@misc{MarkowskiLohseGarcia, author = {Markowski, Jens and Lohse, Anja and Garcia, Javier}, title = {Planning and realization of a plant for the recovery of gold from thin coatings by hydro-biotechnological methods}, series = {GOLD 2022 Conference, Qu{\´e}bec City Convention Centre, July 17-20, 2022}, journal = {GOLD 2022 Conference, Qu{\´e}bec City Convention Centre, July 17-20, 2022}, publisher = {Conferium}, address = {Quebec (Can)}, abstract = {Production waste from the manufacture of printed circuit boards often has gold-containing contact strips and dots whose gold content is very low. Recycling of these gold coatings by means of conventional melting processes is technically hardly possible, since the carrier materials often contain mechanical reinforcements and flame retardants in addition to thermosetting plastics. Furthermore, there would be significant gold losses in the smelting process. Together with two industrial partners, at BTU in the last years a technology was developed, which can be used to decoat gold-bearing waste from PCB-production and contact stripes using biotechnological methods. As a result, a complete and separate recovery of the gold tinsel and the carrier material copper with high purity is possible. The bioleaching process is realized with iron and sulfur oxidizing bacteria, especially Leptospirilum ferrooxidans and Acidithiobacillus ferrooxidans. The first pilot plant with a planned throughput of nearly 2000 kg per year is currently in realization. The biotechnological apparatus consists of a closed leaching reactor (with a capacity of approx. 300 liters of fluid) as the core element and the peripheral equipment (fermenter, cementation reactor, filter systems etc.). Compared to processes using inorganic acids, shorter leaching times can be achieved, partial regeneration and multiple use of the bioleaching solution is possible. After optimizing the conditions, a process time of only 60 hours per leaching-charge is possible. Over a period of 2-3 days, the microorganisms dissolve the copper layers present as gold carriers on the polymer. The dissolved gold flakes are filtered off and the leaching liquid containing copper is fed to the next process stage. There, during approx. 3-4 days, the dissolved copper is recovered by feeding metallic iron (with a sacrificial anode). The microorganisms present in the solution accelerate this process. All process steps take place at moderate temperatures (< 40°C) and in a slightly acidic environment. The separated gold tinsel as main product with a content of over 900 mg/g Au is a suitable input for the precious metal smelter. The copper precipitates in metallic form and can be recovered in high purity (>90\%) as a by-product. Due to the biological leaching and the resulting concentration of the gold components, only < 1 wt.\% of the waste containing precious metals has to be thermally treated. This can significantly reduce the CO 2 -emissions from the gold recycling process compared with thermal processes and with conventional gold mining.}, language = {en} } @misc{MarkowskiAbendrothLapushynskaetal., author = {Markowski, Jens and Abendroth, Christian and Lapushynska, Alina and Lohse, Anja}, title = {Experiences from the commissioning of a bioleaching plant for the recovery of gold from printed circuit boards}, series = {Biomining´23 - 11th International Symposium on Biomining}, journal = {Biomining´23 - 11th International Symposium on Biomining}, publisher = {Mining Engineering}, address = {Falmouth (UK)}, abstract = {Production waste from the manufacture of PCB often contains gold-containing contact-strips, whereby the gold content is < 1 \%. Recycling of these gold coatings with conventional melting processes is technically hardly, since the carrier materials often contain mechanical reinforcements and flame retardants in addition to thermosetting plastics. With mechanical recycling, gold losses of 50\% are possible. Therefore, a bioleaching plant for the recovery of gold and copper as preliminary stage for the smelting process has been in operation on m\&k´s site since May 2022. The bioleaching is realized with iron and sulfur oxidizing bacteria, e.g. Leptospirilum ferrooxidans. The apparatus consists of a 400 litres-leaching bioreactor and peripheral equipment (fermenter, cementation, filters). The plant can process up to 10 kg of gold-containing PCB waste per batch, while simultaneously regenerating a second batch of bioleaching fluid. The process can recover up to 450 mg goldtinsel and 25 g copperpowder per Kilogramm input.}, language = {en} }