Selective extraction of heavy metals from galvanic sludge by chelators

Treatment and disposal of waste water of electroplating industries is a difficult task. The use of complexons for fixation of heavy metal ions from contaminated solutions and galvanic slurries is one of the priority directions. Galvanic slurries are metal hydroxides formed as a result of treatment of wastewater with alkalis. The composition of the sludge is unstable. It’s used dry galvanic sludge with a gross content of heavy metals: copper - 5.62; nickel - 4.83; zinc - 3.64; chromium - 7.65 g/kg. Pyrocatechin and disodium salt of EDTA-Na ethylenediaminetetraacetic acid were used as complexons. The processes of leaching of ions of heavy metals (copper, nickel, chromium, zinc) from waste water of galvanic production by complexons are investigated. In the processing of slurries of galvanic sludge part chelators of metal ions from the sludge is fixed with a chelating agent. Complexonate metals in solution dissociate with the formation of metal ions. To determine the optimal concentrations of complexons, the dependences of the concentration of metal ions in the solution (filtrate) on the concentration of complexons were studied. Measurements of metal ion concentrations were carried out at varying concentrations of complexons in 0.1-1.2 g/l. In this range, the using of increase pyrocatechin concentration undo 1.0 g/l follow increases the concentration of heavy metal ions in the solution: nickel - 6.5-37; copper - 4.6-31.0; chromium - 0.5-3.5; zinc - 0.4-2.3 mg/l. The concentrations of nickel and copper ions exceed the concentrations of chromium and zinc on average 6 times. This fact can be explained from the perspective of mentalnosti ligand. Pyrocatechin with nickel and copper ions forms stronger mononuclear complexes than with chromium and zinc. In addition, complexes with nickel and copper are more dissociated in solutions. When using EDTA-Na as a complexon in the given concentration range, the difference in the concentrations of metal ions in the solution is less significant than in the case of pyrocatechin. With an increase in the concentration of EDTA-Na from 0.1 to 1.2 g/l, the concentration of heavy metal ions in the solution increases, then passes through the maxima at a concentration of complexon 0.5 g/l and decreases: nickel - 1.0-5.0-0.6; copper -1.5-8.0-0.5; chrome - 1.0-3.2-1.5; zinc - 0.6-2.0-1.4 mg/l. Action of complexons selectively. Greater activity is manifested in the case of copper and zinc ions, which is associated with a higher stability of the complexes of these metals in comparison with zinc and chromium. The effect of chelators selectively. The optimizing the leaching conditions occur the degree copper and nickel extraction by complexons more than 90 %, zinc and chromium - more than 60 %.