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Spent pickling acid treatment

February 25, 2010

Q. Hi
I work in HDG plant, using hydrochloric acid as a pickling solution, I try to design a process by which I can neutralize the spent pickling acid
I assume the following steps:
1- add calcium hydroxide or calcium carbonate
2- add a polymer as a flocculant
3- sedimentation by gravity
4- (water discharge) sedimentation overflow
5- sludge thickener and filter press (sludge dehydration)

But the output flow will contain calcium chloride and I do not know what is the environmental effect for it.

What about your recommendation?

M Saad
engineer - CAIRO, EGYPT

February 25, 2010

A. Hi, M. Will the wastewater be going to a municipal POTW or be discharged directly to surface waters? Usually CaCl will not be a problem for discharge as it is a simple salt water. The next step is a laboratory jar test to see what the effluent will actually be like, and comparing this to local requirements.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

February 28, 2010

Q. Thanks Ted,
Actually there is another approach.
It is to convert the ferrous chloride content in the spent acid to ferric chloride by HYPOCHLOROUS ACID (HOCl), it is cheap and effective and will react with the HYDROCHLORIC ACID in the spent solution to produce CHLORINE GAS (Cl2), CHLORINE will convert more ferrous chloride to ferric chloride, I think it will be a multistage unit and need good control system
What is your opinion about the principle and the availability to make such unit?


A. Hi. Sorry, I have no experience with that reaction.


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Pickling acid treatment and re-use

September 26, 2017

Q. We normally use lime neutralization to treat spent HCl and pass through a filter press. filtered cake is sent to an approved waste contractor. But the filtrate is consisting of high chloride, Zinc and some other chemicals we normally do not do further treatment. What are the well known and best method for treatment of waste water generated after neutralization? Is there any way of re-using this water in the Galvanizing process?

Prabath Gunasekara
Galvanizing QA Manager - Colombo

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