Theory And New Technology Investigationof Comprehensive Utilization Of Vanadium And Silicon From Stone Coal

Stone coal is important vanadium resources of our country. Currently, acid leaching process is widely used to extract vanadium from the stone coal. The process has many disadvantages, such as corrosion of the equipment, complex constituents of the leaching solution, leaching agent not recycled. The alkali leaching process overcomes these shortcomings with a high leaching rate, but the leaching agent used is cost which hinders the widely application of the process. To lower the cost, increase the added value of the product and improve the competitive strength of the process, the utilization of the silicon from the stone coal and recycle of the leaching agent were investigated in this paper. The goal is to invent a novel technology of comprehensive utilization of vanadium and silicon from stone coal, which produces high-quality white carbon black products from the silicon in the leaching solution and recycles the leaching agent when efficiently extracting vanadium from the stone coal. On the basis of the systematic research of the process, two key points of the process were investigated theoretically, which are the separation of vanadium and silicon in alkali solution and the extraction of vanadium from alkali solution, starting from the solution chemistry properties of the leaching solution of the stone coal. The major results are as below:(1) Separation of vanadium and silicon in alkali solutionGood separation of vanadium and silicon was achieved by carbonation method? Adding CO2gas to the leaching solution of stone coal in one aspect produces Na2CO3or NaHCO3through the reaction of CO2with the alkali medium NaOHwhich is recycled through the causticization process from the Na2CO3orNaHCO3; in the other aspect reduces the solution pH and the silicon will deposit as precipitate when the solution turns natural or slightly alkaline while vanadium stays in solution. Consequently, the vanadium was separated from silicon in alkali solution.The thermodynamics research of the process of adding CO2to the leaching solution of stone coal indicates that the increase of the supersaturation of the silicon in solution leads to the precipitation of the silicon and the adsorption of CO2is controlled by the film diffusion.The major factors of producing carbon white from alkali leaching solution of stone coal is temperature and the final pH. Besides, certain amounts of surfactants and a secondary carbonation process improves the specific area of the carbon white product.(2)Preparation of high-quality carbon whiteVanadium in the solution didn't influence the precipitation of silicon in the desilication carbonation process? Vanadium in the silicon precipitates exsists in the form of V4O124-physically adsorped, the desorption of which could achieved with dilute sulfuric acid. The key to producing high-specific area carbon white is washing the precipitates with acid, which can not only purify the product but also change its pore structure and improve the specific area. The process of carbonation followed by washing with acid can produce high-quality carbon white with the specific area larger than500m2/g(3) Extracting vanadium from the week alkaline solutionIn this research, the fractional precipitation of calcium carbonate and and calcium vanadate and the extraction of vanadium were investigated to separate vanadium from the alkaline medium. In the system of sodium vanadate coexisting with sodium carbonate, Ca(OH)2can precipitate the two constituents well. Thermodynamics calculations indicated calcium carbonate precipitates first. And the key to the fractional precipitation of sodium vanadate and sodium carbonate is temperature and amount of Ca(OH)2added.In slight alkaline solution N263is a good extractant for vanadium. With N263vanadium can be efficiently recovered from the leaching solution after carbonation process and the separation of vanadium from the alkaline medium was achieved.(4) The novel technology of comprehensive utilization of vanadium and silicon from stone coalThrough tests was formed a process of comprehensive utilization of vanadium and silicon from stone coal, including controlling roast, enhancing alkaline leaching, desilication by carbonation method,extracting and enrichment of vanadium, producing vanadium and carbon white and recycling the leaching agent by causticization. The results of laboratory tests indicate the total recovery of V2O5of the complete process reached higher than75%;9t of high-quality white carbon with specific area of larger than500m2/g can be produced when It V2O5was produced;75%leaching agent of the whole process can be recycled. Efficient utilization of the silicon and the recycle of the leaching agent increase the by-product value and largely reduce the cost of the process of extracting vanadium from leaching stone coal with alkaline, andin addition of alkaline leaching's little environmental pollution, consequently make the alkaline leaching more competitive than acid leaching.