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Published byCatherine Bouldin Modified over 9 years ago
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ENVE 420 Industrial Pollution Control NEUTRALIZATION Dr. Aslıhan Kerç
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Many industrial wastes contain: - Acidic - Alkaline materials Neutralization is required prior to: - discharge to receiving waters - chemical or biological treatment Need for neutralization
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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
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Types of Neutralization Processes Mixing acidic and alkaline waste streams Requires sufficient equalization capacity Neutralization using chemicals
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Neutralization of Acid Wastes Through Limestone Beds Can be designed as upflow or downflow Max hydraulic rate for downflow (unit ?) 4 x 10 -2 m 3 /min m 2 Maximum H 2 SO 4 concentration 0.6% To avoid coating of limestone with non- reactive CaSO 4 To avoid excessive CO 2 evolution which limits complete neutralization
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Neutralization of Acid Wastes Through Limestone Beds v f = 2 – 2.4 m 3 /m 2 hr Up –flow beds higher hydraulic loading rates can be used v f = 3 - 40 m 3 /m 2 hr (~10)
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Mixing Acid Wastes with Lime Slurries Lime Slaked lime NaOH Na 2 CO 3 NH 4 OH Mg(OH) 2 This method is useful below pH 4.2
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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
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Neutralization of Basic (Alkaline) Wastes Any strong acid can be used for neutralization Sulfuric acid, Hydrochloric acid Using flue gas for neutralization? Flue gas that contain 14% CO 2 can be used Bubbled through the waste CO 2 H 2 CO 3 reacts with waste Slow reaction. May be sufficient for pH adjustment ~ pH 7-8 Can also be applied in spray towers
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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
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