Magnetic fly-ash geopolymer for heavy metal removal in aqueous solutions

Novel magnetic geopolymers were manufactured by synthesizing magnetic Fe₃O₄ particles on the surface of prepared geopolymer (Method 1) or by incorporating pre-synthesized magnetic Fe₃O₄ particles into the geopolymer during the manufacture of the geopolymer (Method 2). This study evaluated the effect of the incorporated magnetic Fe₃O₄ on the geopolymer magnetic, physical, and adsorption properties and its separation in aqueous solutions. Based on several preliminary measurements on the synthesized magnetic geopolymers, Method 2 was found to be a better method for producing magnetic geopolymer. Magnetic geopolymer synthesized by Method 2 exhibited ferromagnetic properties comparable to that of magnetic Fe₃O₄, with a saturation magnetization of 8 emu·g^-1 and an intrinsic coercivity of 265 Oe. The magnetic geopolymer was efficiently separated from an aqueous solution within 2 min using a 0.48-T magnetic field. In addition, the magnetic geopolymer has a maximum copper adsorption capacity of 111.1 mg·g^-1, which was similar to the non-magnetic reference geopolymer indicating that the addition of magnetic Fe₃O₄ did not compromise the geopolymer adsorption capacity. The magnetic geopolymer is a promising material with good adsorption and separation properties that can be used for heavy metals removal and recovery in wastewater and metals separation in industrial processes.