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topic 44342

Crystallization Of Hydrochloric Acid Problem in Pickling System

A discussion started in 2007 but continuing through 2017



STEEL - HUGER, South Carolina.

simultaneous 2007

A. The short answer is: something that's not hydrochloric acid. Pure HCl might freeze, but only at subzero temperatures.

Is this pump transferring liquid from a pickle tank, or something? It might be that you have so much dissolved matter in there that it's "freezing out." I used to have a lot of trouble, in field operations, with diaphragm pumps in the cold weather. The explosive release of compressed air during the cycling of the pump cools it down considerably.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


A. Hydrochloric acid is a gas - hydrogen chloride - dissolved in water. It does not crystalise, at all, ever.
You have something else causing the problem. What is the acid used for? What other materials are present?

geoff smith
Geoff Smith
Hampshire, England


A. HCl does not crystallize. What you're likely seeing is metal salts. You'll likely have to reduce the metal concentration of your HCl. Get a metal analysis done and then look at solubility charts.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


A. Hydrochloric acid of 32 wt% freezes at -43 °C, so perhaps unlikely.
Possibly, a corrosion salt such as ferrous chloride tetrahydrate, FeCl2.4H2O (greenish, melts at 105 °C) or ferric chloride hexahydrate, FeCl3.6H2O (reddish, melts at 37 °C). Both are water soluble.

Please give materials of construction of the pump and upstream piping, and any additional info on the crystallized solid.

Ken Vlach
- Goleta, California
contributor of the year honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.


A. Strange that the discharge of the pump is getting blocked. The fluid velocity should make sure it is clear at all times. Is it blocking while the pump is stopped ? If so perhaps flush some clean acid/water to ensure pump remain with 'clean' liquid in - often you can get settlement of solids from product, congregating at the bottom of the tank, and the pump is mounted at the bottom so could be this.

The discharge especially should not clog as it should be smaller than the pump suction bore, so velocities will be really high ? If it is a solids matter, then you will have added issues of bearing lubrication if it is a mag-drive - which needs its own special set of rules applied to overcome these associated issues.

Ashley Fenn
pumps - Northants, England

Is there a pickling additive to prevent crystallization?

January 21, 2015

Q. We have a pickling line in Belgium, Europe and we have the same problem with our FeCl concentration in combination with low temperature.
The valves are getting blocked by crystallization.
Reducing the concentration of iron in the liquid is a solution, but that makes the process less efficient.
Is there a product we can add to the acid to prevent crystallization?

Joeri Bogaert
pickling - Evergem, Belgium
  ^- Privately contact this inquirer -^

January 24, 2015

A. It would be possible to add a chelating agent such as tetrasodium EDTA to increase the solubility of iron. But the cure might be worse than the disease, since it would adversely impact waste treatment.

Tom Rochester
Plating Systems & Technologies, Inc.  
supporting advertiser
Jackson, Michigan, USA
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September 21, 2015

A. We have crystallization problem too, but I think if we set two valves in upward and downward of line to circulating the water to dissolving crystals, maybe we succeed and solve the problem. I haven't tried like this but it seems executable.

maasum maasumi
chlorine - iran, urmia

October 2, 2017

Q. Will adding an inhibitor help to eliminate this problem or could that be the root cause of the issue?

Larry Malone
- Mobile, Alabama

October 6, 2017

A. Keeping Sodium chloride(Common salt) in excess will solve the problem of crystallization of Iron.

Shankaranarayanan Narayanaswamy
- Belgaum, Karnataka, India

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