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.