Investigation on the ultrasound intensification of a leaching process applied to copper recycling

Abstract

A langevin type transducer was used to produce US waves, these create cavitation bubbles that generate micro-events of extreme pressure and temperature. Such conditions change how the electrochemical copper cementation reaction works. Silent (no US) and sonicated (with US) assays were done to measure the degree of influence of the sonication on the reaction. Calorimetric characterization, resonance frequency determination, iron titration, and activation energy (Ea) measurements were performed. Increased initial temperature of solution was found to negatively impact calorimetry reproducibility, contrarily to literature findings. Sonication at 20 kHz did not increase radical species concentration significantly when compared to silent tests. Silent rate of leaching was found to be highest at 60°C, pH 2, and 500 RPM with maximum cu recovery at 83% after 4h, and the reaction to be an intermediate controlled process, regarding Ea. When US were applied to same previous parameters, max, cu recovery was 96% after 1h30 min, with similar precipitant factor at 1.09. Reducing RPM from 500 to 200 while using US did not change the behavior of the reaction. Copper nanoparticles might have been produced during sonication at 20 kHz. Cementation at resonance frequency (~40.5 kHz) damaged the reaction efficiency. Power consumption (Wh) per 80% of cu recovery was lower to substantially lower when US was used. A preliminary LCA study was performed, and the sonication process was shown to be more environmentally friendly in terms of global warming potential and ozone layer depletion