Techno-economic and environmental approaches of Cd<sup>2+</sup> adsorption by olive leaves (<i>Olea europaea</i> L.) waste

<p>In this study, the techno-economic approach of olive leaves (<i>Olea europaea</i> L.) wastes for the removal of Cd<sup>2+</sup> 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 Cd<sup>2+</sup> removal efficiencies of 94.9% at <i>C<sub>o</sub></i> = 50 mg/L and 81.5% at <i>C<sub>o</sub></i> = 100 mg/L. The monolayer adsorption capacity of the Langmuir isotherm model was 32.6 mg/g (<i>R</i><sup>2</sup> = 0.97). The adsorption mechanisms might be related to (a) ion exchange with cations (<i>e.g.</i>, K<sup>+</sup>, Na<sup>+</sup>, and Ca<sup>2+</sup>), (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>i.e.</i>, carbonates, phosphates, and silicates). The total cost of the adsorption process for the treatment of ions-containing wastewater was 0.038 $USD/m<sup>3</sup>. Assuming a benefit-cost of tertiary treated water as 0.044 $USD/m<sup>3</sup>, the adsorption system could attain a payback period of 5.7 years. This period was shorter than the lifetime of the capital investment (<i>i.e.</i>, 10 years), and hence, the project would be economically feasible for an application.</p>