Different performances and mechanisms of phosphate adsorption onto metal oxides and metal hydroxides: a comparative study

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Abstract

Abstract BACKGROUND Adsorption plays a significant role in phosphate removal and recovery. Metal (hydro)oxides are the most popular adsorbents for phosphate adsorption, but their performances differ greatly, with different adsorption mechanisms under different conditions. A comparative study of phosphate adsorption onto iron hydroxide and iron oxide doped activated carbon fiber ( ACF‐FeOH and ACF‐FeO ) was performed. RESULTS The phosphate adsorption performance of ACF‐FeOH and ACF‐FeO with different initial pH , ion strength and competing ions was investigated. The contrasting results showed that the amount adsorbed by ACF‐FeOH is higher than that by ACF‐FeO , and phosphate adsorption on ACF‐FeOH is more dependent on pH and ion strength than on ACF‐FeO . The adsorption mechanisms were studied by zeta potential measurements, X‐ray photoelectron spectroscopy ( XPS ) analysis and batch desorption tests. The significantly higher isoelectric point ( IEP ) of ACF‐FeOH with respect to that of ACF‐FeO resulted in a greater phosphate adsorption by ACF‐FeOH than by ACF‐FeO . XPS analysis showed that the concentration of surface hydroxyl groups on ACF‐FeOH is also higher than that on ACF‐FeO . CONCLUSION ACF‐FeOH performs better than ACF‐FeO with higher adsorption capacity. Electrostatic interaction and ion exchange are the two main adsorption mechanisms both for ACF‐FeOH and for ACF‐FeO . This study should provide some guidance on the preparation and application of iron‐based sorbents in phosphorus removal and recovery. © 2015 Society of Chemical Industry

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