Removal of selenium ions from contaminated aqueous solutions by adsorption using lemon peels as a non-conventional medium

The disposal of heavy metals from various activities has become a pervasive issue. The investigation of sustain-able, low-cost adsorbents for the remediation of these hazardous pollutants has been widely disregarded. This research emphasizes the recovery of selenium ions from contaminated water using lemon peels as a cost-effective adsorbent. The adsorption was explored in a batch unit under various operational parameters, including initial selenium concentration (1-90 ppm), pH (1-11), agitation speed (100-500 rpm), adsorbent dose (0.4-5.5 g), contact time (5-180 minutes), and temperature (25-55 °C). The BET surface area of the lemon peels was found to be 27.86 m²/g before adsorption and 2.18 m²/g after adsorption. FTIR analysis exposed the disappearance or shifting of several peaks, while the FESEM analysis showed significant changes in the surface morphology of the lemon peels due to its interaction with selenium. The results indicated that lemon peels are highly effective at removing selenium, attaining an efficiency of over 87% under optimal conditions: pH 8, agitation speed of 450 rpm, initial selenium concentration of 86 ppm, adsorbent dose of 5 g, contact time of 150 minutes, and temperature of 25 °C. The experimental results were analyzed using isothermal, kinetic, and thermodynamic methodologies. The mathematical model confirmed that the Langmuir theory is the most effective at representing the adsorption isotherm, while in terms of kinetic, the adsorption followed the inter-particle diffusion model, as indicated by the correlation coefficient (R²) values. Moreover, the adsorption process was found to be spontaneous, exothermic, and associated with low entropy over the studied temperature range.