Phosphorus hyperaccumulation in nano-MgO using a circular recovery process based on multiple phase transitions from periclase to brucite

Phosphorus recovery from water is not only necessary for the protection of aquatic environments but also to meet the needs of sustainable development. We find that the adsorption capacity of nano-MgO is far from being fully utilized because of its simultaneous hydration into brucite. Annealing is a useful method of recovering its adsorption capacity without the need for desorption. Phosphate can be accumulated to a much higher level, even surpassing its theoretical equilibrium adsorption limit, so that high-quality fertilizer can be obtained (115.9 mg-P/g-MgO). Phosphate ions exist as HPO4(2-) and PO4(3-) in the sorbent during its phase transition from periclase to brucite, which is the main reason for its extremely high and reactivatable phosphorus recovery properties. This finding not only provides a new efficient phosphorous recovery strategy but will also lead to new understandings of traditional reactive nano-sorbents.