Removal of heavy metals from aqueous solutions containing complexing agents by precipitation with acylthioureas

Several N'-acyl-N, N-dialkylthiourea derivatives have been applied as precipitants for the removal of Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) from aqueous solutions. A general optimization of the experimental conditions was followed by studies concerning the pH dependance of complex formation as well as the influence of competing ligands (such as citric acid, tartaric acid, ammonia, glycine) on the residual concentration of heavy metal ions. After the treatment of model solutions (with initial metal concentrations ranging from 1 to 100 mg/l) with acyltioureas, a decrease of the metal content can be achieved in most cases, often meeting the requirements for indirect delivery of waste water. The selective separation of Cu from solutions containing the above mentioned heavy metals and additionally Fe, alkaline and alkaline earth metals can be achieved by appropriate selection of the pH range. Digestion of the metal chelates with diluted H2SO4 yields (with the exception of lead and cobalt) solutions of the metal sulfates which can be subjected to electrolysis aiming at the recovery of elemental metals, and the ligand. Comparing to solutions having initial concentrations of 100 mg/l enrichment factors up to 100 can be achieved.