The economic potential of activated carbon (AC) synthesis from walnut shell biomass for CO capture was evaluated in the present study. For this purpose, the chemical activation was employed to manufacture ACs and the effect of different impregnation ratios of activation agents, comprising KOH (KH) and HPO (HP), onto the properties of fabricated ACs was examined. The obtained results demonstrated that the synthesized AC by HP activation with an impregnation ratio of 1:2.5, which was identified as HP2.5, possesses the highest surface area (1512.6 m/g), micropore volume percentage (74.65%), and CO adsorption (3.55 mmol/g) at 1 bar and 30 °C. Moreover, the equilibrium CO adsorption data for HP2.5 were better fitted with the Freundlich model, indicating the multilayer CO adsorption onto the heterogeneous AC surface dominantly through a physisorption process. In addition, the economic estimations revealed a cost of about $1.83/kg for the ultimate production that was significantly lower than the most of available CACs in the market. Therefore, walnut shells can be considered as a cost-effective and promising biomass source from a scale-up point of view.