An experimental study was made of the interaction of phosphaterock and aqueous inorganic orthophosphate, calcium, and hydroxylions. A model of the reaction was developed by observing electrondiffraction patterns in conjunction with concentration changes ofchemical components. The model was applied in explaining the performanceof batch suspensions of powdered phosphate rock and packedcolumns of granular phosphate rock. In both cases the reaction consistedinitially of a rapid nucleation phase that occurred in a timeperiod of minutes. In the batch system the calcium phosphate nucleithen ripened into larger micro-crystals of hydroxyapatite, whicheventually became indistinguishable from the original phosphate rocksurface. During column operation the high supersaturation ratio thatexisted after the rapid nucleation phase resulted in a layer of smallnuclei that covered a slowly growing hydroxyapatite crystal.
The column steady-state rate constant was found to increase withincreasing temperature, pH, and fluoride concentration, and to decreasewith increasing concentrations of magnesium sulfate,ammonium chloride, and bicarbonate ion.
An engineering feasibility study indicated that, based on economicconsiderations, nucleation of apatite on phosphate rock ore has apotential use as a wastewater phosphate removal treatment process.
