Chromium　oxide　(Cr2O3)　has　wide　application　in　various　industries.　Its　traditional　production　process,　uses　sodium　carbonate　(Na2CO3),　which　is　converted　into　cheaper　byproducts,　including　sodium　sulfate　(Na2SO4)　and　sodium　bisulfate　(NaHSO4).　These　byproducts　contain　hexavalent　chromium　(Cr(VI)),　which　can　lead　to　serious　environmental　pollution.　In　this　work,　a　cleaner　production　process　for　Cr2O3　through　the　hydrothermal　reduction　of　a　sodium　chromate　(Na2CrO4)　aqueous　solution　with　hydrogen　(H2)　was　studied.　Nearly　single-phase　chromium　oxide　hydroxide　(CrOOH)　formed　as　a　solid　product　after　the　hydrothermal　reduction.　Then,　Cr2O3　was　obtained　by　the　thermal　decomposition　of　CrOOH.　The　advantages　of　the　new　process　are　remarkable.　First,　the　raw　material,　the　Na2CrO4　aqueous　solution,　was　the　direct　intermediate　product　in　the　pressure　oxidative　leaching　of　chromite　ore　with　sodium　hydroxide　(NaOH).　Second,　the　reduction　efficiency　of　Cr(VI)　increased　up　to　97.6%,　and　the　total　yield　of　chromium　from　Na2CrO4　to　Cr2O3　was　as　high　as　94.2%.　Finally,　96.6%　of　sodium　could　be　converted　into　NaOH,　so　the　aqueous　solution　in　the　hydrothermal　hydrogen　reduction　process　could　be　recycled　as　the　leaching　agent　for　the　pressure　oxidative　leaching　process　of　chromite　ore.　Consequently,　a　complete　cleaner　and　shorter　preparation　route　from　chromite　ore　to　Cr2O3　was　achieved　by　integrating　three　processes:　the　pressure　oxidative　leaching　of　chromite　ore,　the　hydrothermal　reduction　of　the　Na2CrO4　aqueous　solution,　and　the　thermal　decomposition　of　CrOOH.　The　new　method　achieves　the　high-efficiency　use　of　chromium　resources,　cyclic　utilization　of　material,　and　extremely　low　environmental　pollution　of　Cr(VI),　and　well　exemplifies　the　principle　of　the　3Rs　(Reduce,　Recycle,　Reuse).　©　2023　Elsevier　B.V.