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topic 39277p2

Why do we use 15-18% HCl for pickling

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A discussion started in 2006 but continuing through 2019

Q. Hi, I am currently looking for ways to reduce or eliminate acid fumes (HCl, H2SO4) from our pickling line. Can I get any suggestion regarding this?

Razin Syamil Zahab
- Johor, Malaysia

Fume inhibitor for HCl

August 22, 2016

Q. Dear !

I am a production GI low carbon wire. Up to now we still don't know a method to inhibit vapor of acid chloride. Please tell me about any commercial chemical that is on sale in world marketing.
We use 12 to 18% HCl (baumé 32)
Mr. Lamvo

Vo Thanh Lam

August 2016

A. Hi Mr. Lamvo. I am not familiar with the distribution channels in Vietnam, and we don't print commercial responses in this forum (for one thing, it leads to unmanageable spam), but any of the worldwide plating supply companies like Chemetall, Macdermid, Atotech, Enthone, or Henkel can probably help if a local plating supply distributor can't. Good luck.

I think you should probably have a local fume extraction system (exhaust hoods) and fume scrubber as well as the inhibitor.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

February 2, 2018

A. The percentage for 15 to 18% is due to the resulting concentration after regenerating or recovering acid from the pickling process in another process with a fluidized bed regeneration plant or another process. This percent is enough in order to get the result for removing the oxide on the layer. The temperature used should not be greater than 88 °C. If you use a greater concentration with the same temperature, you will face HCl loss by evaporation immediately.

Y Garza
- Monterrey Mexico

February 24, 2018

Q. I work in galvanizing department.. which inhibitor may be used to limit the attack on steel.

N m Doshi
- Vadodara, India

February 2018

A. Hi Doshi,
If you can't get Dr. Cook's article in the August 2000 issue of Metal Finishing magazine (or at, you can Google for Rodine, Akzo Armohib (maybe Armohib 28), Columbia Pickle Pal, RI-inhib, Activol 1803, and Stannine LTP for further info. I'm sure there are several other suppliers of pickling inhibitors. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

June 12, 2018

Q. Hi,
I am Shishir Sable, working for a Fnsteel in the Netherlands. I am busy with optimising our wire pickling lines. We have 5 pickling tanks. The fresh rings comes in the tank with 5% HCl concentration. The rings leaves the fifth tank which has 23% HCl. The HCl % in various tanks are 5, 15, 18, 20 and 23%. Is this type of counter current pickling process advisable? Are there other options?

Recently we did lab trials to add extra FeCl2 in the pickling tanks. That reduces the pickling time by almost 20%. Currently I am busy with upscaling it. What is your opinion on upscaling the lab trials?
best regards

Shishir Sable
- Rotterdam, The Netherlands

June 13, 2018

A. Hi Shishir! I think this type of counter current can make good results, but I suggest that you, in order to maximize your pickling line productivity, check:

1- Bath temperature: Below 18 °C you will experience reductions of the reaction speed. We have teflon heat exchangers (steam heating system) for that (we have today 4 °C outside so it's a real problem!).

2- Iron content/Concentration: I think all these trials are already made and their results are available in charts. You can check your results with the Kleingarn curve (check If you have some doubts and an available tank and all you need for your upscaling trial, go ahead!

3- Gap between coils: One of the most difficult problems to solve is the rust between coils. You need to move the coils to make acid clean all the gaps between them, and/or get good wetting agents to improve this.

I think those lines of work, and how you manage to get your best parameters in every one of them, will get you where you want to go in production and quality. They are my three pillars in pickling for our wire process :)

Best of luck! Tell us if you have some interesting results there!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

June 18, 2018

Q. Hi Daniel,
Thanks for your info. I have gone through the Kleingarn curve. My question is validity of this curve at higher temperatures. The curve is designed at 20C. How is the curve look like at 35-40 °C? Does anyone has experience/other literature?

Moreover as I said earlier, we are planning to increase Fe(II) contents in the pickling tanks. I see following options;
1. Pre-mix FeCl2 powder with acid solution is the dosing tanks/buffer tanks which are upstream of pickling tanks. FeCl2 is hygroscopic. So feeding in humid conditions may cause issues.
2. Add Fe powder to HCl dosing tank. It will form FeCl2. But H2 is also formed as a side product.
3. Recycle a part of spent acid. But it contains a number of other heavy elements which are not advisable.

What is the industry practice?


Shishir Sable [returning]
- den haag

June 20, 2018

Q. Hi Daniel,

Thanks for your input.
We do have stable temperature profile between 30-45C in different tanks. My main worry is optimal Fe/HCl concentration in the tanks. The last pickling tank (with fresh acid , 23%) has almost NO Fe in it. The Kleingarn curve suggest that if you start pickling with zero Fe content then you end with sub-optimal pickling till the end of the process.
How do you increase Fe contents of the fresh acid tank? Addition of extra FeCl2 or partial recycle spent acid where the Fe contents are ~150 g/lit? But the spent acid contains lots other heavy metal which may be an issue.
What is your option?
Moreover does someone know how Kleingarn curve behave at higher temp.?
thanks regards

Shishir Sable [returning]
Steel - Rotterdam, The Netherlands

June 22, 2018

A. Hi Shishir!

I would recycle spent or acid from the previous tanks to increase iron content. You're worried about other heavy metals, are they alloy elements? If the answer is yes, I wouldn't worry about them.

