Effective adsorption of Pb(ii) from wastewater using MnO(2) loaded MgFe-LD(H)O composites: adsorption behavior and mechanism

Pb(ii) adsorption by MnO(2)/MgFe-layered double hydroxide (MnO(2)/MgFe-LDH) and MnO(2)/MgFe-layered metal oxide (MnO(2)/MgFe-LDO) materials was experimentally studied in lab-scale batches 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 °C for MnO(2)/MgFe-LDH. Langmuir and Freundlich adsorption isotherm models, pseudo-first-order and pseudo-second-order kinetics, Elovich model, and thermodynamic studies were used for exploring the Pb(ii) adsorption mechanism of the two composites. In contrast to MnO(2)/MgFe-LDH, MnO(2)/MgFe-LDO(400 °C) has a stronger adsorption capacity and the Freundlich adsorption isotherm model (R(2) > 0.948), the pseudo-second-order kinetic model (R(2) > 0.998), and the Elovich model (R(2) > 0.950) provide great fits to the experimental data, indicating that the adsorption occurs predominantly via chemisorption. The thermodynamic model suggests that MnO(2)/MgFe-LDO(400 °C) is spontaneously heat-absorbing during the adsorption process. The maximum adsorption capacity of MnO(2)/MgFe-LDO(400 °C) for Pb(ii) was 531.86 mg g(−1) at a dosage of 1.0 g L(−1), pH of 5.0, and temperature of 25 °C. Through characterization analysis, the main mechanisms involved in the adsorption process were precipitation action, complexation with functional groups, electrostatic attraction, cation exchange and isomorphic replacement, and memory effect. Besides, MnO(2)/MgFe-LDO(400 °C) has excellent regeneration ability in five adsorption/desorption experiments. The above results highlight the powerful adsorption capacity of MnO(2)/MgFe-LDO(400 °C) and may inspire the development of new types of nanostructured adsorbents for wastewater remediation.