Removal Of Cr(Ⅵ) From Aqueous Solutions With Porous Stainless Steel Supported Iron Oxides Membranes

Hexavalent chromium, Cr(VI), is one of the main heavy metal contaminants in water. Long-term drinking water contaminated with Cr(VI) is considered to be carcinogenic, mutagenic and teratogenicon to the human body. Traditional methods for the removal of Cr(VI) are apt to produce secondary pollutant, and require complicated pretreatments, and show higher operational costs. Nanomaterials present high adsorption efficiency and have been widely researched for the environmental remedy. However, the risk of their residual in the environment keeps unknown. Organic membranes based heavy metal removal methods have been considered as a promising technique. The study explores the preparation of an in situ iron oxide membrane from 316 L porous stainless steel tubes and its performance for the removal of Cr(VI) from aqueous solutions. The main results of the study are as follows.1. Different iron oxide membranes were obtained when the porous stainless steel substrate was sintered via different process. An in situ oxidized Fe2O3 membrane was obtained via the one-stage sintering(only in air), and an in situ oxidized Fe3O4 membrane was obtained via the two-stage sintering(in air followed in nitrogen) at an atmosphere changing temperature of 400oC. The surface of the in situ oxidized Fe3O4 membrane was covered with homogenous small particles of Fe3O4. The in situ oxidized Fe3O4 membranes showed better Cr(VI) adsorption ability, better chemical stability and better mechanical strength. The pH of zero point charge of the in situ oxidized Fe3O4 membrane was ~pH8.08.2. Compared with the Fe3O4 membranes derived by the sol-gel technique, the in situ oxidized Fe3O4 membranes showed better Cr(VI) adsorption performance at different Cr(VI) initial concentrations and with different acids to adjust the pH of solutions.3. The detail Cr(VI) adsorption performance of the as-prepared in situ oxidized Fe3O4 membranes were discussed. The results showed that a maximum adsorption percentage of 100% was obtained at the initial pH value of 4.0 and the initial concentration of 5mg/L. The adsorption kinetics followed the pseudo-second order model, and the adsorption isotherms data fitted the Langmuir isotherm equations. The adsorption process was predominantly based on the mechanism of electrostatic attraction, while the chemical adsorption was complementing.4. A desorption ratio of 60–70% was achieved by using the mixed desorption buffer of 0.1 mol/L Na2SO4 and NaOH solution(pH13).