Disposal or Recycling of Hydrochloric Acid

A. Basically, neutralizing it would correct the pH of the acid to an acceptable range, so that the acid would not cause undue corrosion to the sewer pipes, but would leave toxic hexavalent chromium in the waste if there was any to start with. What needs to be done is to reduce any hexavalent chromium to trivalent state, so that it is precipitable, then adjust the pH so it precipitates out, then filter it so the water can be discharged. The chromium-bearing solids would still need to be disposed of in a secure landfill.

A. I would add a small amount of ferrous sulfate ⇦this on eBay or Amazon [affil links] (about 5 lbs. per 1000 gallons) to reduce the chromium to the trivalent form, then adjust the pH to 8.5 - 9 with hydrated lime [affil links]. Lime should be added slowly with lots of stirring. Then add an anionic polymer to settle the solids. Make sure to have the water phase tested for total chromium before discharging it. It may be that you can extend the life of the stripping solution by running it through a column of weakly basic anion exchange resin, to remove the hexavalent chromium. This would have to be regenerated periodically with sodium chloride solution.

A. Another way that my former peers did not mention is to use columns to catch the Chromium (Cationic type I believe ) and to clean the Hydrochloric Acid. Then you can use the stripping solution with small HCl addition. Please consult with your local Environmental company or experts. Yours,

A. Hi James,

Seeing that no Guru had replied, how about having a gander in the archives at letter #12044. Surely there are some useful hints there ... even more if you are (heaven forbid) a dog lover.

A. James, when I want to get rid of hydrochloric acid, I mix it with sodium hydroxide (NaOH) a.k.a caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] , until it is neutralized. HCl + NaOH gives NaCl and water.

Geez, I hope I don't have to emphasize that you should be careful, and to make sure that it's completely neutral (pH 7). I presume you know the strength of the muriatic acid, so it should be simple to calculate the amount of caustic soda you need. If you've any doubt, bring a pizza into your local high school chemistry class and let them calculate it for you.

Good luck! And remember, no one at finishing dot com advocates non-adherence to environmental laws!

A. Hi there,

As above but caustic soda is a little too violent in the reaction and somewhat expensive. Try some Calcium Hydroxide I think its also sold in the plastering trade as slaked lime, it's an alkaline. Dilute your acid and in a large 200 Liter plastic drum feed the calcium hydroxide (Slowly) Stir and check using litmus paper to gauge when when it's neutralized. This time you end up with Calcium Chloride. and water.

Thank you, Lee, yes, I'll hold to my best on the environment. Pizza's great, and I throw the dough, so maybe that's an angle.

Freeman, I'm replying with thanks prior to following your directions back into archives. The car looks great! Robert, you've given me the journeyman's answer, and you nailed my back-off (some experience) from caustic soda. I can get the stuff and already have a drum. If you know (or anybody) whether the resulting calcium chloride is ALSO a problem, please reply.

Thank you, all!

A. I recall that the company I retired from a while back had about 1000 gallons of conc. sulfuric leak into a concrete containment pit. A local environmental services company came in and removed it for shipment to an "acid reclaimer" I believe somewhere there, in Delaware area, possibly at Dupont? We would use soda ash routinely to neutralize small drips of either sulfuric or nitric acid, by the way. Fumes were bad, but tolerable, when ventilation was adequate.

A. Dear James,

Calcium Chloride, like many Calcium Salts are insoluble in water. Our bones for example are mainly Calcium Phosphate. In the reaction converting your unwanted Hydrochloric Acid to Calcium Chloride, dilute the acid first otherwise it may splutter, remember that they use Hydrochloric, or when tainted with Iron, then sold as muriatic for cleaning cement off new brickwork, the product is Calcium Chloride and lesser amounts of other things (Silicates) and on construction sites doesn't this normally flow straight down the drain or into ground water. Check with your local E.P.A on acceptable disposal methods. Then again if you dried out the Calcium Chloride (Anhydrous) it makes a great desiccant (Water Absorber) but it is an Irritant...When it's this dry...gets up your nose, arh-choo.

A. If this acid is new, uncontaminated then why destroy it? Maybe you can find someone who can use it? There is a group of Yahoo mailing lists called FreeCycle where people go to give things away they don't want but might still be useful. Or there's CraigsList. I've gotten rid of quite a few things that way. It's nice when somebody shows up, takes the unwanted item away in THEIR car at YOUR convenience and is even grateful to do so!

I came across your post looking for information about using Muriatic acid for PCB etching. I live too far away to consider taking it but for that use I think just about any Hackerspace would love to have it and be very appreciative. I checked the Hackerspace wiki though and the only one I found for Newark was a group of people interested in starting one. You could try contacting them but their website and twitter links don't actually work so I don't know if their email contact is any better or not. I don't know what other cities are near Newark to check them too.

Good luck!

A. Muriatic acid is used in many, many applications. If I were in your area, I would take the stuff from you for nothing ...then I would put it into my swimming pool as I do on an almost weekly basis for pH adjustment.

Find a neighbor or pool company and offer it to them. I use about three gallons/month. Ironically, I also purchase about 2,500 gallons a month at my job, which becomes contaminated and has to be disposed of properly.

Hope this answer came soon enough.

