Final Report Summary - E4-CRITMAT (Engineering of Energy Efficient Extraction of Critical Materials- Application to the Processing of Niobium and Tantalum Minerals)
Europe is facing a progressive depletion of raw materials for energy technology applications, because of global market instability and a lack of its own resources. Several initiatives to look into the viability of recovering valuable metals from electronic waste and other finished products are currently under study. However, there are few proposals which are focus on the beneficiation of the existing European mineral resources and mining tailings. Moreover, to the best of our knowledge, these projects are also based on traditional mineral processing technologies which have remained unaltered over the past fifty years, leaving many environmental issues without accurate evaluation. It is within this context, the Marie Curie project E4CritMat was proposed to provide technical and environmental solutions for the extraction of materials considered as critical by the European Union with special emphasis on the “recovery of niobium and tantalum chemicals”by avoiding the use of hydrofluoric acid and improving the energy efficiency for mineral to chemical processing.
During the first year of the Marie-Curie project it was proven that the alkali roasting in oxidizing conditions and further leaching with a mixture of oxalic and ascorbic acid is a viable processing route for upgrading niobium/tantalum and titanium bearing minerals and recovering rare earth minerals associations which are embodied in the main mineral matrix. Results which are in agreement with the previous background knowledge existing at Leeds University for titanium based minerals. Figure 1 is a schematic mass flow diagram in which the investigations carried out during the first year are summarized (for more detail about experimental findings we recommend the reading of the mid-term report submitted on the 16/05/2014).
Figure 1. Block diagram for the treatment of Nb/Ta based minerals using alkali roasting in oxidizing conditions.
The roasting in oxidizing conditions followed by the leaching with a mixture of oxalic and ascorbic acid, allows the upgrade of the mineral to values higher than 75% of Nb2O5 + Ta2O5 together which is particularly useful for low grade minerals. Moreover, additional benefits of this process are the concentration of rare earth elements up to 30% as mixed oxides, the alkali recovery step by bubbling CO2 in the water leach solution, will work as a carbon capture system, decreasing the environmental impact and reducing the operation costs and, finally the iron oxalate produced after the organic acid leaching has applications in agriculture for correcting iron deficiencies in soils and medical applications as reliever of dentine hypersensitivity.
During the second half of the project, the alkali roasting in reducing conditions was investigated; a schematic diagram of the process is presented in Figure 2.
Figure 2. Block diagram for the treatment of Nb/Ta based minerals using alkali roasting in reducing conditions.
The main difference with the roasting in oxidizing conditions is the production of a magnetic fractions which mainly consist on an iron-tin alloy useful for the construction industry and iron manganese oxides, which can be used as starting material for the production of nano-powders with applications in the fabrication of magnetic nano-arrays and as a contrast agent for magnetic resonance imaging.
After, stablishing the alkali roasting parameters in oxidizing and reducing conditions, the microwave heating of the minerals and the selective separation of niobium and tantalum was studied. Despite the investigations are in an early stage, the findings presented in this report allowed us to develop collaborations with Nottingham, Exeter and Leicester Universities to move forward in these aspects. His work has been patented and is in the pipe-line for major exploitation for which a significant pilot project is being developed with industry partners in UK and US.
Other important aspect of the Marie Curie Fellowships, is it contribution towards the independence of the early career researchers. During the length of the project Dr. Sanchez-Segado has been trained in a different variety of transversal skills related with academic and patent writing, project management and research student supervision. He also has taken an active role in developing collaborations with new academic partners and in the preparation of grant applications. Currently, he is being introduced to the Open Access and research data management procedures of the University of Leeds.
During the first year of the Marie-Curie project it was proven that the alkali roasting in oxidizing conditions and further leaching with a mixture of oxalic and ascorbic acid is a viable processing route for upgrading niobium/tantalum and titanium bearing minerals and recovering rare earth minerals associations which are embodied in the main mineral matrix. Results which are in agreement with the previous background knowledge existing at Leeds University for titanium based minerals. Figure 1 is a schematic mass flow diagram in which the investigations carried out during the first year are summarized (for more detail about experimental findings we recommend the reading of the mid-term report submitted on the 16/05/2014).
Figure 1. Block diagram for the treatment of Nb/Ta based minerals using alkali roasting in oxidizing conditions.
The roasting in oxidizing conditions followed by the leaching with a mixture of oxalic and ascorbic acid, allows the upgrade of the mineral to values higher than 75% of Nb2O5 + Ta2O5 together which is particularly useful for low grade minerals. Moreover, additional benefits of this process are the concentration of rare earth elements up to 30% as mixed oxides, the alkali recovery step by bubbling CO2 in the water leach solution, will work as a carbon capture system, decreasing the environmental impact and reducing the operation costs and, finally the iron oxalate produced after the organic acid leaching has applications in agriculture for correcting iron deficiencies in soils and medical applications as reliever of dentine hypersensitivity.
During the second half of the project, the alkali roasting in reducing conditions was investigated; a schematic diagram of the process is presented in Figure 2.
Figure 2. Block diagram for the treatment of Nb/Ta based minerals using alkali roasting in reducing conditions.
The main difference with the roasting in oxidizing conditions is the production of a magnetic fractions which mainly consist on an iron-tin alloy useful for the construction industry and iron manganese oxides, which can be used as starting material for the production of nano-powders with applications in the fabrication of magnetic nano-arrays and as a contrast agent for magnetic resonance imaging.
After, stablishing the alkali roasting parameters in oxidizing and reducing conditions, the microwave heating of the minerals and the selective separation of niobium and tantalum was studied. Despite the investigations are in an early stage, the findings presented in this report allowed us to develop collaborations with Nottingham, Exeter and Leicester Universities to move forward in these aspects. His work has been patented and is in the pipe-line for major exploitation for which a significant pilot project is being developed with industry partners in UK and US.
Other important aspect of the Marie Curie Fellowships, is it contribution towards the independence of the early career researchers. During the length of the project Dr. Sanchez-Segado has been trained in a different variety of transversal skills related with academic and patent writing, project management and research student supervision. He also has taken an active role in developing collaborations with new academic partners and in the preparation of grant applications. Currently, he is being introduced to the Open Access and research data management procedures of the University of Leeds.