Enhanced removal of lead and zinc from high-salinity waters of Chah Afzal, Yazd using nano-activated carbon adsorbent

This study investigated the efficiency of nano-activated carbon (NAC) for the simultaneous removal of lead (Pb 2+ ) and zinc (Zn 2+ ) ions from saline waters of the Chah Afzal region in Ardakan, Yazd. Water samples with three different salinity levels (0.8, 9.67, and 20.8 dS/m) and initial heavy metal concentrations (0–200 mg/L) were tested. Structural characterization of NAC using X-ray diffraction (XRD) and BET analysis confirmed its high specific surface area (1528.2 m 2 /g) and dominant mesoporous structure (pore diameter of 3.478 nm). Results showed that NAC exhibited high adsorption capacity for both metals, with significantly superior performance for lead (theoretical maximum capacity of 64.94 mg/g from the Langmuir model) compared to zinc (35.59 mg/g), attributed to the combined effects of its lower hydration energy, smaller hydrated radius, greater coordination flexibility, and higher polarizability, which together facilitate dehydration, pore penetration, and stronger binding to NAC surface functional groups. Kinetic and isotherm studies were best described by the pseudo-second-order (R 2 = 0.997 for Pb 2+ , 0.996 for Zn 2+ ) and Langmuir (R 2 = 0.985 for Pb 2+ , 0.992 for Zn 2+ ) models, respectively, suggesting that the adsorption process is consistent with a mixed mechanism dominated by physisorption, involving relatively strong surface interactions and monolayer formation on relatively homogeneous surfaces for both metals. FTIR and SEM analyses indicated the involvement of oxygen-containing functional groups in the adsorption process and morphological changes of the adsorbent surface after adsorption, respectively. This study demonstrates the effectiveness of NAC as an efficient adsorbent for removing heavy metals from complex and saline aqueous matrices.