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

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, Cs=K.m[Ca]Cs=K.[Ca]m, where CsCs (μmoles g−1 iron) and CaCa (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 5.6×10−25.6×10−2 (μmole g−1 iron)/(μmole L−1), respectively. Sorption (k2k2) and desorption (k3k3) rate constants were determined to be 5.60×10−1 h−1g−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 (dCT/dt)=−k1.M.N(Ca)(dCT/dt)=−k1.M.(Ca)N, where CTCT (μmoles L−1) was the total 2-CN concentration and M (g iron L−1) the concentration of HCIF. The values of k1k1 and N   were determined to be 1.09×10−2 h−1g−1 iron L and 1.647, respectively. In poorly mixed conditions, adsorption (k2k2) and desorption (k3k3) rate constants were 3.92×10−5 h−1g−1 iron L and 7×10−4 h−17×10−4 h−1, respectively, i.e., several orders of magnitude less than in well-mixed systems. The dehalogenation rate parameters, k1k1 and N   were determined to be 2.22×10−4 h−1g−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.

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