A comprehensive study of As(V) removal by starch-coated magnetite nano-adsorbent based on waste iron sludge

Abstract

Combining natural polymer starch with magnetite nanoparticles (MNPs) can reduce the aggregation of MNPs and enhance their adsorption capacity and stability. Iron sludge from a de‑ironing water plant and starch were employed as basic ingredients in this study. Bare magnetite nanoparticles (MNPs) and starch-coated magnetite nanocomposites (ST2-MNPs) were synthesized by a “green” co-precipitation method for the removal of low-concentration As(V) solutions. TEM, XPS, FTIR, XRD, VSM, BET, and TGA techniques were used to examine the physicochemical properties of the synthesized ST2-MNPs. TEM verified that the magnetite nanoparticles in the composites were evenly distributed. The ST2-MNPs (5.26 nm) possessed a smaller average particle size than MNPs (6.24 nm). And VSM confirmed their remarkable magnetic properties. The starch-to‑iron-sludge ratio was optimized and the influence of adsorbent dosage, pH, and co-existing anions on As(V) adsorption were studied. The acquired arsenate adsorption data were found to be consistent with the Langmuir isotherm model, with maximum adsorption capacities of 23.04 mg/g for MNPs and 42.88 mg/g for ST2-MNPs. This shows that the active sites on MNPs and ST2-MNPs are energetically homogenous, and that the addition of starch coating significantly increases magnetite's adsorption capacity for As(V). The adsorption kinetics follow a Pseudo-second-order kinetic model, indicating chemisorption between As(V) and ST2-MNPs. In addition, the adsorption mechanism of As(V) by ST2-MNPs including chemical adsorption and electrostatic attraction was determined through in-depth discussion of characterization methods and adsorption experiments. This study offers references for the removal of As(V) and the resourceful application of backwash iron sludge.