ENVE 420Industrial Pollution Control

NEUTRALIZATION

Dr. Aslıhan Kerç

• Many industrial wastes contain:- Acidic- Alkaline materials

Neutralization is required prior to:- discharge to receiving waters- chemical or biological treatment

Need for neutralization

Neutralization requirement for biological treatment

• For biological treatment pH ?6.5 – 8.5

Biological process itself provides a neutralization and buffer capacity due to carbon dioxide production.

Requirement for pre-neutralization

Types of Neutralization Processes

• Mixing acidic and alkaline waste streamsRequires sufficient equalization capacity

• Neutralization using chemicals

Neutralization of Acid Wastes Through Limestone Beds

• Can be designed as upflow or downflow• Max hydraulic rate for downflow (unit ?)

4 x 10-2 m3/min m2

Maximum H2SO4 concentration 0.6%To avoid coating of limestone with non-

reactive CaSO4

To avoid excessive CO2 evolution which limits complete neutralization

Neutralization of Acid Wastes Through Limestone Beds

vf = 2 – 2.4 m3/m2 hr

Up –flow beds higher hydraulic loading rates can be used

vf = 3 - 40 m3/m2 hr

(~10)

Mixing Acid Wastes with Lime Slurries

• Lime• Slaked lime• NaOH• Na2CO3

• NH4OH

• Mg(OH)2

This method is useful below pH 4.2

Mixing Acid Wastes with Lime Slurries

• In lime slaking reaction is accelerated by heat and agitation

• Neutralization can be defined by basicity factor.

• Titration of 1 g sample with excess HCl, boiling 15 minutes followed by back titration with 0.5N NaOH to phenol phtalein end point

Neutralization of Basic (Alkaline) Wastes

• Any strong acid can be used for neutralizationSulfuric acid, Hydrochloric acid

• Using flue gas for neutralization?Flue gas that contain 14% CO2 can be used

Bubbled through the waste CO2 H2CO3 reacts with waste

Slow reaction. May be sufficient for pH adjustment ~ pH 7-8

• Can also be applied in spray towers

• Stepwise addition of chemicals• Selection criteria for neutralization agents:

- Reaction rate- Sludge production and disposal- Safety- Ease of handling- Cost, Equipment cost

- Side reeactions (dissolved salts, scale formation, heat produced)- Effect of overdosage