Vivianite precipitation for iron recovery from anaerobic groundwater

Iron in anaerobic groundwater is commonly removed by oxidation followed by sand filtration. This produces large volumes of iron(III)(hydr)oxide sludge with little value. Our research investigates the novel concept of anaerobic iron(II) recovery from groundwater as the valuable mineral vivianite (Fe-3(PO4)(2) center dot 8 H2O) by the addition of phosphate to the water. We found that vivianite precipitated both in synthetic and natural groundwater when the saturation index (SI) was higher than 4. The SI can be increased by elevating the pH, which allows for iron removal at lower concentrations. Anaerobic iron removal reached 93.7% in natural groundwater, which increased further to 99.9% after a subsequent aeration step. Vivianite precipitation followed second order kinetics with a rate constant of 2.3 M(-1)s(-1) and the sludge volume decreased by two third compared to iron oxidation. We therefore conclude that anaerobic iron removal is a promising new approach towards sustainable groundwater treatment.

Automated summary

The addition of phosphate to groundwater can recover anaerobic iron(II) as valuable vivianite. Increasing the pH can enhance the precipitation of vivianite, resulting in higher iron removal efficiency. Therefore, anaerobic iron removal is a promising and sustainable approach for groundwater treatment.