The aim of this research was to separate mercury from gold refining wastewater using activated carbon (AC) from natural shells. To this end, walnut and coconut shells were used as the main source of AC. The characterizations of both ACs were compared by FTIR, BET, and SEM analyses. The FTIR results revealed interactions between the solute and the functional groups on the adsorbent surface. According to the BET results, the mean pore diameter (MPD) of AC from coconut shells (CSAC) was smaller than that derived from walnut shells (WSAC). The specific surface areas for CSAC and WSAC were 1069.1 and 119.6 m2/g, respectively. SEM results revealed that the porous texture of ACs emanates from their cellular structure. This research further studied the impact of operational parameters “adsorbent dose” (0.3-3.8 g/L), “pH” (2-9), and “residence time” (10-120 min) on mercury removal. Under optimal operational conditions, the mercury removal rate reached 97% (for WSAC) and 93% (for CSAC). Kinetic model assessments revealed the highest agreement between the experimental data and the pseudo-first-order (PFO) model. Both adsorbents were regenerable, with their performance (compared to fresh adsorbents) exceeding 90% after each regeneration.
