Effectiveness of commercial reagents for heavy metal removal from water with new insights for future chelate designs

Toxic heavy metals in air, soil, and water are global problems that are a growing threat to the environment. To meet the federal and state guidelines for heavy metal discharge, companies often use chemical precipitation or chelating agents. In order to be competitive economically, many of these chelating ligands are simple, easy to obtain, and, generally offer weak bonding for heavy metals. Laboratory testing of three commercial reagents, trimercaptotriazine (TMT), Thio-Red(R) potassium/sodium thiocarbonate (STC), and HMP-2000 sodium dimethyldithiocarbamate (SDTC) has shown that the compounds were unable to reduce independent solutions containing 50.00 ppm of divalent cadmium, copper, iron, lead, or mercury to meet EPA standards. Additionally, the compounds displayed high leaching rates and in some cases decomposed to produce toxic substances. In contrast, the studies demonstrate that a recently reported sulfur-containing multidentate ligand is both safe and effective for the removal of these metals. (C) 2002 Elsevier Science B.V. All rights reserved.