Stone Coal Of Low Temperature Sulfuric Acid Roasting Process Of Vanadium

The process of extracting vanadium from stone coal was studied and the raw stone coal sample was taken from the kaili Distrilt in Guizhou province.The analysis results show that the vanadium of the sample occur mainly in muscovite in isomorphism,which is belong to unmanageable ore.The technology of roasting the stone with sulfuric acid under low temperature,leaching with water,depositing vanadium in leaching solution,decreaming vanadium slag,concentrating vanadium by nanofiltration,precipitating vanadium with ammonium salt was used to extract vanadium from the stone coal.Experiments focus research on the decomposing of stone coal,such as roasting time,roasting temperature,sulfuric acid addition volume, leaching time,leaching temperature and leaching ratio of liquid to solid. The leaching rate of vanadium are mainly related with sulfuric acid addition volume,roasting temperature,leaching ratio of liquid to solid. Before the sulfuric acid addition volume is less than per 100g stone coal with 20 mL concentrated sulfuric acid,the leaching rate of vanadium increase quickly with the addition of sulfuric acid volume,after that,although the leaching rate of vanadium can increase with the addition of sulfuric acid volume,the impurities and the concentration of free acid increase sharply,which bring difficultly to follow on test.The roasting temperature is very important to the leaching rate,when the temperature is lower than 250℃,the leaching rate increase rapidly with rapidly by the increase of roasting temperature and 250℃is the best point of roasting temperature,when the temperature is higher than 250℃,the leaching rate decrease with the increase of roasting temperature.When the leaching ratio of liquid to solid of leaching calcine is smaller than 1.2 mL.g^-1,the leaching rate increase with the increase of the ratio of liquid to solid,leaching ratio of liquid to solid beyond 1.2 mL.g ^-1,the leaching rate decrease with the ratio of liquid to solid.The research results show that the leaching rate of vanadium can reach 78.2% at the mass ratio of sulfuric acid to stone coal of 36%,roasting temperature 250℃,roasting time 2 hours,leaching ratio of liquid to solid 1.2 mL.g^-1,leaching temperature 100℃and leaching time 2 hours.Selectivity precipitation method was used to separate and concentrate the vanadium of leaching water.Most of aluminum can be removed through adjusting the leaching solution pH to 1.5 by the addition of ammonia.The leaching solution pH was adjusted continually by addition of sodium hydroxide to 3.5～5.0 to precipitate vanadium and then filtering.The filtrate return to leach and filter residue was roasted with sodium chloride to extract vanadium.The experiments show that the pH of leaching water is the maximum factor of concentration nanofiltration, the rejection rate of vanadium increases with pH from 3.16 to 6.15,and the peak rejection 92%is reached at pH 6.15,then the rejection declines sharply with pH increase,when the pH raise to 8.5,the nanofiltration can hardly intercept vanadium.The concentration of vanadium of leaching water is another factor of concentration nanofiltration,under operation pressure 12.5 kg/cm²,when V₂O₅ concentration in the feed was increased from 6g/L to 35.8g/L,the flux was decreased from 84.53 L/(h·m²) to 50.71 L/(h·m²),and V₂O₅ concentration in the permeate was increased from 0.49g/L to 2.22g/L.NH₄VO₃ was precipitated in the rejected solution by adding NH₄Cl in the stoichiometric proportion of 2.2.The product V₂O₅ with purity 98.6%was obtained by the thermal decomposition of the precipitated NH₄VO₃ at 500℃for 1 hour.