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Treatment of Acidic Rinsewater with Hydrated Lime

2004

We use HCl to remove the oxide from steel rod and wire. As a result an acidic rinsewater is produced that has varying amounts of HCl and FeCl. Treatment is with a hydrated lime [affil links] slurry followed by a reaction tank before going to a clarifier. It has always been hard to stabilize the treated rinsewater pH to remain within the POTW requirements (6 to 9). Is there some good reference materials or guidelines to use for lime treatment of acidic rinsewaters. Especially information on location of pH sensors/reaction tank sizing, etc.

Thanks,

Tom Couch
Steel Wire Manufacture - Rome, GA, USA

It takes a bit of time for the neutralization to take effect. A quick guess is that you do not have adequate mixing or adequate retention time in the mixing tank. a second guess is that you arenot calibrating or cleaning the tank pH probe often enough. 6-9 is a large range that should be a piece of cake to do. 6-8 would be 10 times harder to do, as pH is a logarithim.

James Watts
- Navarre, Florida
2004

Tom,

Lime slurry while pretty efficient, can be a nightmare on your equipment. pH probes are fouling out frequently, I'm guessing. Would it be possible to neutralize with caustic soda [affil links] in your application? Reaction time is quicker and (in my application) is easier to control and not near the mess of lime.

Good Luck

Trent Kaufman
electroplater - Galva, Illinois
2004

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2004

If the principal problem is pH control, and you have sufficient reaction time, magnesium hydroxide is perfect because it can't drive the pH too alkaline, and it's very safe (milk of magnesia)--but it takes hours. Caustic is quicker and easier as Trent notes.

But if you need to get dissolved metals low, nothing (and no combination) beats lime in most cases. But it's an unholy mess from a maintenance perspective.

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