Study On Treatment Of Electroplating Wastewater Containing Copper Ions, Nickel Ions And Complexing Agents By Chemical Methods

Organic electroplating wastewater contained a large amount of heavy metals, if not treated and discharged directly into water bodies; it caused great damage to the ecological environment. Electroplating wastewater contained a large number of complexing agents too, heavy metal ions and complexing agent would form a stable chelate, which was difficult to removel by forming hydroxide or sulfide precipitation, and therefore it was hard to remove heavy metal ions from wastewater in the conventional chemical precipitation method. This maked complexing heavy metal wastewater be a typical difficulty in electroplating wastewater. So the main purpose of our research project was to explore the process of dealing with such waste water, and the best process parameters of the mehtods.The study explored the feasibility of a sequential for treating electric plating wastewater containing copper ions, nickel ions and complexing agents established the optimum parameters for it. It broken complexation of heavy metal wastewater by Fenton or Fenton-like, and then we used hydroxide precipitation to remove heavy metals ions and other pollutants from wastewater. The effects of initial pH, H₂O₂initial concentration,[Fe²⁺orFe³⁺]/[H₂O₂]、 reaction time, reaction temperature, pH of hydroxide precipitation, precipitants were investigated on the whole process. Then taking into account less effective treatment of the ordinary neutralization and sedimentation, and the problem of secondary pollution of metal sludge, we used ferrite coprecipitation to treat wastewater, and explored the reaction mechanism of the whole procedure.The conclusions can be drawn as following:（1） The study explored the feasibility of a sequential procedure （the combination of the Fenton method and the hydroxide precipitation）, for treating electric plating wastewater, and established the optimum parameters for it. Conclusions showed that at pH=3,[H₂O₂]=4.162g/L,[Fe²⁺]/[H₂O₂]=0.2, T=25℃, t=60min, Stirring speed was150r/min, pH of Hydroxide precipitation was10, the optimistic conditions were determined65.38%of COD、99.01%of Cu²⁺、99.03%of Ni²⁺ removal were achieved. At the same condition, when the Ca（OH）2was used as the Precipitant,80.41%of COD、99.35%of Cu²⁺、99.68%of Ni²⁺ removal were achieved. So the efficiency of Ca（OH）2was better than NaOH as the precipitant.（2） It was effective to remove copper and nickel from wastewater by hydroxide precipitation combined with Fenton process or Fenton-like process. The optimum process conditions for these two process systems:pH=3、[H₂O₂]=4.162g/L、[Fe²⁺]/[H₂O₂]=0.2、 T=25℃、t=60min、pH of Hydroxide precipitation was10; Removal efficiency of the two processes was quite high, and because of the ligand exchange mechanism, the Fenton-like process is more efficient than the Fenton process for the water treatment.（3）The optimum conditions for the following ferrite co-precipitation process: precipitation pH=11, aeration flow rate was25mL/min, Fe/Me=10, the reaction temperature was50°C, aeration contact time was60min.99.94%of Cu²⁺、99.81%of Ni²⁺ removal were achieved.The treated water reached the first-grade national discharge standard.（4） Under the optimum conditions, the magnetic ferrite crystal could be gotten from the ferrite process. The structural determination of the sludge was investigated by using XRD. It was determined that the nickel-iron compounds obtained in the process were in the form of Pentlandite （NiFe₂O₄）.The composition of sludge may also contain Fe₃O₄, CuO·3H₂O and so on. Not only these crystals are not causing secondary pollution, but also they could be used as magnetic materials for recycling.