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Minerals 2017, 7(8), 129;

Carbonate Apatite Precipitation from Synthetic Municipal Wastewater

Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, ON K1N 6N5, Canada
Author to whom correspondence should be addressed.
Received: 31 May 2017 / Revised: 18 July 2017 / Accepted: 18 July 2017 / Published: 25 July 2017
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An important component of phosphorite (phosphate rock) is carbonate apatite, as it is required for phosphorous fertilizer production due to its increased phosphate solubility caused by carbonate substitution in the apatite mineral lattice. High phosphate concentrations in municipal wastewater treatment plants are commonly reduced by precipitating iron phosphate by addition of iron chloride. We investigated the possibility of precipitating carbonate apatite from a potential range of phosphate concentrations that could be available from municipal wastewater treatment plants with anaerobic digestion reactors (5 mM–30 mM). Synthetic phosphate solutions at neutral pH were mixed in batch experiments with a calcium carbonate solution produced by dissolving calcite in contact with carbon dioxide gas, with and without carbonate apatite seed. Batch experiments were used to identify the carbonate apatite supersaturation ranges for homogeneous and heterogeneous nucleation, and the precipitates analyzed with Raman spectroscopy, powder X-ray diffraction, inorganic carbon coulometry, and scanning electron microscopy. Some precipitates contained carbonate weight fractions within the range reported for geological phosphate rock (1.4–6.3 wt %). The precipitates were spherical, poorly crystalline carbonate apatite, suggesting an amorphous precursor transformed to a poorly crystalline carbonate apatite without changing morphology. View Full-Text
Keywords: amorphous precursor; nucleation; carbonate apatite; amorphous calcium carbonate phosphate amorphous precursor; nucleation; carbonate apatite; amorphous calcium carbonate phosphate

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Ross, J.; Gao, L.; Meouch, O.; Anthony, E.; Sutarwala, D.; Mamo, H.; Omelon, S. Carbonate Apatite Precipitation from Synthetic Municipal Wastewater. Minerals 2017, 7, 129.

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