Sodium Hypochlorite - Bleach Stability and Filtration
By Gilbert Gordon, Miami University, Oxford, OH
Novatek, A Division of EBB, LLC
Liquid Sodium Hypochlorite (bleach) is an alternative to gaseous chlorine for water
disinfection. Commercially produced liquid bleach typically contains excess caustic
and possibly dissolved transition metal ions. In basic solution, bleach (OCL(-)
decomposition to form chlorate ion has been shown to be a second-order process (Rate
= k2[OCl-]2). The formation of oxygen from decomposing
bleach is a slow side reaction in solutions of very pure sodium hypochlorite. However,
in the presence of transition metal ions, the rate of bleach decomposition by the
oxygen pathway is increased.
The chemistry of the catalytic decomposition of bleach is complex. In general, nickel
ion appears to effectively catalyze decomposition either alone or in combination
with other transition metal ions (Ni > Co > Cu > Fe > Mn > Hg). The addition of
Mn2+ and Ni2+ together produced the highest rate of decomposition
when compared to other transition metal ion combinations. The initial rate of decomposition
with 10.3 mg/L Cu2+ is increased by a factor of 11 relative to Sodium
Hypochlorite (NaOCl) containing 1.03 mg/L Cu2+. This indicates that the
decomposition of Sodium Hypochlorite is roughly first-order in Cu2+.
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