Adsorption properties of synthetic iron oxides: as(V) adsorption on goethite (alpha-FeOOH)

Abstract: The iron in the form of hydroxides and oxide-hydroxides are relatively
abundant in nature. They are ubiquitous in soils and rocks, lakes and
rivers, on the sea floor, in air and in organisms. One of the several
applications of the iron oxides is the implementation of the iron oxides as
adsorbents of organic and inorganic compounds in the soils and sediments.
Iron oxide has been, for instance, proposed for remediation of arsenic
contaminated soils due to their adsorption capacity. In the present work,
three different iron oxides, goethite, 6-line ferrihydrite and hematite,
were synthesized and their adsorption properties were characterized
performing BET N2 adsorption measurements. The adsorption capacities of
these iron oxides followed the trend: ferrihydrite >goethite > hematite,
agreeing with the information found in the literature. As goethite is the
most abundant iron oxide in soils, synthetic goethite was chosen as a model
system in order to study As(V) adsorption on iron oxides in the soil. The
aim of the experiments was to determine adsorption isotherms of As(V) on
goethite at different pHs and at room temperature. Unfortunately, the
quality of the adsorption isotherms was poor and it was found that the
ionic strength is an important factor in order to obtain reliable adsorption
data for the system.