The　bio-oxidation　leaching　process　of　the　refractory　gold　concentrate,　which　proceeds　in　a　gas-liquid-solid　stirred　bioreactor,　is　a　new　type　of　the　lower　pollution　and　cleaner　production　technology.　In　gas-liquid-solid　stirred　bioreactor,　the　just　suspension　is　the　optimal　condition　for　bio-reaction,　because　of　its　advantage　in　the　minimum　of　shear　stress　and　power　consumption　and　the　maximum　of　mass　transfer　efficiency　between　phases.　In　order　to　save　the　energy　and　ensure　the　bio-reaction　efficiency,　this　paper　is　devoted　to　study　the　optimal　location　of　the　impeller.　Based　on　the　previous　studies,　a　general　formula　for　calculating　the　just　suspension　speed　is　derived　and　verified　by　the　experimental　data.　The　results　show　that　the　overall　errors　of　the　prediction　result　are　less　than　20%　when　the　refractory　gold　concentrate　is　used　as　solid　phase　in　gas-liquid-solid　three　phase　flows.　The　formula　and　method　recommended　in　this　paper　can　quickly　acquire　the　optimal　parameters　for　engineering　design,　so　that　the　energy　saving　and　reducing　pollution　in　the　bio-leaching　of　the　refractory　gold　concentrate　can　be　realized.　©　2019,　Science　Press.　All　right　reserved.