A decontamination system uses magnetic molecules having ferritin cores to selectively remove target contaminant ions from a solution. The magnetic molecules are based upon a ferritin protein structure and have a very small magnetic ferritin core and a selective ion exchange function attached to its surface. Various types of ion exchange functions can be attached to the magnetic molecules, each of which is designed to remove a specific contaminant such as radioactive ions. The ion exchange functions allow the magnetic molecules to selectively absorb the contaminant ions from a solution while being inert to other non-target ions. The magnetic properties of the magnetic molecule allow the magnetic molecules and the absorbed contaminant ions to be removed from solution by magnetic filtration.