Adsorption and removal of hydroxychloroquine from aqueous media using Algerian kaolin: Full factorial optimisation, kinetic, thermodynamic, and equilibrium studies

The large diffusion of drugs and their derivatives in our life has become a very serious environmental problem, which requires the development of new and low techniques for their removal from aquatic media. In this context, we studied the use of Algerian kaolin as alow-cost and eco-friendly adsorbent for the elimination of hydroxychloroquine (HCQ) from water. The natural kaolin was characterised by FTIR, SEM, BET, and XRD technique. To obtain a suitable removal of this drug, three physicochemical factors, including the kaolin dose (0.05-0.15 g/L), HCQ initial concentration (5-50 mg/L), and medium pH (3-7) were optimised using the full factorial design (FFD) model. Additionally, a regression quadratic model representing the HCQ adsorption amount (Q(e)) was developed and validated by analysis of variance (ANOVA). The compromise optimal conditions for the three input variables and Q(e) as the dependent output variable were obtained using response surface methodology (RSM) and the composite desirability function approach. The optimal parameters were found to be 0.15 g/L of kaolin, 5 mg/L as HCQ initial concentration, and pH 7. The modelling study indicated that the sorption mechanism obeys the pseudo-second-order kinetic model, and the adsorption isotherms follow the Langmuir model with Q(e) reached 51 mg/g. The thermodynamic study indicates that the adsorption of HCQ is spontaneous, exothermic, and has a stable configuration.