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The oxidation of the MC-LR by Fe(VI) followed a second-order kinetics (-d[Fe(VI)]/dt = kapp[Fe(VI)][MC-LR]). The values of kapp showed a pH dependence with values ranged from 1.3 ± 0.1 × 102 mol−1 Ls−1 at pH 7.5 to 8.1 ± 0.08 mol−1 Ls−1 at pH 10.0. This indicates a rapid degradation of MC-LR (Jiang et al. 2014). The comparison of the rate constants for the oxidation of MC-LR with different oxidants at neutral pH is presented in Table 1 (Kull et al. 2004; Acero et al. 2005; Onstad et al. 2007; Rodríguez et al. 2007). Ozone showed the highest value of kapp (Table 1). The efficient attack on the double bond of MC-LR by ozone may be responsible for orders of magnitude faster reactivity in comparison with other oxidants. The increasing order of the reactivity with MC-LR may be presented as chlorine dioxide < chlorine < Fe(VI) < Mn(VII) < O3 (Table 1). The half-life (t1/2) for oxidizing MC-LR by O3 is less than a second whereas Fe(VI), Mn(VII), and chlorine oxidize MC-LR in seconds. Ozone, chlorine, Mn(VII), and Fe(VI) are thus suitable oxidants to eliminate MC-LR in water treatment.

Table 1

Second-order rate constants and half-lives for oxidation of MC-LR by different oxidants at 22–25 °C

  k,kapp M−1s−1t1/2
OxidantSpeciesM−1s−1pH 7.0
Ferrate(VI)a HFeO4 (3.9 ± 0.2) × 102 2.5 × 102 155 s 
(pK3 = 7.23)f FeO42− 8.0 ± 2.0   
Permanganateb MnO4 3.6 × 102 3.6 × 102 107 s 
Chlorinec HOCl 1.2 × 102 7.2 × 101 504 s 
(pKa = 7.54)g OCl 6.8   
Chlorine dioxided ClO2 1.0 1.0 13.1 h 
Ozonee O3 4.1 × 105 4.1 × 105 0.08 s 
  k,kapp M−1s−1t1/2
OxidantSpeciesM−1s−1pH 7.0
Ferrate(VI)a HFeO4 (3.9 ± 0.2) × 102 2.5 × 102 155 s 
(pK3 = 7.23)f FeO42− 8.0 ± 2.0   
Permanganateb MnO4 3.6 × 102 3.6 × 102 107 s 
Chlorinec HOCl 1.2 × 102 7.2 × 101 504 s 
(pKa = 7.54)g OCl 6.8   
Chlorine dioxided ClO2 1.0 1.0 13.1 h 
Ozonee O3 4.1 × 105 4.1 × 105 0.08 s 

aThis study and half-life at dose [Fe] = 1 mg L−1 or [FeO42−] = 2.2 mg L−1.

bFrom Rodríguez et al. (2007) and half-life at dose [Mn] = 1 mg L−1 or [MnO4] = 2.2 mg L−1.

cValues at pH 7.2 taken from Acero et al. (2005) and half-life at [HOCl] = 1 mg L−1.

dFrom Kull et al. (2004) and half-life at [ClO2] = 1 mg L−1.

eFrom Onstad et al. (2007) and half-life at [O3] = 1.0 mg L−1.

fAt 25 °C.

gAt 25 °C from Carrell Morris (1966).

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