Effect of Ca(OH)₂ on the chemical precipitation of phosphates from solutions of a low concentration in fluidized bed reactor: hydrodynamic evaluation

Abstract

In this present work, the phosphate is precipitated chemically at 22°C using synthetic water at different Ca/P molar ratios ranging from 0.5 to 12. Various parameters have been optimized to a range of realistic conditions relative to chemical precipitation of phosphates (superficial velocity of fluid U_f = 0.58 cm/s, [PO₄] = 10 mgP/L). A hydrodynamic evaluation of the chemical precipitation of phosphates in a fluidized bed reactor, contains sand particles as a substrate for the precipitate layer, from an ascending water stream using Ca(OH)₂ was made. As a function of Ca/P, the occurrences domains of the different hydrodynamics parameters are given. The effect of the Ca(OH)₂ on the porosity and the velocity of the fluidized bed it also presented. For the inlet Ca/P molar ratio, was lower than 4, the phosphate removal efficiency is 35~74%. While, for the suitable conditions of Ca/P>4, the phosphate removal efficiency ranging from 75 to 92%. It is found that the [Ca] and [PO₄] significantly affect the velocity of fluidization and the porosity of the fluidized bed. In this connection, the experimental data of several authors provide a useful starting point for our comparisons.

Keywords: Chemical precipitation - Fluidized bed - Phosphate - Porosity - Molar ratio