Get rid of NOx fumes and get stronger nitric acid

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philddreamer

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Thanks brother butcher!

I'm starting the 2nd batch of the GP stash.
Also got for free from my wife & son 61.5gm 14k, & 23.7gm 10k, & 52 gm of .925!!!!! :lol: :lol: :lol:

I thank God, & all of you for the expert advised that you share thru this forum. I always dreamed of this, now its a reality. WOW! :shock:
This is only the tip of the iceburg! I need to make more room under the house... :roll:

philddreamer
 

Noxx

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philddreamer said:
Just finished dryi'n & weighing the 69gm batch, recovered 1.8gm of gold! :p

That's 1/8th of the scrap I bought. I hope the other 7 parts will yield close to that, ea.

Thanks guys!

philddreamer

Phil, I now you will be tempted to melt the powder into a button, but if you wish to improve quality greatly, refine it another time.

Aim for a color like this:



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philddreamer

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Thanks Noxx!

I will do that from now on. I'm becoming more patient & want to be better organized, save "energy", chemicals, produce less waste...
This I'm starting to achieve thanks to all of you & your expert advise.
Yeap, things are look'n brighter! 8)

philddreamer
 

Neild

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This is terrific information as we are trying to be as "green" as possible in our approach to scrap and ore refining. We have already spent a horrendous number of hours designing a flume scrubber for AR digestion exhaust. We'll have to try this.
 

goldenchild

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Neild said:
This is terrific information as we are trying to be as "green" as possible in our approach to scrap and ore refining. We have already spent a horrendous number of hours designing a flume scrubber for AR digestion exhaust. We'll have to try this.

Yes. I havent had time to revisit this and experiment but if you get the proportions just right with the right amount of heat you will be substantially reducing the amount of NOx fumes produced. Also you will be saving your company money on the chemicals that are saved and time used to refine. They will be happy about that :p
 

MarcoP

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goldsilverpro said:
STARTING FORMULA FOR 1000 mL OF SOLUTION:

This starting formula is for 1000 mLs to make it easy. If you only make 100 mLs, divide everything by 10.

The acid solutions with the additives, should work the same as without the additives. If fact it may work faster, with all that oxygen from the H2O2 present.

(1) 57 mL of 30% H2O2 or, 49 mL of 35% H2O2. Using 3% H2O2 (570 mL) might add so much water that the acid performs too poorly. However, 3% may work for certain metal combinations.

(2) 22mL of the old standard, green, ethylene glycol anti-freeze. Read the label to make sure it's only ethylene glycol. The EG is probably stable and won't need replenished.

(3) The remainder is either aqua regia, 50/50 nitric, or HCl/sodium nitrate.

Can we prepare and store the solution or it needs to me made fresh when needed.
 

Lou

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Never prepare and store aqua regia--it will over pressurize its container.

The same is true with H2O2, peroxide. It must be kept in very clean containers, out of the light in a cool, dark area. Do not ever add it to halide salts or contaminate it with those--it causes catalytic decomposition into steam and oxygen, and is vigorous when it picks up. Silver, platinum, and several other metals also destroy peroxide.
 

butcher

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As Lou stated you do not want to make aqua regia and seal it in a bottle that will explode, because of the pressure building up as the gases try to leave the solution.

When you make aqua regia, a reaction begins when these acids are mixed, it is mainly this reaction and their gases which form during this initial reaction that oxidize and dissolve your gold into the chloride solution, You need these gases to do the work.

If you did make the aqua regia and let it sit, these gases would leave the solution, and the aqua regia would not work, or would not work as well.
always make your aqua regia as you need it.

You will read that aqua regia is a mix of one part HNO3 and 3 to 4 parts HCl used to dissolve gold.
But a better way to dissolve gold is to measure how much acid you need to dissolve the gold you have by weight, add the amount of HCl needed (a slight excess of HCl is no problem), and then add the calculated amount of nitric in small portions until the gold is dissolved (you may not even use all of the nitric you figured you might need), heating the solution also helps to drive the reaction, this will help insure you react, or use up, all of the free nitric acid in solution, and do not have excess nitric to deal with in the later steps of recovering the gold from solution...

How much acid is needed to dissolve gold?
many people when learning this tend to use way more acid than is needed, this not only wastes their acid but can create problems for them.

From Hoke's book she states that approximately: 1 fluid ounce (29.57ml) of 70% HNO3 and 4 fluid ounces (118.29ml) of 32% HCl will dissolve about a troy ounce (31.103 grams) of gold, using these we can do some math and get a good idea of how much acid we may need for different amounts of gold. we can make ourselves a chart with these.
rounding figures a bit here are some I get.

