Abstract: Sodium roast using NaCl, Na₂SO₄ and compound of both as roasting additives was studied in vanadium extraction from low grade stone coal with high calcium from Hubei Province.On the condition of roasting with sodium chloride, the water leaching rate of vanadium was affected because of too much free calcium oxide in the raw ore, which inclines to combine with vanadium, producing water-insoluble calcium vanadate.On the condition of roasting with sodium sulfate, even though it can fix calcium, the dosage of sodium sulfate was too large, and economic costs and environmental costs were very high.When roasting with the mixture of 7% NaCl and 16% Na₂SO₄ at the conditions of roasting temperature of 850 ℃ and roasting time of 3 h, the water leaching rate increased to 51.47%, and the total leaching rate of vanadium could reach 79.81%.The leaching results were good at small dosage of roasting compound additives.On one hand, roasting with Na₂SO₄ can fix calcium, so as to inhibit the formation of water-insoluble calcium vanadate.On the other hand, the strong oxidizing atmosphere of HCl and Cl₂ produced by adding NaCl can strengthen the destruction of the crystal structure of mica and promote the oxidation of vanadium.

Key words: Stone coal, Sodium roast, Calcium fixing, Leaching rate