Irreversible precipitation of mercury and lead

There are immediate concerns with current commercial reagents that are used for heavy metal precipitation; in particular the fact that the reagents ar e not specifically designed to bind the targeted metals. The current litera ture reveals that not only do commercial reagents lack sufficient ability t o strongly bind the metals, but they also fail to provide long-term stabili ty as ligand-metal complexes under a variety of moderate conditions. For th is reason a new ligand was designed and synthesized: 1,3-benzenediamidoetha nethiol (BDETH2). It offers multiple, concerted, bonding sites for heavy me tals and forms a stable metal-ligand precipitate. In this study, the format ion of compounds comprised of this ligand with the divalent metals, lead an d mercury, was explored and the pH stability of the water insoluble precipi tates was determined. The leaching properties of the metal-ligand precipita tes were determined using inductively coupled plasma (ICP) spectroscopy and cold vapor atomic fluorescence spectroscopy (CVAF). The results indicate t hat a 50.00 ppm lead solution at a pH of 4.0 may be reduced to a concentrat ion of 0.05 ppm (99.9% lead removal) and to 0.13 ppm (99.7% lead removal) a t a pH 6.0. A 50.00 ppm mercury solution at pH 4.0 may be reduced to a conc entration of 0.02 ppm (99.97% mercury removal) and to 0.02 ppm (99.97% merc ury removal) at a pH of 6.0. (C) 2001 Published by Elsevier Science B.V.