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Homogeneous precipitation of magnesium phosphates from seawater solutions

Abstract : Homogeneous (unseeded) nucleation of Mg phosphate from modified Ca-free seawater solutions was investigated at 20°C and pH of 8. Precipitated solid phase was characterized using chemical analysis, X-ray diffraction, scanning electron microscopy, and IR-spectroscopy. Effect of aqueous phosphate and ammonia concentrations and the intensity of stirring on the induction period time ( τ) of Mg phosphates nucleation were studied. A linear relationship between logarithm of bobbierite (Mg 3(PO 4) 2 · 8H 2O) saturation index and log τ was established with a slope close to 2. Aqueous NH 4+ (up to 0.002 M) has no effect on the nucleation kinetics and does not incorporate in the precipitated solid phase. Stirring of solution has a dramatic effect on nucleation kinetics: the induction period decreases by a factor of 100-10 000 in unstirred solutions compared to stirred ones. The relative diffusion/chemical reaction control mechanism of Mg phosphates precipitation from supersaturated solutions is discussed. It is shown that spontaneous inorganic precipitation of Mg-(ammonium) phosphates (struvite and bobbierite) in modern marine environment is impossible because of very sluggish kinetics.
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Submitted on : Friday, April 15, 2022 - 1:45:58 PM
Last modification on : Saturday, June 25, 2022 - 8:53:36 AM

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S.V. Golubev, O.S. Pokrovsky, V.S. Savenko. Homogeneous precipitation of magnesium phosphates from seawater solutions. JOURNAL OF CRYSTAL GROWTH, 2001, 223, pp.550-556. ⟨10.1016/S0022-0248(01)00681-9⟩. ⟨insu-03642948⟩

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