Interaction of 2-chloronaphthalene with high carbon iron filings (HCIF): Adsorption, dehalogenation and mass transfer limitations

Abstract

Interaction of 2-chloronaphthalene (2-CN) with high-carbon iron filings (HCIF) was studied in anaerobic batch systems, both under well-mixed and poorly-mixed conditions. In well-mixed conditions, partitioning of 2-CN between solid and aqueous phases was fast, resulting in rapid attainment of equilibrium. Equilibrium partitioning could be described by a Freundlich isotherm, C s = K . [ C a ] m , where C s (μmoles g −1 iron) and C a (μmoles L −1) were the solid and aqueous phase 2-CN concentrations, respectively. Isotherm parameters, m and K were determined to be 0.76 and 5.6 × 10 −2 (μmole g −1 iron)/(μmole L −1), respectively. Sorption ( k 2 ) and desorption ( k 3 ) rate constants were determined to be 5.60 × 10 −1 h −1 g −1 iron L and 10 h −1, respectively. Reductive dehalogenation of aqueous phase 2-CN occurred concurrently but at a slower rate, and could be described by the expression ( d C T / d t ) = − k 1 . M . ( C a ) N , where C T (μmoles L −1) was the total 2-CN concentration and M (g iron L −1) the concentration of HCIF. The values of k 1 and N were determined to be 1.09 × 10 −2 h −1 g −1 iron L and 1.647, respectively. In poorly mixed conditions, adsorption ( k 2 ) and desorption ( k 3 ) rate constants were 3.92 × 10 −5 h −1 g −1 iron L and 7 × 10 −4 h −1 , respectively, i.e., several orders of magnitude less than in well-mixed systems. The dehalogenation rate parameters, k 1 and N were determined to be 2.22 × 10 −4 h −1 g −1 iron L and 0.986, respectively, suggesting slower dehalogenation. These results highlight how mass-transfer limitations during the interaction between HCIF and 2-CN in poorly mixed systems, such as permeable reactive barriers (PRBs), can potentially impact the dehalogenation process.