DEHALOGENATION OF 2-CHLORONAPTHALENE BY CAST IRON

摘要

Aqueous 2-chloronapthalene was contacted with cast iron in batch systems, resulting in an initial rapid increase in the sorbed 2-chloronapthalene concentration (C_s) followed by a slow decline, and an initial rapid decline in the aqueous 2-chloronapthalene concentration (C_a) followed by a slower decline. The initial rapid partitioning of 2-chloronapthalene to the solid phase was due to its adsorption on elemental carbon present on the cast iron surface, while the residual aqueous phase 2-chloronapthalene underwent reductive dehalogenation at a slower rate through interaction with the metallic iron surface. The overall rate of change of total 2-chloronapthalene concentration (C_T = C_s + C_a) with time, i.e., ((dC_T)/(dt))could be described by the expression, -k_1 · M · (C_a)~n, where Mis the concentration of cast iron. The values of k_1 and n were determined to be 1.576 x 10~(-5) hr~(-1) g~(-1) iron L and 1.945 respectively. Equilibrium partitioning of 2-chloronapthalene between solid and aqueous phases could be described by a Freundlich isotherm, C_s = K · [C_a]~m, where m and K were determined to be 0.55 and 4.92 x 10~(-3) Lg~(-1). Considering K to be the ratio of the adsorption (k_2) and desorption (k_3) rate constants, expressions were developed for describing the evolution of C_s and C_a with time. Putting k_3 = 1 hr~(-1) in these expressions resulted in adequate model fit to the experimental data. Napthalene was identified as the major dehalogenation by-product, with greater than 99 percent of the naphthalene produced partitioning to carbon present on the cast iron surface. No competition between 2-chloronapthalene and naphthalene for adsorption on the carbon surface was observed, suggesting non-specific adsorption of these compounds restricted only by the physical size of the molecules and the available carbon surface area.