How to deal with sulfuric acid fumes.

"Wet ashing" seems to be the name given for dissolving with boiling concentrated sulfuric acid the epoxy cases on IC's, i.e., memory chips on ram memory sticks.

I tried this recently with some very promising results. So nice to see the gold wires still intact after dissolving the encapsulating epoxy. I would like to find a good way to deal with the fumes coming off of boiling concentrated sulfuric acid.

My first thought is to do this under an inverted large glass bowl of sorts. Have it resting in a container filled with sand, and have the sand saturated with a solution of sodium hydroxide. Then as the fumes build up pressure and escape through the sand and are forcing their way through the sodium hydroxide solution, the sulfuric acid should be neutralized.

Suggestions on how to deal with the terrible sulfuric acid fumes would be appreciated.

I am aware of the hazard and concerns of dealing with boiling concentrated sulfuric acid. My method has been to use a hot plate located out in a field, with me far away. This allows me to plug or unplug it into the power source while being a good distance away from the hazards. Everything can also be contained in a large dog cage or similar item for added protection.

I would not advise anyone to use this method personally but without a proper fume hood and scrubbing its sheer madness and a very bad accident waiting to happen, there’s not enough gold in the world that would get me doing this without proper equipment and safety properly in place.

Thank you.

The hazards of hot concentrated sulfuric acid cannot be over stated. Both the acid and the fumes are extremely dangerous.

With that said, many dangerous chemical reactions are done all the time on an industrial scale with the proper equipment and safety precautions.

Does anyone know what would be a safe method?

You may want to ask diamond proffesionals, they use hot sulfuric for cleaning(...) diamonds

Thanks for the tip. i'll check it out.

Here's what I found on cleaning diamonds with acid:

Diamond Acid Bath Explained | CAUTION: Use Great Care
Published May 3, 2017 | By LD

One type of beaker for diamond acid boiling. The upper chamber contains a fiberglass filter to minimize the dangerous fumes released in the heating process.

Once the acid mixture becomes very hot it will begin to let off fumes that turn a brownish color.

USE EXTREME CAUTION IN EMPLOYING THE FOLLOWING PROCEDURE! The following protective gear is highly recommended. These should be resistant to nitric and sulfuric acids: rubber coated splash apron, gloves, safety glasses and an acid storage cabinet.
The ideal method for cleaning diamonds uses the acid bath. A mixture of 1 part nitric and 2 parts sulfuric acids in a small beaker over heat will clean the diamonds thoroughly. Even the smallest particles of metal shaving and dirt will be removed in such an acid bath. The color of a diamond can often be dramatically improved, perhaps due to a pitted girdle that has collected grime over years of wear, or a cutter who did not clean the diamond properly after the final polishing process. After a small amount of the solution has been mixed in a small Pyrex beaker — 20 to 50 milliliters (depending on the quantity of diamonds to be boiled) — under an exhaust fan or outdoors, and the diamonds have been dropped in it, place the beaker on your heating device, such as a hot plate. Heat the solution until it boils for about a minute or longer, depending on how soiled the stones are.

Noble Metals Recovery said:

Does anyone know what would be a safe method?

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The safe method is to do it in a proper fume hood with the fumes extracted through a proper scrubber.

Small fume hoods and scrubbers can be built from commonly available materials for not that much money. This forum has many posts on really nice DIY systems.

An upside down bowl in some sand that’s been salted with KOH outside somewhere is not a safe way to do this. I advise you to give up on that idea.

It's unlikely you will recover enough gold to cover the cost of the acids, not to mention dealing with the waste acids, using this method. IMHO you'd be better off just incinerating the chips and panning the ash. Again plenty of posts on the forum explaining how to recover gold from chips using this.

Thank you. Great advice.

I am trying something different at the moment. I put a few black IC's in some sulfuric acid just at room temperature.

Since sulfuric acid doesn't seem to put out fumes at room temperature, I'm just going to give it a long time and see if it will destroy the epoxy casing.

