NOx Removal and Copper Recovery from the Leaching process for Waste Printed Circuit Boards: Performance Evaluation and Potential Environmental Impact Assessment

Abstract

Abstract Resource recovery is vital for small and medium-sized enterprises to achieve a circular economy. The economic benefits of the recovery of precious metals from electronic waste, such as waste printed circuit boards (WPCBs), are reduced by the emission of secondary pollutants emissions from pre-treatment processes. This study recovers copper from the WPCB acid leaching process and removes NOx post-process using a high gravity rotating packed bed (RPB). The results show that the copper recovery ratio increases to 99.75% for the displacement reaction between iron powder and copper nitrate. The kinetic analysis of copper dissolution is used to simulate the NOx emissions during acid leaching with an R-square value equal to 0.872. Three oxidants, including H2O2(aq), ClO2(aq), and ozone solutions with an adjusted pH corresponding to different NaOH concentrations, are used to remove NOx. A significantly greater amount of NOx is removed using a 0.06 M NaOH solution as an absorbent. The highest NOx removal ratio is 91.2% for ozone oxidation, a 152-fold gravity level and a gas-to-liquid (G/L) ratio of 0.83. The gas side mass transfer coefficients (KGa) for NOx range from 0.003 to 0.012 1/s and are comparable to the values for previous studies. The results of a life-cycle analysis show that the NOx removal ratio, the nitric acid recycling ratio and the copper recovery ratio are 85%, 80%, and 100% so environmental impact on the ecosystem, human health and resource depletion is reduced by 10%, compared to a situation whereby no NOx is removed.