Scotland meets BAM

Prof. Carole Morrison, Prof. Caroline Kirk & Prof. Colin Pulham, School of Chemistry, University of Edinburgh

Summary

Opportunities and challenges in electronic waste recycling

Carole A. Morrison, Jason B. Love

The rapid global rise in technology, tied in with consumer pressures for upgrades in functionality and design, has generated advanced electrical and electronic equipment with short lifespans. A consequence of this is the production of electronic waste which in 2016 amounted to 44.7 million metric tons; with a projected annual growth of 3-5 % this is three times more than for any other waste stream. An end-of-life printed circuit board (PCB) may contain up to 60 different chemical elements and have a metal content as high as 40% by weight, so should be viewed as a valuable secondary source of precious and base metals. The metal content of a PCB is typically ten to a hundred times higher than that of conventionally mined ores. It is estimated that recycling one ton of mobile phones could produce on average 130 kg of copper, 3.5 kg of silver, 0.34 kg of gold and 0.14 kg of Pd. In this short lecture we will explore the opportunities (economic, social and environmental) and challenges (the chemistry!) presented by the recycling of waste electronics. In particular we will focus on recent case studies explored in our research group,7-8 and highlight potential opportunities for collaborative research.

Investigating the Environmental Stability of Potential Materials for Remediation Applications using Advanced Synchrotron Techniques

Caroline Kirk

This presentation will explore two different systems:

Ettringite, Ca6[Al(OH)6.12H2O]2(SO4)3(H2O)2 is a common phase formed in cement pastes and concretes. They have complex structures that can accommodate a wide range of cations and anions. It is this property of ettringite that makes it an excellent candidate for the remediation of hazardous and toxic ions from waste effluents. We have successfully produced new ettringite-type analogues Ca6[Al(OH)6.12H2O]2(XO4)3(H2O)2; X=Cr, Se and shown solid solution behaviour between the parent sulphate ettringite phases and these analogues Ca6[Al(OH)6.12H2O]2(SO4)3-x(XO4)x (H2O)2; X=Cr, Se. We have also investigated the time dependence of the formation of ettringite-type phases through addition of tricalcium aluminate (Ca3Al2O6, C3A), a phase that is present in cement clinkers, to solutions containing either selenate or chromate ions. The reaction was stopped at various time points and results show that the ettringite phase starts to form within 1 hour. To fully understand the anion incorporation mechanisms during the formation of these ettringite-analogue phases, we have monitored the structural changes in situ through experiments on the high resolution beamline I11 using a capillary flow cell and preliminary results will be presented here.

Uranyl phosphates, such as metatorbernite (MT) (Cu(UO2)2(PO4)2.8H2O), are known for their low solubility at circumneutral pH. They are important in the control of uranium mobility, and even being considered as materials for remediation of contamination in groundwater. Our analysis of samples taken from spoil heaps at a disused uranium mine site, have found the presence of mineral phases which can be thought of as members of a metatorbernite (MT)-metazeunerite(MZ) solid solution (Cu(UO2)2(PO4)2-x(AsO4)x.8H2O). We have successfully synthesised materials based on these minerals and shown a complete solid solution exists between these two end member phases. We have found that stability of member phases of this solid solution, under different conditions of pH and temperature, are linked to composition, which we suggest are related to structural differences between the end member phases. To understand the structures of this solid solution in more detail and link with the stability differences we have found, investigations using high resolution powder synchrotron diffraction data have been carried out.

Enhanced Phase-Change Materials for Heat-Storage Applications

Colin R. Pulham

46% of world energy consumption is used for heating and cooling of domestic and commercial buildings, and the heating/cooling requirements for a wide range of industrial processes. These heating and cooling requirements rely ultimately on the combustion of fossil fuels, and inevitably this has a major impact on emissions of CO2. Furthermore, with the ever-increasing price of fuel and electricity, there are significant economic impacts for both domestic and industrial customers. Hence there is a very strong driver towards the exploitation of renewable heat, and a key challenge for renewable heat must be effective heat storage.

In collaboration with a small company (Sunamp Ltd), we have therefore developed a compact store (known as a Heat Battery) which can replace domestic boilers, hot water tanks and air conditioning units, and can connect to solar panels and other forms of renewable energy heating and cooling equipment. A key technology component of the store is the use of Phase-Change Materials (PCMs). Such chemical compounds absorb heat and undergo a phase transition, e.g. dissolution or melting. Such chemical compounds can include inorganic salt hydrates, (e.g. sodium acetate trihydrate) or organic materials (e.g. beeswax) that absorb heat and undergo a phase transition, e.g. dissolution or melting.

On cooling, the reverse phase transition occurs, e.g. crystallisation or freezing, and heat is released. Although PCMs based on salt hydrates offer several advantages over organic materials (e.g. higher energy densities, non-flammability), they often suffer from disadvantages of incongruent melting and sub-cooling, resulting in non-reproducible performance and poor long-term stability. This is particularly true for sodium acetate trihydrate (mpt 58 °C), which melts incongruently to form anhydrous sodium acetate and which has a marked tendency to sub-cool. These factors severely limit the use of this material as a PCM. We have overcome both of these problems and have developed a polymer additive that suppresses the formation of the anhydrous salt, together with nucleating agents that prevent sub-cooling. Using in situ X-ray powder diffraction, we have interrogated in real time the structural and chemical evolution of these formulations during repeated temperature cycling, and have identified the mechanisms by which phosphate-based nucleating agents can be thermally deactivated by excessive heating.

We have also successfully modified the freezing temperature and thermal-profile behaviour of sodium acetate trihydrate in order to optimise its performance for specific applications. These new PCM formulations retain their high energy densities and have been incorporated in Sunamp Heat Batteries, which are currently being used in domestic applications in order to balance electrical
demand from the grid, store solar thermal energy, and reduce heating bills for customers.

Speaker:

Prof. Ulrich Theodor Schwarz, TU Chemnitz, Institut für Physik