Study on the thermodynamic viability of NiO and CuO chlorination with C2Cl4 at high temperatures

Abstract

Direct chlorination roasting is a worldwide applied industrial process for extracting metals from oxides and oxide mixtures, whereas specific oxides react with chlorine resulting in volatile chlorinated molecules, which can then be separated and further reduced to metallic products. In this context, the presence of a reducing agent, graphite for example, has proven to stimulate not only the thermodynamics but also the kinetics of the reactions involved. However, the search for alternative, and environmental friendlier, chlorination agents leaded to a strong development of research regarding the possible substitution of chlorine by either solid (NaCl, CaCl2) or gaseous compounds (CCl4, COCl2, C2Cl4), preserving the thermodynamic viability and desired process kinetics. In this context, the merit of processes using gaseous chlorinated agents containing carbon atoms in their structure should be considered. Among the alternative chlorinating agents already explored in literature, a considerable lack of information regarding the use of C2Cl4 can be clearly detected. This fact served as a start motivation for the development the present work, which focuses on the theoretical (thermodynamic simulations) and experimental study of the thermodynamic viability of chlorination of NiO and CuO pure samples under a C2Cl4/N2 atmosphere in the temperature range between 1123K and 1323K, which were characterized, both initially and during the process, through X-Ray diffraction (XRD) and electron scanning microscopy (SEM). According to the simulations, both NiO and CuO should react with C2Cl4 under diluted conditions, thereby forming only volatile chlorides. These facts have been confirmed by the experimental data, although in the case of NiO a much lower mass loss has been detected. The results also confirm that C2Cl4 can be viewed as a potential chlorination agent for metallic oxides, and that significant driving force and kinetics can be found even under high dilution conditions, as exemplified by the reaction conversions determined for CuO (1123K) and NiO (1323K). In both cases neither graphite nor condensed chlorides have been detected, but regarding the kinetics, CuO reacted much faster, which could be explained by its lower thermodynamic stability, and weaker metal to oxygen chemical bond.