Methylene blue removal from contaminated waters using heterogeneous catalytic ozonation promoted by natural zeolite: mechanism and kinetic approach.

This paper presents experimental results of a methylene blue removal system based on heterogeneous catalytic ozonation in the presence of natural zeolite. The effect of pH (2-10) and the presence of radical scavengers (acetate ions) on homogeneous and heterogeneous ozonation systems are assessed at laboratory scale. Results show that heterogeneous catalytic ozonation using natural zeolite increases methylene blue removal rate with respect to the single ozonation process at all pH values. The inhibitory effect of free-radical scavengers is impaired by zeolite, suggesting that methylene blue oxidation reactions take place mainly on the zeolite surface. The increase in methylene blue removal rate could be related to ozone interaction with hydroxyl groups present on the zeolite surface (S--OH2(+), S--OH, S--O(-)), which plays a key role in the reaction mechanism.