Azo Dye Decolorization by FeCl₂/Fenton: Optimizing Fe²⁺:H₂O₂ Ratio

Azo Dye Decolorization by FeCl₂/Fenton: Mechanism and Optimal Fe²⁺:H₂O₂ Ratio

Azo dye decolorization by Fenton (Fe²⁺ + H₂O₂) works through hydroxyl radical (•OH) attack on the azo bond (–N=N–) and benzene ring — the stable structure of Reactive Black 5 (CAS 17095-24-8). Optimal Fe²⁺:H₂O₂ ratio 1:9.6 at pH 3 achieves >95% decolorization in 15 minutes. For Reactive Blue 19 (CAS 2580-78-1), ratio adjustment is needed due to anthraquinone structure differences.

Fenton Mechanism for Azo Dye Decolorization

The Fenton reaction uses Fe²⁺ ions as catalyst to decompose H₂O₂ into hydroxyl radical (•OH) — the strongest oxidant in industrial wastewater treatment with redox potential E° = 2.80 V/SHE, higher than ozone (2.07 V) and chlorine (1.36 V).

General Fenton Reaction: Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + •OH

The classic Fenton reaction was described by Haber and Weiss in 1934: Fe²⁺ reduces H₂O₂ to produce hydroxyl radical (•OH) and Fe³⁺ ion. Rate constant k = 76 M⁻¹s⁻¹ at pH 3.0 — optimal pH because Fe²⁺ exists as free ions without precipitation.

Optimal Fe²⁺:H₂O₂ Ratio for Reactive Black 5

According to Lucas & Peres (2006, Dyes and Pigments), the optimal molar ratio is Fe²⁺:H₂O₂ = 1:9.6 with [H₂O₂]₀/[RB5]₀ = 4.9:1 at pH 3.0. Decolorization efficiency reaches 97.5% in 15 minutes.

Fe²⁺ Source Selection: Loc Thien FeCl₂

FeCl₂ solution 28.5%, density 1.348, pH 1-2. Lot-specific COA, ZDHC MRSL v3.1 Level 1 certification. Loc Thien — direct FeCl₂ manufacturer since 2016 — supplies liquid FeCl₂ via 5-30 ton tankers from 6 warehouses nationwide.

Case Study: Textile Mill 2,500 m³/day at Song Than Industrial Park

Switching from FeSO₄ to Loc Thien liquid FeCl₂ with Fe²⁺:H₂O₂ = 1:9.6 at pH 3.0: decolorization >95%, COD reduction from 1,500 mg/L to 350 mg/L, Fe²⁺ cost reduced 28%.

FAQ

Can Fenton decolorize azo dyes?

Yes. >95% decolorization efficiency proven in over 200 peer-reviewed studies since 1995.

What Fe²⁺:H₂O₂ ratio for Reactive Black 5?

Fe²⁺:H₂O₂ = 1:9.6 with [H₂O₂]₀/[RB5]₀ = 4.9:1 (Lucas & Peres, 2006).

What is optimal pH for Fenton?

pH 2.8-3.5, with ideal value of 3.0.

What FeCl₂ concentration does Loc Thien supply?

FeCl₂ solution 28.5%, density 1.348, pH 1-2. Lot-specific COA, ZDHC MRSL v3.1 Level 1.

🛒 Need FeCl₂ for Fenton process? Get FeCl₂ 28.5% quote — lot COA/ZDS, 5-30 ton tanker nationwide. Hotline 0979 891 929.