# How dangerous is Aqua regia



## martymcfly (Aug 28, 2013)

Ok so this is probably a no brainer. Its really dangerous . but im wondering just how much of this stuff do you have to inhale before your going to see problems?

For instance would getting a whiff from mixing a small amount like 10ml do you harm or would you have to be mixing a litre of the stuff and having serious smoke before its a proper danger?

Has anyone on here had any accidents where they have been exposed and felt ill due to it?


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## 9kuuby9 (Aug 28, 2013)

martymcfly said:


> Ok so this is probably a no brainer. Its really dangerous . but im wondering just how much of this stuff do you have to inhale before your going to see problems?
> 
> For instance would getting a whiff from mixing a small amount like 10ml do you harm or would you have to be mixing a litre of the stuff and having serious smoke before its a proper danger?
> 
> Has anyone on here had any accidents where they have been exposed and felt ill due to it?




Well the amount doesn't matter, since the damage builds up with time you should try to completely avoid it's fumes which are very harmful.

Build a fume hood or use a closed container as a vessel for your reaction vessel.


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## solar_plasma (Aug 28, 2013)

I agree with 9kuuby9, blind is blind and burned lungs are burned lungs. I see a main difference between 10ml and 1 l, that 10 ml are easier to control (....or better to get under control again, if something reacts more violently), since there is 100 times more chemical energy stored in 1 l, if you start an exotherm reaction.

edit: And very important, small amounts over a long period causes diseases of the lungs without you necessarily get aware of it - similar to e-welding.


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## martymcfly (Aug 28, 2013)

ive actually built my fume hood but was just wanting an idea of how dangerous ar is before i started any reactions. I read somewhere on the forum that jewelers used to smell there A/R which made me think a whiff of it must be not too bad but high exposure to it is obviously much worse. 

Also once your reaction is away and in your fume hood, If you can smell the A/R is the damage already done?


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## solar_plasma (Aug 28, 2013)

You do it every morning, when you inhale the exhaust from the car in front of you. But don't try this on fresh or reacting AR!



> If you can smell the A/R is the damage already done?



Often you are warned by the smell, but you can't be sure of it.


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## JHS (Aug 28, 2013)

Best to work under fume hood start to finnish.
john


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## butcher (Aug 28, 2013)

A smell of a poisonous gas may not kill you instantly, but that would not mean that some damage is not done.

You will not fall over dead if you get a whiff of the fumes of aqua regia, but you do want to breath poisonous gases.


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## martymcfly (Aug 28, 2013)

My main concern is that my fume hood is just vented straight outside and was worried that a small draft of reacting A/R fumes could blow my way and i could inhale some. Basically im treating it as if this stuff is going to kill me if i get anywhere near it but am i just being too safety conscious? Like does anyone know how much would need to be in the air to do you harm? Would your lungs be melting and coughing up blood or would it be slower to take effect?

Sorry im just paranoid about things like this.


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## JHS (Aug 28, 2013)

Would it help if you raised the hight of your vent pipe?
THERE IS NO SUCH THING AS TOO SAFETY CONSIOUS
it is when we lack in safety that it become a problem


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## solar_plasma (Aug 28, 2013)

Try and read the msds of HCl, HNO3, NO, NO2 and you will get a good impression. Also you will find how many ppm or mg over how long time will cause harm.

Expecting the worst case is never wrong.


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## martymcfly (Aug 28, 2013)

JHS said:


> Would it help if you raised the hight of your vent pipe?
> THERE IS NO SUCH THING AS TOO SAFETY CONSIOUS
> it is when we lack in safety that it become a problem




currently ive got it vented out at the maximum height i can which is about 7 foot. i managed to find some data on nitrogen dioxide:-

nitrogen dioxide

LC50 Inhalation Vapor Rat 790 mg/m3 5 minutes
LC50 Inhalation Vapor Rat 310 mg/m3 30 minutes
LC50 Inhalation Vapor Rat 220 mg/m3 1 hours
LC50 Inhalation Gas. Mouse 1000 ppm 0.67 hours
LC50 Inhalation Gas. Rat 200 ppm 30 minutes
LC50 Inhalation Gas. Rat 115 ppm 1 hours
LC50 Inhalation Gas. Rat 88 ppm 4 hours
LC50 Inhalation Gas. Rat 88 ppm 4 hours

Im not quite sure how much that is actually in the air and it deosnt state if that was the subject dead or just ill. So im guessing that a blast of fumes is not great but as long as you dont hang about in them you should be ok?


