Facile preparation of iron oxyhydroxide–biopolymer (Chitosan/Alginate) beads and their comparative insights into arsenic removal

Bare iron-based nanoadsorbents have been explored extensively for arsenic removal owing to the inherent affinity of iron for arsenic. However, bare nanoparticles have poor hydraulic properties and tend to agglomerate when used as adsorbents. Encapsulation of nanoparticles into polymeric materials is a safer way to restrict the transportation of highly reactive nanoparticles in the surrounding media without compromising the efficiency of these adsorbents. This study presents a modified method for synthesizing bionanocomposite beads intending to achieve optimal dispersion of nanoparticles throughout the biopolymer. In-situ iron oxyhydroxide alginate beads (IIAB) and chitosan beads (IICB) were prepared via gradual precipitation of ferric ions within the polymeric gel matrix. Electron microscopy images were used for morphological analyses of beads. Batch trials were conducted to assess the effect of dose, pH, contact time, and ionic strength on arsenic adsorption. Maximum adsorption capacities obtained via Langmuir isotherm model fitting were in the following order: IICB for As (V) > IICB for As (III) > IIAB for As (V) > IICB for As (III). 1.2 g/L of IICB and 2 g/L of IIAB were found to be sufficient for treatment of arsenic spiked groundwater. FTIR and XPS analyses reveal the role of hydroxyl and amino groups in the adsorption process. Spent beads could be easily harvested, regenerated using 0.1 M NaOH, and used for multiple cycles without significant leaching.