Reductive degradation of azo dyes in aqueous solution by zero-valent iron

Kinetics of zero-valent iron remediation of two azo dyes in aqueous solution were investigated. Both show pseudo first-order reaction kinetics. Typical apparent reaction rate constants (k) are 0.70 min"' at 33.3 revolutions per second, k decreases with both increased pH and initial dissolved oxygen content increased over 5 mg l", but increases with both increasing iron conc­ entration and mixing speed. The increase with iron concentration is linear at 3 x 10 s mg 1"' correlation, k increases linearly with the inverse square root of mixing speed—corresponding directly with increasing k with decreasing thickness of adhering boundary layer. Half-lives correlate well with values reported in the literature. The mass transfer limitation and surface dependency of these heterogeneous reactions is demonstrated.