Enhanced removal of multiple metal ions (Fe3+, Mn2+, Ni2+, Cd2+, and Sr2+) from aqueous solutions using modified natural clinoptilolite

The effective removal of multiple metal ions from aqueous solutions in a single-treatment process was explored using modified natural clinoptilolite (NCP). Batch adsorption experiments were conducted to evaluate the impact of critical factors, such as adsorbent dosage, contact time, adsorbate concentration, pH, and temperature, on the removal efficiency. The modified NCP achieved maximum adsorption capacities of 81.4, 78.4, 75.2, 72.2, and 68.8 mg·g −1 for Cd 2+ , Fe 3+ , Ni 2+ , Mn 2+ , and Sr 2+ , with removal efficiencies of 95.0 %, 90.1 %, 90.0 %, 86.5 %, and 82.5 %, respectively, at pH 3.0 and 25 °C for Fe 3+ , and pH 7.5 and 85 °C for the others. Adsorption kinetics followed the pseudo-second-order model while intra-particle diffusion, analyzed via the Weber-Morris model indicated that pore diffusion was a dominant mechanism, particularly for Fe³⁺. The Langmuir isotherm provided the best fit to the equilibrium data. Thermodynamic analysis confirmed the viability of the adsorption process, with Fe 3+ exhibiting exothermic adsorption, while the uptake of Mn 2+ , Ni 2+ , Cd 2+ , and Sr 2+ was endothermic. Negative entropy changes indicated enhanced ordering of adsorbed metal ions via strong electrostatic interactions. The modified NCPs demonstrated excellent regeneration capability and stability under acidic, basic, and thermal conditions. These findings provide valuable insights for designing effective multi-ion adsorption systems with enhanced performance and reliability.