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Journal of Chemistry
Volume 2015, Article ID 269387, 10 pages
http://dx.doi.org/10.1155/2015/269387
Research Article

Characterization, Dissolution, and Solubility of Lead Hydroxypyromorphite [Pb5(PO4)3OH] at 25–45°C

1College of Environmental Science and Engineering, Guilin University of Technology, Guilin 541004, China
2College of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China

Received 28 February 2015; Revised 16 April 2015; Accepted 17 April 2015

Academic Editor: Yuangen Yang

Copyright © 2015 Yinian Zhu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Dissolution of the hydroxypyromorphite [lead hydroxyapatite, Pb5(PO4)3OH] in HNO3 solution (pH = 2.00), ultrapure water (pH = 5.60), and NaOH solution (pH = 9.00) was experimentally studied at 25°C, 35°C, and 45°C. The XRD, FT-IR, and FE-SEM analyses indicated that the hydroxypyromorphite solids were observed to have indistinguishable change during dissolution. For the hydroxypyromorphite dissolution in aqueous acidic media at initial pH 2.00 and 25°C, the aqueous phosphate concentrations rose quickly and reached the peak values after 1 h dissolution, while the aqueous lead concentrations rose slowly and reached the peak values after 1440 h. The solution Pb/P molar ratio increased constantly from 1.10 to 1.65 near the stoichiometric ratio of 1.67 to 209.85~597.72 and then decreased to 74.76~237.26 for the dissolution at initial pH 2.00 and 25°C~45°C. The average values for Pb5(PO4)3OH were determined to be 10−80.77 (10−80.57−10−80.96) at 25°C, 10−80.65 (10−80.38−10−80.99) at 35°C, and 10−79.96 (10−79.38−10−80.71) at 45°C. From the obtained solubility data for the dissolution at initial pH 2.00 and 25°C, the Gibbs free energy of formation [] for Pb5(PO4)3OH was calculated to be −3796.71 kJ/mol (−3795.55~−3797.78 kJ/mol).