The　reduction　diffusion　(RD)　process　for　Nd-Fe-B　sludge　has　been　reported　as　a　green　and　efficient　method　for　synthesizing　recycled　Nd2Fe14B　magnetic　powders.　In　this　work,　recycled　Nd-Fe-B　powders　with　low　impurity　content　and　uniform　particle　size　distribution　were　successfully　prepared.　M3　T　increased　to　146.25　emu/g,　which　was　about　17%　and　32%　higher　than　the　purged　and　original　sludge,　respectively.　Then,　the　recycled　Nd-Fe-B　sintered　magnets　with　properties　of　Br　=　12.14　kG,　Hcj　=　12.00　kOe,　and　(BH)m　=　35.05　MGOe　were　successfully　prepared　by　doping　with　37.70　wt%　Nd4Fe14B　powders.　Based　on　experimental　studies　of　calcium　thermal　reduction　of　Nd-Fe-B　sludge　and　thermo-kinetic　analysis,　the　reaction　mechanism　of　the　RD　method　for　sludge　waste　recovery　was　clarified.　In　the　RD　process,　the　oxides　in　the　sludge　were　selectively　reduced　by　Ca　at　600–950　°C　and　the　reduced　Nd　diffused　to　the　surface　of　the　Fe　core,　forming　the　Nd-Fe-B　alloy,　where　the　formation　process　included　the　nucleation　stage,　the　alloy　layer　high-speed　growth　stage,　and　the　completion　stage.　And　the　relationship　between　the　alloy　layer　thickness　and　time　during　the　high-speed　growth　period　of　1–3　h　was　more　in　line　with　linear　law　(d　=　5.41　t–4.31).　The　RD　reaction　conformed　to　the　unreacted　shrinking　core　model,　and　its　reaction　rate　control　step　consisted　of　a　one-way　diffusion　process　for　the　diffusion　of　Nd　into　the　Fe　core.　©　2022　Elsevier　B.V.