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## solar_plasma (Aug 28, 2013)

and you can smell it at 0,075-0,150 mg/m³, but I would not only look on the lethal concentration, but also what is allowed in work areas.



> Im not quite sure how much that is actually in the air and it deosnt state if that was the subject dead or just ill. So im guessing that a blast of fumes is not great but as long as you dont hang about in them you should be ok?



Without calculating the moles, just imagine all your 10g of acid vaporizes at once, and imagine this acid vapor is similar in its toxicity to NO2 - how many m³ air can you fill with lethal concentration? Just to get a feeling for the LC's.

LC50 5min means 50% of the rats died when they were exposed to the poison over a period of 5 minutes. LC = lethal concentration


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## MysticColby (Aug 28, 2013)

I read a lot of NOx MSDS's when I started refining. From what I could tell, you can smell it at about half the concentration that it is immediately harmful to you. by 'immediately harmful', I mean the listed minimum safe exposure level. long term, low concentration, exposure can still build up and cause problems later in life.
Now the fun part: NOx also reduces your smell sensitivity. So the more you are exposed to it, the later you will realize you are exposed to it, eventually you won't be able to smell it even if it is above dangerous concentrations.
So don't cash in on your ability to detect problems because you were careless.


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## goldsilverpro (Aug 28, 2013)

A friend of mine just got a fairly large burn, probably 2nd degree, on his arm from working, for a short period of time, over the hot red fumes produced from dissolving copper with nitric in a bucket.

NO2, the red fumes produced from dissolving metals in nitric or aqua regia, rats seemingly have an LD50 of 88 ppm over a 4 hour exposure. That's a little less than 1 part NO2 per 10,000 parts of air. LD50 (lethal doze for 50%) means that 50% of the rats exposed to that dosage will die. I also read that the symptoms may not show up for 72 hours.

Although the gases produced from just mixing AR are noxious and toxic, the greatest danger is the NO2 gas produced when dissolving metals.


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## Magiskt (Aug 28, 2013)

Due to this topic i wonder is it possible to filter out some or most of the fumes by the vent of your fume hood?


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## solar_plasma (Aug 28, 2013)

> Due to this topic i wonder is it possible to filter out some or most of the fumes by the vent of your fume hood?


Yes.Try a search for "scrubber".


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## Magiskt (Aug 28, 2013)

That got me to some interesting reading, thanks for the input. If I'm getting this right its the water scrubber we would like for our commonly used chemicals since they are soluble in water?


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## 9kuuby9 (Aug 28, 2013)

Magiskt said:


> That got me to some interesting reading, thanks for the input. If I'm getting this right its the water scrubber we would like for our commonly used chemicals since they are soluble in water?



Yes, Since most of the commonly used chemicals are actually "gas in water" Like HCl for instance, Cl is a gas Held by the Hydrogen atom in water.


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## Geo (Aug 28, 2013)

your scrubber needs to have a basic solution instead of water. exposure to NOx fumes are two fold, immediate one time exposure to long term exposure. immediate one time exposure is measured in both concentration of fumes and length of time of exposure. symptoms of one time limited exposure can range from burning, stinging sensation on the skin to respiratory distress including inflamed mucous glands and a light cough with limited exposure. prolonged exposure to heavy fumes on a one time exposure can cause acute respiratory distress with pulmonary edema (swelling in the lungs) that have to be treated as soon as possible with steroids to avoid asphyxiation over the short term. full effects may not present for days with shortness of breath, wheezing, bloody phlegm, nose bleed, weakness and a general feeling of discomfort.

the real danger for people who work with these chemicals are long term, limited exposure of minimum concentration of fumes. exposures of concentrations too small to detect by smell is (in my opinion) very insidious in its effects. irreversible lung damage occurs with every exposure no matter how small. its an accumulative effect that resembles a long time smokers cough. these long term exposure effects will not go away by ending exposure as the damage is permanent. if you plan on working with these chemicals for any length of time, fume control should be the first and foremost priority before you begin processing.


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## butcher (Aug 28, 2013)

Water will somewhat absorb some of the fumes, if the gases are in contact with the water long enough, but there are many gases that are not easily soluble in water or will not dissolve in water at all, like NO gas from nitric acid, which would pass on through the water, many scrubbers will use a chemical in solution at least in one stage of the scrubber, like a solution of NaOH to neutralize the acidic fumes and form a soluble salt from the fumes. 

The scrubber can be also used to collect the gases and convert them back to acid, example NO2 gas will absorb into water forming HNO3 acid.

The clear NO gas will not dissolve in water but in oxygen (or air) can be converted to NO2 the red brown gas, if we bubble NO through a solution of hydrogen peroxide (water with an extra oxygen), the Hydrogen peroxide can convert the NO gas into NO2 and then into dilute HNO3 in the solution.

