In this study, olive stone (OS), one of the largely-gathered agricultural wastes, was investigated as an adsorbent in modified and less efficient raw form in order to remove trace elements that have negative effects on human health and environment. Citric acid (CA) assisted mechanochemical modification method (MCM) proposed as an alternative to traditional chemical modification was presented as an innovative approach with advantages of being an easy-to-use, low-cost and eco-friendly technology. As an effective adsorbent, modified olive stone (M-OS) was used for removing Cu2+, Pb2+ and Zn2+ metals from aqueous solutions. Kinetic analysis was fitted with Pseudo-second-order model and equilibrium data with Langmuir model. Adsorption capacities were found as 3.49, 4.67, 2.50 mg/g with OS, and 10.10, 21.28, 18.18 mg/g with M-OS for Cu2+, Pb2+ and Zn2+ respectively. The removal efficiencies of all metals were above 94% for modified adsorbent in optimum conditions (C-o: 0.30 mM, pH: 5.40, and m: 0.300 g). According to thermodynamic parameters, adsorption process was spontaneous and endothermic for both adsorbents. Activation energy values indicated that nature of adsorption process was physical for OS and chemical for M-OS. In desorption and reusability studies, removal efficiencies were found as 40% and below in third cycle. In addition, financial advantages of method were revealed by cash flow and alternative selection cost analysis methods. As a result, the applied modification method was proposed as an effective, economical and green technology for modification of similar materials in today's conditions, where it is important to achieve high efficiency with lower cost.