Mechanism of Reductive Stripping-Precipitation of Ultrafine Au Particles from Au(III)-Loaded MIBK

Abstract

Experimental studies were conducted to elucidate a possible mechanism for the reductive stripping-precipitation of ultrafine particulates of Au from Au(III)-loaded MIBK. The principal findings are as follows: (1) Under the irradiation of day light, the yellow color of Au(III)-loaded MIBK fades gradually at the same time, the equilibrium potential shifts towards the noble direction, suggesting the decomposition of (H⁺MIBKAuCl₄⁻)_o into (H⁺MIBKAuCl₂(OH)₂⁻)_o or (H⁺MIBKAuCl₂⁻)_o via a photochemical route. (2) Water acts as a reductant of Au(III)-loaded MIBK under the catalytic action of a small amount of a suitable reducing agent to precipitate ultrafine particulates of Au. (3) The role of H⁺ or Cl⁻ on the reductive stripping-precipitation reactions was also studied. The rate of reductive stripping-precipitation of Au increases with the increase in temperature under the presence of NaCl, exhibiting an activation energy of 43.7 kJ·mol⁻¹.