Abstract: Chemical durability behavior of simulated crystalline oxyapatite wasteforms CaLa3.4Ce0.1Pr0.1Nd0.1Sm0.1Gd0.1Y0.1(SiO4)3O [WF-1] and Ca0.8Sr0.1Pb0.1La3.4Ce0.1Pr0.1Nd0.1Sm0.1Gd0.1Y0.1(SiO4)3O [WF-2] was studied. Soxhlet leach tests (MCC-5) were conducted and the leachates were analyzed by ICP-MS/OES techniques. The results indicate that the release of ions from the wasteform was found to be strongly dependent on chemical compositions, as WF-1 shows relatively more resistance towards leaching than parent and WF-2. The leachability of immobilized rare-earth ions in WF-1 and WF-2 was found to be negligible. The observed trend of leaching behaviour in all three systems is Si4+ > A2+ > RE3+. Further, the investigation on the mechanism of leaching suggested that the leaching process is predominantly governed by diffusion. Graphic abstract: [Figure not available: see fulltext.] © 2020, Akadémiai Kiadó, Budapest, Hungary.