Decomplexation & Neutralization & Precipitation by NH ₃∙H ₂O Coupling with Oxidation by O ₂ for the Improved Removal of Cu(II) and Cu(I) from Acidic Copper Etching Wastewater: Efficiency and Mechanisms

Abstract

The lack of developed method for the treatment of acidic copper etching wastewater has always been a tricky problem in the printed circuit board (PCB) industries. In this study, an improved approach of decomplexation & neutralization & precipitation by NH₃∙H₂O coupling with oxidation by O₂ for the removal of Cu(II) and Cu(I) from acidic copper etching wastewater was explored. After the wastewater being treated using NH₃∙H₂O with the constant addition of O₂ at 30 °C under the v(NH₃•H₂O):v(waste) of 0.35, 96.9% of Cut was effectively removed in the form of Cu2(OH)3Cl precipitates. The removal mechanisms for Cu(II) are as follows. (1) NH₃•H₂O reacts with H⁺, leading to the enhancement in the pH value. (2) Cu(II)-Cl(-I) complex reacts with NH₃•H₂O to produce Cu₂(OH)₃Cl. For Cu(I), the removal mechanisms were proposed as follows. (1) The stable CuCl₄^3- is de-complexed by NH₃•H₂O to produce Cu(NH₃)₄+. (2) Then, Cu(NH₃)₄+ is oxidized by O₂ to produce Cu(NH₃)₄²⁺. (3) Cu(NH₃)₄²⁺ reacts with Cl(-I) and H₂O to produce Cu₂(OH)₃Cl.

Keywords: Acidic copper etching wastewater, Decomplexation, Oxygen oxidation, Precipitation, Valence transformation of Cu(I)