Acidic leaching of steam gasified, pyrolyzed and incinerated PCB waste from LCD screen

Abstract

In the recycling of WEEE, two approaches are common: a pyrometallurgical or hydrometallurgical treatment, preceded by a mechanical and/or physical separation. In this study, twostep processing of unmodified waste samples of LCD screen inverters was investigated: hightemperature processing followed by acidic leaching under fixed conditions (1M H2SO4, 90 °C, 1 bar). The analysis carried out concerned a correlation between the type of HT treatment (pyrolysis, incineration, or gasification) and the dynamics of metals' leaching from samples pretreated this way. It was found that HT method can act as "thermal disintegration", since it affects, to a varying degree, the structure of the samples and cause elimination of organics and carbonaceous residue (incineration/gasification). The greatest mass loss (~18%) and the most loosened structure was observed for the gasified sample. Varying oxygen potential in HT-processes correlates well with the leachability of thermally treated inverters. The incineration was found to be the most favorable for copper extraction (>95%) by acidic leaching due to oxidized form of Cu, whereas Cu leaching from pyrolyzed and gasified samples needed oxygen and was controlled by the oxygen supply achieving only 36/43% after 6 h. The course of Pd leaching was similar to copper, although with lower efficiencies; 47% of palladium was extracted from the incinerated sample, and only 4 or 7% from gasified and pyrolyzed samples, respectively. Au was leached immediately but only to a slight extent. Contrary to Pb, leaching of Zn, Sn, Sb, and Ni was gradual, probably due to the formation of alloys with copper.