Deep Purification of Copper from Cu(Ii)-Edta Acidic Wastewater by Fe(Iii) Replacement/Diethyldithiocarbamate Precipitation

Cu(II)-EDTA is a highly stable typical metal-organic complex in a wide pH range (3.0-12.0) and difficult to deeply purify Cu(II) by conventional precipitation methods. In this study, Fe(III) replacement/diethyldithiocarbamate (DDTC) precipitation combined process was proposed as a promising method to achieve deep purification of Cu(II) from Cu(II)-EDTA acidic wastewater. The underlying mechanism was elucidated by experimental, chemical equilibrium, and density functional theory (DFT) calculations, laying the basis of development and application. Experimentally, Cu(II) was removed (over 99.99%) and deeply purified (under 0.008 mg/L), which is lower than the most stringent discharge standards for copper in electroplating effluent in China. Chemical equilibrium calculations showed that Fe(III) replacement favor the stoichiometric release of Cu(II) from Cu(II)-EDTA and the formation Fe(III)-EDTA complex under acidic conditions. DFT calculations revealed that DDTC could further precipitate the released free copper ions via the carbon disulfide (–C(=S)–S) functional group while exhibiting a slight effect on the Fe(III) in Fe(III)-EDTA. By introducing a low dosage of Fe(III), the DDTC could efficiently remove the Cu(II) from the Cu(II)-EDTA acid wastewater and realize the near-zero discharge of metal pollutants in metal-organic complex wastewater. It is believed that the main findings may benefit the water pollution reduction and comprehensive recycling of metal resources