A Hydrodynamic Cavitation - High Voltage Discharge in Water Procedure for Recycling Platinum Group Metals Contained in Three-way Catalyst Converters

Abstract

A simultaneous “hydrodynamic cavitation - high voltage discharge in water” (HCHVD) procedure used for recycling platinum group metals (PGM), such as Pd and Pt, found in three-way catalyst converters is presented. During hydrodynamic cavitation high shear forces was provided by using a nozzle with a throat diameter of 0.2 mm. A pressure of 60 MPa was obtained by using a piston pump. For the first stage of the procedure cavitating submerged jets acted locally on the milled catalyst dispersed in deionized water in the absence of electric discharge. In the second stage, hydrodynamic cavitation and high voltage discharge in water - at 5 kV - was simultaneously used. As-obtained samples from both stages were analyzed by scanning electron microscopy and transmission electron microscopy. Results highlighted that for the first stage one obtained round shaped Pd and Pt nanoparticles (22.8 nm) randomly distributed on the Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> matrix. For the second stage electron microscopy showed crystals of Pd and Pt with rectangular faces about 20 times larger then the first case (503.08 nm) for the nanoparticles randomly distributed on the Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> matrix.