Treatment of Heavy Metals from Wastewater Containing EDTA with Sulfide Precipitation

On the base of analysis of species distributions of heavy metals in solutions with MINTEQA2 computer programme at working condition,Na_2S addition was used to remove metals from wastewater containing EDTA solution.The results showed that metal ion Cd~(2+),Cu~(2+),Pb~(2+),and Zn~(2+) were main species in the simulated wastewater without EDTA solution.However,metal-EDTA was found to be predominant fraction among metal species in the simulated wastewater with EDTA solution.Heavy metals Cd~(2+),Cu~(2+),Pb~(2+) were precipitated completely by low concentration of Na_2S from without EDTA solution,and 57.0% of Zn~(2+) was removed.The precipitation percentages of heavy metals decreased with the increasing EDTA concentration.However,the removal of heavy metals increased with increasing Na_2S concentration.At the same condition,the precipitation percentages of Zn by Na_2S addition were lower than those of other metals.According to engineering experimental results,metals and EDTA were separated efficiently by Na_2S addition from the extraction solution.However,high concentration of Na_2S was required to remove all the metals including Zn.