Efficient removal of methylene blue using Algerian purified bentonite/sodium alginate beads in batch, recirculating, and continuous adsorption processes

In this study, an encapsulated purified bentonite/sodium alginate composite (PB/SA) was successfully prepared by solution intercalation and ionic crosslinking using calcium chloride. The PB/SA adsorbent was characterised by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller method (BET) from N-2 adsorption-desorption isotherm at 77 K, thermogravimetric analysis (TGA), and the point of zero charge (pH(PZC)). Adsorption efficiency of PB/SA was studied by using methylene blue dye (MB) in batch, recirculating and continuous systems. The effect of certain parameters on the adsorption capacity in the different systems was investigated. The results from batch study showed that MB removal increased with increasing adsorbent dose and pH solution. The test of operating parameters in continuous system, such as the bed height and the adsorbate flow rate, showed that MB removal increases at lower flow rate (2 mL/min) and higher bed height (2.4 cm). Kinetics modelling shows that the adsorption of MB onto PB/SA in batch and recirculating processes was well described by the pseudo-first-order model with high coefficient correlation R-2 (0.99). Regarding results from isotherms, the MB adsorption follows the Langmuir isotherm with R-2 exceeding 0.99 justifying monolayer and homogeneous adsorption. In addition, when comparing batch and recirculating processes, we observed that for a range of initial concentrations from 10 to 100 mg/L, the maximum adsorbed amounts were found to be 100 mg/g and 86.6 mg/g respectively for batch and recirculating systems. However, these values are higher in isotherms modelling because the results were fitted and compared only for low concentrations without the equilibrium lines. Hence, PB/SA beads can be a promising material for enhancing the elimination of dyes from an aqueous solution in different adsorption processes.