Neutralizing 98% Sulfuric Acid

I would tentatively suggest dilution with water as the easiest option, but I don't know what your local regulations say about disposal of diluted sulfuric acid (and the material safety data sheets are a little contradictory indicating violent reaction with water).

http://cartwright.chem.ox.ac.uk/hsci/chemicals/sulfuric_acid.html

http://fscimage.fishersci.com/msds/22350.htm

http://en.wikipedia.org/wiki/Sulfuric_acid

Perhaps it is necessary to use a solid PH neutraliser like soda ash, then perhaps you could flush the tank clean with water to remove the soda ash and neutralised acid (again a guess).

http://www.jtbaker.com/msds/englishhtml/S8234.htm

Ventilate area of leak or spill. Wear appropriate personal protective equipment as specified in Section 8. Isolate hazard area. Keep unnecessary and unprotected personnel from entering. Contain and recover liquid when possible. Neutralize with alkaline material (soda ash, lime), then absorb with an inert material (e. g., vermiculite, dry sand, earth), and place in a chemical waste container.

Hopefully this is of some help (at the very least someone here can enlighten me as well), but at the very least make sure you carefully study the information located in the Material Safety Data Sheet (MSDS).

Here's a suggestion: Mix up 15-20 lbs. (or more) of baking soda in warm water to saturation (ie, where no more baking soda will dissolve into the water at that temperature) and decant the liquid (only) into the tank or into a transfer vessel. Some solids will remain at the bottom of your mixing vessel; do not pour these out but leave them in the vessel if you'll be mixing another batch.

Pour only a bit at a time into your acid tank as foaming will likely occur, and by all means do not look into the tank (if this is possible) as you're pouring.

Above all, be safe.

I gotta add a huge "DITTO" to the warning. I have a cousin who's blind from this.

Sulfuric acid reacts STRONGLY with water. If you add water to 98% sulfuric acid, the acid will dissociate into H₃O+ and SO₄- with a huge amount of heat released. It will not just boil, it will explode. Adding a mild, dry base will much, much safer.

Dear Creede

Instead of using soda ash (sodium carbonate - Na2CO3) you can also use caustic soda solution (sodium hydroxide - NaOH).

The reaction produces sodium sulfate and then dilute with lot of water until pH about 7 before discharging to sewer.

Determine the amount of NaOH required based on following reaction.

H2SO4 + 2NaOH ---> Na2SO4 + 2H2O

The time taken is about the same as if soda ash is being used.

That is what we normally do for discharging acid in chemical plant.

Hope the above helps.

I have had a little experience with neutralizing acids.

Diluting the acid does not reduce the ph, so don't do it!

First, I wore long chemical-resistant gloves that covered my arms to my elbows. I wore a faceshield and a chemical reistant apron. I also wore high rubber boots.

I had a water hose next to me and baking soda and vinager to use on myself if I came in contact with the chemicals. A respirator is necessary when using caustic flakes because of the dust.

I took a small amount of caustic soda flakes and mixed with hot water into a plastic 55 gallon open-top drum until dissolved. I then pumped this solution using a low volume, acid resistant sump pump to circulate the product into the vessel, and return the contents of the vessel into the plastic open-top drum. The heat produced by mixing the caustic and acid will provide ease of dissolving more caustic into the drum.

I tried to maintain about 140 - 180 F.

It takes at least 15 minutes for the caustic to begin to produce a reliable ph. In other words, if you add caustic to the acid, your ph paper will show highly caustic (14). 15 minutes later it may show (6). 30 minutes later it may show (1). The process can be slow, but easy to control. Manytimes I had added the caustic too fast - I didn't wait long enough, and after an hour the caustic level was too high, and I had to add acid slowly to get to the final ph desired.

Where I live, my sewer district told me that I could flush into the sewer system a ph between 5 & 7. Once I achieved this ph, I waited another 1/2 hour while continually recirculating the mixture to make sure there were no residual pockets of caustic that had not yet reacted.

I then dumped the solution down the drain and rinsed the container.

Use lime (Ca(OH)₂) to neutralize the acid. You can recover valuable gypsum (calcium sulphate (CaSO₄)) for sale.

We used to neutralise residual acid in big mild steel tanks by tipping in a few bags of soda ash and then flushing with water but we did have an effluent treatment plant to deal with the discharge. If it is a steel tank you do need to neutralise as quickly as possible to avoid, as stated by Kaisan, corrosion by partially diluted acid. If you must use a solution rather than solid, dissolve the soda ash in water first but be aware of the potentially violent exothermic reaction between sulphuric and water/soda ash; if your tank is thermoplastic corrosion by dilute acid is not an issue but overheating could be. Use sufficient solution to neutralise followed immediately by plenty of water to remove heat. Hope this is of some help.

i agree with Kaisan.. diluted sulfuric acid can corrode steel with corrosion rate very high.. even if the acid is diluted by atmospheric condensing water, humidity, you will have corrosion..

http://www.outokumpu.com/applications/corrosion/image_viewer.asp?image=sulphuric1.jpg

http://www.corrosionist.com/corrosion_protection_sulfuric_acid.htm

S

corrosion rust prevention

Any material added to conc sulphuric to neutralise it will produce an exothermic reaction. The results in terms of 5-10 gallons could be violent and spectacular, producing heat, fumes and projectiles of corrosive liquids.

The material of the tank is of interest. Though safe for 98% sulphuric acid, mild steel, a popular material for concentrated sulphuric acid storage tanks, does not take kindly to being exposed to lower concentrations.