I would worry if you have large quantities of zinc, if you are doing some rework of galvanized wire, but if you don't I would make this spent acid recycling to increase pickling speed.

About pickling speed around 35-40 °C, they are obviously higher than at room temperature, but optimal concentrations don't change too much. They change with solution activity and I would take this curve as valid with a small correction of speed because of the change in temperature.

This values and curves are measured in laboratory, with controlled solutions and so, and your industrial pickling line, I suppose, has many many more variables in it. Don't take the curve or any other book value as written in stone. You always need to measure what you get and make some experiments in your line to get your optimum parameters, as there are variables not taken into account in these charts.

Sorry if there's something not clearly formulated! It's a complex subject and my technical english isn't good enough!

Best of luck!!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

July 10, 2018

thumbs up sign Hi Daniel

Thanks a lot for your advise. I am now engineering the recycling option.
Yes all other heavy elements are alloy metals. Cr, Ni and Zn are prominent. We don't rework galvanised products. So it looks like a good solution to recycle a stream from higher Fe content tanks.

I shall keep you update with the results.
Thanks again.


Shishir Sable
- Rotterdam, The Netherlands

August 1, 2018

Q. Please anyone can tell me how many percent of HCl do I use for acid pickling of metal for zinc plating process?

vinay gawade
- mumbai,maharashtra,india

August 2018

A. Hi Vinay. That's the title and the subject of this page. Please try to digest it and request clarification of any points you didn't understand. And please explain your situation -- have you never done zinc plating before and are in the startup phase, or are you already doing zinc plating and you wish to change the percentage of HCl you are using for some hopefully interesting reason? You say "pickling of metal", but be aware that it can depend on what kind of metal you are pickling or acid dipping. What inhibitor are you using/planning to use? Thanks!

For a deeper understanding you may want to try the search term 'Kleingarn' on this site or elsewhere.


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

September 26, 2018

Hi Daniel/Ted,

We did meanwhile many lab scale trials and we could reduce the pickling time by 20%. Great results. We will be carrying out trials in our pickling lines next week.

That brings me to another question on further optimisation. For some of the annealed products we use scale conditioning bath with a solution of KMnO4, NaOH and water. The scale conditioning is then followed by water rinsing and 3 pickling baths. In the new condition, the scale conditioning will become a bottleneck (wrt time). Hence I am looking for options to reduce the conditioning time. My questions is;

1. Is there other chemistry available which is faster and can replace KMNO4 solution?
2. Can we completely discard scale conditioning bath and instead use couple of extra pickling baths (so 5 instead of 3)

Thanks for your advise.


Shishir Sable [returning]
- den haag

October 1, 2018

A. Hi Shishir!

Scale conditioning bath with KMnO4 and NaOH hasn't so many alternatives. I would try to make this scale removable in HCl, or make the HCl solution more aggressive in order to do that.

We had some problems with some steel grades, but usually we can process without any problem with HCl pickling with some acid degreaser and wetting agents.

Is this an option? If not, you don't have (as my knowledge let's me see) option for this kind of bath.

Best of luck!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

December 12, 2018

Q. Working with one of the largest steel group of India. We are having four acid tanks in our pickling line (Push-Pull type / cascading).
The following is the technical parameters currently being practiced. Is it okay?! Please suggest. We are using acid inhibitor also.

          Acid%   Iron(gm/L) Acid temp (°C)
Tank 1   (3-8)     200 max   70 - 80
Tank 2   (6-12)    150 max   70 - 80
Tank 3   (10-16)   100 max   70 - 80
Tank 4   (14-20)    50 max   70 - 80

Ashok Kumar Vishwakarma
Integrated steel plant - Odisha, India

Recovery of spent HCl

September 5, 2019

Q. Hi I am Kailash FreeLance Consultant in Steels. Now I am involved with a Project of Recovery of HCl from Spent Acid Pickled Liquor. I am starting from Having A Electro Dialysis Set up for Recovering HCl using an AEM in between SS Anode and MS Cathode. I am starting with 7.47 Amp/cm Sq. Current and Voltage up to 24 Volts. I am using a AEM of Acrylic Sheet of 200 Microns. Has anyone come across this type of Electrodialysis Process, We are planning to Arrive at an Equation for calculation of Equipment Dimensions also from our Prototype. Can I get the know how from any experienced person in this field.


KAILASH Subramanian
Metallurgical Consultant - CHENNAI, TamilNadu, INDIA

September 19, 2019

Q. I am a new chemical engineer. I would like to know why we should test Fe and other elements, and sulfate and sulfide in entrance acid? What problems will happen if those exist in HCl acid that charge in pickling line?

razieh gh
galvanize - Iran, qazvin

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