Alginate-bentonite beads for efficient adsorption of methylene blue dye

In this study, alginate/bentonite adsorbent beads (Alg/Ben) were prepared by encapsulating natural bentonite (Ben) in calcium alginate (Alg). Different Alg/Ben ratios were applied during bead preparation, yielding beads denoted Alg-Ben1 (1/1 w/w), Alg-Ben2 (1/2 w/w), and Alg-Ben3 (1/3 w/w), respectively. These adsorbents were characterized by Fourier-transform infrared spectroscopy and X-ray diffraction. The adsorption of methylene blue (MB) from aqueous solution on the Alg/Ben beads was investigated as a function of several parameters, including initial MB concentration and contact time. The Langmuir and Freundlich adsorption models were applied to describe the equilibrium adsorption isotherms, and they were found to be well described by the Langmuir model. Encapsulating Ben in Alg led to a substantial increase in maximum amount of methylene blue adsorbed by Ben, from 345 to 1237 mg g−1. The results showed that, among the three types of Alg/Ben beads, Alg-Ben1 presented the greatest MB adsorption capacity. A kinetic study indicated that the adsorption was governed by second-order kinetics.