating, the higher temperature has made the free nitric acid a strong enough oxidizing agent to attack the sulfite. In the process, nitrate turns into NOx (mostly NO2) with the loss of an electron. It isn't a high efficiency reduction, and it takes much sulfite to effect the complete reduction of the nitrate anion. This only happens with acid conditions: you can bubble sulfur dioxide through sodium nitrate solution and nothing will happen, no NOx will be formed. It also takes heat: if SO2 is bubbled through cold nitric acid with calcium nitrate present the precipitate will be miniscule of sulfite/sulfate, but when heated, it is pronounced as the potentials have shifted (both kinetics and thermodynamics are increased towards favoring oxidation of sulfite by nitrate). Also occurring is the continuous re-dissolution of the microfine gold crystals that are precipitating from solution by the residual aqua regia extant in the system. You still have aqua regia, and it is hot, so the gold will be dissolving/oxidizing again as quickly as it gets reduced. This continuous reprecipitation process prevents proper ripening/growth of the precipitate and the base metal concentration relative to gold is now higher than in the beginning, so it is statistically more likely for the gold precipitated to be of less quality with more base metals entrained. This is why the last gold that comes out of solution is dirtiest and the finest (in size) powder. The darker and higher surface area the gold, usually the less purity it will have. A very pure gold precipitate will be almost fluffy and very blonde.

Thanks Lou, That was awsume.

I guess their was a bit of confusion on my part, most threads referr to removing the "nitric", where it's removing the unreacted nitrate from solution in the form of nitric oxide/nitric acid and HCl.

Anyone tried purging with air while evapourating off the nitric oxide/HCl?

Cheers

Deano

well i tried it with common household ventilator , it was winter and i couldn't denoxx my palladium outside , so I did it in my bathroom near window with that ventilator to blow it outside, and I was successful partialy, some of the fumes didn't go outside the window so I almost destroyed my bathroom :-(( the smell was intense for few months...)
I was in need of money then so I was forced to do so... and at the time i didn't had fume hood....
I guess it can be done but you'll need something to direct the air directly on the opening of the beaker and to deflect it of the surroundings , some sort of closed system... but fume hood would be the best.

Kats