Conversion of tin and alkali chlorides to phosphates and vitrification into silicate glasses

Mixtures of tin(II) chloride and tin(II)-sodium–potassium chlorides were converted into phosphate salts by reaction with ammonium dihydrogen-phosphate at 400 °C. Element analyses showed that no loss occurred during the treatment, and Mössbauer and wet analyses indicated no change in tin valence. The converted tin phosphate and tin–sodium–potassium phosphates were then dissolved into silicate glasses at 1350 °C without loss. Structural analyses were realized with 31P, 29Si, 119Sn NMR and 119Sn Mössbauer, which revealed a complete dissociation of tin phosphate into the silicates. Phosphate units consisted in ortho- and pyro-phosphates. Tin(II) was partially oxidized into tin(IV), but there was no evidence for a phase separation into SnO2 or SnP2O7, tin being mainly bonded to silicate units. These results are discussed in terms of O2− exchange between phosphate and silicate units during the melting process.