Aqueous leaching properties and environmental implications of cadmium, lead and zinc trimercaptotriazine (TMT) compounds

2,4,6-Trimercaptotriazine, trisodium salt nonahydrate (TMT-55) is a commerc ial product that is widely used to chemically precipitate cadmium, lead, zi nc and other heavy metals from wastewaters and contaminated natural waters, When mixed with aqueous solutions of TMT-55, aqueous solutions of either r eagent-grade zinc, cadmium, or lead salts precipitate crystalline "Zn-TMT", amorphous or crystalline "Cd-TMT" or amorphous "Pb TMT" (M-3[S3C3N3](2).nH (2)O, where M=Cd2+, Pb2+, and Zn2+ and n greater than or equal to0) that ma y eventually crystallize if stored in air. Laboratory aqueous leaching stud ies over 78-106 days using pH 3 HCl, distilled water (pH 6)and pH 9-10 NaOH evaluated the stability of the Cd-, Pb-, and Zn TMT precipitates. Under pH 3 conditions, the amorphous Cd- and Pb-TMT compounds converted to their cr ystalline forms and amorphous Cd-TMT also crystallized in distilled water, Otherwise, no decomposition products were detected in the leached solid res idues. When compared with the aqueous solubilities of corresponding sulfide s and most hydroxides, the TMT compounds were significantly more soluble in distilled water and pH 3 HCl. (C) 2001 Elsevier Science Ltd. All rights re served.