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Hydrolysis

KMPStriple salt, can be degraded abiotically by hydrolysis to H2O2 and by disproportionation to O2 and to H2O. In both cases, potassium and hydrogensulfate ions are formed.

KHSO5 + H2O -> K+ + HSO4- + H2O2 (hydrolysis)

KHSO5 -> K+ + HSO4- + ½ O2 (disproportionation)

The degradation of KMPS triple salt in aqueous solution is pH and temperature dependant.

In the study, the degradation of KMPS triple salt was measured by determining the loss of active oxygen by iodometric titration. As the hydrolysis of KHSO5 does not result in a net loss in active oxygen (see equation above) but only in a transfer of the active oxygen from KHSO5 to water, which leads to the formation of hydrogen peroxide, only the degradation by disproportionation was determined in the above test.

The degradation of KMPS in aqueous solution is pH and temperature dependant. Degradation is accelerated with increasing temperature and increasing pH. While KMPS has a half-life of above 800 h (at 20°C) in a buffered solution of pH 4, the half-life at pH 7 is 145 hours and only 2.8 hours at pH 9. Degradation in seawater is considerably faster (DT50 = 5.5 hours, pH 8.0-8.2, 20°C) than in freshwater (DT50 = 215 hours, pH 7.8-8.2, 20°C).

The reason for the faster degradation of KMPS in seawater is the so-called Haber-Will-Statter Reaction. In this, the sodium chloride of the seawater is oxidised by KMPS so that chlorine is released.

HSO5- +2Cl- + 2H+ -> HSO4- + Cl2 +H2O

The chlorine reacts with water to form hypochlorous acid:

Cl2 +H2O -> HOCl +HCl

Hypochlorous acid (HOCl) is only of transient nature, hypochlorous acid is extremely rapidly eliminated in the environment due to reaction with ammonia and organic material which act as reductants.

In the recent study on the “Depletion of Potassium Monopersulfate in Synthetic Pool Water”, it was shown that the decomposition of KMPS triple salt in water is very dependent on the presence of oxidisable contaminants. The addition of a ‘body fluid analog’ to the synthetic pool water used in this laboratory test reduced the half-life for decomposition of KHSO5 from ca. 120 hours (synthetic pool water without ‘body fluid analog’) to ca. 3 hours. This is explained by the consumption of KHSO5 in many different oxidation reactions with reduced amine substrate components of the added ‘body fluid analog’, according to the general reaction:

KHSO5 + X -> KHSO4 + X=O.

It can be assumed that KHSO5 is degraded at similar rates in natural waters, such as pond and river water. The higher the concentration of oxidisable organic substrate is in the water, the faster KHSO5 will be degraded.