Techniques And Solution Chemistry For Vanadium Extraction From Stone Coal

Stone coal is an important vanadium mineral, which has been mined industrially with vanadium grade more than 0.8%. The existing techniques of extraction vanadium have some faults. In the paper, the stone coal in Hunan province had been studied with a new technique of extraction vanadium. The advantages of sulfuric acid direct leaching process, sulfuric acid leaching process under microwave, and sulfuric acid leaching process using hydrofluoric acid as assistant had been summarized, the sulfuric acid leaching process using hydrofluoric acid as assistant under microwave has been improved.Sulfuric acid direct leaching process has been used to extract vanadium from stone coal with vanadium leaching rate to reach 63.4 percent. There are several disadvantages in this process without microwave facilities: high sulfuric acid dosage, difficult operational process and low leaching rate, but it also has its unique advantage: low capital cost and simple process flows. The best leaching conditions of this process is as follow: mineral grain size of -0.074mm 100% and liquid/solid of 1.5:1 are chosen to leach 6 hour in 90 centigrade degree with sulfuric acid dosage of 40%.Vanadium leaching rate can reach 77.3 percent used by sulfuric acid leaching process under microwave. It is easy to use microwave to heat mineral particle to get advisable temperature and shorten the leaching time, but high acid dosage, high energy consumption and much wastewater produced in this process. The best leaching conditions is as follow: microwave power of 3000W and liquid/solid(3:1) are chosen to leach 80 minute with sulfuric acid dosage of 40%.Sulfuric acid leaching process using hydrofluoric acid as assistant is used with low liquid/solid, low sulfuric acid dosage and traditional heating method. Vanadium leaching rate can reach 75.4 percent when the rate of liquid/solid is 1:1 and hydrofluoric acid dosage (8%) are chosen to leach 6 hour in 90 centigrade degree with sulfuric acid dosage of 30%.The sulfuric acid leaching process using hydrofluoric acid as assistant under microwave has been studied by using orthogonal experiment. The effects of sulfuric acid dosage, hydrofluoric acid dosage, microwave power, leaching time and liquid/solid have been studied. Vanadium leaching rate can reach 85.6% while in following condition: Liquid/solid of 1:1, microwave power of 3000W, leaching time of 80 minute, sulfuric acid dosage of 25% and hydrofluoric acid dosage of 7%.Leachate has been pretreated before extraction. Extractant consisted of 15%P204 +5%TBP+80%sulfonated kerosene is used to extract vanadium from pretreatment leachate with extraction rate of 99%. Back extraction solution is oxidized by hydrogen peroxide and then ammonium polytrioxovanadate is precipitated by ammonium sulfate. The product can reach national standards.Reaction enthalpy and reaction Gibbs free energy can be calculated by thermodynamic calculations and we can draw the fig.△rH_T^θ-T and fig.△rG_T^θ-T. Dissociation equilibrium of leaching agent, assistant infusion, the solution equilibria and charge balance of the main oxygen compounds in stone coal has benn studied and we drew the fig. lgC-pH. The two kinetic models are listed and showed by following two equations: Control of chemical reaction kinetic model: 1-(1-η)^1/3=0.0062t. Kinetic model of solid-film control: 1-2/3η-(1-η)^2/3=0.0014t. The air pollution can be eliminated radically. Ammonia is recycled to produce weak aqua ammonia. Wastewater can be also recycled after simple treatments. The stone coal powder can be produced by solid waste, which can be used to produce cement and burning-rate accelerator.