Adsorption of Sb(V) in wastewater by Fe/Mn binary oxides loaded sludge derived activated carbon: performance, mechanisms and applicability

Fe/Mn binary oxides loaded sludge derived activated carbon (Fe/Mn-SAC) was prepared with co-precipitation & calcination method for the adsorption of Sb(V) from aqueous solution. The preparation parameters were analyzed and optimized by response surface methodology, with the optimal parameters as 2.73 h and 295.7 ℃ of calcination time and temperature, 0.62 mol/L of the concentration of immersed solution. Fe/Mn-SAC presented fine Fe/Mn binary oxides mingling with Fe oxides and seldom Mn oxides on SAC, leading to newly formed micropores, vacancy as well as both more free and metal coordinated -OH. Mn doping and loaded on SAC carrier retarded oxides aggregation and crystal transformation, expanding adsorption sites and strengthening phase stability. The pseudo second order kinetic model and Langmuir model were preferable to describe the adsorption process of Sb(V) on Fe/Mn-SAC. The adsorption of Sb(V) on Fe/Mn-SAC was governed by monolayer heterogeneous chemical adsorption with two stages. The initial rapid adsorption stage was affected by concentration gradient, electrostatic effect, surface energy and boundary layer. The rate in the subsequent slow adsorption stage was controlled from the relay conveyance of Sb(V) (Sb(OH)6-) by -OH. The adsorption of Sb(V) involved the inner-sphere complexation between Sb(V) and Fe/Mn-SAC through Fe/Mn-O-Sb bond with the participation of various -OH and other functional groups. Fe/Mn-SAC exhibited exceptional reusability, adaptability and applicability with the assistance of magnetic separation, evaluated in cyclic, different water matrix and dynamic adsorption processes. This work provides valuable information and insight into the efficient binary oxides loaded adsorbent to remove Sb(V) from aqueous environment.