Abstract
This study aimed to determine whether seeding with low-solubility dolomite improves the efficiency, product quality, and scalability of phosphorus (P) recovery by fluidized-bed crystallization compared with an unseeded (homogeneous) mode, and to identify operating conditions that maximize recovery while yielding a reusable product. Two continuous 350-mL reactors were run in parallel under identical hydrodynamics (up-flow 30 m·h⁻¹; surface loading 0.9 kg·m⁻²·h⁻¹) and chemistry designed to favor calcium phosphate formation (pH 7.7; Ca/P = 3.5): a seeded system using dolomite as heterogeneous nuclei and an unseeded control. Seeding increased crystallization of both P and Ca from about 60% to about 80%; under optimal conditions, total removals reached ~85% for P and ~92% for Ca. X-ray diffraction and Raman spectroscopy confirmed tricalcium phosphate (Ca₃(PO₄)₂·xH₂O) as the dominant phase in both modes, while microscopy showed that the seeded bed produced larger, denser pellets with fewer fines, simplifying solid–liquid separation and supporting scale-up. Sensitivity tests across pH 6–8.7 validated the selected set-point, and “blank” runs with dolomite alone showed minimal P removal, indicating that performance gains arise from controlled supersaturation with added calcium. The recovered P, in a stable crystalline form, is suitable for slow-release fertilizers and as feedstock for bio-ceramics and bioactive glass.
Note: The results presented in this abstract have been published in Separation and Purification Technology as: Ha, T.H., Mahasti, N.N., Lu, M.C., and Huang, Y.H. (2022). Sep. Purif. Technol. 303, 122192. https://doi.org/10.1016/j.seppur.2022.122192