Characterization,dissolution,and solubility of lead hydroxypyromorphite [Pb5(PO4)3OH] at 25-45°C

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 209.85597.72 and then decreased to 74.76237.26 for the dissolution at initial ph 2.00 and 25°c45°c. the average ksp 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 [δgfo] for pb5(po4)3oh was calculated to be -3796.71 kj/mol (-3795.55-3797.78 kj/mol). © 2015 yinian zhu et al.