one of the biggest needs in the separations and waste handling and reduction area is a method for dewatering ion - containing solutions . unexpectedly , it has been found that phosphazene polymers can discriminate between water and metal ions , allowing water to pass through the membrane while retaining the ions . this unexpected result , along with the inherent chemical and thermal stability of the phosphazene polymers , yields a powerful tool for separating and dewatering metal - ion - containing solutions .