Preparation of a novel Fe3O4/HCO composite adsorbent and the mechanism for the removal of antimony (III) from aqueous solution

A novel adsorbent (Fe₃O₄/HCO) was prepared via co-precipitation from a mix of ferriferrous oxide and a Ce-rich waste industrial sludge recovered from an optical polishing activity. The effect of system parameters including reaction time, pH, dose, temperature as well as initial concentration on the adsorption of Sb(III) were investigated by sequential batch tests. The Sb(III)/Fe₃O₄/HCO system quickly reached adsorption equilibrium within 2 h, was effective over a wide pH (3-7) and demonstrated excellent removal at a 60 mg/L Sb(III) concentration. Three isothermal adsorption models were assessed to describe the equilibrium data for Sb(III) with Fe₃O₄/HCO. Compared to the Freundlich and dubinin-radushkevich, the Langmuir isotherm model showed the best fit, with a maximum adsorption capacity of 22.853 mg/g, which exceeds many comparable absorbents. Four kinetic models, Pseudo-first-order, Pseudo-second-order, Elovich and Intra-particle, were used to fit the adsorption process. The analysis showed that the mechanism was pseudo-second-order and chemical adsorption played a dominant role in the adsorption of Sb(III) by Fe₃O₄/HCO (correlation coefficient R² = 0.993). Thermodynamic calculations suggest that adsorption of Sb(III) ions was endothermic, spontaneous and a thermodynamically feasible process. The mechanism of the adsorption of Sb(III) on Fe₃O₄/HCO could be described by the synergistic adsorption of Sb (III) on Fe₃O₄, FeCe₂O₄ and hydrous ceric oxide. The Fe₃O₄/HCO sorbent appears to be an efficient and environment-friendly material for the removal of Sb(III) from wastewater.