If it works, then I will have to see if it's cost effective. Of course, I can always go with your suggestion as to what has already been shown to be a good method with incineration.

Noble Metals Recovery said:

Thank you. Great advice.

I am trying something different at the moment. I put a few black IC's in some sulfuric acid just at room temperature.

Since sulfuric acid doesn't seem to put out fumes at room temperature, I'm just going to give it a long time and see if it will destroy the epoxy casing.

If it works, then I will have to see if it's cost effective. Of course, I can always go with your suggestion as to what has already been shown to be a good method with incineration.

Click to expand...

Hi,

Looking forward to your result

I'm wondering what will happen, if the beaker is covered with a stretchable silicon cover. Will it be enough tight to stop the fumes? Will the acid (or fumes) dissolve the silicon? Will the fumes create pressure, or will dissolve back in the acid?

Look

At some point you're going to make a mistake. We all do. Concentrated Sulphuric acid is not one of the things you want to make a mistake with.

People can say bah humbug all they like but it's a fact.

I respect you urging caution. It is very much needed, especially in a public forum such as this.

One of my favorite things about the forum is that newbees can be warned of the dangers, and oldbees too.

Here in the USA, we have WalMart's all over the country. I don't know if you have them where you live, but there must be something similar.

Anyone can just walk in to a WalMart and purchase a bottle of concentrated sulfuric acid, it is used for clearing drains. I find it hard to believe that is so easy to obtain. I don't know if it even has an age restriction. I'll find out the next time I buy a bottle. If there is an age restriction, the purchase will not finalize until my I.D is checked by a store clerk.

They also sell HCL. Someone in corporate must have made the decision to make these available to the public at large.

With your cautious nature, which I'm not criticizing, I wonder, what is the most hazardous chemical mix that you do handle? I would imagine that you work with AR?

Thanks for the reply.

You raise a good question and it warrants a good reply. 8)

I handle all kinds of dangerous chemicals, but a more salient point is what dangerous chemicals do I NEED to use to get a particular job done?

I use AR frequently. I do use concentrate H2SO4 for particular small things like final cleans on gold powder for high purity, or in dilute form for converting Silver Chloride, and Ive also done a lot of work with Cyanide.

What I don't do is set up a home grown rig for deplating gold in a coffee jar and fill it full of hot concentrated H2SO4 and hope that it's not going to spit or splash. That's just my personal choice.

Understanding the chemistry and using the correct equipment and safety measures counts for a great deal when working with the more dangerous stuff. The concerns I raise are more looking towards people using no safety equipment and refining "when the wind is blowing in the right direction."

Don't mistake me- that isn't a prod at these people- we all do what we can with what we have got however without the correct equipment should people really be using the really dangerous stuff in the first place because it's almost like russian roulette. At some point the law of averages says it will go wrong, so what's the backup plan and the disaster recovery system when you're on your own in a field or your garden or your shed?

Ive had proper lab glassware crack or explode in a fume cabinet on occasion. I make mistakes just like anyone else does but everything needs sensible risk management. As I've said on another thread- it's funny how the guys most comfortable with using cyanides are the ones being the most cautious about concentrated sulphuric acid, hot concentrated sulphuric acid, PGM salts, and burning things on a barbeque.

We're certainly not risk averse but I think we choose and manage risks in a more complete way. After all - getting it wrong with cyanide is a one way street.

To your last point about being able to buy concentrated H2SO4 in a supermarket. You're right - it's crazy. We have people throwing it in others' faces over here in certain parts of the country.

Does that answer your points? Happy to expand on any if required.

Jon

Jon,

Excellent job. I consider your reply a "word to the wise". You are a good balance to my somewhat cavalier approach.

I hope anyone reading the thread I started continues to the end to read your comments.

Steve

Good thread.

My noobness will show again:

Jewelers have been using a "warm" (120F to 140F) "dilute" solution (10% H2S04) as a pickling solution for a very long time. Many use a mini-crockpot (16oz) like this and it sits on their benches within easy reach:





Do the pros consider this dangerous? I know that there are many pickling substitutes out there that don't use H2SO4, but they are more expensive.

