2019

Lahtinen, Elmeri

Growing interest towards making industrial processes and waste management more efficient has created an increasing demand for efficient and easy-to-use metal scavenging methods. Many processes today still operate with the mentality that only the metal of interest should be recovered during the process, while the rest of the metals can be treated as waste. In the long term, this is not a sustainable model. In many cases, the difficulty and cost of incorporating a metal recovery process into an already existing operation are some of the main reasons why metal management often remains on a very basic level. In this work, Selective Laser Sintering (SLS) 3D printing is suggested as a way to prepare highly customizable metal scavenging filters that could easily be incorporated into already existing processes. Usually, 3D printing is only utilized for the production of objects with mere mechanical or aesthetical properties. However, in this study, the focus was on incorporating chemical functionality into the 3D printed objects. The 3D printing method was evaluated in terms of the usability for metal scavenging processes by studying the ability to alter both the chemical and physical properties of the SLS 3D printed objects. In the introduction section of the thesis, typical metal separation techniques, with a focus on sorption, are discussed and then compared with the advantages and disadvantages of the SLS 3D printed metal scavenging filters. In the original publications discussed in this thesis, different types of chemically functional SLS 3D printed filters are presented. First, a highly selective method for scavenging gold as tetrachloroaurate from acid leached Printed Circuit Board (PCB) waste was developed. The method utilized SLS 3D printed Polyamide-12 (PA12) filters which achieved nearly quantitative selectivity towards tetrachloroaurate. This was followed by a study where a method for separating palladium and platinum from a similar matrix by using SLS 3D printed filter was developed. Finally, a different approach was taken, where the SLS 3D printed PA12 filters were converted to functional nanocatalysts by first selectively adsorbing the gold from PCB waste and then reducing it into nanoparticles.