Abstract: Lead-hydroxyapatite was a new mineral phase of leadbearing phosphate formed from the stabilization of fly ash treated by phosphate. The control conditions of the formation of various new phosphates from reaction between PO₄^3- and lead ions (X_Pb) in terms of different molar ratios were studied. The products’ characteristics, thermal behaviors and chemical stability were also discussed. It is indicated that Ca₈Pb₂(PO₄)₆(OH)₂, Ca_5.5Pb_4.5(PO₄)₆(OH)₂, Ca_2.12Pb_2.22(PO₄)₃(OH)_0.67, Ca₂Pb₈(PO₄)₆(OH)₂ and Pb₁₀(PO₄)₆(OH)₂ are synthesised respectively with the increase of X_Pb at the pH value of 10. And the products are changed from clavate polymer, granulated aggregate to massive aggregate. Furthermore, they can exist stably below 400℃. The lead leached via TCLP are decreased with the increase of the pH value of leaching solution. When the X_Pb is in the range from 0.1 to 0.7, the products perform good chemical stability. However, the stability is weakened when the X_Pb is above 0.7.

Key words: lead-hydroxyapatite, chemical stability, thermal behaviors