Synthesis and characterization of sodalite using natural kaolinite: an analytical mathematical approach to simulate the loss in weight of Cl during the synthesis process.

ABSTRACT Transformation of metakaolinite to basic sodalite [Na4(AlSiO4)3Cl]2 in the presence of NaCl was investigated. Experimental synthesis was performed in alumina crucibles at 850°C and ambient pressure. Reaction progress was monitored by X-ray powder diffraction from 1h to 400h. During the crystallization of sodalite, the presence of reacting residual halite was testified throughout the run synthesis; intermediate-phase carnegieite was detected in the initial stage of the synthesis run (1h-24h). Both sodalite and residual halite were evidenced between 24 and 101h, where sodalite reaches a climax in the crystallization degree. Progressive replacement of sodalite by nepheline was testified starting from 171h. Synthesized sodalite was submitted to chemical-crystallographical and mineralogicaltextural studies and Infra-Red Spectrometry (IR), providing values comparable to the ones available in the literature on this mineral. A continuous loss in weigth of the NaCl plus metakaolinite starting matrix contained in the alumina crucible heated in oven was testified and attributed to Cl vaporization. An analytical mathematical model to solve the parabolic differential equation related to the chlorine diffusion processes occurring within the crucible is proposed. Experimental data and numerical results, when compared, although satisfactory, suggest the necessity of some modelling improvements. KEYWORDS: sodalite, kaolinite, infrared analysis, calcination, mathematical modeling.