Nepheline--Alkali Feldspar Equilibria: I. Experimental Data and Thermodynamic Calculations |
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| Authors: | ZYRIANOV V N; PERCHUK L L; PODLESSK K K II |
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| Institution: | Institute of Experimental Mineralogy, USSR Academy of Sciences 142432, Chernogolovka,Moscow district, USSR |
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| Abstract: | Nepheline-alkali feldspar equilibria with alkali chloride aqueoussolutions have been determined for the temperature range 400to 700 °C at 1000 bars pressure. Nepheline-alkali feldsparequilibria with alkali chloride melts have been determined forthe temperature range 800 to 1100 °C at approximately 6bars pressure. (1) NaAlSiO4 + KCl(aq) = NaCl(aq) + KAlSiO4 (2) NaAlSiO4 + KCl(melt) = NaCl(melt) + KAlSiO4 (3) NaAlSi3O8(high) + KCl(aq) = NaCl(aq) + KAlSi3O8(San) (4) NaAlSi3O8(low) + KCl(aq) = NaCl(aq) + KAlSi3O8(Mic) (5) NaAlSi3O8(high) + KCl(melt) = NaCl(melt) + KAlSi3O4(San) (6) NaAlSi3O8(low) + KCl(melt) = NaCl(melt) + KAlSi3O8(Mic) From these, two diagrams of phase relationships were derivedfor the following exchange equilibria: (7) NaAlSiO4 + KAlSi3O8(San) = NaAlSi3O8(high) + KAlSiO4; (8) NaAlSiO4 + KAlSi3O8(Mic) = NaAlSi3O8(low) + KAlSiO4. The effect of pressure on these equilibria has been determinedby comparing the experimental data for 1000 and 5000 bars (t= 500 °C) and thermodynamic calculations. It has also beenshown that the effect of excess silica in nepheline solid solutionon the K—Na distribution between nepheline and alkalifeldspar is substantial and opposite to that of temperature.In the high temperature region an increase in silica contentin nepheline of 2 wt. per cent eliminates the effect on theredistribution of a temperature increase of 100 °C. Thesecation exchange data and unit cell data for the crystal phasesare used to calculate thermodynamic mixing properties of nephelinesolid solution and alkali feldspar solid solution for a widerange of temperature and pressure. |
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