Utilization of wastewater drainage of galvanic production with the use of complexons

The processes of leaching heavy metals ions - copper, nickel, chromium, zinc - by complexes from the wastewater drainage of galvanic production have been studied. Pyrocatechol and disodium salt of ethylenediaminetetraacetic acid (EDTA-Na) were used as complexons. Chelators in a specific concentration were treated with a suspension of galvanic sludge in the ratio S:L=1:5. The filtrate was used to determine the content of heavy metals transferred into a solution from galvanic sludge. The recovery rate of heavy metals reaches 87 % for copper and nickel, and about 70 % for zinc and chromium. The chelator influence is selective. The greater activity is demonstrated by copper and zinc ions, which is related to higher stability of these complexes as compared to zinc and chromium complexes. The dependence of the metal ions concentration (CM) in the solution on the concentration of complexons (CK) has been studied. The dependences CM from CK are linear for pyrocatechol complexes with all metals in the entire interval of concentrations of the chelating agent. At CK = 1 g/L, the CM values are maximal in the solution and equal 31.0 and 37.0 mg/L for copper and zinc, 3.4 and 2.3 mg/L for chromium and zinc, respectively. Lower concentrations of chromium and zinc ions are explained by low rates of complex formation, as well as their low stability in comparison with complexonates of other metals. In the case of EDTA-Na, CM-CK dependences have maxima with a further decrease in concentration of metal ions in the solution with an increase in concentration of the complex. This fact is explained by the tendency of EDTA-Na to form multi-ligand complexes with different solubility. The maximum concentration of metal ions amount to 8.0 and 6.0 mg/L for copper and nickel, respectively, 3.2 and 2.0 mg/L for chromium and zinc at the chelating agent concentration of 0.5 g/L. Complexation with metal ions significantly depends on the medium acidity. The degree of extraction of copper ions by pyrocatechol at different pH has been studied. At pH = 4.0 the degree of extraction is more than 80 %. Increasing the pH value from 4.0 to 10.0 leads to a decrease in the degree of extraction by almost 3 times. Acid leaching of metal ions from galvanic sludge by the sulfuric acid treatment in the presence of pyrocatechol complex has been carried out. In an acidic environment, the complexing processes are accelerated while maintaining a high degree of extraction. The metal complexonate stability values are different. The factors affecting the extraction of metals from the complexonates have been considered.