REMOVAL OF HEAVY-METALS FROM AQUEOUS-SOLU TIONS CONTAINING COMPLEXINGAGENTS 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 expe rimental conditions was followed by studies concerning the pH dependan ce 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 solut ions (with initial metal concentrations ranging from 1 to 100 mg/l) wi th acyltioureas, a decrease of the metal content can be achieved in mo st cases, often meeting the requirements for indirect delivery of wast e water. The selective separation of Cu from solutions containing the above mentioned heavy metals and additionally Fe, alkaline and alkalin e earth metals can be achieved by appropriate selection of the pH rang e. Digestion of the metal chelates with diluted H2SO4 yields (with the exception of lead and cobalt) solutions of the metal sulfates which c an be subjected to electrolysis aiming at the recovery of elemental me tals, and the ligand. Comparing to solutions having initial concentrat ions of 100 mg/l enrichment factors up to 100 can be achieved.