Study On Novel Technology Of Vanadium Extraction From Stone Coal Using Sulfuric Acid

Extracting vanadium from stone coal has an important strategic significance, for over87%of gross reserves of vanadium in China formed in stone coal ore. As one of environmentally-friendly technologies, stone coal decomposition using sulfuric acid has been dominantly adopted in industrial production. However there also exist some problems. Firstly, not only is the usage of sulfuric acid in minerals decomposition larger, but the vanadium leaching ratio is low; secondly, the common method used to separate and enrich vanadium from acid leaching solution-solvent extraction, exists such problem as high-reagent consumption and difficulity to recycling highly salty spent water; besides, due to the interference of iron ions, it is also infeasible to separate and enrich vanadium from acid leaching solution using ion exchange. For those shortcomings, a novel technology, primarily composed of two-step low temperature sulphation roasting and water leaching, V(V) coprecipitation with Fe(III), alkaline roasting of vanadium-containing precipitate followed by water leaching was proposed and the technology can achieve a higher vanadium leaching efficiency as well as circulation utilization of process water.74.12%of vanadium was extracted from stone coal using two-step low temperature sulphation roasting and water leaching under these suitable condiions:thoroughly mixing100g stone coal with moderate volume of sulfuric acid solution containing22g H2SO4, roasting the mixture at240℃for2h, adding30mL H2O to wet the water-free calcinate, then roasted it again at210℃for1h, leaching the final calcine with water at liquid-to-solid (L/S) of1.5:1and rome temperature for1.5h. Whilst under the same H2SO4/stone coal ratio and leaching conditons, only65.09%of vanadium was leached from the calcine obtained by one-step low temperature sulphation roasting; only59.48%of vanadium was leached using direct acid leaching under the same H2SO4/stone coal ratio at L/S of1.2:1and leaching temperature98℃for52h.Adding (NH4)2SO4into stone coal acid leaching solution to remove Al3+through crystallization of ammonium alum, then vanadium was recovered from solution by V(V) coprecipitation with Fe(III) under the suitable conditions of adding3.64g NaC103per liter solution with initial pH1.73under stirring for0.5h at95℃, V2O5conetent in the obtained vanadium-containing precipitate reached up to13.02%and two crystals, namely KFe3(SO4)2(OH)6and HNaV6O16-4H2O were detected in the vanadium precipitate. The tailwater from precipitating vanadium was reused in stone coal decomposition using sulfuric aicd, which did not cause negative effect to vanadium extraction.97.00%of vanadium was recovered from vanadium-containing precipitate by roasting the mixture of25g of the precipitate with22.5g NaOH at170℃for1.0h, and then water leaching the roasted mixture at98℃for1.0h under stirring with L/S ratio of3.3:1.After adding MgCl2to remove P、 As and Si from the prepared alkaline leaching solution, vanadium pentoxide with purity99.3%was obtained by adding NH4Cl to precipitate ammonium polyvanadate from the solution at pH about2.0, and then roasting the ammonium polyvanadate at520℃for2h. The quality of vanadium pentoxide is in accordance with requirements of GB3283-1987metallurgical99-level.