31g. gold -- 118ml HCl + 29.5ml HNO3

With some playing around with numbers and math we get:

1g. gold -- 3.8ml HCl + 0.95ml HNO3
2g. gold -- 7.6ml HCl + 1.9 ml HNO3
3g. gold -- 11.4ml HCl + 2.8ml HNO3
4g. gold -- 15.2ml HCl + 3.8ml HNO3
5g. gold -- 19ml HCl + 4.75ml HNO3
6g. gold -- 22.8ml HCl + 5.7ml HNO3
7g. gold -- 26.6ml HCl + 6.6ml HNO3
8g. gold -- 30.4ml HCl + 7.6ml HNO3
9g. gold -- 34.2ml HCl + 8.5ml HNO3
10g. gold -- 38ml HCl + 9.5ml HNO3
11g. gold -- 41.8ml HCl + 10.5ml HNO3
12g. gold -- 45.6ml HCl + 11.4ml HNO3
14g. gold -- 53.2ml HCl + 13.3ml HNO3
15g. gold -- 57ml HCl + 14.2ml HNO3
16g. gold -- 60.6ml HCl + 15.2ml HNO3
17g. gold -- 64.6ml HCl + 16.2ml HNO3
18g. gold -- 68.5ml HCl + 17.11ml HNO3
19g. gold -- 72.3ml HCl + 18ml HNO3
20g. gold -- 76ml HCl + 19ml HNO3
21g. gold -- 79.8ml HCl +20 ml HNO3
22g. gold -- 83.6ml HCl + 21ml HNO3
23g. gold -- 87.4ml HCl + 21.8ml HNO3
24g. gold -- 91ml HCl + 22.3ml HNO3
25g. gold -- 95ml HCl + 23.7ml HNO3
26g. gold -- 98.8ml HCl + 24.7ml HNO3
27g. gold -- 102.6ml HCl + 25.6ml HNO3
28g. gold -- 106ml HCl + 26.6ml HNO3
29g. gold -- 110ml HCl + 27.5ml HNO3
30g. gold -- 114ml HCl + 28.5ml HNO3
31g. gold -- 118ml HCl + 29.5ml HNO3

just to get an idea of volumes I will use these approximate equivalents

1Gallon=3.8 liter=3800milliliter=4quart=8pint=16cup=128fluid ounce=256tablespoon=768teaspoon
1/2Gallon=1.89liter=1800milliliter=2quart=4pint=8cup=64fluid ounce= 128tablespoon= 384teaspoon
1/4Gallon=0.95liter=950milliliter=1quart=2pint=4cup=32fluid ounce=64tablespoon= 192teaspoon
1/8Gallon=0.47liter=480milliliter=1/2quart=1pint=2cup=16fluid ounce=32tablespoon=96teaspoon
1/16Gallon=0.24liter=240milliliter=1/4quart=1/2pint=1cup=8fluid ounce=16tablespoon= 48teaspoon
1/32Gallon=0.12liter=120milliliter=1/8quart=1/4pint=1/2cup=4fluid ounce=8tablespoon=24teaspoon
1/64Gallon=0.06liter=60milliliter=1/16quart=1/8pint=1/4cup=2fluid ounce=4tablespoon=12teaspoon
1/128Gallon=0.03liter=30milliliter=1/32quart=1/16pint=1/8cup=1fluidounce=2tablespoon=6teaspoon
1/256Gal=0.015liter=15milliliter=1/64quart=1/32pint=1/16cup=1/2fluidounce=1Tblspoon=3teaspoon
1/512Gal=0.007liter=7ml=1/128quart=1/64pint=1/32cup=1/4fluidounce=1/2Tblspoon=11/2teaspoon
1/1024Gal=0.0035liter=3.5ml=1/256Qt=1/128pint=1/64cup=1/8fluidounce=1/4Tblspoon=3/4 tsp.

From this we can see it takes about 8 tablespoons of 32% HCl and about 2 tablespoons of HNO3 to dissolve a troy ounce of gold or about 31 grams of gold.


