Pecan shells-based activated carbon for the removal of copper metal ions: optimization of the adsorption process using a full factorial design

This work investigates the removal of copper ions (Cu2+) from an aqueous solution by adsorption onto the surface of activated carbon (AC) produced from pecan shells. The research aims to identify a feasible and effective route for cleaning the wastewater from Cu2+. Chemical activation was carried out using sodium hydroxide. The AC physicochemical properties were characterised by scanning electron microscopy, Fourier-transform infrared, X-ray diffraction, and Brunauer-Emmett-Teller for measuring its specific surface area. To obtain a suitable removal of this metal ion, four physicochemical factors, including the contact time (120-360 min) the adsorbent dose (10-100 mg), initial concentration (10-50 mg/L), and pH (2-6) were optimised using the 24-full factorial design approach. A quadratic regression model representing the capacity of Cu2+ adsorption (Qe) was developed and validated by the analysis of variance. This approach was used to determine independent factors' main and interaction effects on adsorption equilibrium capacity. The results consolidate similar studies showing that all the factors were significant, and the interactions among the factors were also significant. The optimum conditions for circumscribed fractional factorial design were adsorption time (120 min), adsorbent amount (10 mg), initial metal ions (50 mg/L), and pH 6. The pseudo-first-order model correctly describes the adsorption kinetics with Qe, reached 51.41 mg/g. Modeling adsorption isotherms showed that the Freundlich model adequately describes the adsorption process.