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 commercial product that is widely used to chemically precipitate cadmium, lead, zinc and other heavy metals from wastewaters and contaminated natural waters. When mixed with aqueous solutions of TMT-55, aqueous solutions of either reagent-grade zinc, cadmium, or lead salts precipitate crystalline 'Zn-TMT', amorphous or crystalline 'Cd-TMT' or amorphous 'Pb-TMT' (M₃[S₃C₃N₃]₂·nH₂O, where M=Cd²⁺, Pb²⁺, and Zn²⁺ and n≥0) that may eventually crystallize if stored in air. Laboratory aqueous leaching studies 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 crystalline forms and amorphous Cd-TMT also crystallized in distilled water. Otherwise, no decomposition products were detected in the leached solid residues. When compared with the aqueous solubilities of corresponding sulfides and most hydroxides, the TMT compounds were significantly more soluble in distilled water and pH 3 HCl.