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Neutralizing Problem with Pickling Wastewater

Dear Sir,

I have a problem with neutralizing process of pickling wastewater. Our process is to remove the rust from "C" Channel (Mild Steel) by using 30% conc. HCl. By doing this, the effluent generated is of lower pH (less than 1). So we have a problem with neutralising. We used hydrated lime [affil links] (80%) for neutralising, but it is not get neutralised well. Please suggest the basic problem of this and what is the solution.

If you need further information, then please let us inform, so that we can forward it.

I wish I could get the solution from your side.

Thanking you.

Jignesh Dabhade
Director - India
2007

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Due to the low solubility of hydrated lime, greater mixing and longer reaction time may be necessary for neutralization. The reaction rate decreases as pH rises. With incomplete reaction, a 10% excess of lime is typically used in reaching the pH setpoint, which after further reaction time results in overly high pH downstream.

One improvement uses low cost lime for primary neutralization, e.g., to pH 3-3.5, and then highly soluble NaOH solution for a precise final pH adjustment.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007