Phosphorous adsorption using Al3+/Fe3+-modified bentonite adsorbents-effect of Al3+ and Fe3+ combinations

This study focused on assessing the impact of using a variety of Al3+ and Fe3+ combinations to prepare modified bentonite adsorbents to remove phosphorous from water. Eight adsorbents with various Al3+ and Fe3+ combinations were used; four where prepared by adding Al3+ then Fe3+ to the bentonite, and four were prepared by adding Fe3+ then Al3+ to the bentonite. The adsorption capacities and kinetics of the eight adsorbents were experimentally assessed and compared. The experimental results best fitted the Langmuir adsorption isotherm model and the kinetic data best fitted the pseudo-second-order kinetic model. The Langmuir maximum adsorption capacities of the various adsorbents were in the range of 5.6-11.3 mg P/g adsorbent. The results suggested that combining Al3+ and Fe3+ in preparing the adsorbents improved the adsorption capacity and adsorption rate compared to using Al3+ alone or Fe3+ alone. Furthermore, equal amounts of Al3+ and Fe3+ resulted in the maximum phosphorous adsorption capacities. Adding Al3+ then Fe3+ to the bentonite resulted in adsorbents with higher adsorption capacities and adsorption rates compared to adding Al3+ then Fe3+ to the bentonite. The adsorbent prepared using Fe3+ alone achieved higher adsorption capacity and adsorption rate than the adsorbent prepared using Al3+ alone, which achieved the least adsorption capacity among all adsorbents. The results confirmed that using Al3+ and Fe3+ to modify bentonite and produce phosphorus adsorbents is technically feasible and is subject to optimization.