Selective adsorption of phosphate from seawater and wastewater by amorphous zirconium hydroxide

Phosphate adsorption from single electrolyte (NaH2PO4), phosphate-enriched seawater, and model wastewater was studied using amorphous zirconium hydroxide, ZrO(OH)2⋅(Na2O)0.05⋅1.5H2O, as an adsorbent. Batch experiments were carried out to investigate the adsorption of phosphate. The effect of pH on phosphate adsorption from seawater showed that the uptake of phosphate increased with an increase in pH up to 6, and then decreased sharply with a further increase in pH of the solution. The equilibrium data of phosphate adsorption were followed with a Freundlich isotherm. The uptake of phosphate at the adsorbent/solution ratio 0.05 g/2 L was 10 and 17 mg-P/g for the phosphate-enriched seawater and the model wastewater, respectively. A much higher adsorptivity toward phosphate ions in seawater was observed on ZrO(OH)2⋅(Na2O)0.05⋅1.5H2O than on other representative adsorbents based on layered double hydroxides of Mg(II)–Al(III), Mg(II)–Fe(III), and Ni(II)–Fe(III). The effective desorption of phosphate ions on ZrO(OH)2⋅(Na2O)0.05⋅1.5H2O could be achieved using a 0.1 M NaOH solution. The usefulness of experimental data for practical applications in removing phosphate in seawater and wastewater is discussed.

ZrO2 has two types of hydroxyl groups, which are responsible for phosphate adsorption: (i) terminal OH groups exist on the surface of the solid, and (ii) bridging OH groups lie in the interior part of the solid and are connected by two metal atoms.Figure optionsDownload as PowerPoint slide