Mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes from stone coal

The mechanisms of aid-leaching reagent calcium fluoride in the extracting vanadium processes were researched by comparing the blank extraction with the extraction with calcium fluoride as aid-leaching reagent. The leaching experiments were carried out under the conditions of 95 ℃, 6h, 1.5 mlg-1 , 15 vol % H2SO4 , and 5 % calcium fluoride (mass ratio of CaF2 to stone coal). The concentrations of hydrogen ion were adjusted from initial 1.82 and 4.79 mol L -1 to the pH of 1.80 ± 0.05 by 200 g L-1 lime milk, respectively. The solvent extraction experiments were carried out under the organic phase using 15 vol% D2EHPA, 5 vol% TBP, and 80 vol% sulfonated kerosene and O/A phase ratio of 1/4. The leaching rate of vanadium and six-stage countercurrent solvent extraction rate of vanadium can be remarkably improved from 66.71 to 92.97 % and 81.15 to 98.81 %, respectively, when calcium fluoride was added as aid-leaching reagent. In the leaching process, fluorine can enhance the breakage of the structure of vanadium-bearing minerals. Meanwhile, fluoride ion can combine with iron ion to generate acid-insoluble iron fluoride hydrate (Fe2F57H2O) and consume all ferric ions and a portion of ferrous ions. In adjusting pH value process, the massive impurities are decreased to form KAlSO4 and FeAlF5 . In solvent extraction process, fluorine can prevent the formation of ferric hydroxide colloids and eliminate the formed unstable ferric hydroxide colloids and the silicon-containing colloids to promote the sufficient contact between the aqueous phase and the organic phase and the sufficient reaction.