Zirconium and iminodiacetic acid modified magnetic peanut husk as a novel adsorbent for the sequestration of phosphates from solution: Characterization, equilibrium and kinetic study

The development of adsorbents based on agricultural biomass for the remediation of polluted waters offers unique benefits and also fits into the concept of green chemistry. In this study, a highly efficient adsorbent (PN-Fe3O4-IDA-Zr) based on peanut husk chemically modified with zirconium, iminodiacetic acid and Fe3O4 was employed for the sequestration of phosphates in synthetic and real water samples. The characterization of PN-Fe3O4-IDA-Zr via analytical techniques confirmed it as a crystalline mesoporous adsorbent with superparamagnetic properties which ensures its easy retrieval from the solution under an external magnetic field. The adsorption capacity and associated mechanisms of the adsorbent were assessed via the batch method. Results from adsorption studies showed the maximum adsorption capacity of PN-Fe3O4-IDA-Zr for PO43- (50 mg L-1, mass as P) to be 13.2 mg g(-1) at 313 K and was influenced by factors such as contact time, pH, initial phosphate concentration, salts and temperature. The experimental data were well fitted by the Freundlich model and Elovich equation suggesting the formation of a multilayer on the surface of PN-Fe3O4-IDA-Zr which was mainly influenced by the chemisorption process (mainly via coordination). A comparison of the efficiencies of the adsorbent at its various stages of development shows that the presence of zirconium plays a significant role in the adsorption process thus confirming the design concept of the adsorbent. PN-Fe3O4-IDA-Zr exhibited high stability and efficiency in real water samples that were spiked with high concentrations of phosphates. These results as well as the facile synthetic route for PN-Fe3O4-IDA-Zr under benign conditions promote its prospects as a promising adsorbent for practical applications.