Adsorption of Cr(Ⅵ) in Water by Maifanite Modified with Different LDHs Coatings

Abstract

Under alkaline conditions, the hydrothermal coprecipitation method was used to form different layered double hydroxides (LDHs) by combining different bivalent and trivalent metal compounds, such as ZnCl2, MgCl2, AlCl3, and FeCl3, and then LDHs were coated on the surface of the original maifanite. The effect of LDHs coating-modified maifanite on the improvement of Cr(Ⅵ) adsorption in water was studied using isothermal adsorption, desorption, non-isothermal adsorption, adsorption kinetics, pH, and competitive adsorption tests, respectively. The results show that the maximum theoretical adsorption capacity of modified maifanite for Cr(Ⅵ) is close to ten times that of original maifanite at 15℃. The adsorption effect of ZnAl-LDHs coating-loaded modified maifanite is better than that of other LDHs-coating modified maifanites. In contrast, the results of the desorption experiments show that maifanite coated with LDHs enhances the reuse of substrates. The thermodynamic parameters of the substrate for Cr(Ⅵ) adsorption in the experiment were △Gθ < 0, △Hθ < 0, △Sθ > 0, indicating that the substrate adsorption process of Cr(Ⅵ) is spontaneous and exothermic. Based on the adsorption kinetics study, the adsorption process of Cr(Ⅵ) by maifanite could be fitted using a pseudo-secondary reaction process. The adsorption type was mainly chemisorption. By selecting the suitable metal ion combination method to prepare different LDHs-coating modified maifanites, the Cr(Ⅵ) performance can effectively be improved.