Autocatalytic formation of colloidal mercury in the redox reaction betweenHg2+ and Fe2+ and between Hg-2(2+) and Fe2+

The reaction in perchloric acid solution between Hg2+ and Fe2+ was found to proceed extremely slowly until it suddenly exhibited an autocatalytic surg e. In conjunction with this rise, a yellow-green by-product formed and disa ppeared again when the reaction came to an end. In the related reaction bet ween Hg-2(2+) and Fe2+, the autocatalytic behaviour started early and the y ellow-green by-product again appeared. No metallic mercury or other solid f ormed in either reaction, but the production of colloidal mercury was demon strated by the Tyndall effect and by electrophoresis experiments. A five-st ep mechanism for these reactions is proposed and incorporated into a comput er simulation called Mercury. The behaviour predicted by these simulations agrees well with the unusual experimental findings. (C) 2000 Elsevier Scien ce B.V. All rights reserved.