Synthesis of Fe3O4@Phoslock® composites and the application in adsorption of phosphate from aqueous solution.

Abstract

Assisted with an organosilane, Fe3O4@Phoslock® composites with different constituents were synthesized to separate phosphate from aqueous solution. The experimental adsorption data of kinetics and isothermal studies by the composites were well fitted by pseudo-second order and Freundlich models, respectively, suggesting the chemical and heterogeneous adsorption process, i.e., ligand exchange and precipitation. After loading of Fe3O4, Phoslock® became magnetic at the expense of the certain decrease of phosphate uptake from 10.4 to 8.1mg P/g when [P]0 = 1.0mmol/L and the solid/liquid ratio of 1.0g/L were applied. However, compared with the original Fe3O4 nanoparticles, Fe3O4@Phoslock® showed more favorable phosphate uptake and stability against pH variation. The inhibitory influence of anionic ions on phosphate adsorption by three composites followed the order: HCO3- > humate > SiO32- > NO3- ≈ Cl- ≈ SO42-, while the facilitating effect of cations followed the order: Ca2+ > Mg2+ > NH4+. The regeneration rate was higher than 50% for all composites after recycled for 5 times by NaOH, and two of the composites successfully removed 75% phosphate from the landfill leachate treated by the Anammox process with the solid/liquid ratio of 5.0g/L. This suggests that Fe3O4@Phoslock® composites would be a competitive adsorbent for phosphate removal from real wastewater.