Removal of diclofenac sodium from aqueous solution using ionic micellar flocculation-assisted adsorption

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Abstract
Diclofenac is a highly toxic anti-inflammatory detected in effluents and wastewater treatment plants. Adsorption is one of the most widely applied technologies to remove micropollutants using activated carbon, but requires a costly and inefficient separation stage, compromising adsorption. In this respect, a novel process is proposed based on ionic micellar flocculation-assisted adsorption (IMFA) using the surfactant sodium dodecanoate to increase adsorption capacity and facilitate phase separation. The efficiency of adsorption and IMFA was assessed based on a kinetic study, equilibrium isotherms, thermodynamic and kinetic separation properties. Adsorption kinetics followed the pseudo-second model indicating a process governed by ionic exchange between sodium diclofenac and the ions present in the activated carbon layers and dodecanoate, with velocity constants of 8.51 and 5.24 g.mg−1.min−1, respectively. Based on the equilibrium isotherms, the maximum adsorption capacity obtained was 49.43 and 51.85 mg.g−1 in adsorption and IMFA, respectively, best represented by the Langmuir adsorption model, assuming adsorption on homogeneous surfaces in the form of monolayers. Thermodynamic analysis revealed that the processes occurred spontaneously, exothermically and that randomness declines at the solid-solution interface. Sedimentation analysis showed that the higher the surfactant concentration the greater the compaction height, higher the decantation speed, and shorter the wastewater clarification time.

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