Artículo de publicación ISIChemical oxidation using ozone in the presence of appropriate catalysts offers an attractive option for removing poorly biodegradable pollutants. However, the effect of such catalysts on ozone aqueous decomposition is not well documented. This study compares experimental results on ozone aqueous decomposition promoted by zeolite and volcanic sand. These are two low costs natural materials identified as suitable catalysts for heterogeneous ozonation. The effects of pH (2-8) and free radical scavengers (acetic acid) on the dissolved ozone decay rate are evaluated at laboratory scale. Results show that the ozone decay rate increases in the presence of natural materials tested here. Under alkaline conditions, the effect of free radical scavengers on ozone self-decomposition is significantly reduced when such materials were present, particularly in the case of volcanic sand. Results suggest that ozone aqueous decomposition in the presence of zeolite and volcanic sand take place mainly on the natural material surface. The presence of metal oxides in zeolite and volcanic sand might catalyse ozone decomposition into more active radicals, thus enhancing the oxidation of organic pollutant.