Or about: less than one teaspoon of 32%HCl acid and just a few drops of 70%HNO3 to dissolve a gram of gold.
 

jason_recliner

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Does anyone have equivalent figures for Poor Man's Aqua Regia, 32% HCl + NaNO3 salt?
I'm sure I use way too much 32% HCl, but that's ok. I add very small increments of sodium nitrate but it would be nice to have a target idea, to avoid:

Nothing happening.
Nothing happening.
Nothing happening.
Nothing happening.
Too much!
 

butcher

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My memory is not good, but I do believe I made a post of a study I had done on that, that would give you some numbers, chemical formulas, and some explanation of the reactions involved.
A quick search turned up this, I do not know what you will find in it.
http://goldrefiningforum.com/phpBB3/search.php?keywords=poormans+aqua+regia+how+much&terms=all&author=butcher&sv=0&sc=1&sf=all&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=Search
 

g_axelsson

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Even following the above amounts of nitric / HCl could be too much nitric. I've dissolved 53g of gold powder with 29 ml nitric. Used heating until steaming and reflux with a glass plate put on top of the beaker. Reflux and absorption of the vapors stretched my nitric way beyond my expectation.

Göran
 

justinhcase

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Irons said:
aflacglobal said:
How about a little cheaper Yet :idea:

Oh here he goes again. :wink:

How about capturing the fumes, subject them to Ozone and passing them thru cold water until the concentration build up :?:

Will it work :?:

http://www.fas.harvard.edu/~scdiroff/lds/Geophysics/SmoginaBottle/SmoginaBottle.html

Actually, it's a lot easier than that. Plain old O2 will oxidize the NO to NO2. The NO2 combines with water vapor in a refluxer and they condense into Nitric acid. All you have to do is provide a continuous flow of Oxygen to the reactor and the Nitric Acid keeps being regenerated. The best part is that it doesn't add any additional water to the reaction.All you need then, is to feed in some HCl vapor to top it off. :idea:

Is it economical to just use bottled O2 with a regulator straight into the glass ware?
Both O2 and Acid are expensive consumables and it is hard to quantify the relative cost's
 

MarcoP

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I've got 1 liter of full strength clear ethylene glycol but I've just noticed its inhibited, would this work as well? And the above equation was it intended for full strength (I think it does since it asks for clear one, not colored).

Description says that this inhibited ethylene glycol contains 3 times over normal ones while red contains 40% and yellow 30%.
Not diluted will work up to -80°C while adding 2 parts of water will work up to -20°C.

Then looking into my garage I've also found some blue wynn's longlife antifreeze, 1:1 -40°C, 1:2 -20°C, 1:3 -12°C and 1:4 -7°C.
And now I'm more confused then before since both (clear inhibited and blue) when diluted as 1:2 works at -20°, so I guess they both contains the same concentration.

Not even the easiest thing like buying an antifreeze end up to be easy :| but I'd like to do things the proper way.

Thanks in advance.
 

butcher

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I would not use antifreeze or ethylene glycol.

Fairly dilute H2O2, or just concentrated enough to provide enough oxygen to the water, will work just fine without the antifreeze (ethylene glycol).

The ethylene glycol being a carbon based organic, with nitric acid (especially if concentrated), just sounds to me like an accident waiting to happen, or in the best case just cause other problems...

I would keep the antifreeze in the garage for my truck, and out of the lab away from my nitric acid...
 

MarcoP

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Roger that. I've already and only used 50/50 nitric and 30% H2O2 skipping the ethylene glycol due my doubts and the risks on making a similar recipe... covered, it did act vigorously and less dense brown fumes were produced a minute after the reaction begun.
 

butcher

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Concentrated nitric acid HNO3 and copper Cu, forms a visible brown gas of nitrogen dioxide NO2 gas.

Cu + 4HNO3 --> Cu(NO3)2 + NO2(g) + H2O

Dilute solution (about 3 M molar solution) of nitric acid HNO3 with copper form the clear gas of nitrogen oxide NO gas (g).

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

A solution in between concentrated and dilute can produce both of these NOx gases, and in reality several of the NOx gases can form from these reactions.

The clear gas of nitrogen oxide NO with oxygen O2 (or oxygen in the air) can form the visible brown gas of nitrogen dioxide NO2.

2NO(g) + O2 --> 2NO2

Note this oxygen can come from the H2O2 in the water solution used to dilute the acid, or from the hydrogen peroxide and water we use to bubble our NOx gases through when we make nitric acid.

Note also the NO gas is really not soluble in water, but the NO2 gas is soluble in water.

The brown gas of nitrogen dioxide NO2 gas mixed with water and some oxygen will form nitric acid.

