title: Kinetics of cyanogen chloride destruction by chemical reduction methods.
abstract: In this study, membrane introduction mass spectrometry (MIMS) was applied to evaluate the kinetics of cyanogen chloride (ClCN) destruction by chemical reduction methods, using thiosulfate, sulfite, metabisulfite, ferrous ions and zero-valent iron at various concentrations and pH. The ClCN destruction followed second-order reaction kinetics in all cases of using sulfur compounds, though the second-order rate constants varied substantially from approximately 0.3-25.7 M(-1)s(-1) under different experimental conditions. The destruction of ClCN was primarily attributable to the chemical reduction pathway. Hydroxide-assisted ClCN hydrolysis was only significant at pH 9 and also when the observed reduction rate was relatively slow. The second-order rate constants achieved by sulfur(IV) compounds in the form of sulfite were found to be higher than those obtained with thiosulfate and S(IV) compounds in the form of bisulfite. Ferrous ions and zero-valent iron demonstrated slow or no ClCN reduction up to dosages of 1000 mgL(-1) and 100 gL(-1), respectively. These findings suggest that applying moderately high dosages of S(IV) compounds under neutral or alkali conditions with sufficient contact time is required for wastewater ClCN destruction. In addition, ClCN losses during long-term preservation with excess reducing sulfur compounds prior to analysis can be substantial and should be avoided.
authors.affiliation: Department of Civil Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. cechii@ust.hk
authors.forename: Chii
authors.initials: C
authors.lastname: Shang
authors.forename: Yinan
authors.initials: Y
authors.lastname: Qi
authors.forename: Li
authors.initials: L
authors.lastname: Xie
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.forename: Xin
authors.initials: X
authors.lastname: Yang
mesh_terms: D003486:Cyanides / Q000737:chemistry / Q000302:isolation & purification*; D005296:Ferrous Compounds / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D006878:Hydroxides / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D010084:Oxidation-Reduction; D013447:Sulfites / Q000737:chemistry; D013885:Thiosulfates / Q000737:chemistry; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D003486:Cyanides; D005296:Ferrous Compounds; D006878:Hydroxides; D013447:Sulfites; D013885:Thiosulfates; C014430:cyanogen chloride; C030981:metabisulfite; D007501:Iron