Phosphate Adsorption Removals by Five Synthesized Isomeric α-, β-, γ-FeOOH

The FeOOH polymers commonly existing in nature are potential adsorbent materials for phosphate ions (P). In this work, five synthesized isomeric α-, β-, γ-FeOOH (goethite, akaganéite and lepidocrocite samples of Gth1 and Gth2, Aka1 and Aka2, and Lep, respectively) were used to investigate their P adsorption characteristics and mechanisms, under various times, the levels of phosphate and FeOOH, solution pH, temperatures, and coexisting anions. Under 1.0 g/L of dosage and 20 mg/L of P, Lagergren second order rate model could describe well kinetic behaviors of P adsorptions for FeOOH (R 2 being 0.999) at pH 7. Phosphate adsorption behaviors could be described well by both Langmuir (R 2 being 0.968 − 0.999) and Freundlich (R 2 being 0.945 − 0.988). The maximum adsorption capacities (mg/g) were 8.09(Gth1), 6.5(Gth2), 5.49(Aka1), 12.9(Aka2), and 7.36(Lep). In addition, P adsorptions presented the better capacities in a pH range of 3 − 8. The SO 4 2− had the stronger effects on P adsorptions, while the other anions (Cl − , NO 3 − and CO 3 2− ) had little effects. The possible P adsorption mechanisms by FTIR and XPS results for FeOOH mainly were electrostatic attractions and ion exchanges. It is obvious that isomeric FeOOH are the promising adsorbents for P removal.