**7. References**


**29** 

*Brazil* 

**On the Chlorination Thermodynamics** 

Chlorination roasting has proven to be a very important industrial route and can be applied for different purposes. Firstly, the chlorination of some important minerals is a possible industrial process for producing and refining metals of considerable technological importance, such as titanium and zirconium. Also, the same principle is mentioned as a possible way of recovering rare earth from concentrates (Zang et al., 2004) and metals, of considerable economic value, from different industrial wastes, such as, tailings (Cechi et al., 2009), spent catalysts (Gabalah Djona, 1995), slags (Brocchi Moura, 2008) and fly ash (Murase et al., 1998). The chlorination processes are also presented as environmentally

In general terms the chlorination can be described as reaction between a starting material (mineral concentrate or industrial waste) with chlorine in order to produce some volatile chlorides, which can then be separated by, for example, selective condensation. The most desired chloride is purified and then used as a precursor in the production of either the pure metal (by reacting the chloride with magnesium) or its oxide (by oxidation of the chloride). The chlorination reaction has been studied on respect of many metal oxides (Micco et. al., 2011; Gaviria Bohe, 2010; Esquivel et al., 2003; Oheda et al., 2002) as this type of compound is the most common in the mentioned starting materials. Although some basic thermodynamic data is enclosed in these works, most of them are related to kinetics aspects of the gas – solid reactions. However, it is clear that the understanding of the equilibrium conditions, as predicted by classical thermodynamics, of a particular oxide reaction with chlorine can give strong support for both the control and optimization of the process. In this context, the impact of industrial operational variables over the chlorination efficiency, such as the reaction temperature and the reactors atmosphere composition, can be theoretically appreciated and then quantitatively predicted. On that sense, some important works have been totally devoted to the thermodynamics of the chlorination and became classical references on the subject (Kellog, 1950; Patel Jere, 1960; Pilgrim Ingraham, 1967; Sano

Originally, the approach applied for the study of chemical equilibrium studies was based exclusively on <sup>o</sup> *G*r x *T* and predominance diagrams. Nowadays, however, advances in computational thermodynamics enabled the development of softwares that can perform more complex calculations. This approach, together with the one accomplished by simpler techniques, converge to a better understanding of the intimate nature of the equilibrium states for the reaction system of interest. Therefore, it is understood that the time has come

**1. Introduction** 

Belton, 1980).

acceptable (Neff, 1995, Mackay, 1992).

Brocchi E. A. and Navarro R. C. S. *Pontifical Catholic University of Rio de Janeiro* 

