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Assessment of the thermodynamic rarity of mobile phones PCB

Abstract:

Mobile Phones (MP) have become the reference product for telecommunications in an increasingly connected world. A MP can be divided into several components such as battery, screen, camera, Printed Circuit Board (PCB)... Among them, the MP PCB is one of the most important components of the phone as it connects all the previous parts and represents up to a quarter of the weight of the device. This paper presents a review of the chemical composition of PCB in MP. PCB raw materials in MP have been assessed using exergy, based on thermodynamic rarity (TR), which considers scarcity in the earth's crust and energy requirements for extracting and refining minerals. The results show that the PCBs in MP are composed of more than 50 different chemical elements, including precious elements such as gold and silver, others considered critical by the EC, such as rare earth elements, and toxic elements such as cadmium, lead and mercury. TR of the PCB results in approximately 87,000 kJ per MP, however, recent studies based on metallurgical process simulation indicate that the TR values could be much higher than those used in this paper. Considering the large amount of MP produced in recent years, our estimates indicate that the total amount of MP in the world could contain only in their PCBs: 74 tonnes of palladium, 600 of tantalum, 46 of gallium and 250 of gold, which are scarce in the earth’s crust as indicated by their high TR value and low annual production. In addition, PCB could contain up to 750 tonnes of silver and 98,000 of copper. As it is not possible to recover all elements from PCBs, due to the chemical characteristics of the elements and the so-called “entropy backfire”, the TR shows an exergy-based approach to select the scarcest elements from a thermodynamic point of view, to develop future procedures for their recycling.