Thermodynamic and kinetic investigation of heavy metals sorption in packed bed columns by recycled lignocellulosic materials from olive oil production

Agricultural wastes derived from olive oil production were used in wastewater engineering as lead, cadmium, and nickel ions sorbents. Experiments were carried out in distilled water (Troom) by the use of packed bed columns filled with grains (1–3 mm) which were eluted with single and multimetal solutions in the 3–10 mg/L concentration range. Operations were performed with different sorbent dosage (4–8 g) at flow rates ranging 0.3–0.7 L/h until exhaustion. Best retention capacities were 8.15, 3.5, and 2.9 mg/gsorbent respectively for Pb+2, Cd+2, and Ni+2 in the case of the multimetal system (0.3 L/h, 8 g of sorbent, and 10 mg/L influent solution). EDX analysis carried out on the sorbent surface showed that the wt % ratios between the sorbed metals were similar to the ratios between the column overall capacities. Inter-diffusion of the ions in the Nernst stationary liquid film around the particle was identified as the step which controls the kinetics of the process. Exhausted wastes were successively recycled in cement mortars together with another aggregate as exhausted porous glass in order to obtain a lightweight composite with good consistency and interesting mechanical resistances.