Sulfur mustard destruction using ozone, UV, hydrogen peroxide and their combination.

Numerous methods are used for destruction of sulfur mustard. Oxidation is one of those methods. There have been only limited data concerning application of the advanced oxidation technologies (AOTs) for mustard destruction available before. In this study sulfur mustard oxidation rate depending on kind of the oxidative system and process parameters used was assessed using selected AOT. The following were selected for mustard oxidation: ozone (O(3)), UV light (UV), hydrogen peroxide (H(2)O(2)); double systems: UV/O(3), UV/H(2)O(2), and O(3)/H(2)O(2); a triple system: O(3)/H(2)O(2)/UV and Fenton reaction. Effectiveness of the selected AOT methods has been evaluated and the most suitable one for mustard destruction was chosen. Using ozone in various combinations with hydrogen peroxide and UV radiation mustard can be destroyed much quicker comparing to the classical oxidizers. Fast mustard oxidation (a few minutes) occurred in those systems where ozone alone was used, or in the following combinations: O(3)/H(2)O(2), O(3)/UV and O(3)/H(2)O(2)/UV. When those advanced oxidation technologies are used, mustard becomes destroyed mainly in course of the direct oxidation with ozone, and reactions of mustard with radicals formed due to ozone action play a secondary role. Rate of sulfur mustard oxidation in the above mentioned ozone-containing oxidative systems decreases with pH value increasing from 2 to 12. Only when pH value of reaction solutions is close to pH 5, mustard oxidation rate is minimal, probably due to "disappearance" of radicals participating in oxidation in this pH. Sulfur mustard can be most effectively destroyed using just ozone in pH 7. In that case mustard destruction rate is only slightly lower than the rate achieved in optimal conditions, and the system is the simplest.

Photoassisted reaction of sulfur mustard under UV light irradiation.

The photoassisted reaction of sulfur mustard (HD) in both the vapor and droplet states under UV light irradiation was investigated. It was found that HD molecules in either the gas or the condensed phase could be easily converted into other chemicals under the irradiation of a germicidal lamp. The products detected upon reaction suggested that the photoassisted reaction of HD molecules in the gas phase produced a kind of nontoxic heavy polymer, and this method seemed to be applicable for decontamination of air. Nevertheless, the photoassisted reaction of HD droplets would produce a series of products containing -SCH2CH2Cl or -OCH2CH2CI groups, some of which were proven to be even more toxic than HD. Therefore, it was not an effective method forthe decontamination of HD droplets. The obtained experimental results would indicate that two possible pathways might be involved in the destruction of HD molecules: (1) HD molecules may undergo a photochemical reaction upon absorbing photons of sufficient energy, which leads to cleavage the C-S bond in HD molecules at the primary step, or (2) HD molecules could be oxidized by the photogenerated ozone.