Improvement of As(V) Adsorption by Reduction of Granular to Micro-Sized Ferric Hydroxide

The remediation of groundwater containing arsenic is a problem that has been addressed using adsorption processes with granulated materials in columns, but the remediation itself could be improved by using micro-sized adsorbents in stirred systems. In this study, arsenate (As(V)) batch adsorption experiments were performed using granular ferric hydroxide (GFH) and two derived micro-sized materials. Reduced-size adsorbents were produced by energetic ball milling, giving final sizes of 0.1-2 mu m (OF-M samples) and ultra-sonication, producing final sizes of 2-50 mu m (OF-U samples). Equilibrium isotherm studies showed that the Langmuir model was a good fit for the three sorbents, with the highest maximum adsorption capacity (q(max)) for OF-U and the lowest for OF-M. The adsorption of the two groundwater samples occurred according to the obtained equilibrium isotherms and indicated the absence of interfering agents for the three adsorbents. Batch kinetics tests in stirred beakers followed a pseudo second-order model and indicated that the kinetics of the OF-U sorbent was faster than the kinetics of the GFH sorbent. The tests also showed an increase in the q(e) values for the reduced-size sorbent. The application of ultrasonication to the GFH produced an increase of 23% in the q(max) and b term and an increase of 34-fold for the kinetic constant (k(2)) in the stirred batch systems tested. These results suggest that this new approach, based on ultra-sonication, has the potential for improving the adsorption of arsenic in groundwater.