Metal Recovery from the Enviroment
Plants have the ability to concentrate metals from soil. This is evident in every day life where we eat foods such as tomatoes (rich in pottasium) or spinach (rich in iron). There are some plants even better at concentrating metals and can concetrate toxic, precious or valuable metals to a much higher degree. These plants are known as phytoremediators or hyperacumiltors and have been used in places like Chernobly to remove radioactive metals from the soil. The plants are then harvested and landfilled. This project offers the oppurtunity to process the resulting biomass and recover the metals.
Figure 1: Phytoremediation Concept
This project aims to develop a low cost and sustainable method to recover the metal present in biomass. As shown in Figure 4, the metal rich biomass is placed into a molten salt where a well known decomposition process known as "biomass gasificiation" takes place. As the decompose the biomass into biofuel and char the molten salt absorbs the metals. These metals can then be electrochemically recovered in a pure form. The challenges in this project encompass several disciplines, which include thermal management, process engineering, electrochemistry, materials engineering, design and construction of test cells.
Figure 2: Schematic of the process used to recover metal from biomass
This process has the potential to provide a low cost and sustainable method for cleaning up contaminated land and Brownfield sites. This land would then be used for housing, commercial or environmental development, which is critical if we are to protect our valuable Greenfield sites and promote sustainable development within the UK. On average a further 250 contaminated sites have been added per year since 2000, reflecting the growing need within the UK for sustainable land remediation technology.
Molten Chloride Processes
Most titanium produced today was achieved through the Kroll Process. The Kroll process is a non-continuous process meaning that despite being the fourth most common engineering metal in the earths crust the qunaitities produced are dwarfed by steel and aluminium. The FFC Cambridge process was discovered in 2000 when trying to deoxidise oxide thin oxide films on titanium rods using a chloride salt. This has since manifested into one of the technologies being scaled up to produce industrial quantities of titanium and tanatalum powders.
Figure 3. The FFC Cambridge process: An electrochemical process that gradually deoxidises metal oxides into metal alloys.
The FFC process relies on electrochemical removal of oxide ions from a metal oxide cathode. As this continues the metal oxide cathode begins to deoxidise. The oxide ions are released into the chloride salt where they are transported to the carbon anode and released as a gaseous phase. Our most recent research in this area involves study of the process using X-ray Sychrotron facilities. The sychrotron allows us to analyse the cathode as its reducing giving an un unparraelled view of the reduction in real time (DOI: 10.1016/j.actamat.2010.05.041).
Figure 4. Schematic of the FFC Cambridge process apparatus as used at the X-ray synchrotron
Molten Salt Batteries
Current energy distribution is built around a central tenant; electricity must be produced when it is needed and used once it is produced. So energy generation is perpetually monitored and perfectly balanced to energy demand. Energy storage would break dependency, allowing excess electricity generated to be stored for later use, as one would for other commodities. This has benefits to the consumer by enabling a risk management strategy and allowing energy generators to be utilised more effectively.
The Molten Salt Battery (MSB) project aim is to develop a battery architecture, which can readily be up scaled to address the needs of load balancing on national grids. The challenges in this are encompass several topics and engineering challenges, which include thermodynamic measurements of candidate electrode couples, computational thermal modelling, electrochemical studies of potential electrolytes, long term corrosion testing, design and build of test batteries. The figure below show two concepts MSBs: Firstly, the intercallation MSB relies on transport and storage of lithium to an intercallation compound, which is similar in concept to commercial lithium batteries. Secondly, the metal air battery stores energy by breaking down an molten oxide into its consituent metal and oxygen, which is released into the atmosphere. To relase the stored energy the oxygen must be reintreoduced into the molten oxide.
Figure 5: Schematic of the intercallation MSB (left) and metal-air MSB (right)