4NO2(g) + 2H2O + O2 --> 4HNO3

Nitric acid is a strong oxidizer, concentrated nitric acid can be so strong it can form a layer of the passivation of metal oxide onto the surface of the metal, making it hard for them to be attacked, or dissolve into solution, being protected by this oxide coating, you will even notice this with copper or silver where with using concentrated nitric acid there is a delayed reaction as the metal forms a layer of passivation, until gas of nitrogen dioxide NO2 gas. Until the nitric acid begins to break down into solution forming HNO2 and NOx gases which we can then begin to attack the metal in a vigorous reaction, compounded by the heat evolved from this reaction, while we begin to see our nitric acid foam and boil over out of the beaker taking much of our metals with the foaming boil over.

We can see here were dilution of the nitric will actually dissolve the metal easier, with less chance of a boil over.
We can see also where even just water alone will make our nitric acid go further in the reaction where the NO2 in solution can reform making more nitric acid in solution instead of evolving, or leaving the solution as wasted gases, we can also see from the reactions above where the oxygen in solution provided by a little added Hydrogen Peroxide can supply oxygen in solution to convert the insoluble invisible NO gas back into solution as NO2, and then with the water to more HNO3 to react further with the metal, instead of being wasted as dangerous gases.

Diluting the nitric acid, I will normally dilute mine more that the recommended 50/50 mix, and add small additions of H2O2 as the reaction proceeds, I do this with heat.

Note heating also can have a reverse effect of pushing gases out of solution, as well as concentrating the acid in solution as the heat evaporates water, so we keep this in mind.

The heat helps to speed the reaction of the dilute nitric, the H2O2, can provide oxygen and water to solution, which can convert the NOx gases formed in solution back into nitric acid with the water and oxygen in solution to make your nitric acid go further at making metal nitrates instead of being evolved as gas.
Heating also concentrates the remaining nitric in solution, as the process proceeds.

You may have noticed that towards the end of the reaction that the silver (or copper) does not seem to dissolve in the remaining nitric acid, well with water forming from the reaction, (see the reactions above), this water dilutes the remaining acid that would take a very long time to attack the remaining metal, this is where we can still have free nitric acid, even after we think it has all reacted or is used up, heating towards the end of this reaction can evaporate the water concentrate the remaining nitric acid in solution with the metals, and dissolve more metals into the silver or copper nitrate solution, again dissolving much more of the metal than we could have without using heat in the process, you can be surprised by how much more silver can be dissolved into this remaining solution even after you think the nitric has depleted or has stopped reacting with the silver.

By diluting the acid in the beginning and using heat in a controlled manner, along with your H2O2 additions, to dissolve your silver or copper, you can keep gases in solution making your nitric go further, and heating the solution during the process to slowly evaporate the excess water added, and the water formed from the reaction,
( the water formed from the hydrogen gas that is set free from the acid as the acid reacts with metals forming water in this case with these metal less reactive than hydrogen in the reactivity series of metals, see below).
Then with this heat evaporating the solution to get the most from the nitric acid concentrating it in solution to make it stronger to dissolve more metal into solution without using up your nitric acid as wasted gas, or having to use it up later with a metal like copper when trying to cement silver from solution later.

If we look at the reactivity series of metals we will see hydrogen in this series (hydrogen is not a metal) and there as a reference, reactive metals above hydrogen, will displace hydrogen (from the acid as gas from solution as it dissolves, this hydrogen gas leaves the reaction as H2gas.
With unreactive metals like copper and silver the hydrogen is also set free from the acid when the metal is oxidized by the strong oxidizing acid, but in this case the hydrogen does not leave the solution as a gas, but hydrolyzes the water to form H3O and then more H2O in solution as the HNO3 helps to provide oxygen to form water in the reaction.

3Cu + 6HNO3 --> 3Cu(NO3)2 + 6H
then
2HNO3 + 6H --> 4H2O + NO (gas)
overall of the above reactions
3Cu + 8HNO3 --> 3Cu(NO3)2 + 2NO +4H2O
Here we see water forming in this reaction of the unreactive copper metal and the strong oxidizing acid of nitric acid.
 

MarcoP

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butcher,
I understood the meaning of the entire process and it did actually worked. I used a more diluted HNO3 (15%) with a little 10-12%H2O2 and I did not see any brown NOx gasses! Slightly evaporating at the end it saved me to use more acids and it consumed more metals. Tomorrow I'll add few more silver contacts and evaporate it little further and stop when I see brown NOx gas then I'll let it stand till no more reaction.

Thank you, your explanation is highly appreciated, it took me a couple of days to understand it and eventually I did! Thank you again.
 

MarcoP

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As a side note, it's pretty nasty working with nitric. I will put on hold some projects until I make a fume hood with scrubbers and will be still staying outside under a covered area and all powered with 12V from a car battery always on charge (idea taken from a recent post). You won't believe how nasty is until you try it.
 
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