Effective adsorption of Pb (II) from wastewater using MnO2 loaded MgFe-LD(H)O composites: Adsorption behavior and mechanism

Abstract

Abstract Pb (II) adsorption by MnO2/ MgFe-layered double hydroxide (MnO2/ MgFe-LDH) and MnO2/ MgFe- Layered metal oxides (MnO2/ MgFe-LDO) materials were experimentally studied in lab-scale batch for remediation property and mechanism analysis. Based on our results, the optimum adsorption capacity for Pb (II) was achieved at the calcination temperature of 400 ℃ for MnO2/ MgFe-LDH. Langmuir and Freundlich adsorption isotherm models, quasi-primary and quasi-secondary kinetics, Elovich model, and thermodynamic studies were used for exploring Pb (II) adsorption mechanism by the two composites. In contrast to MnO2/ MgFe-LDH, MnO2/ MgFe-LDO400℃ have a stronger adsorption capacity, the results show that the Freundlich adsorption isotherm model (R2 > 0.948), the quasi-secondary kinetic model (R2 > 0.998), and the Elovich model (R2 > 0.950) provide great fits to the experimental data, indicating the adsorption of a predominantly chemisorption. The maximum adsorption capacity of MnO2/ MgFe-LDO400°C for Pb (Ⅱ) was 531.86 mg·g− 1 at the dosage of 1.0 g·L− 1, pH of 5.0, and temperature of 25°C. The thermodynamic model suggests that MnO2/ MgFe-LDO400℃ is spontaneously heat-absorbing during the adsorption process. Through characterization analysis, the main mechanisms involved in the adsorption process were include precipitation action, complexation with functional groups, electrostatic attraction, cation exchange and isomorphic replacement, and memory effect. Besides, MnO2/ MgFe-LDO400°C has excellent regeneration ability in five adsorption/desorption experiments. The above results highlight the powerful adsorption capacity of MnO2/ MgFe-LDO400°C and may inspire the development of new types of nanostructured adsorbents for wastewater remediation.