Coal　fly　ash　has　been　considered　as　a　potential　resource　for　alumina　production　by　Bayer　process.　However,　the　implementation　is　always　limited　by　low　alumina-silica　mass　ratio　(A/S)　of　coal　fly　ash.　Previously,　we　reported　an　approach　to　realize　the　desilication　of　coal　fly　ash　and　the　A/S　could　reach　5.34.　However,　this　A/S　was　still　not　high　enough　for　Bayer　process.　Following　the　previous　study,　herein　we　systematically　optimize　the　desilication　conditions　to　further　improve　the　A/S,　and　also　evaluate　the　applicability　of　desilication　residue　for　Bayer　alumina　production.　First,　the　digestion　properties　of　amorphous　silicon　dioxide　and　γ-alumina　in　the　two-stage　roasted　calcines　are　analyzed　by　thermodynamic　calculation.　The　results　indicate　that　their　alkali-digestion　properties　become　remarkably　different　at　relatively　high　temperature,　thus　amorphous　silicon　dioxide　could　be　digested　while　γ-alumina　is　preserved　in　the　residue　by　controlling　the　pH　and　digestion　temperature.　The　desilication　ratio　and　the　A/S　ratio　could　reach　82.27%　and　7.46　at　the　optimal　conditions　of　116　g/L　Na2O,　95　°C,　15　min　digestion　time　and　1/10　solid-to-liquid　ratio.　The　obtained　desilication　residue　becomes　acceptable　and　economical　high　grade　raw　material　for　Bayer　process,　which　is　confirmed　by　the　production　of　standard　alumina　(AO-2,　China).　This　research　could　provide　an　alternative　economic　process　for　recycling　alumina　from　high-alumina　coal　fly　ash.　©　2021　Elsevier　Ltd