Fabrication and characterization of manganese ferrite/expanded vermiculite as a magnetic adsorbent of nickel ions

Abstract

Adsorbents based on magnetic materials are the subject of numerous researches. Beside good magnetism and functional surface, manganese ferrite is unstable and prone to form low mechanical strength agglomerates, which necessitate its deposition on the substrate surface. Expanded vermiculite outer surfac, is a useful medium for the deposition of nanoparticles whereas intercation layer is suitable for holding cation species (distance of 2:1 layers may be greater than 10 Å). Due to its relatively high surface area, cation exchange capacity and natural abundance of vermiculite, this mica mineral and its composites could be valorized as potentially low-cost adsorbents. In this study, manganese ferrite/expanded vermiculite (MnFe2O4/EV) composite was prepared by in-situ method. Deposited manganese ferrite particles on the surface of EV were formed in the solvothermal reaction using suitable reagents. Both composite and base material are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area (SSA), cation exchange capacity (CEC) and pH point of zero charge (pHPZC) determination. The adsorption properties of MnFe2O4/EV and EV have been investigated in a batch system at pH close to the pHPZC for the removal of Ni (II) from water. Considering process parameters such as contact time, adsorbent dosage and temperature: adsorption type, isotherm parameters (Langmuir and Freundlich) and rate of adsorption parameters were determined. Results of the kinetic studies gave fine correlations with pseudo – second order and Weber – Morris model. Taking into consideration fact that EV had low CEC values and SSA, obtained composite have high adsorption capacity (more than 30 mg Ni g-1). Also, X-ray diffractograms showed alteration of biotite vermiculite (formed during solvothermal action) into phlogopite (formed after adsorption process and aging). The methodology applied in this work may be utilized for the fabrication of other ferrite spinels, perovskites and other oxide systems.