Chemical calcium phosphate precipitation using lime hydrates in a fluidized bed reactor

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ABSTRACT This study aimed to study the behaviour of the chemical precipitation of calcium phosphate by means of hydrated lime (Ca(OH) 2 ) using solutions with different concentrations of phosphate [PO 4 3– ] ranging from 5 to 30 mg P/L. A hydrodynamic evaluation of the chemical precipitation of phosphates in a fluidized bed reactor (FBR) was carried out. Under optimal conditions relative to chemical precipitation of phosphates (Ca/P = 3, pH = 9.6, U f = 0.58 cm s –1 and T = 22°C), the phosphate removal efficiency η and the conversion χ were 95% and 99%, respectively. [PO 4 3– ] concentration in the outlet of FBR was lower than in pure water. A low and uncontrolled instantaneous elimination efficiency of 49%–71% was obtained. This work was also aimed at examining the effect of the porosity of the bed and the fluidization velocity, which are among the least impacting parameters, on the efficiency of the operation. The height of the fluidized bed is exceeded by 10%, with an expansion of H/H mf = 2. There was a quasi-linear increase in expansion as a function of PO 4 3– concentration. The effect of PO 4 3– concentration on these different hydrodynamic parameters (i.e., expansion, porosity and fluidization velocity) was also investigated.

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