Vivianite recovery from anaerobic groundwater reverse osmosis concentrate

To meet the increasing drinking water demand, membrane technologies are used to treat previously unavailable water sources. A byproduct of membrane technologies is the concentrate stream, containing valuable resources in higher concentrations. We studied the recovery of iron from different groundwater matrices and anaerobic reverse osmosis (RO) concentrates via precipitation of vivianite and the co-removal of other common groundwater divalent cations Mn²⁺, Mg²⁺ and Ca²⁺ during vivianite precipitation. The formed precipitates were characterized using X-Ray Diffraction and Scanning Electron Microscopy. Vivianite precipitation removed a maximum of 89 % of Fe²⁺ in raw groundwater and 52 % Fe²⁺ from RO concentrate. Substantial co-removal of Mn²⁺ (max 91 %) and limited co-removal of Mg²⁺ (max 7 %) were found, without hindering Fe removal efficiencies or altering morphological changes of the vivianite crystal. In contrast, co-removal of Ca²⁺ occurred at the expense of iron removal, forming amorphous calcium phosphate precipitates. This study shows the potential of vivianite precipitation for iron recovery across a wide range of groundwater matrices and highlights the need for further research to optimize this novel method to treat concentrate streams that are challenging to dispose of.