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Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
January, 2003

Lime or Sodium Hydroxide?

Q. How are the majority of metal finishers treating their process wastewater? (i.e. Are they using lime or caustic and why might they prefer one over the other?) Any and all information that you can provide regarding wastewater treatment in the metal finishing industry would be very helpful to me. Thanks!

A. I know some have used lime in the past and I have used it for acid neutralization (especially HF), but the 50% liquid sodium hydroxide is much easier to dispense and control than the lime. It also produces less sludge (typically). Also some are using magnesium hydroxide (also a solid or powder feed) instead of lime since it produces several times less sludge than lime, and it it has an upper pH limit of 10, which makes it very safe to use and hard to over treat.



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