Recovery of Rare-Earth Elements from Printed Circuit Boards by Vacuum Pyrolysis and Multiple Electrostatic Separation

Abstract

The influence of the multi-stage electrostatic separation (ESS) of mechanically treated and magnetically separated waste electronic material and the pyrolysis of the selected ESS fraction on the distribution of metal elements (MEs), elements contained in refractory oxides (EROs), bromine (Br), and rare-earth elements (REEs) contained in waste electronic material was studied. The concentration of MEs, Br, and EROs in the tested samples was determined by X-ray fluorescence analysis, and the concentration of REEs and uranium was determined by inductively coupled plasma mass spectrometry (ICP-MS). The analysis of the distribution of elements during the multi-stage ESS showed that MEs were predominantly distributed in the conductive fraction and Br, EROs, and REEs were distributed in the nonconductive fraction. The nonconductive fraction (NC2) of the two-stage ESS was subjected to a low-temperature vacuum pyrolysis (T = 550 °C, p = 10 mbar). The distribution of pyrolysis products of the NC2 fraction was determined. The main products of the vacuum pyrolysis experiments were the solid residue phase (54.4 wt.%) and oils (35.4 wt.%). It has been proven that pyrolysis can significantly increase the concentration of MEs, EROs, and REEs in raw materials, thereby providing a method for cost-effectively obtaining of REEs from waste printed circuit boards.