New extraction method for precious metals using pulsed discharge in supercritical carbon dioxide

Technology for the recycling of precious metals is growing increasingly important due to their scarcity and high industrial utility value. In recent years, a precious metal extraction technology using the mixed solvent of supercritical carbon dioxide and a chelating agent has been researched. The experiment is shown in the following steps: 1) The chelating agent dissolves in supercritical carbon dioxide; 2) Extraction process: metal combines with the chelating agent in supercritical carbon dioxide, with the combined compound called the complex; 3) Back extraction process: the complex is separated into the chelating agent and the metal. Reduction of gas pressure during the post extraction process and separation of the complex during back extraction process allows reuse of the carbon dioxide and chelating agent. However, this system is not entirely green due to the use of acid or alkali for complex separation during back extraction process.In contrast, the authors here report on success in generation of pulsed streamer discharge in supercritical carbon dioxide by pulsed power technology and on the study of discharge initiation mechanism under positive and negative polarity 2, 3. The aim of this study is the realization of a solvent-free back extraction process using pulsed discharge phenomena in supercritical carbon dioxide. Back extraction efficiency is calculated from extracted material after discharge treatment. In this study, acetyl acetone and platinum are adopted as chelating agent and sample, respectively.