Ion sequestration for scale prevention

A method for sequestering cations that can precipitate from an aqueous composition, the method comprising:

• adding a multi-dentate ligand to an aqueous composition that includes monovalent ions and at least one type of dissolved divalent cation that can precipitate from the aqueous composition to produce scaling;
• then enabling the multi-dentate ligand to bond with the dissolved divalent cation to form an aqueous non-scaling ionic complex;
• then filtering the aqueous non-scaling ionic complex from the aqueous composition with a membrane that retains the aqueous non-scaling ionic complex in a retentate stream and that passes a filtrate stream comprising water and monovalent ions;
• reducing the pH of the retentate stream to release the dissolved divalent cation from the multi-dentate ligand;
• and
• after the dissolved divalent cation is released from the multi-dentate ligand, reintroducing the multi-dentate ligand into additional aqueous composition to form additional non-scaling ionic complex in a predominantly closed loop.