In this study, the sorptive removal of As 3+ with promising sorption efficiency up to a very low concentration has been investigated using chitosan-montmorillonite (MMT) composites (in the form of powder and beads). In addition, the recovery of the composite from the sorbent is proposed as well. The sorbent has been observed to show a sorption efficiency of 42.0% from 0.006 µg ml -1 of metal ion. The batch adsorption model was developed to predict the equilibrium adsorption capacity with respect to the pH of As 3+ solution, contact time and initial concentration of metal ion. The maximum As 3+ sorption capacity of 48.7 mg g -1 (achieved within 10 minutes of contact time) was obtained using chitosan-MMT beads at the pH of drinking water (8.0) at 298 K. The equilibrium sorption data were fitted to the Langmuir and Freundlich adsorption models and the model parameters were evaluated, wherein the Freundlich model shows the most favourable representation of As 3+ adsorption behaviour. The biocomposites show comparable high sorption capacity with detection and estimation of As 3+ from 0.004 (4.0 ppb) to 100.00 µg ml -1 (100.0 ppm) of aqueous solution. The adsorption kinetics demonstrated intra-particle diffusion as the rate-determining step during the initial phase of adsorption (up to 10 minutes of contact time), which were supported by X-ray diffraction studies; by contrast, chemisorption was found to be the rate-determining step during the later part of adsorption (after 10 minutes of contact time), which were confirmed by Fourier transform infrared spectroscopy-attenuated total reflectance studies. Desorption of As 3+ from the sorbents was optimized using potassium dihydrogen phosphate, wherein 0.1 M of the desorbate was found to be an appreciable regenerating agent supporting the reusability of the sorbent up to three cycles, retaining 4402 µg g -1 of the metal ion.
The effluent from various industries is the potential source of water contamination during last few decades. Thus effective methods have been adopted for the removal of toxic heavy metals from industrial effluents that show carcinogenic and mutagenic effects. The present research involves removal of Sb 3+ that has been investigated using chitosan-montmorillonite biocomposites. The kinetics and adsorption equilibrium was determined respectively using batch adsorption model, taking into account solution pH, contact time and initial metal ion concentration. The adsorption isotherm parameters were evaluated wherein Freundlich model best represents the experimental data. The highest adsorption capacity of 48.7 mg/g of chitosan-montmorillonite beads was attained from an initial concentration of 100 g/m 3 at 300 K. The equilibrium was achieved during initial phase of contact of 10 minutes only. The biosorbent show comparable high adsorption capacity for Sb 3+ and is efficiently functional in broad range of metal ion concentration from 4 mg/m 3 (4 parts per billion) to 100 g/m 3 (100 parts per million) of solution. The adsorption kinetics follows chemical adsorption as the rate determining step. The interaction forces between Sb3+ and adsorbent/s were determined by Fourier Transform Infrared-Attenuated Total Reflectance (FT-IR-ATR). The metal ion desorption and reusability of biosorbent/s up to three cycles was supported by 0.1 M potassium dihydrogen phosphate solution. The Scanning Electron Micrographs and X-Ray Diffractograms of the adsorbents before and after metal interaction were found to correspond to the batch adsorption studies of the metal ion.
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