From a chemistry and refining standpoint, at what point does "dilute" become "concentrated" and "warm" becomes "hot"?

James

There's a massive difference between 10% and 98% plus James.

The reasoning is this - Sulphuric acid is extremely hungry for water. Incredibly so. At 10% it has plenty of water but at concentrated levels it literally drags the water out of anything it touches. This is why it damages flesh and eyes so badly and so instantly.

Add temperature to that and you get a vastly increased "need" to do this. Sulphuric acid wet ashing works at high temperatures - I may be wrong but I have heard around 180 degrees C. It can achieve this temperature because it has no water in it, and the effect of either a drop of liquid or the fumes coming into contact with flesh are truly terrible.

There are technical terms for all this- I've chosen to use normal terms because it drives the point home more effectively. For more deterrence look up images under the search term "sulphuric acid burns" to see what it does cold- never mind hot.

At 180 degrees C - it's the closest thing to the Alien blood you probably saw on the James Cameron films that you'll find when it hits flesh. I don't need that crap in my life man. 8) 8)

Jon

The real problem with this process is it works and very well but the downside is what Jon has been trying to warn everyone about, we all handle and use dangerous chemicals but the three most dangerous mentioned in my opinion are definitely hydrofluoric, sulfuric and sodium hydroxide or lye, all can and will cause terrible damage cold but hot they become horribly dangerous and need treating as such or in my opinion avoiding at all costs :shock:

To "cool" things down a bit I offer the following.

I see that "wet ashing" is done at high temperatures, what's do say that it wouldn't also work at lower temperatures?

As mentioned earlier, I have put some black IC's in concentrated sulfuric acid in a beaker at room temperature and have it covered with plastic wrap.

Nothing exciting is happening, but I may be detecting the beginning of the break down of the epoxy.

If this works, given enough time, it would diminish the level of danger, both for contact, and for fumes.

Be patient, I will report the results here.

Someone else may want to experiment with UV light. Strong UV, the type that is dangerous to work around. UV destroys most plastics including many types of epoxy.

My thanks again, to any and all who urge caution, I know I need to be less compulsive, and I'm probably not the only one.

Steve

I might be wrong here, shooting from my hip, so please pitch in and correct me as needed.

I guess the "ashing" part of "wet ashing" is, at least partly, due to the high temperatures. Not necessarily the acid by itself. Concentrated sulfuric acid boils at 337 deg C, so I guess the pyrolization part could just as easily be done by any other liquid at a comparable temperature. For instance molten salts of different kinds.

You still have the carbon to deal with after, so in my eyes, pyrolizing and incineration will give you a cleaner product to reclaim your values from. There may or may not be solvents for different kinds of polymers/resins and such, but I don't know how practical they are for our use.

For small scale, the method Tzoax use seems quite simple and straight forward, but I guess it emits a significant amount of smoke. The end product seems excellent though.

Thermodynamics and the the direct relationship between chemical reactions and heat is why high temperatures are required for wet ashing to work properly.

For many reactions the reaction rate doubles for every additional 10 degrees C of temparature. So Steve your H2SO4 at 180 degrees C is working 262,144 times faster than it would at 10 degrees C. That's a big jump - so to put it in perspective- what would wet ash in one hour at 180 C will take 30 years at 10 C.

Look this is very rough- the equation isn't linear and the temperature difference to double reaction speed alters as the temperature increases, but the general principle is correct and this is why it works.

The same principle applies with AR - running at 70 degrees C is twice as fast as 60 degrees C and that's something everyone here has seen. That given because AR is water based you cannot exceed 100 degrees C so there is a limit. The boiling point of pure H2SO4 allows many many more multiples - hence the use.

With regards to the process Tzoaz uses. I'd like to know what's in all that smoke before I'm breathing it in. Wouldn't anyone?

Well, let's see. since I'm now 69, if I get a batch started now, it may be done by the time I'm 99. Hmmmm.