The current study focused on the comparative removal of hexavalent chromium using two magnetically modified hybrid adsorbent composites. Their precursor chars were prepared from bio sludge and plastic waste derivatives. The coating of magnetite on the chars' surface was evident from the SEM micrographs. Infusion of magnetite nanoparticles in the native chars aided in the reduction of the composite particles' sizes, thus, forming high surface area composites. Screening of uptake capacities among various blends of char and magnetite were surveyed. Composites of both kinds with a 1:5 ratio of char: iron salts composition answered well. The pHZPC and zeta potential values of the composites indicated the neutral charge on the composites' surface. This suggested the need for a highly acidic environment for efficient Cr(VI) removal. Optimum economic conditions for Cr(VI) removal were obtained from the batch studies (solution pH - 1.5; contact time - (a) MPC [magnetic plastic char] - 60 min (b) MBC [magnetic biochar] - 40 min; temperature - 25 °C). The maximum monolayer adsorption capacity of MPC and MBC were found to be 84.67 mg/g and 53.83 mg/g respectively. Isotherm, kinetic and thermodynamic studies revealed the adsorption systems' inclination towards physisorption. From the characterization and modeling results, electrostatic force of attraction and pore filling was anticipated to be the mechanism of adsorption for both MPC and MBC. Thus, in the relative removal studies, MBC was found to compete better than MPC due to its enhanced porosity and surface area.
Keywords: Biochar; Cr (VI) ions; Magnetite; Mesoporous composites; Toxic pollutant.
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