Exercise extreme caution, whatever the chosen procedure, on Health & Safety grounds.

man some body is right you better listen to this guy mixing water and soda ash gets vary hot and can catch of fire and mixing water and acid ya you will here a big thunder noise in the tank not good to use water with acid thats a no no and watch the soda ash and water do the math right and be safe

Invitation declined.

Concentrated H2SO4 will evolve exothermic reactions even when diluting with water and more on neutralizing with soda or caustic solution.When you directly add these neutralizing solutions fumes and heat may evolve.

My suggestions to counter exothermic reactions while adding water or alkali solutions for neutralizing are,

1]add urea and possible ice cubes into the acid tank.

2]Keep cooling the outer surface of the tank by cold water sprays from hose.

3]You can also add some amount of glycerin or coconut oil if required into the tank which can absorb heat of reaction.

Suggestion 2 holds good even without other aids.

Take care and go for smooth dosing.

dVader suggested sulfuric acid and making "valuable gypsum". For this volume, creating a small quantity of insoluble sludge in the bottom of a tank with little access does not sound like a good approach. Simplest would be NaOH, which will not create insoluble byproducts. NaOH is hazardous; add safely.

Mg(OH)2 slurry is a possibility too, since MgSO4 is soluble byproduct and would not create sludge. However, the Mg(OH)2 is harder to come by. Mg(OH)2 is much safer safe to handle compared to NaOH. Add only what is needed and there will be no insoluble material left in the tank.

Is this tank located at your place of work? There should be some Standard Operating Procedures available at the company that tell you exactly how to handle such materials.

Why does the tank need to be completely emptied?

Can it be tilted with a forklift so the materials can flow towards the opening?

Maybe you should get a pump and pump the remaining materials out?

I don't think you want to be introducing any other foreign materials into the tank when you can't get in there to clean those out.

Hello Creede and Welcome to CR4.

I'm sure somewhere in the plethora of responses you will receive, there will be a good solution to your problem. We have a lot of VERY smart people on this forum that love to help others in need.

For me, however, I don't deal with your product often enough to contribute to your specific issue, but...

I would like to provide a little bit of caution from a regulatory standpoint. As I am not aware of the size of your facility, it's generator status, or how often you receive compliance audits; I would recommend that you involve your environmental contact to look at a few things:

The material you have is hazardous but it is now destined for disposal, so now it is a hazardous waste.

The container it is in now is probably a hazardous 'material' storage tank not a hazardous 'waste' storage tank. (different labeling/management requirements.)

But now you are looking at performing elementary neutralization in the tank, which makes it an 'Elementary Neutralization Unit' ref 40 CFR 260.1

Elementary Neutralization has some permitting exclusions so you should be ok there. But, it was not designed as one, it was originally a hazardous materials storage tank, that is now containing waste. So, it could be agured by a compliance auditor that until the actual neutralization process begins that it is a hazardous waste storage tank and should have proper labeling.

Finally, for wastes that were hazardous solely due to ICR (Ignitability, Corrosivity, Reactivity) at the point of generation (inside your tank as soon as you decided to dispose of it) but no longer exhibit these characteristic due to Elementary Neutralization; they may no longer be 'hazardous' but they are still subject to LDRs (Land Disposal Restrictions.) Ref. 40 CFR 261.3(g) and 66 FR 27269, May 16, 2001.

So, while you are trying to figure out how to achieve your Elementary Neutralization, you may want to throw Hazardous Waste identification on the tank. Then, once you are done and are ready to dispose of the neutralized material, don't forget about any pertinent LDRs.

Good luck and, again, welcome to CENSORED CR4.

JavaHead

Thanks to all of you for the great response. The tank we're emptying is a steel tank, inside a tight containment area, so it is not possible to lift the tank to facilitate draining it. We are planning on using a Wilden diaphragm pump, with all compatible components to essentially vacuum up the bottom of the tank. After we've emptied the tank, it will be cut up for scrap, but we want to make sure that it's safe, since we will not be the ones cutting it up. All of the work will be done in Level B PPE, including air, to make sure that the guys doing it are protected. I absolutely do not want to add water to the sulfuric, we don't want exothermic reactions beyond what we can control. We do have a similar sized tank nearby that contains 50% NAOH, which we could use to help in neutralization. The NaOH tank will similarly have to be disposed of at the end of the project. I just want to be careful with the whole thing, so I'm asking for the best way to carefully neutralize. Once again, thanks for the great response.

Isn't the rule "acid to water"? Do you have to neutralize it in that tank? OR can you slowly pump the material into another tank containing a larger volume of the neutralizing solution (whatever flavour you go for).

You can neutralize sulfuric acid with 50%caustic soda. If you can tap into the discarge line from the tank to the pump.lockout all other valves on the pump, tank, etc. Should be part of zero energy on your lockout. Verify that the discharge valve on the tank is open. Line up a 11/2" hazardous material high preassure hose from a tote to the stabin of discharege line. Should be a valve on the end of the discarge stabin or the high pressure hose. Pressurize the hose. Slowly open the valve to the discharge line into the tank. You are going to get a bit rumbling from the tank. Do this slowly, when the tank begins to rumble, quickly close valve. When rumbling stops. Open the valve again slowly. When you get no reaction, the acid is neutralized. Good idea to do a ph test before hoseing and dumping test of solution. Always were all proper Poe, acid suit, rubber boots and gloves, goggles and faceshield. Be safe, redflag the entire and communicate to others what you are doing. Also always have a charged water hose nearby. It doesn't take only very little 50% caustic to do the job.