A coupled electrochemical process for schwertmannite recovery from acid mine drainage: Important roles of anodic reactive oxygen species and cathodic alkaline

The increasing need for sustainable acid mine drainage (AMD) treatment has spurred much attention to strategic development of resource recovery. Along this line, we envisage that a coupled electrochemical system involving anodic Fe(II) oxidation and cathodic alkaline production will facilitate in situ synthesis of schwertmannite from AMD. Multiple physicochemical studies showed the successful formation of electrochemistry-induced schwertmannite, with its surface structure and chemical composition closely related to the applied current. A low current (e.g., 50 mA) led to the formation of schwertmannite having a small specific surface area (SSA) of 122.8 m 2 g −1 and containing small amounts of –OH groups (formula Fe 8 O 8 (OH) 4.49 (SO 4 ) 1.76 ), whereas a large current (e.g., 200 mA) led to schwertmannite high in SSA (169.5 m 2 g −1 ) and amounts of –OH groups (formula Fe 8 O 8 (OH) 5.16 (SO 4 ) 1.42 ). Mechanistic studies revealed that the reactive oxygen species (ROS)-mediated pathway, rather than the direct oxidation pathway, plays a dominant role in accelerating Fe(II) oxidation, especially at high currents. The abundance of •OH in the bulk solution, along with the cathodic production of OH − , were the key to obtaining schwertmannite with desirable properties. It was also found to function as a powerful sorbent in removal of arsenic species from the aqueous phase.