Selective adsorption of gold and silver in bromine solutions by acetate cellulose composite membranes coated with polyaniline or polypyrrole

This paper presents the selective adsorption of bromine-metallic complexes of Au and Ag on composite membranes, as well as the desorption process and redoping of the conducting polymers. The polyaniline (PANI) and polypyrrole (PPy) membranes exhibited relevant adsorption properties. 72% for gold and 98% for silver with PANI, 50% for gold and 97% for silver with PPy, in bromine complexes. The adsorption capabilities of the composite membranes were attributed to the ion exchange between the dopant and the AuBr₄ ⁻ or AgBr₂ ⁻ complexes. Both materials fitted to a Langmuir isotherm. PANI-based membranes reached 31.4% of gold and 54.4% of silver desorption whereas PPy-based membranes reached 54% of gold and 28.8% of silver. Redoping studies suggested the potential reuse of the PANI-based membranes at least for six cycles of the adsorption/desorption process. The preparation of cellulose acetate membranes modified with poly (acrylic acid) and triphenyl phosphate and coated with the conducting polymers, PANI or PPy was in accordance to our previously reported method. The composite membranes were characterized by FT-IR, scanning electron microscopy, electrical conductivity measurements, I–V, mechanical tests, contact angle measurements, XRD and energy disperse spectroscopy. The novelty of the present work is the combination of electroconductive polymers, for the recovery of metals, and bromide as a leachate, less harmful than the traditionally used leachers.