Vanadium Extraction and Recovery by Alkaline Heap Leaching of Mineralized Material from the Gibellini Project in Eureka County, Nevada
AuthorOlson, Jared Reed
Materials Science and Engineering
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Vanadium is an important metal used in ferrous and non-ferrous alloys, industrial catalysts, pigments and dyes, and as a charge carrier in vanadium redox flow batteries. Demand for and price of vanadium have increased in recent years, primarily due to a greater global demand from China. As the need for grid-level energy storage continues to expand, the demand for vanadium to be used in redox flow batteries is expected to grow as well. Low cost methods for vanadium extraction and recovery are required to ensure a stable and economic supply of vanadium. This study demonstrates that alkaline heap leaching with sodium hydroxide may be a low-cost alternative to conventional vanadium extraction methods.Vanadium in an oxidized state is known to be soluble in alkaline solutions, and historically, vanadium has been leached from finely ground ores with solutions of soda ash or caustic soda. Alkaline heap leaching of cement agglomerated ore is a proven low-cost method that is commonly used for extraction of gold and silver. It is proposed that these two proven processes could be combined into a single low-cost and effective method for vanadium extraction. In this work, this theoretical process was simulated at a laboratory scale to extract vanadium from a vanadium-bearing sample of mineralized material from the Gibellini Hill project in Eureka county, Nevada. At a commercial scale, this process would consist of cement agglomeration of a crushed vanadium ore and stacking in a heap, irrigation with sodium hydroxide solution, neutralization of the solution to remove impurities, and solvent extraction to upgrade the solution and further reject impurities. In a commercial circuit, vanadium from this solution would then be precipitated in an insoluble form such as ammonium metavanadate; however, this final step was not tested here. When simulating this process in the laboratory by column leach testing, a 68.8% vanadium extraction was observed in 44 days of leaching and rinsing. The primary impurities observed in the leach solution were aluminum and phosphorous. Aluminum was effectively removed by neutralizing the solution pH to 10 or lower, while phosphorous was rejected during solvent extraction processing. It was demonstrated that the vanadium contained in the leach solution could readily be extracted using Aliquat 336 based solvents. An extraction of 98.6% was observed, and a highly pure strip solution was produced by stripping the loaded organic with strong caustic solution. Sulfuric acid leaching is more commonly used for extraction of vanadium from its mineral sources, but alkaline leaching can have many benefits relative to acid leaching, including improved selectivity. The improved selectivity was demonstrated in this work using multi element analysis of pregnant solutions generated from both processes. In a heap leaching circuit, alkaline leaching would also enable the use of cement during agglomeration, which increases the strength of agglomerates and in turn reduces the risk of heap “ponding”. This may allow the leaching of ores with high clay contents that would not otherwise be suitable for heap leaching. Alkaline heap leaching may be especially suitable for vanadium ores that contain significant quantities of carbonate minerals, which would not respond well to sulfuric acid heap leaching due to excessive acid consumption. Unfortunately, these benefits do not come without compromise. Overall, vanadium solubility is somewhat lower in alkaline solution than in acidic. This was also demonstrated in this work. A tradeoff analysis will be required to determine what processing method is optimum for a given vanadium resource, however, this work shows that alkaline heap leaching is an option that should be considered. It should be noted that not all mineral occurrences of vanadium are expected to be soluble in alkaline solution, so laboratory testing will always be required to evaluate the utility of this process for a given ore.