Removal of phosphate from contaminated water using activated carbon supported nanoscale zero-valent iron (nZVI) particles

Abstract

In the current study activated carbon supported zero-valent iron nanoparticles were synthesised, characterized and used for phosphate adsorption study. Batch adsorption experiments were carried out to study the effect of activated carbon supported nZVI nanocomposites on the removal of phosphorus (P) from 50 mg/L P contaminated water at various pH values. When the activated carbon supported nZVI dosage increased from 2 g/L to 8 g/L the percentage P adsorbed increased from 69 % to 99.5%. The amount of P adsorbed increased with an increasing concentration of activated carbon supported nZVI dosage and decreasing pH values. Increasing adsorption of P with increasing adsorbent dosage can be due to higher adsorption site, however at higher adsorption dosages beyond 8 g/L the adsorption showed a decreasing trend due to the saturation and overlapping of adsorption sites. When the pH value of the solution increased from 3 to 11 the percentage removal of P decreased from 99.5 to 12 %. The reduction in adsorption at increasing pH values can be attributed to the repulsion between hydroxylic ions (OH¯ ) on the surface of iron nanoparticles and the existence of P in the form of phosphate anions (H2PO4¯, HPO4¯and PO4 3¯ ). Langmuir and Freundlich adsorption models were fitted in the experimental data, and it was found that the Langmuir model fitted well, and the calculated maximum adsorption capacity of phosphate was 68 mg/g, suggesting significantly higher and remarkable uptake of phosphate by activated carbon supported nZVI particles. The findings of this study showed that silica coated ZVI Particles could be promising adsorbents for removal of phosphates from polluted water bodies effectively.