Simultaneous Valorisation of Metallic Iron-Rich Waste and Carbon Dioxide by Hydrothermal Reactions
14 October 2016
UAntwerpen, Campus Drie Eiken, Promotiezaal Q0.02 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Organization / co-organization:
Department of Chemistry
Vera Meynen & Jeroen Spooren
PhD defence Koen Michiels - Faculty of Science, Department of Chemistry
This doctoral research focuses on the simultaneous valorisation of two waste materials, namely fine industrial metallic iron waste powders and anthropogenically produced carbon dioxide, by a hydrothermal method for the production of hydrogen gas as well as the conversion of carbon dioxide and this hydrogen gas into organic chemicals. Hydrogen gas is obtained through water splitting, which occurs together with the oxidation of metallic iron that is present in fine industrial waste powders. As a result, the latter become iron oxide products.
Current technical bottlenecks for reuse and recycling of fine metallic iron waste powders are their fine particle size and/or their composition. Carbon dioxide, on the other hand, is a highly stable molecule, produced in excess as exhaust gas and putting pressure on our ecosystems. Hydrothermal synthesis is a promising technique that could serve as a solution: reactions take place in a sealed reactor that is (partially) filled with water and heated to a temperature above 100 °C, leading to advantageous conditions for certain reactions.
During this doctoral research a carefully chosen, stepwise experimental approach is followed to study the valorisation of fine metallic iron waste powders and carbon dioxide. The study evolves from the use of pure (commercial) metallic iron powder, via the addition of diverse but single compounds, to the application of real fine industrial metallic iron waste powders. This approach allows to reveal the fundamental reaction parameters and understand the occurring reaction mechanisms. Subsequently, the effects of individual added compounds are determined. Finally, the identified, occurring phenomena are validated during the hydrothermal treatment of real waste powders.
This doctoral research concludes on the benefit of a two-step hydrothermal method. In the first step, pure hydrogen gas is produced at high yield under mild hydrothermal reaction conditions. The second step takes place at higher temperatures and converts dissolved carbon dioxide and the produced hydrogen gas to mainly formate salts, again with high yields. Through this method, metallic iron present in fine industrial metallic iron waste powders is oxidised to iron(II,III) oxide/magnetite, which can be applied for different applications. Therefore, the obtained oxidised iron-rich powders have the potential to be used as products.