Adsorption of pharmaceutical residues on adsorbents prepared from olive stones using mixture design of experiments...

In this work, inexpensive and easily available olive stone (OS) waste was used as the source material to prepare activated carbons (ACs) by chemical activation with phosphoric acid and zinc chloride. The mixture design of experiments (MDOE) method was applied to study the effect of the composition of the mixture of unmodified olive stones (UOS) and ACs prepared from olive stones activated with ZnCl₂ (ACOS ZnCl₂) and H₃PO₄ (ACOS H₃PO₄) on the absorption of pharmaceutical residues. The adsorbed tetracycline (TC) amounts at equilibrium predicted from the model equation developed using Microsoft Excel were found to be in good agreement with the experimental values (R² = 0.999). Based on the results of the model, the amount of TC removed increased as the proportion of ACOS H₃PO₄ in the adsorbent mixture increased and the highest amount of TC adsorbed was obtained with an adsorbent made up entirely of ACOS H₃PO₄. Separate adsorption tests for sulfamethazine (SMT) and amoxicillin (AMX) on ACOS H₃PO₄ showed that SMT was adsorbed best (189.81 mg/g), followed by TC (183.11 mg/g) then AMX (155.69 mg/g). However, when these molecules were present together in the same solution, it was TC that adsorbed best, followed by SMT then AMX. In addition to this, the sorption process studied was best described by a pseudo-first-order model and it was the Langmuir model that satisfactorily described the equilibrium data.