Pretreatmental Processes For PCB Electroless Copper Plating Wastewater

With the rapid development of PCB electroplating industry, electroplating wastewater quantity is becoming vaster, the quality is becoming more complex. Electroless copper on PCB wastewater containing heavy metal ions of copper and organic pollutants which is harmful to human body and environment, must be properly handled before discharge.In this article, based on electroless copper liquid as the research object, which was treated by reduction-acidification process to make waste recycled, then,the electroless copper plating wastewater after recycling was treated by sulfide precipitation process and micro-electrolysis-Fenton process, In order to obtain better pretreatment effect,at the first, conducting the single factor experiment to confirm the change range of relevant parameters.And then,according to the results of orthogonal experiment,analyzing the influence degree of various factors on the experimental results.Finally,based on the results of experiments, the advantages and disadvantages are discussed,the optimal experiment scheme has been defined. The research results are as follows:(1) Using the reduction method of hydrazine,the copper ion concentration in the electroless copper plating bath was reduced greatly.The single factor experiment and orthogonal experiment results showed that the optimal process conditions were as follow:pH=12,the concentration of hydrazine of 60mmol/L,heating temperature of 60 ℃,heating time of 25min,standing time of 70min.The removal rate of Cu2+ could reach to 97.56%,and the concentration of residual Cu2+ was 96.75mg/L under the optimal conditions.Then,treat the waste liquid after reduction method by acidification,to make the EDTA separate out the waste liquid with the precipitation rate of 96.84%.(2) The electroless copper plating wastewater after recycling was treated by further treatment,the following conclusions could be drawn:Sulfide precipitation process could further remove the residual Cu2+.The experiment results showed that the optimal process conditions were as follow:neutralization precipitation time of 15min,pH=12.5,the molar ratio of S to Cu of 1.6:1,sulfide precipitation time of 40min,reaction temperature of 25 ℃,the dosage of PAM of 8.0mg/L.The removal rate of Cu2+ could reach to 99.81%,and the concentration of residual Cu2+ was 0.184mg/L under the optimal conditions.The process got a further removal rate of Cu2+,but there is no obvious treatment effect on COD.The micro-electrolysis method has a certain degree of removal rate of Cu2+ and COD.The single factor experiment and orthogonal experiment results showed that the optimal process conditions were as follow:the mass ratio of Fe to C of 3:2,the total mass of Fe and C of 35g/L,pH=2.0,reaction temperature of 25 ℃ reaction time of 40min.The removal rate of Cu2+ and COD could reach to 99.23% and 69.49%,respectively.And the concentration of residual Cu2+ and COD were 0.745mg/L and 157.99mg/L under the optimal conditions.Then,further treatment were used to the wastewater after the treatment of micro-electrolysis method,it could be found that the treatment effect of Fenton was the best,the concentration of residual Cu2+ and COD were sunk to 0.212mg/L and 37.61mg/L,respectively.(3) In this article, different treatment processes for electroless copper plating wastewater are compared from the aspects of reaction conditions to water quality et al. The results show that the electroless copper plating waste liquid with high concentration could be treated by the reduction-acidification process to recycle the copper powder and EDTA;the removal of copper could reach to a good effect by using sulfide precipitation process aim to the electroless copper plating wastewater with low concentration;micro-electrolysis-Fenton process had a great pretreatment effect on both copper and COD.