An efficient process for recovering copper as CuO nanoparticles from acidic waste etchant via chemical precipitation and thermal decomposition: Turning waste into value-added product

A succinct process for recovering Cu from acidic waste etchant (AWE) was developed in this work, which included recycling Cu via oxalate precipitation, preparing CuO nanoparticles by thermal decomposing the precipitate, and recovering NaCl via evaporation crystallization. A comparison of copper precipitation by H2C2O4 and Na2C2O4 suggested that an efficient recovery efficiency of Cu was obtained by Na2C2O4 (similar to 99%), which was higher than that by H2C2O4 (80.31%). Through thermodynamic analysis, a H+-release mechanism was proposed to explain the significant difference in copper precipitation between Na2C2O4 and H2C2O4. By parameter optimization, 99.8% of Cu was recovered without adjusting pH value under optimal conditions, such as temperature of 40 degrees C, sodium oxalate of 1.2 mol/mol, and reaction time of 2 h. Furthermore, CuO nanoparticles with a purity of 99.92% and particle size of 30 nm were prepared, and the phase transformation of Cu was investigated in-depth using X-ray diffraction (XRD), Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectrum (FT-IR). Finally, the chloride ions were recovered as NaCl at 99.51% purity. This study provides a potential route to deal with strongly acidic waste etchant and achieve its high-value utilization.