Biosorption potential of olive leaves as a novel low-cost adsorbent for the removal of hexavalent chromium from wastewater

This study reported the use of olive leaves Chemlali pruning waste (OLC) as biosorbent for Cr(VI) ions removal from aqueous solution via a batch process. An ideal experimental model was applied using central composite design (CCD) based on response surface methodology (RSM) to find the best operating conditions. The optimum removal efficiency of Cr(VI) onto OLC was ascertained as 99.98% at 3.9 initial solution pH, 0.73 g adsorbent mass, and 37.25 °C temperature for 100 mg/L initial Cr(VI) concentration. Analysis of variance (ANOVA) showing a high coefficient of determination (R² = 0.999) and low probability values signified the validity of the predicted model. Results showed that the CCD was an effective tool for enhancing the adsorption procedure. Several adsorption models were used to study the investigative data as well. The experimental data best fitted with Langmuir isotherm with maximum Cr(VI) biosorption capacities equaling to 21.157, 22.634, 30.672, and 40.312 mg/g at 283, 298, 308, and 318 K, respectively. The removal of Cr(VI) onto OLC followed pseudo-second-order kinetics. The thermodynamic studies indicated a spontaneous and endothermic process. The OLC was characterized using different physicochemical methods. The FTIR revealed the interaction of some functional groups in the adsorption of chromium ions, including carboxylic acid, hydroxyl, and amide. The OLC adsorbent was regenerated with NaOH, NaCl solution, and distilled water until five recycle runs for further reuse. Overall, results showed that OLC is an effective and economical alternative with great potential for hexavalent chromium recovery. Graphical abstract: (Figure presented.)