Adsorption capacity of iron- or iron–manganese-modified zeolite-rich tuffs for As(III) and As(V) water pollutants

In this study, the sorption properties of iron- and iron–manganese-modified clinoptilolite-rich tuffs used to remove As(III) and As(V) from aqueous solutions were investigated. Factors taken into account included the initial concentration of the arsenic in the aqueous media, the concentration of Mn(II) in the Mn–As bicomponent solutions, and the pH and concentration of the iron and iron–manganese in the zeolitic materials. The modified zeolitic rocks were analyzed via scanning electron microscopy, and their elemental composition was determined via energy-dispersive X-ray spectroscopy EDS. The aggregates of the non-zeolitic material (iron and iron–manganese chemical species) were observed via transmission electron microscopy. X-ray diffraction patterns were also obtained to determine the components of the unmodified and iron and iron–manganese modified zeolites. All the analyses of As(III) and As(V) adsorption by the modified zeolites were carried out in a batch system. Arsenic and manganese were analyzed using an absorption atomic spectrophotometer, and a hydride generator was used for the arsenic analysis. The pH was measured before and after the contact of the arsenic solution with the zeolitic materials. Aggregates of iron or iron–manganese species on the surface of the iron and iron–manganese-modified zeolitic materials were observed. The arsenic adsorption processes were best described by the Langmuir–Freundlich model. In general, the results suggested that the removal of As(III) and As(V) by the zeolitic materials is influenced by the nature of the arsenic chemical species, the origin of the natural zeolite and the textural characteristics of the iron and iron–manganese clinoptilolite-rich tuff. The presence of manganese in the iron–manganese-modified crystalline zeolite network improved the adsorption capacity of the zeolitic material for As(III) and, to a lesser degree, for As(V). It was also found that the Mn(II) from the Mn–As bicomponent aqueous solutions and the pH affect the capacity of the unmodified and iron- or iron–manganese-modified natural zeolite to adsorb As(III) or As(V).