Bioleaching of pyritic coal wastes: bioprospecting and efficiency of selected consortia.

Pyrite-bearing coal wastes are responsible of the formation of acid mine drainage (AMD), and their management to mitigate environmental impacts is a challenge to the coal mine industry in Europe and worldwide. The European CEReS project sought to develop a generic co-processing strategy to reuse and recycle coal wastes, based on removal of AMD generating potential through bioleaching. Chemolitoautotrophic iron- and sulfur-oxidizing microbial consortia were enriched from a Polish coal waste at 30 °C and 48 °C, but not 42 °C. Pyrite leaching yield, determined from bioleaching tests in 2-L stirred bioreactors, was best with the 48 °C endogenous consortium (80%), then the 42 °C exogenous BRGM-KCC consortium (71%), and finally the 30 °C endogenous consortium (50%). 16S rRNA gene-targeted metagenomics from five surface locations on the dump waste revealed a microbial community adapted to the site context, composed of iron- and/or sulfur-oxidizing genera thriving in low pH and metal rich environments and involved in AMD generation. All together, the results confirmed the predisposition of the pyritic coal waste to bioleaching and the potential of endogenous microorganisms for efficient bioleaching at 48 °C. The good leaching yields open the perspective to optimize further and scale-up the bioleaching process.

Recycling-oriented methodology to sample and characterize the metal composition of waste Printed Circuit Boards.

As spent printed circuit boards (PCBs) are among the most valuable components in waste electrical and electronic equipment (WEEE), their recovery makes economic and strategic sense. However, their composition varies considerably depending on the location, year and type of appliance in which they were used. Developing new treatment processes requires representative sampling of spent PCBs from large samples and accurate determination of their raw material composition. This study aimed to characterize spent PCBs by milling, sampling and leaching with an appropriate reagent. Sampling was performed on 526 kg of spent PCBs, to obtain different samples milled at 750 µm in order to access the metals. The samples were leached with aqua regia and the metal contents of the leachates were determined. For most metals, the analyses of 40 g-samples of spent PCBs showed limited variation in the composition of the different samples. These results concurred well with other studies reported in the literature.