Removal of heavy metal ions from zinc-nickel electrodeposition process dragout tank wastewater

A technology has been developed for treating wastewater from a drag out tank after the Zn-Ni alloy electroplating stage from alkaline electroplating solutions in order to remove zinc and nickel ions.This technology includes three successive stages: acidification of wastewater up to a pH = 8.5, leading to partial removal of zinc in the form of hydroxide, then treatment with a low-molecular precipitant (LMP) of the inorganic sulfide class, ensuring a decrease in the concentration of zinc ions to the required value, and subsequent treatment of wastewater with an organosulfide precipitant (OSP), as a result of which removal of nickel ions to the value of maximum allowable concentration (MAC) is achieved.To remove the resulting sediments, filtration should be carried out between stages.The developed technology does not require significant modernization of existing treatment facilities.The possibility of wastewater purification by electroplating of zinc and nickel ions on the cathode was investigated.It was shown that when using copper-plated carbon fiber as a cathode material, the concentration of zinc in wastewater was reduced by 15 times, and nickel by 2 times.Treating wastewater from heavy metal ions to MAC values was not achieved by this method and, given its labor intensity and high costs, it does not seem appropriate in this case.