Electroless recovery of silver by inherently conducting polymer powders, membranes and composite materials

A wide variety of inherently conducting polymers, including polypyrroles and polyanilines, were shown to reduce silver ion in aqueous solution, demonstrating that these materials may form the basis of a novel approach to silver recovery. The effect of varying the polymer, dopant, and underlying substrate (reticulated vitreous carbon or fabric) was investigated, as was the effect of changing the pH of the solution containing silver. Silver recovery was found to proceed more readily from solutions with near neutral pH than from solutions with strongly acidic pH, and to occur selectively from solutions containing both silver and iron. Scanning electron microscopy (SEM) showed deposits that formed on polymeric materials after prolonged exposure to concentrated silver nitrate solutions were partially crystalline in nature. XPS spectra provided support for a mechanism of silver recovery involving a redox reaction between the polymer and silver ions leading to the formation of silver metal.