Full components recovery of organic matter and indium from discarded liquid crystal display panels

Abstract

In the present study, organic matter and indium were fully recycled from discarded LCD panels by microwave extraction - nitrogen pyrolysis - vacuum reduction. Triphenyl phosphate, an environmentally friendly halogen-free flame retardant, was extracted from the polarizing film using microwave extraction technology. The extraction rate under optimized conditions (acetone, 55 °C, 20 min, 1:50) was 95.89%. After the microwave extraction process, the polarizing film was treated with nitrogen pyrolysis. Uncondensed pyrolysis gas/oil (mainly acetic acid) was used to prepare an environmentally friendly snow melting agent. In addition, 26.42 wt% of the pyrolytic carbon residue was obtained under the optimized conditions (350 °C, 2 °C·min−1, 0.05 L min−1, 120 min), which could be used as a reductant to recycle indium from waste LCD panels. In the vacuum reduction process, the indium conversion rate could reach 99.92% without the addition of reductant. The reaction dynamics results show that the reduction process of pyrolytic carbon and In2O3 is initially controlled by a chemical reaction, followed by a mixed control that transitions to a diffusion control. Moreover, the results of the contrast experiment show that the conversion efficiency of pyrolytic carbon to indium was comparable to that of activated carbon, and both were better than that of coke. This study can be used as a practical reference for the recycling of major components of LCD panels.