Efficient solid amino acid–clinoptilolite nanoparticles adsorbent for Mn(II) removal: A comprehensive study on designing the experiments, thermodynamic and kinetic aspects

Glutamic acid-clinoptilolite nanoparticles (GA-CNP) was used for the Mn(II) removal in aquatic media. XRD, FT-IR, SEM, TG analyzer and energy dispersive analysis X-ray spectroscopy (EDX) were used for the characterization of the raw and the modified samples. Initial experiments showed a maximum adsorption capacity of 0.572 mmol Mn/g for the raw CNP while the modified CNP-GA showed a value of 0.691 mmol Mn/g, confirming the positive role of the CNP modification in Mn(II) removal. Designing the experiments by response surface methodology (RSM) showed a quadratic model for the processing of the data obtained in the removal process. The optimum conditions to achieve maximum adsorption were suggested as initial Mn(II) concentration: 583 mg/L, contact time: 132 min, CNP-GA dosage: 5 g L−1 and manganese solution pH: 3.5. The importance of each term was calculated by the Parreto analysis and the results showed that the singular factors have the sequence of adsorbent dosage (37.4%)>CMn (24.1%) >contacting time (2.2%) which agrees with the sequence obtained by the F-values. For the terms containing interaction effects the most importance percentages of 11.1% and 7% obtained for time-dosage and pH-CMn, respectively. Among the quadratic terms, the most percentage of 9.8% was obtained for (CMn)2. Adsorption isotherms of Mn(II) well modeled by Langmuir equation, showing a monolayer sorption of Mn(II), while a pseudo-second-order rate equation well modeled the kinetics of the process, confirming a chemical reaction limits the rate of the removal process. [Display omitted] •Efficient Mn(II) removal by both raw CMP and CNP.•Successful modification of CNP or CMP by glutamic acid in acidic medium.•Synergistic removal efficiency of the modified samples concerning the raw samples.•Higher interactions of adsorbent dosage-time on the Mn(II) removal.•Monolayer sorption of Mn(II) confirmed by Langmuir model.