In this study, the ability of pistachio shells, as an unconventional adsorbent, to recover thallium cations from contaminated aqueous solutions was investigated. To achieve the objective of the study, practical experiments were conducted using a batch-mode adsorption unit under various operating conditions. The results obtained showed that the pistachio shells have the ability to remove thallium cations with a high efficiency exceeding 86% at room temperature. The results indicated that the maximum treatment efficiency was achieved at values of 7, 350 rpm, 86 ppm, 5 g, 150 min of pH, agitation speed, initial concentration of thallium, dosage of pistachio shell used, and contact time, respectively. Morphological results confirmed that the adsorbed pistachio shells suffered significant changes compared to the virgin shells, as SEM examination showed that the accumulation of thallium cations in their pores led to the formation of a heterogeneous layer of metal particles. On the other hand, adsorption resulted in the consumption of functional groups, according to FT-IR analysis, while the remaining surface area after adsorption was less than 5% of the original surface area.