Kinetic Study on Volatilization of the SnO–SiO2 and SnO–SiO2–CaO Systems

The high-temperature volatilization behavior of the SnO–SiO 2 and SnO–CaO–SiO 2 slag systems was studied by simultaneous thermal analysis. The volatilization characteristics of the two systems with different SnO contents and different heating rates were discussed, and the kinetic parameters, reaction mechanism, and thermodynamic parameters of the volatilization reaction of the slag system at high temperature were calculated. The results of thermal analysis show that the volatilization of tin slag at high temperature is related to the activity of SnO and the decomposition of stannous silicate in tin slag. The slag system has obvious volatilization effect when the content of SnO is more than 60% in the SnO–SiO 2 binary slag system. When CaO is added into the binary slag system, the volatilization of slag system becomes easier. The volatilization rate decreases with increasing heating rate. The volatilization kinetic parameters and mechanism functions of the SnO–SiO 2 and SnO–CaO–SiO 2 systems were calculated by Coats–Redfern and Achar–Brindley–Sharp–Wendworth methods. It is concluded that the volatilization of tin slag at high temperature is controlled by three-dimensional diffusion mechanism. The mechanism function is Jander equation with integral form of [1 − (1 −  α ) 1/3 ] 2 and the differential form of 3/2(1 −  α ) 2/3 [1 − (1 −  α ) 1/3 ] −1 . The rate constants of the SnO–SiO 2 and SnO–CaO–SiO 2 systems are \(k\, = \,1.36\, \times \,10^{16} \,\exp \,\left( {{{ - \,61408.61} \mathord{\left/ {\vphantom {{ - \,61408.61} T}} \right. \kern-\nulldelimiterspace} T}} \right)\) and \(k\, = \,1.61\, \times \,10^{17} \,\exp \,\left( {{{ - \,64869.66} \mathord{\left/ {\vphantom {{ - \,64869.66} T}} \right. \kern-\nulldelimiterspace} T}} \right)\) , and the isokinetic temperatures are 1174.4 and 1208.3 °C, respectively. Finally, the thermodynamic parameters of the slag system in the high-temperature volatilization process are discussed. The activation enthalpy ΔH of the SnO–SiO 2 and SnO–CaO–SiO 2 systems is 498.33 and 526.96 kJ/mol, respectively. The activation Gibbs free energy ΔG is 436.56 and 433.87 kJ/mol, and the activation entropy ΔS is 42.66 and 62.84 J/(mol K), respectively. Graphical Abstract