Summary for spent pickling acid treatment Discussion
Spent pickling acid treatment is discussed as a practical wastewater question for an HDG plant using hydrochloric acid. M. Saad proposed neutralizing spent acid with calcium hydroxide or calcium carbonate, then flocculating, settling, thickening, and filter-pressing the sludge, but asked about the environmental impact of the resulting calcium chloride. Ted Mooney, P.E. replied that the key issue is where the wastewater will go: a municipal POTW or direct surface-water discharge. He said calcium chloride is usually not a problem because it is essentially simple salt water, but emphasized that the next step should be a laboratory jar test and comparison with local discharge requirements. A later question from Prabath Gunasekara described lime neutralization of spent HCl with filter-pressed sludge disposal, but noted the filtrate still contains high chloride, zinc, and other chemicals and asked about further treatment and possible reuse in galvanizing. The thread does not provide a detailed follow-up solution for reuse.
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
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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 [affil link] 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 [affil link] , 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
Need quick confidential answers? $25
Need project assistance? $100/hr.
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