The transport of Au(III) acid across polymer inclusion membranes (PIM) from concentrated hydrochloric media using Kelex 100 (7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline) as carrier and 2-nitrophenyloctylether as plasticizer is studied. The experimental conditions employed (feed HCl concentration, nature and concentration of stripping reagents, and membrane composition) were optimized for the quantitative recovery of the metal, and a quantitative evaluation of the efficiency factors of the separation system (permeability, selectivity, and stability) is performed. The membrane extraction equilibrium reaction and its corresponding extraction equilibrium constant were determined as well. Percolation theory was applied for modeling the system because a threshold concentration value in the transport profiles was observed. In addition, a Teas graph based on Hansen tri-dimensional solubility parameters was used to account for component interactions within the membrane while transmission infrared mapping microspectroscopy was employed to verify predictions obtained from the theoretical schemes.