Adsorptive potential of apricot (Prunus Armeniaca) stone in the removal of Cr (VI) and Fe (II) ions from Aquatic Systems: Kinetic and isothermal investigations

• Water treatment. • Heavy metals removal. • Adsorption kinetics. • Natural adsorbents. Biogenic adsorbents have emerged as a promising alternative to the traditional remediation techniques of heavy-metals contaminated water treatment. Using apricot ( Prunus Armeniaca ) stone as a naturally derived adsorbent, the current study provides a comprehensive analysis of the kinetic and isothermal characteristics associated with Cr (VI) and Fe (II) ion adsorption. The results show that 0.5 mg of the adsorbent removed approximately 90 % of Cr (VI) and Fe (II) ions from 100 ppm solutions within 120 min at 298 K at 300 rpm stirring speed. Equilibrium was attained within 90 to 120 min, with a significant increase in the removal percentage observed in the first 30–40 min for both metals compared to the subsequent 80–90 min. The optimal pH conditions for adsorption were determined to be acidic (pH = 1.5) for Cr (VI) and neutral (pH = 7) for Fe (II). The adsorption kinetics followed a pseudo-second order model, while the isothermal equilibrium data best fit the Freundlich model over the Langmuir model. Moreover, the thermodynamic parameters, including ΔG°, ΔH°, and ΔS°, indicated that the sorption process is spontaneous, feasible, and endothermic. The response surface methodology (RSM) analysis showed a high level of accuracy in predicting the percent removal. These findings illustrate the effectiveness of apricot stone as a low-cost and environmentally conscious adsorbent, contributing to the development of sustainable water treatment technologies.