Kinetic dissolution of phosphate glasses containing toxic heavy metals

The dissolution kinetics of a series of phosphate glasses with the compositions 50P2O5–15ZnO–(35−x)PbO–xCdO (x=20 and 35) and (100−y)[50P2O5–15ZnO–15PbO–20CdO]–yAl2O3 (y=6 and 8) have been studied in aqueous solution. The dissolution process of aluminium free metaphosphate glasses is interpreted as hydration of glass surface with a congruent dissolution for x=35 and controlled by both mechanisms with incongruent dissolution for x=20. The addition of Al2O3 in metaphosphate glass (x=20) considerably improves the corrosion resistance. The dissolution kinetics are strongly depending on the leaching solution temperature with linear and non-linear behavior at 50 and 90 °C, respectively. This effect can be interpreted in relation to the acidity change of leaching solution and the insoluble thin layer formation on glass surface. The hydrolysis dissolution mechanism can be explained taking into account the increase of cross-linking of the short polyphosphate chains inducing a stiffness of the glass network as alumina content increases. The y=8 glass exhibits a dissolution rate in order of 10−9–10−10 g cm−2 min−1 at room temperature.