The use of banana peel as a low-cost adsorption material for removing hexavalent chromium from tannery wastewater: optimization, kinetic and isotherm study, and regeneration aspects

Abstract

When the concentration of hexavalent chromium (Cr(VI)) in the environment is greater than a certain limit, it becomes a global concern. Thus, the aim of this study was to use banana peel as an adsorbent to remove heavy metals, specifically Cr(VI) ions from wastewater. Banana peel (BP) was activated in a furnace for 2 h (h) at 450 °C and 50% humidity. Subsequently, the activated BP was characterized by proximate analysis, elemental analysis, scanning-electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer Emmett Teller (BET) analysis, and thermogravimetric analysis (TGA). According to the characterization results, the activated BP possessed a porous surface and high surface area of 200 m² g⁻¹, which are important adsorption parameters. Additionally, the removal efficiency for Cr(VI) was evaluated in terms of pH, contact time, initial concentration, and adsorbent dose. Consequently, the optimal operating conditions for removing 94% of Cr(VI) were found to be an adsorption time of 92 min, adsorbent dose of 1.5 g L⁻¹, pH of 3, and initial Cr(VI) concentration of 38 mg L⁻¹. In addition, the adsorption kinetics and isotherms were examined. The pseudo-first-order model with an R² of 0.996 and the Langmuir isotherm with an R² of 0.997 were found to be the most effective mathematical representations of the rate and nature of Cr(VI) adsorption on the surface of the activated BP, respectively. Furthermore, it was discovered that the activated BP could be reused six times before its removal efficiency was reduced to less than 70%.