Bioleaching of Metals from Pyrolised Printed Circuit Boards using Coal as External Sulphur Source

Copper-rich char from pyrolysis of obsolete printed circuit boards (PCBs) was processed using bio- and hydrometallurgical means. Preliminary results demonstrated the potential of copper leaching using an acidic, ferric iron lixiviant derived from coal waste containing pyrite and subjected to accelerated bioleaching. The presented results report on the role bacterial presence plays in the leaching system, the main challenge being to outline the optimal con-ditions under which bacteria survive in the harsh leaching environment. The results are highlighting the importance of finding an appropriate sulphur source to be added in the char leaching system in order to keep the moderate thermophile microbial consortia viable. Tail-ings fraction derived from gravity beneficiation of coal was chosen as such due to its sulphur content and in view of its reutilization potential. The influence of the coal addition degree (%wt ratio) to the char, on the dissolution of the zero valent metals (copper, aluminum) and bacterial activity was studied. Other process relevant parameters such as pH, redox potential and ferric-ferrous iron balance were followed as well. It was found out, that an addition of coal fraction, do stimulate bacterial activity inside the reactor which results in higher degree of copper dissolution (97%) after 168 hours, in comparison to the abiotic system (89%) and biotic system where coal is absent (93%) over the same time span. Although a very fine granulometric fraction of the coal was explicitly used, there was virtually no indication of metal back-sorption onto coal particles. The fact that copper was brought into solution by ferric iron at starting concentrations well below the stoichiometric requirement, implies bacterial regeneration of the ferric iron and its cycling in the system.