Techno-economic and environmental approaches of Cd²⁺ adsorption by olive leaves (Olea europaea L.) waste

In this study, the techno-economic approach of olive leaves (Olea europaea L.) wastes for the removal of Cd²⁺ from aqueous solutions was demonstrated. The adsorption process was illustrated regarding batch experiments and scanning electron microscopy, energy dispersive X-ray, and Fourier-transform infrared characterization. The optimum pH and contact time were 6.6 and 123 min, respectively, giving Cd²⁺ removal efficiencies of 94.9% at C_o = 50 mg/L and 81.5% at C_o = 100 mg/L. The monolayer adsorption capacity of the Langmuir isotherm model was 32.6 mg/g (R² = 0.97). The adsorption mechanisms might be related to (a) ion exchange with cations (e.g., K⁺, Na⁺, and Ca²⁺), (b) formation of cadmium chloride complexes, (c) interaction with oxygen-containing functional groups, (d) physical agglomeration in the pore surface, and (e) precipitation interaction using inorganic minerals (i.e., carbonates, phosphates, and silicates). The total cost of the adsorption process for the treatment of ions-containing wastewater was 0.038 $USD/m³. Assuming a benefit-cost of tertiary treated water as 0.044 $USD/m³, the adsorption system could attain a payback period of 5.7 years. This period was shorter than the lifetime of the capital investment (i.e., 10 years), and hence, the project would be economically feasible for an application.