A. There are two commonly used technologies to purify and re-use HCl: Diffusion Dialysis and Acid Retardation. Neither actually regenerates the acid, the acid used in dissolving metal and lost due to dilution is not recovered, and must be replenished. There is good information on both these technologies that is readily available on the internet.

A. Mr. Kirman offers sage advice, as usual. If you are choosing to dispose, calcium hydroxide is best. It leaves CaCl2 in the effluent. Won't upset many applecarts.

Trying to reclaim? You can get back some of the acid via acid retardation tech. Big time investment in equipment, sorry to say; it will pay off in the long run.

Hi cousin. I really don't want to argue semantics about whether your question is "abstract" :-) ...

... but we don't know what industry or sector you come from (plating shop, college laboratory, sidewalk contractor, waste hauler, etc.), and that can be crucial in knowing what laws apply. For example, a university in the USA often has the freedom to neutralize and dispose of its waste, but a plating shop cannot legally dispose of their waste except under a permitting process. And neutralizing the acid may not be the heart of solving the environmental problem, as the first question about acid with chromium contamination discussed ... thus the question remains: what is the source of this enormous amount of HCl?

Further, neutralization and disposal is generally not the right answer for disposal of huge amounts of waste, as the question about regeneration of pickling acid from galvanizing mentions.

A. Neutralization with slaked lime or sodium hydroxide remains a feasible approach regardless of the volume of solution. Still, while disposal of small quantities may not justify the expense of research, the disposal of enormous quantities probably does. I would suggest retaining a specialist in acid handling and disposal to make a suggestion. Best of luck.

Regards,

A. Hi. Everything is relative, but 5 tons is not a massive and huge amount by some standards. It may be possible to neutralize a portion of the HCl with the waste tri-sodium phosphate, and then neutralize the balance of the HCl with slaked lime.

But the thing is, who can say what the applicable regulations are, if any, for some undisclosed place on the world's 2nd largest continent. And who can say what contaminants are in a witches' brew collected from different industrial factories? Any sort of poison could be in the waste: lead, mercury, cadmium, arsenic, hexavalent chromium, dioxin ...

That is not the correct way to approach the project! ...

- The first step is to do a survey of the sources of the waste for what to expect in the waste;
- Step two is to do as assay to confirm that the survey was accurate;
- Step three is to do bench tests on small samples of the waste to neutralize and de-toxify it;
- Step four is to test the treated effluent to see if it will be suitable for discharge after the bench-test treatment, and to determine what if anything must be done with the precipitated solids.

Through those steps you will have determined whether slaked lime treatment is a viable answer for the 5-ton batch. Good luck.

Regards,

Times Beach, MO

A. Hi Rico. I personally don't feel that it is the right approach in most cases to accept a waste for treatment if you're not confident of and familiar with the source. You don't want to become another Times Beach :-)

Step 1 is to find out what this waste material was used for and why it has this unexpected material in it. Perhaps it's a waste pickling solution from a galvanizing shop which uses an ammonium chloride flux?

Regards,

A. Neutralize with Mg(OH)2 to a pH of about 8.5. Add a sulfur based precipitant to drop metals. Add a bit of aluminum sulphate, then floc out with an anionic polymer.

A. Hi Julieta. Everyone wants to reduce their acid usage, but it's not really as simple as just adding a commodity chemical to remove the iron...

The first step is to use an "inhibitor" from the outset. This is a chemical which has the ability to react with clean bare steel in such a way as to at least partially shield it from reacting with the acid. In this way your acid is used to remove rust & scale, but less of it is wasted dissolving good steel. If you search this site for "inhibitor" and "Clarke's Solution" you can learn about inhibitors, but most good inhibitors involve proprietary organic chemistry. So these are bought rather than mixed from basic salts. Rodine, Stannine, and Parkin are a few names.

After that there is an approach you may or may not wish to use called the Kleingarn Method to make acid and water additions intended to maximize the usability of the acid values of the solution. You may wish to read Barlow Campano's paper on the Kleingarn Method in our on-line library.

Another approach, the use of "acid extenders", is intended to precipitate out the iron so you can essentially just keep going by adding more acid without the need to dump the tank, and this seems closest to what you asked about. To my limited knowledge, these acid extenders are proprietary, so you must buy them from the supplier -- I am not personally familiar with using generic chemicals for that purpose. Good luck.

Regards,

A. Hi Karthick. On this page we have already discussed inhibitors to reduce acid use, the Kleingarn method to insure that you get maximum use from your acid, and acid extenders so you don't have to dump your pickle tank as often if at all.

But the fact that running an acid pickling operation or doing acid zinc plating increases the TDS in your water is not some weird anomaly that you must uncover the reason for -- it's part & parcel of metal processing, and something you must deal with. Presumably, dealing with the wastewater is the purpose of your ETP (effluent treatment plant).

Take a sample of this 28,000 ppm TDS or 35,000 ppm TDS effluent and do a jar test, treating it with hydrated lime and filtering the result, and tell us what the TDS is after filtration and how that compares with your discharge limits. Thanks!

Switching to H2SO4 pickling, the opposite direction from what most of the world did in the last several decades, is probably not the right approach. Good luck, and please give us some facts and figures.

Regards,