Gases can pass through a scrubber and only a portion of them may get absorbed for this reason you will normally have several stages so that more of these gases are absorbed into solution or converted to a dissolve liquid salt or an acid.


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## chlaurite (Aug 28, 2013)

Jewelers carefully wafting the scent from their AR *while not actively using it* differs rather a lot from getting a good dose of its fumes while actually working with it.

/ Just say NO.


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## 9kuuby9 (Aug 29, 2013)

Even whit a small amount of the acid and a very reactive metal can produce; a very dangerous reaction.

[youtube]http://www.youtube.com/watch?v=-S9w_40QJ9Q[/youtube]


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## solar_plasma (Aug 29, 2013)

Very impressive. Though, the guy had no heavy gloves, I wonder how many times he will survive those dangerous experiments. Nothing anybody should try, is making such experiments for the government, like BAM in germany. What is the equivalent to the Bundesamt für Materialprüfung in the USA?


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## Geo (Aug 29, 2013)

solar_plasma said:


> Very impressive. Though, the guy had no heavy gloves, I wonder how many times he will survive those dangerous experiments. Nothing anybody should try, is making such experiments for the government, like BAM in germany. What is the equivalent to the Bundesamt für Materialprüfung in the USA?



that would be a couple of different agencies here like http://en.wikipedia.org/wiki/Occupational_Safety_and_Health_Administration and http://en.wikipedia.org/wiki/Epa


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## solar_plasma (Aug 29, 2013)

And not to forget: Myth Busters


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## NobleMetalWorks (Aug 29, 2013)

martymcfly said:


> Ok so this is probably a no brainer. Its really dangerous . but im wondering just how much of this stuff do you have to inhale before your going to see problems?
> 
> For instance would getting a whiff from mixing a small amount like 10ml do you harm or would you have to be mixing a litre of the stuff and having serious smoke before its a proper danger?
> 
> Has anyone on here had any accidents where they have been exposed and felt ill due to it?



Any amount of unnecessary exposure is unacceptable. It's accumulative. Each time you are exposed would make the next more dangerous. If you take the proper precautions and being as safe as is possible, you shouldn't have too much to worry about barring acts of God.

Scott


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## LorenD (Sep 17, 2022)

Magiskt said:


> Due to this topic i wonder is it possible to filter out some or most of the fumes by the vent of your fume hood?


What about a carbon filter in your fume hood vent?


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## galenrog (Sep 17, 2022)

Magiskt has not visited the forum since November of 2013. You might try sending a private message.

Time for more coffee.


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## FrugalRefiner (Sep 17, 2022)

But private messages are only read when a member visits the forum.

Dave


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## galenrog (Sep 17, 2022)

FrugalRefiner said:


> But private messages are only read when a member visits the forum.
> 
> Dave


Forgot, since I seldom use the feature. Sorry.


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## cejohnsonsr1 (Sep 18, 2022)

No need to filter the fumes. While nitric fumes are very deadly in an enclosed space, they dissipate quickly. If your fume hood vents out through your roof (20’+- agl) there’s nothing to worry about.


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## orvi (Sep 18, 2022)

cejohnsonsr1 said:


> No need to filter the fumes. While nitric fumes are very deadly in an enclosed space, they dissipate quickly. If your fume hood vents out through your roof (20’+- agl) there’s nothing to worry about.


Yeah, to the certain point. Thy disperse quickly, but downside is they can be smelled in very low concentrations  and thus dragging unwanted attention.


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## 4metals (Sep 18, 2022)

Here in the US you can apply for and be granted a “de minimus” status which usually means you use less than 10 pounds of Nitric acid a day. The catch is if anyone complains about the smell, even if your usage is under the limit, you still need to scrub it. 



cejohnsonsr1 said:


> If your fume hood vents out through your roof (20’+- agl) there’s nothing to worry about.


Maybe the 20’ above ground level works in suburbia or rural settings but in a city it’s much different. I knew a refiner in a single story building who had much taller buildings on both sides. He had to move because both neighbors could look out their windows and look at his stacks. He knew sooner or later he would piss someone off. 
He moved to a tall building on the top floor for that very reason.


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## orvi (Sep 18, 2022)

4metals said:


> Here in the US you can apply for and be granted a “de minimus” status which usually means you use less than 10 pounds of Nitric acid a day. The catch is if anyone complains about the smell, even if your usage is under the limit, you still need to scrub it.
> 
> 
> Maybe the 20’ above ground level works in suburbia or rural settings but in a city it’s much different. I knew a refiner in a single story building who had much taller buildings on both sides. He had to move because both neighbors could look out their windows and look at his stacks. He knew sooner or later he would piss someone off.
> He moved to a tall building on the top floor for that very reason.


