Removal of Cr(VI) from wastewater by artificial zeolite spheres loaded with nano Fe-Al bimetallic oxide in constructed wetland.

In order to solve the problems of poor adsorption capacity and low stability in treating heavy metal wastewater with traditional constructed wetland (CW) fillers, a new type of filler, artificial zeolite spheres loaded with nano Fe-Al bimetallic oxide (hereinafter referred to as composite zeolite spheres), was prepared for Cr(VI) removal from wastewater. The results indicated that nano Fe-Al bimetallic oxide was an effective material for Cr(VI) removal with the maximal removal efficiency of 84.9% at initial Cr(VI) concentration of 20 mg/L (pH = 3). The micro-reactor experiment further verified that composite zeolite spheres had better removal performance on Cr(VI) than traditional filler. Fourier-transform infrared (FT-IR), X-ray diffractometry (XRD) and X-Ray photoemission spectroscopy (XPS) results demonstrated that -OH groups reduced Cr(VI) to Cr(III), and then the Cr(III) was removed by forming CrxFe1-x(OH)3 precipitation with Fe(III) or formed Cr(OH)3 precipitation with Al-OH through the ion exchange. This study provided an effective approach for treating Cr(VI) wastewater by using a new composite zeolite in constructed wetlands (CWs).