If you know a non-solvent of the polymer that is miscible with water, slowly add that solvent to water till a cloudiness forms and then use a centrifuge to precipitate the polymer. Otherwise you can try dialysis. But these methods work only if the polymer and metal are not linked by any type of bonds.
If this solution consist of dissolved polymer and the colloids of the metal ions you can try to centrifuge this solution directly, if you see a sediment that means it is done.
I think the use of membrane dialysis is the best choice according to your requirements. Just look for a membrane with molecular cut-off with respect to the molecular weight of your polymer. Other possibility is to work under polyelectrolyte salting-out conditions. Finally, ion-exchange chromatography is also possible to use. This question is strongly covered in the field of polymer-metal complexes sorption and disorption. Regards