Formation of Fe3O4@ZrO2 nanocomposite and its performance as a magnetic adsorbent for phosphate uptake: Influences of end-point pH and stirring rate during synthesis process

In developing a magnetic material for the recovery of phosphate from water/wastewater, both high magnetization and high uptake ability for phosphate are highly desirable. In our quest to obtain such a magnetic material, hydrous zirconia-coated magnetite nanocomposite (Fe 3 O 4 @ZrO 2 ) has been synthesized at different end-point pH values and stirring rates. The results indicated that the saturation magnetization of Fe 3 O 4 @ZrO 2 increased almost linearly with increasing end-point pH, and high stirring rate caused low magnetization. The magnetization behavior was closely related to the formation of the mineral magnetite, which was hindered at either low end-point pH or fast stirring rate. In contrast to magnetization, phosphate adsorption capacity decreased with increasing end-point pH, whereas the stirring rate had little effect. It is concluded that adopting a relatively low end-point pH and a low stirring rate is a good strategy for obtaining a Fe 3 O 4 @ZrO 2 material with good magnetic separability and a high affinity for P.