Microbial Extraction of Critical Raw Materials (CRM) and Gold Recovery from outdated Printed Circuit Boards (PCBs)

Abstract

In light of the global energy transition and the concomitant growth in demand for critical raw materials, coupled with the advent of a modernised economy, the European Union's Parliament has recently enacted the Critical Raw Materials Act (CRMA). The objective of this legislation is to bolster the EU's strategic autonomy, diversify its critical raw material supply, and reinforce recycling and circularity. In this context, the INN4MIN project has tested an optimised approach to the recovery of gold, copper, zinc, tin and other metals from printed circuit boards (PCB). In order to de-solder the respective components of the PCB, a combined chemical and biotechnological approach was adopted. A ferric iron solution was employed to facilitate the transformation of the solder metals, namely tin and lead, into their respective oxides and sulphates. Concurrently, metals such as copper, iron, nickel, cobalt, silver and zinc are dissolved and can be recovered from the solution. The regeneration of ferric iron was achieved through the utilisation of iron-oxidising bacteria within an aerated bioreactor.

Notwithstanding the relatively long residence time, approximately 96% of the aforementioned metals can be recovered in an environmentally friendly manner. Following the separation of gold from the aforementioned components, further processing may be conducted using environmentally preferable leaching reagents, such as a solution of thiourea and ferric sulphate. The recovery of gold is dependent upon a number of influencing parameters, including the temperature and concentration of the individual components, as well as the pH and Eh conditions.