STUDY OF THE OZONE-MANGANESE REACTION AND THE INTERACTIONS OF DISULFONATE INDIGO CARMIN OXIDIZED MANGANESE FORMS AS A FUNCTION OF PH

Ozone used in preoxidation for water treatment processes allows the re moval of inorganic compounds such as iron and manganese. The reactivit y of ozone and manganese has been studied in a wide pH range. However, some difficulties appeared in the determination of the different spec ies because of secondary reactions, the main difficulty being the inte raction between indigo (used to determine ozone concentration) and man ganese dioxide formed during ozonation. In order to define the optimal conditions allowing the minimization of this interaction, the mechani sm of the reaction between ozone and manganese has been studied at var ious pH levels. The oxidized manganese species have been characterized as permanganate ion at pH = 2 and manganese dioxide at pH = 4-8. Thes e compounds were able to react with indigo, inducing a regeneration of Mn2+. A pH value close to 8 allowed the best evaluation of the kineti c parameters of the reaction between ozone and manganese, the indigo s econdary reaction being minimized.