Clean process for recovery of metals and recycling of acid from the leach liquor of PCBs

Abstract

The present work reports the application oriented systematic basic studies for the recovery of copper, nickel and iron from scrap printed circuit boards (PCBs) of computer. Initially, the PCBs were depopulated and crushed with the help of scutter-crusher and then subjected to pyrolysis under vacuum at 300 C for 4 min. Thereafter, this pyrolysed PCBs (poly-cracked PCBs) were further beneficiated to separate high and low metal concentrate (small fraction). The small fraction (10 mesh size) of poly-cracked PCBs was leached in 2.4 M H2SO4 at 150 C maintaining 20 bar pressure and pulp density 100 g/L. Systematic scientific studies were also carried out to recover base metals (Cu, Fe and Ni) from leach liquor of small fraction of poly-cracked PCBs. To recover acid from the leach liquor, the experiments were carried out using 70% TEHA diluted in kerosene, which resulted in the extraction of 99.99% H2SO4 in three stages at O/A ratio 2/1 in 5 min. The recovered acid could be recycled for leaching of materials in continuous close loop of operation. Subsequently, air sparging was performed to separate and recover Fe as precipitate. After the recovery of acid and iron from the leach liquor, the solution was further processed to recover Cu using 10% LIX 84IC diluted in kerosene. 99.99% copper was found to be extracted in two stages at pH 2.5, O/A ratio 1/1 in 5 min, leaving Ni in the raffinate. Further, nickel was separated completely from the solution in two stages using 1% LIX 84IC at pH 4.58, O/A ratio 2/1 in 15 min. From the pure metallic solutions, the pure metal and its salt could be produced using electrolysis, evaporation, crystallization etc. The novel pyro-hydro hybrid metallurgical process consists of pyrolysisebeneficiationeleaching esolvent extraction for the recovery of metals from scrap PCBs is reported. The developed process is cleaner and environmental with zero waste generation concept and has potential to be commercialized after validation on pilot scale trials.