Contents lists available at ScienceDirect Resources, Conservation & Recycling journal homepage: www.elsevier.com/locate/resconrec Full length article Assessing alternative pre-treatment methods to promote metal recovery in the leaching of printed circuit boards T. Moyo*, B.H Chirume, J. Petersen Minerals-to-Metals Signature Theme, Department of Chemical Engineering, University of Cape Town, South Africa ARTICLE INFO Keywords: E-waste Printed circuit board Pre-treatment Liberation Recycling Hydrometallurgy ABSTRACT Printed circuit boards are a metals rich fraction of e-waste streams and their recycling to recover the metals promotes growth of a secondary resources economy. Reported successful cases of PCB recycling are carried out in large volumes using high-level technology and high capital investment smelter house operations. Hydrometallurgical processes have the potential to provide an option for the scalable processing of smaller volumes of PCBs and can be set up at relatively lower capital costs. However, to date, the hydrometallurgical treatment options available rely on precursor communition processes that also require high capital and energy costs. This study evaluates the options of using NaOH pre-treatment, milling, combustion and other alternative PCB pre-treatment methods to promote the leaching of metals which are otherwise inaccessible. A batch of custom-made PCBs of known and consistent metal content has been used to allow effective comparison. The effectiveness of each pre-treatment method is evaluated through carrying out an ammoniacal copper leach and recoveries are compared. X-ray CT scans are used to characterise the boards and map out accessibility of metals for leaching as well as to demonstrate the effectiveness of each pre-treatment method. Results from the X-ray CT scans showed 69% of the copper to be located in the inner layers of the PCB rendering chemical pre-treatment which only exposes metal on the outer surfaces of the board ineffective. It was concluded that an integration of pre-treatment methods effectively liberates metals without the use of heavily mechanised tools and at relatively minimum environmental impacts. 1. Introduction Waste Printed Circuit Boards (PCBs) are a valuable fraction of electronic waste (e-waste) streams and are often the focal stream of e- waste recyclers. PCBs form about 1–3% (Widmer et al., 2005; Robinson, 2009) of electronic waste in developed countries and 0.01–1% (Amit, 2008) in developing countries. With electronic waste being one of the fastest growing waste streams in the world, the global shift towards sustainable management of resources and the continuous depletion of high grade virgin ore bodies, there is an increased need to explore re- cycling options for the metals found in PCBs, as well as characterise and carry out safe disposal of the residue after recovering the desired me- tals. In developed countries, waste PCB recycling is typically done in large volumes at centralised, state-of-the art integrated pyro-hydro- metallurgical operations which require high capital investment to set up. Developing countries do not only lack the capital to set up such operations but also still need to develop their e-waste collection infra- structure. Furthermore it is questionable whether or not generated waste volumes are sufficient to justify the setting up of operations such as the ones found in developed countries. Developing countries have large resource of unskilled labour and hence recycling operations use manual dismantling and sorting with operations in China (Wang et al., 2011; Huo et al., 2007), South Africa (Lydall et al., 2017; Sadan, 2019) and India (Sadan, 2019) using chisels, hammers and cutting torches in the dismantling process. In African countries, e-waste recycling is slowly establishing itself as an industry. However, the focus is primarily on the collection, sorting and in some instances size reduction then exporting, usually of the value fractions to be processed elsewhere, typically in developed countries. The pre-treatment of PCBs varies de- pending on the intended processing methodology. For integrated smelter house operations such as that at Umicore’s Hoboken plant (Hageluken, 2006), size reduction is primarily done in effort to generate a homogenous sample for analysis prior to processing. In other opera- tions, pre-treatment (post dismantling and sorting) for the purposes of upgrading the materials and liberating the metal prior to processing (akin to the treatment of primary ores) is usually carried out. Shred- ding, milling and separation/classification are used for liberating and upgrading the metal content of PCBs. This typically requires heavy duty https://doi.org/10.1016/j.resconrec.2019.104545 Received 17 May 2019; Received in revised form 17 September 2019; Accepted 11 October 2019 ⁎ Corresponding author. E-mail addresses: thandazile.moyo@uct.ac.za, moyothandazile@gmail.com (T. Moyo). Resources, Conservation & Recycling 152 (2020) 104545 0921-3449/ © 2019 Elsevier B.V. All rights reserved. T