Study On Process And Mechanism Of Carbonate Method Roasting In Extracting Vanadium From Stone Coal

The chemical valence of vanadium in stone coal is mostly three, and the vanadiumsubstitutes for aluminum of valence3as an isomorphism to exist in the stable dioctahedral ofmica. Under the condition of high temperature and additives it is possible to change the chemicalvalence of vanadium from3to4or5, which is soluble. To improve the leaching rate ofvanadium, the paper focused on how to develop carbonate compound additives with the stonecoal from Jiangxi somewhere as raw material. Then the mechanism was discussed on extractingvanadium with carbonate roasting method.First of all, parallel experiments were conducted using common carbonates as additives toselect which carbonate has the best roasting effect. Then, the admixtures were reseached to mixwith the above carbonate so as to improve the leaching rate of vanadium. Through comparisonand analysis, the results are shown in the following.The best proportion of the carbonate additives is5%MgCO₃and4%CaF₂. The bestroasting parameters are as follows: the raw ore doesn’t have to be decarburized before roasting,and the particle size after grinding should be at minus0.074mm with a content of60%while theroasting temperature should be set to750℃and the roasting time is1.25h. The leaching ratecan reach85%, if sulfuric acid of10%volume concentration is adopted for leaching at95℃for2h.Reasons have been explained from the point of heat stability of carbonate on the subject thatsmaller radius of Mg²⁺makes MgCO₃decompose into CO₂gas at a relatively lowtemperature（about400℃）, thus making the material loose and porousin early time whenroasting so that oxygen in the air gets to diffuse and permeate amid the material. Then a betterenvironment is created for the oxidation of vanadium of low valence. At the same time, CO₂isconducive to the formation of compound which contains vanadium and calcium and dissolveseasily in acid. The approximate radius of F-and O^2-and the strong diffusivity of F^-help todeconstruct the tetrahedron network of Si-O. So CaF₂exposes the vanadium of valence3andmakes it easier to transform to vanadium of higher valence. The two compounds contained in thecarbonate additives improve the roasting effect together, thus increase the leaching rate. Theyalso have the desulfurization effectiveness without producing toxic gas, thus achieving cleanerproduction.