In utmost simplification, nitric is just an oxidant. Hard to get, causing problem anywhere it appears in classic AR refining scheme. NOx gasses, need for de-oxidation of nitric residues... 

Chlorine is much friendlier in these terms, simultaneously order of magnitude more dangerous. Cl2 cylinder is out of option for majority of refiners... But small chlorine generator/electrolyzer ? Produce only that much you need, feed would be HCl or some metal chloride. RuO2 electrodes are expensive but purchasable... 

Just a thought. It would be more expensive than nitric, but for many people it would suit their needs.


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## 4metals (Sep 18, 2022)

Atomizing the material allows for easier digestions with Hydrochloric Acid and chlorine. A convenient source of chlorine is sodium chlorate. Just keep
It from getting too hot and running away. Keep
it around 50°C and you can control it easily. Ice is your friend.


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## orvi (Sep 18, 2022)

4metals said:


> Atomizing the material allows for easier digestions with Hydrochloric Acid and chlorine. A convenient source of chlorine is sodium chlorate. Just keep
> It from getting too hot and running away. Keep
> it around 50°C and you can control it easily. Ice is your friend.


I need to get familiar with chlorate dissolution, as it can easily be made by electrolysis in bulk. As I have quite a bit of fear using chlorates in general in acid media, from one incident with ClO2.
Are you dosing the chlorate directly to the reaction mixture or you have some separated dedicated generator ? If yes, which acid you use to liberate Cl2 and chlorine oxides ?


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## 4metals (Sep 19, 2022)

I have always used it as a powder added directly to the reaction. I always use the Hydrochloric Acid at azeotrope strength for the process. With care, attention to the temperature, and slow additions, it produces an aqua regia like reaction that can be stopped by stopping the additions and cooling. This is only doable with finely divided feed material, such as atomized alloy. 

Storage is a big concern, keep it dry and away from organics and keep it from interaction with the environment. 



orvi said:


> As I have quite a bit of fear using chlorates in general in acid media, from one incident with ClO2.


Say a little more about your encounter with the dioxide.


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## orvi (Sep 19, 2022)

4metals said:


> I have always used it as a powder added directly to the reaction. I always use the Hydrochloric Acid at azeotrope strength for the process. With care, attention to the temperature, and slow additions, it produces an aqua regia like reaction that can be stopped by stopping the additions and cooling. This is only doable with finely divided feed material, such as atomized alloy.
> 
> Storage is a big concern, keep it dry and away from organics and keep it from interaction with the environment.
> 
> ...


Yeah, that is the way. It was presented to me very similarly by my boss once he talked about it´s use from his early days in refining.
Solid NaClO3 or KClO3 is OK to store in glass containers for practically infinite period of time. But of course, apart from any organic or reducing agents  I once produced it by electrolysis, when I was young and interested in pyrotechnics 

ClO2 background

I knew about ClO2 possibilities of formation, as I few times intentionally produced some by acid decomposition of chlorate. Light is all it need to spontaneously pop or "explode", even in not closed space. Also very very nasty gas, I hate that smell very much.
I was using chlorate to oxidize Pd to red salt with NH4Cl. Solution was fairly concentrated, but I didn´t realized HCL content isn´t very big. It does not worked at all, so I decided to heat it up on the hotplate to facilitate it... And yeah, I should guess what can it become. As I added relatively fair portion into the beaker, and started heating, in PGM enviroment it somehow catched very rapid reaction, with evolution of yellow gasses and then it started popping  I barely managed to put watchglass on top and quickly getting it off heat. But as it popped, watchglass danced on the top of the beaker and it spitted the expensive solution quite vigorously. Luckily, also as you say, as it cooled below that threshold temperature, it calmed down. Practically nothing bad happened, practically no spill at all... But it is still in my head, that bouncing watchglass sound and stuff... So I didn´t used it for anything from the time it happened to me. Luckily, it does not have a big explosion force, more scarry than really dangerous (as explosive). After the incident, I realized that putting watchglass on top wasn´t very good idea in terms of concentrating explosive gas inside


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## 4metals (Sep 19, 2022)

Sometimes heat is good, sometimes pressure is good, sometimes both are good. And sometimes all of the above are bad! But every reaction is different and that is what you learn with first hand experience. 

I am glad you escaped with your health intact and a lesson learned. That’s the important part.


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