The Effects of Sodium Ions, Phosphorus, and Silicon on the Eco-Friendly Process of Vanadium Precipitation by Hydrothermal Hydrogen Reduction

Abstract

The effects of sodium ions, phosphorus, and silicon on the eco-friendly process of vanadium precipitation by hydrothermal hydrogen reduction were investigated to establish the suitable concentrated solution system for this eco-friendly process. The results showed that sodium ions had no negative effects on the vanadium precipitation process. Phosphorus can reduce vanadate ion activity, and results in the decrease of vanadium precipitation percentage from 99.5% to 61.3%, as the phosphorus concentration in the feed solution increased from 0.05 g/L to 3 g/L. As a result, the aimed products of V 2 O 3 were hard to be obtained, and the purity of the precipitates was lowered. Silicon can absorb in the form of H 3 Si 3 O 7 on the surface of the precipitates, thus it was difficult for H (activity hydrogen atom) to react with the intermediate vanadium-bearing precipitates. As a result, the vanadium precipitation percentage decreased from 99.5% to 86.2% as the silicon concentration in the feed solution increased from 0.1 g/L to 3 g/L. The aimed products of V 2 O 3 were not easy to be obtained, and only the intermediate vanadium-bearing precipitates containing sodium ions were obtained. The upper limits of the concentrations of phosphorus and silicon in the feed V (V) solution were ascertained as 0.5 g/L and 0.1 g/L, respectively. As the concentrations of phosphorus and silicon in the purified alkaline-concentrated V (V) solution extracted from vanadium-bearing shale are usually below the upper limits of the concentrations, the eco-friendly process of vanadium precipitation by hydrothermal hydrogen reduction has a great application prospect in the field of vanadium extraction from vanadium-bearing shale.At present, vanadium precipitation is an indispensable process for vanadium extraction from vanadium-bearing shale [7]. The most popular vanadium precipitation method is vanadium precipitation with ammonium salt, due to its high recovery of vanadium and high purity of the obtained vanadium products [7,[17][18][19]. But this process can cause serious water and air pollution due to the addition of a large amount of ammonium salt. This environmental problem has become one of the most important factors restricting the green and sustainable development of the vanadium extraction industry.In order to solve the environmental problem in the present vanadium extraction process, an eco-friendly vanadium precipitation process without the addition of ammonium salt has been developed and reported in our previous study [20]. In this eco-friendly process, the hydrothermal hydrogen reduction technology was used for precipitating V 2 O 3 products from the stripped pentavalent vanadium (V (V)) solution extracted from vanadium-bearing shale. Both of the vanadium precipitation efficiency and the purity of the products can reach more than 99%. However, the contents of the impurity elements, such as phosphorus and silicon, in the stripped vanadium solution were very low, which cannot represent all the concentrated vanadium solutions obtained from...

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