Aloha, fun & authoritative answers -- no cost, no passwords, no popups
(as an eBay Partner & Amazon Affiliate we earn from qualifying purchases)

Metal finishing Q&As since 1989

-----

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?
Thanks

M Saad
engineer - CAIRO, EGYPT

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.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 25, 2010

Q. Thanks Ted,
Actually there is another approach.
It is to convert the ferrous chloride content in the spent acid to ferric chloride [on eBay or Amazon] 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 [on eBay or Amazon], 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?
thanks

M.Saad
- CAIRO, EGYPT
February 28, 2010

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

Regards,

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

Pickling acid treatment and re-use

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
September 26, 2017

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories: