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"Sulfuric Acid Solution Recovery Q&A"

Current question and answers:

April 8, 2021

Q. Sulfuric Acid pickling issues (heptahydrate crystal?) in galv. pickling process?

We have been experiencing white crystal on materials through one of our sulfuric pickling tanks. We often have to use an adjacent tank to remove the crystal as it is affecting the finish quality of the material.


We have an acid recovery system in place and remove roughly 2 bags of iron sulphate per day. We have not been stripping zinc in the tank other than rigging equipment as usual. Acid in the tank is high in the 15+ range and iron is roughly 3-4%. Has anyone experienced this phenomenon -- and apart from dumping the entire tank, how was it resolved? Thanks in advance for your help.

Jeff Boychuk
- Delta British Columbia

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Previous closely related Q&A's, oldest first:


Q. We need to reuse a spent 20% Sulfuric Acid solution used to pickle steel. The main contaminant is iron. Is there a technology like Ion Exchange that we can use to remove the iron and reuse the acid? We generate about 3 batches per week of 700 gallons each. We don't want to drain this solution to our waste water treatment plant because we will exceed our discharge limits.

Jesus Quinonez
- Riverbank, California, USA


A. Ion exchange is not generally used for this application. The three technologies most commonly used are freeze crystallization, acid retardation (which is like ion exchange), and diffusion dialysis. All of them have been used for this application. The best choice for you will be difficult to calculate and may depend heavily on the acid strength and the iron concentration of the solution at the time that it is dumped.

Lyle Kirman
consultant - Cleveland Heights, Ohio


Do you know some technology providers that sell equipment which can purify sulfuric acid from contaminants especially iron? Thanks very much

Vanessa Dagal
chemicals - Makati City, Philippines

December 8, 2011

A. We operate a sulfuric acid recovery system by Beta Control Systems which operates all the time between three 6000 gallon baths of sulfuric. The old way we used to was to decant the bath we would pump the acid out into an off-line tank and let it set for a couple of days. The used acid would start to crystallize to the sides and to the bottom of the holding tank then we would pump out of the center then return the solution back to the process and use it for make-up on for the other baths of acid. After the solution has been pumped out we would go in and then remove the crystals from the tank which took a little time and labor but it worked. With your acid% being at that level I would first try it out on a small scale then make sure you check the iron% before and after to see if it will work for you. When the acid must cool no heat.

Paul Doney
- Spokane, Washington

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