Recovery of gold by electroless precipitation from acid solutions using polyaniline

Abstract

The oxidation of the leucoemeraldine (LM) and emeraldine (EM) states of polyaniline (PAN) and the subsequent reprotonation and reduction of the nigraniline (NA) and pernigraniline (PNA) in acid gold solution were utilized for the spontaneous and sustained reduction of gold. The rate of Au reduction is strongly dependent on the intrinsic oxidation state of the polymer and the polymer surface area. The rate also increases with decreasing pH of the chloroauric solution to about pH ~ 1. X-ray photoelectron spectroscopic (XPS) results indicate that only elemental gold or Au(0) accumulates on the polymer surface. The N1s core-level spectra of the protonated and base form of EM films after Au reduction confirm that the intrinsic structure of the polymer remains intact. The process, however, is limited by the decreasing effective surface area of the polymer due to Au deposition. The results indicate that an LM film accumulated up to five times its own weight of Au (Au/monomer mole ratio > 2) before the recovery rate was significantly retarded.