In situ oxidized magnetite membranes from 316L porous stainless steel via a two-stage sintering process for hexavalent chromium [Cr(VI)] removal from aqueous solutions

• A two-stage in situ oxidization was conducted to 316L porous stainless steel tube.
• Crystalline magnetite membranes were achieved.
• The membranes possess excellent mechanical strength and chemical stability.
• The membranes present excellent Cr(VI) removal capability.

Hexavalent chromium, Cr(VI), has seriously polluted groundwater and presents a great threat to human health. The efficient removal of the pollutant remains a high-priority challenge. In this experimental research, magnetite (Fe3O4) membranes were investigated for efficient removal of Cr(VI) from aqueous solutions. The Fe3O4 membranes were achieved via an in situ oxidization of 316L porous stainless steel (PSS) tubes by a two-stage sintering process. Compression tests showed that the elastic limits (σe) of the membrane tubes remained close to those of the unsintered tube. Cr(VI) adsorption on the membranes was highly pH dependent with a maximum adsorption percentage of 100% at pH 4.0. The adsorption kinetics followed the pseudo-second order model, and the adsorption isotherms data fitted the Langmuir isotherm equations. The concentration of Fe ions leached from the membranes was ∼0.01 mg/L. The results verified that the two-stage in situ oxidization of PSS tubes endowed the resultant Fe3O4 membranes with an excellent adsorption potential for Cr(VI) while maintaining high mechanical strength and good chemical stability. The desorption ratio was ∼65% using 0.1 mol/L Na2SO4 solution (pH 13). The membrane is quite promising for the efficient removal of Cr(VI) from aqueous solutions and is readily adaptable to industrial and environmental clean-up applications.