Degradation of azo and anthraquinone dyes by a low-cost Fe 0/air process

Abstract

Degradation of two different kinds of dyes, anthraquinone Reactive Blue 4 (RB4) and azo Reactive Black 5 (RB5), by low-cost zero valent iron (Fe 0) in a N 2 bubbling system (Fe 0/N 2 process) and air bubbling system (Fe 0/air process) was investigated. The operating parameters, including initial solution pH, dye concentration and Fe 0 dose, were also evaluated. The Fe 0/air process shows a higher decolorization rate compared to the Fe 0/N 2 process. Both RB4 and RB5 solutions at 100 mg L −1 were rapidly decolorized by Fe 0/air process within 9 and 3 min, respectively, at initial solution pH 3, Fe dose of 50 g L −1 and air flow rate of 5 L min −1. The optimal initial solution pH was 3. The Fe 0/N 2 process removed only <17% of COD. However, significant COD removals were achieved for RB 4 (87%) and RB5 (43%) by the Fe 0/air process after 9 min of treatment. Spectra analysis results indicated that the Fe 0/N 2 process destroyed only the anthraquinone group (A 594) for the RB4 solution and decreased the azo (A 596) and naphthalene group (A 310) for the RB5 solution. However, the Fe 0/air process rapidly removed A 594, A 370, A 296 (anthraquinone group) and A 256 (aromatic and dichlorotriazine group) for RB4, and A 597 and A 310 (naphthalene group) for RB5. The results indicated that the low-cost Fe 0/air process is a potential technique for rapid degradation of RB4 and RB5 solutions.