Electrolytic magnesium recovery from drinking water membrane residuals

The application of advanced membrane processes for drinking water treatment is hampered by the management of the concentrated membrane residuals. This byproduct is typically treated as waste, with the associated costs for disposal. In this study we tested electrolysis as an approach to recover potentially useful products from this waste stream, mitigating its cost of disposal. Aqueous solutions of Mg(NO 3 ) 2 , MgCl 2 , or MgSO 4 similar in concentration to those measured in typical membrane concentrates were utilized as test solutions. Cathodic reduction of these solutions resulted in the deposition of brucite, Mg(OH) 2 , coatings on the surface of the carbon electrode. Recovery was tested in potentiostatic and galvanostatic modes as a function of process parameters and solution composition. Recovery was observed to increase with time, applied voltage, and cell current. The mass deposited also depended upon the electrolyte anion, with under the conditions studied solutions of MgCl 2 being the most amenable to electrolysis.