Perpustakaan Digital ITB

Tin (Sn) is one of nonferrous metals which has been used for many applications in human society. Arsenic (As) and lead (Pb) are the common impurities in tin ore. They are categorized as one of the toxic metals for the environment, so it must be handled accurately. The vacuum distillation method has been considered as a novel technology to remove the impurities, but there is not enough knowledge on the behavior of the volatile impurities in the tin containing system to receive a lower content of impurities. Therefore, an updated thermodynamic model of Sn-Pb-As system that can be used to understand and simulate the removal of hazardous impurities from tin metal is needed. The modelling of the Sn-Pb-As system was carried out consecutively from their elements until its ternary system to ensure the thermodynamic parameters wasassessed with the most updated and most suitable data. The whole modelling process wascarried out using MS.Excel and Factsage 8.0. The modelling steps consist of literature study, optimization or assessment of the parameter, calculation of the phase diagram, comparison or validity, and the application of the model. The literature study consisted of collecting the thermodynamic data, i.e., heat capacity, liquidus and solidus point, activity, and mixing enthalpy of the system. After that, the collected data were reviewed to choose whether the data had to be optimized using error minimization procedure. The assessed parameter was then compared with the existing database to validate the model. Then, the final model was used to define the optimum pressure and temperature in the vacuum distillation process. In the present study, the Gibbs energies of solid and liquid solution are expressed using a regular solution approximation based on one lattice Redlich Kister (R-K) model using the CALPHAD method. The model is used to optimize the binary and ternary parameter of the Sn-Pb-As system. It described the Pb-Sn and Sn-As system well and fit all of the experimental data. The optimized model for Pb-As system gave a better description in the liquidus line compared to the previous model. Ternary diagram of Sn-Pb-As had not been optimized yet as there was no experimental data nor interaction parameters for this system available in literature. The model was then used to calculate the simulation process of tin refining operation using vacuum distillation method. The value of pressure used in the simulation is between 1-10 Pa. The optimum condition calculated from this study were P=1 Pa and T=1430 K with %Pb, %As, and %Sn that volatilized into gas phase equal to 99.29%, 31,93%, and 3,31% respectively.