Boron adsorption by composite magnetic particles

We prepared Fe3O4 particles and two types of composite magnetic particles derived from Fe3O4 and bis(trimethoxysilylpropyl)amine (TSPA), and from Fe3O4 and a flocculating agent 1010f (a copolymer of acrylamide, sodium acrylate, and [2-(acryloyloxy)ethyl]trimethylammonium chloride). Using these particles, boron adsorption in aqueous solution was comprehensively investigated. The adsorption was found to occur rapidly in the first 2 h and the particle composition did not have a significant effect on the equilibrium time. We found that Fe3O4–TSPA particles presented the highest adsorption capacity, whereas the pure Fe3O4 particles showed the lowest capacity. For all particles, amount of boron adsorption decreased with the initial pH in the order of 6.0 > 2.2 > 11.7. In general, the adsorption amount appeared to decrease with the increase in ionic strength. We propose that boron is adsorbed in the form of both H3BO3 and B(OH)4− through the interactions of hydrogen bonding, electrostatic and hydrophobic attractions. The information gained in this study would be helpful for both understanding the adsorption mechanism and designing low-cost and easily available adsorbents for boron.