Honeywell UDA2182 15.5Appendix D Chrome Waste Treatment, Use of Chromates, Corrosion inhibition

Models: UDA2182

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Appendices

15.5Appendix D – Chrome Waste Treatment

Use of Chromates

Corrosion inhibition

Chromates are used as corrosion inhibitors in cooling towers and in metal-finishing operations including bright dip, conversion coating, and chrome plating.

Necessity for removal of chromium ion from wastewater

The wastewater form rinse tanks, dumps, and cooling tower blowdown contains toxic soluble chromium ion, Cr+6, which must be removed, typically to a level less than 0.5 ppm before discharge.

Technique for chrome removal

The technique most often used for this chrome removal is a two-stage chemical treatment process. The first stage lowers the pH and adds the reducing agent to convert the chrome from soluble Cr+6 to Cr+3. The second stage neutralizes the wastewater, forming insoluble chromium hydroxide, which can then be removed.

Consistent treatment and stable control in this type of process requires well-mixed reaction tanks with enough volume for adequate retention time (see Figure 15-5). Retention time is calculated by dividing the filled or usable tank volume by the waste flowrate. Typically, it is ten minutes or more.

ACID

 

BISULFITE

ON/OFF

 

 

ORP

CHROME

WASTE

ON/OFF

pH

CAUSTIC

PROPORTIONAL

RECORDER

 

Ph ANALYZER/

CONTROLLER

NOTE: The separate pH and ORP measurements and control shown in the first stage may be handled with a single UDA2182 Analyzer with combined input

POLYELECTROLYTE

REDUCTION

NEUTRALIZATION

SETTLING

SLUDGE

 

 

 

Figure 15-5 Chrome Treatment System

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UDA2182 Universal Dual Analyzer Product Manual

January 2009

Page 220
Image 220
Honeywell UDA2182 manual 15.5Appendix D Chrome Waste Treatment, Use of Chromates, Corrosion inhibition