The adsorption of Mn(II) by insolubilized humic acid.

The eco-friendly and non-toxic natural organic substance, insolubilized humic acid (IHA), was used to remove Mn(II) from aqueous solutions. The adsorption characteristics were studied through a series of static adsorption tests. The results show that conditions such as the dose, the pH of the solution and the initial concentration of Mn(II) all affect removal efficiency, and the optimal pH value was 5.5. The sorption process for Mn(II) on IHA conforms to the pseudo-second-order adsorption kinetic model and intra-particle diffusion is not the only factor affecting the adsorption rate. Both Langmuir and Freundlich models can describe this adsorption behavior, and the experimental maximum adsorption capacity of IHA was 52.87 mg/g under optimal conditions. The thermodynamic analysis of adsorption shows that the adsorption process is a non-spontaneous endothermic physical reaction. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to characterize the samples, it was found that as IHA successfully adsorbed Mn(II), the surface morphology of IHA changed after the adsorption reaction. The adsorption mechanism for Mn(II) on IHA is to provide electron pairs for carboxyl, phenolic hydroxyl and other functional groups to form stable complexes with Mn(II).