Physicochemical Properties of Acidic Ammonium Phosphate Slurries

Abstract

Acidic ammonium phosphate slurries with different degrees of neutralization were obtained by neutralizing dilute phosphoric acid with ammonia. They were then concentrated to different water contents. The effects of the degree of neutralization and water content on the density, boiling point, fluorine volatility, thermal conductivity, and viscosity were studied. The results indicate that the density of the slurry increases with decreasing water content and/or neutralization degree. The density of acidic ammonium phosphate slurries can be calculated by the formula ρ = k[ρSxv + ρL(1 − xv)]. The experiments show that the boiling point of an acidic ammonium phosphate slurry increases with decreasing water content and/or neutralization degree. When the water content is below 40%, the boiling point strongly depends on the water content. The fluorine in the slurry, brought in with wet-process phosphoric acid, volatilizes when the slurry is heated. The volatility increases with increasing concentration of the slurry. The volatilization is significant in low range of neutralization degrees. It increases sharply with decreasing neutralization degree. Increasing the degree of neutralization above 0.6 causes the volatility to drop to a rather low level. The thermal conductivity of acidic ammonium phosphate slurries varies from 0.471 to 0.608 W·m-1·K-1. For an acidic ammonium phosphate solution, the thermal conductivity increases with increasing water content or neutralization degree. However, for such a slurry, the presence of a crystalline phase makes the thermal conductivity increase with decreasing water content. The viscosity is the lowest for a slurry with a neutralization degree of 0.52. The viscosity increases with decreasing water content. The slurry behaves as a Newtonian fluid when its water content is above 40%. However, it switches to act as a pseudoplastic fluid when its water content decreases below 40%. Increasing the temperature can reduce the viscosity.