title: Kinetics of zero-valent iron reductive transformation of the anthraquinone dye Reactive Blue 4.
abstract: The effect of operational conditions and initial dye concentration on the reductive transformation (decolorization) of the textile dye Reactive Blue 4 (RB4) using zero-valent iron (ZVI) filings was evaluated in batch assays. The decolorization rate increased with decreasing pH and increasing temperature, mixing intensity, and addition of salt (100gL(-1) NaCl) and base (3gL(-1) Na2CO3 and 1gL(-1) NaOH), conditions typical of textile reactive dyebaths. ZVI RB4 decolorization kinetics at a single initial dye concentration were evaluated using a pseudo first-order model. Under dyebath conditions and at an initial RB4 concentration of 1000mgL(-1), the pseudo first-order rate constant (kobs) was 0.029+/-0.006h(-1), corresponding to a half-life of 24.2h and a ZVI surface area-normalized rate constant (kSA) of 2.9x10(-4)Lm(-2)h(-1). However, as the initial dye concentration increased, the kobs decreased, suggesting saturation of ZVI surface reactive sites. Non-linear regression of initial decolorization rate values as a function of initial dye concentration, based on a reactive sites saturation model, resulted in a maximum decolorization rate (Vm) of 720+/-88mgL(-1)h(-1) and a half-saturation constant (K) of 1299+/-273mgL(-1). Decolorization of RB4 via a reductive transformation, which was essentially irreversible (2-5% re-oxidation), is believed to be the dominant decolorization mechanism. However, some degree of RB4 irreversible sorption cannot be completely discounted. The results of this study show that ZVI treatment is a promising technology for the decolorization of commercial, anthraquinone-bearing, spent reactive dyebaths.
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Epolito
authors.forename: Hanbae
authors.initials: H
authors.lastname: Yang
authors.forename: Lawrence A
authors.initials: LA
authors.lastname: Bottomley
authors.forename: Spyros G
authors.initials: SG
authors.lastname: Pavlostathis
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003116:Color; D004396:Coloring Agents; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D010084:Oxidation-Reduction; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D013783:Textile Industry; D014227:Triazines / Q000737:chemistry*
chemical_list: D004396:Coloring Agents; D014227:Triazines; C036598:procion blue MX-R; D007501:Iron