Adsorption characteristics and mechanisms of ciprofloxacin on polyanion-modified laterite material

In this work, polyanion polystyrene sulfonate modified laterite (PML) was used as an excellent material to remove ciprofloxacin (CFX) in water. The CFX adsorption on PML was affected by factors such as pH, PML dosage, contact time, ionic strength, and operating temperature. Under optimum conditions (pH 5; 150 min; 5 mg/mL, 10 mM NaCl, 25 °C) with an initial CFX concentration of 20 ppm, the maximum removal of CFX using PML reached greater than 96%. Langmuir isotherm model provided the best fit to the experimental results of the CFX adsorption process onto PML with the maximum capacity was 10.51 mg/g. Adsorption kinetics were in good agreement with pseudo-second-order. The ∆H⁰ value was − 12.090 kJ.mol⁻¹, and the ∆G⁰ value was − 2.345 kJ.mol⁻¹, declaring that the CFX adsorption onto PML was a spontaneous process and exothermal. Adsorption mechanisms of CFX on PML were controlled by both electrostatic interaction and non-electrostatic interaction. The adsorption constant in the Temkin model was 1.700 J/mol, and the energy value in Dubinin–Radushkevich model was 2.371 kJ/mol, proving that CFX adsorption on PML is a physical adsorption process. After five recycles, the CFX removal was still higher than 77%, while the CFX removal from wastewater was approximately 96%.