Abstract: In order to reveal the universal law of direct vanadium precipitation from acid leaching solution of Pangang vanadium slag，and determine the appropriate technological parameters of precipitation，the effects of ratio of ［V］/［P］，［V］，initial pH value on precipitation rate and the quality of V₂O₅ products were studied with acid leaching solutions in three different ［V］ and ［P］ concentration and their mixtures as object.The results showed that：①As the concentration ratio of ［V］/［P］ increases，the precipitation rate rises，and P content decreases in V₂O₅ products.②The requirement for ［P］ in leaching solution of calcium roasting process is lower.With ［V］/［P］ greater than 767 and ［P］ less than 0.042 g/L，the vanadium precipitation in calcium roasting process is the same as that in sodium roasting process with ［V］/［P］ greater than 1 100 and ［P］ less than 0.015 g/L.③The lower ［V］ in leaching solution is the lower of precipitation ratio.The optimal initial concentration for vanadium precipitation is between 32~40 g/L，as the pH of the supernatant is greater than 2.5，replenish of acid，heating，precipitating should be taken to improve the efficiency.④When the initial pH is about 2.0 and ［V］/［P］ is greater than 767(or ［P］ is less than 0.042 g/L)，the precipitation rate can reach more than 99.5%，and V₂O₅ content will be greater than 98.5% with less than 0.016% of P respectively.

Key words: Vanadium slag, Vanadium, Phosphorus, Calcific roasting, Pickle liquor, Ration of ［V］/［P］, Precipitation of vanadium