Features of the synthesis of highly dispersed alumophosphates AlPO4·nH2O

Abstract

Aluminum orthophosphate of the composition AlPO4·2H2O with a monoclinic structure identical to the structure of the natural mineral metavariscite was obtained by condensation method during hydrothermal treatment of alumophosphate solutions with a concentration (g/l) of Al2O3 90 – 115, P2O5 340 – 440 in the temperature range 95–99 °C. For the first time, the role of aging of the alumophosphate system in shortening of the induction period, simultaneous nucleation of primary particles in the entire volume of the solution and the formation of a pasty product with a predominant particle size of 1–10 μm, in contrast to 30–50 μm, characteristic of a fine-crystalline product obtained without aging of the solution, is established. It is shown that pasty AlPO4·2H2O, in comparison with fine-crystalline, is hardly soluble in HCl even under prolonged heating. The influence of P2O5 content in the alumophosphate solution, the conditions of its aging and the duration of hydrothermal treatment on the particle size distribution for synthesized aluminum orthophosphates have been established. Anhydrous alumophosphate obtained by dehydration of pasty AlPO4·2H2O in the temperature range of 150–200 °C with subsequent heat treatment at 900 °C is readily soluble in acids, and the predominant particle size is 5–13 μm.