cations that can precipitate from an aqueous composition to produce scaling are sequestered by adding a multi - dentate ligand to the aqueous composition . the multi - dentate ligand bonds with the cation to form a non - scaling ionic complex ; and the aqueous solution with the ionic complex is used in a process that produces substantially pure water from the aqueous composition , where the cation , absent formation of the ionic complex , is subject to scaling . the ph of the aqueous composition is then reduced to release the cation from the multi - dentate ligand ; and the multi - dentate ligand , after the cation is released , is then reused in a predominantly closed loop .