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

Abstract

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.

Keywords:

• Phosphorus removal
• Al³⁺/Fe³⁺-modified bentonite
• Adsorption
• Adsorption capacity
• Adsorption rate