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

Abstract

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.