Abstract
During the acid leaching process of black shale, with the destruction of the aluminosilicate mineral structure, a large amount of aluminum (Al) is leached, accompanied by the release of vanadium (V). To separate aluminum from the vanadium-containing solution, the precipitation behavior of aluminum ions (Al3+) was investigated under hydrothermal conditions with the formation of alunite and natroalunite. In the solution environment, alunite and natroalunite are able to form stably by the Al3+ hydrolysis precipitation process at a temperature of 200 °C, a pH value of 0.4 and a reaction time of 5 h. When Al3+ was precipitated at a K/Al molar ratio of 1, the aluminum precipitation efficiency and the vanadium precipitation efficiency were 64.77% and 1.72%, respectively. However, when Al3+ was precipitated at a Na/Al molar ratio of 1, the precipitation efficiency of the aluminum decreased to 48.71% and the vanadium precipitation efficiency increased to 4.36%. The thermodynamics and kinetics results showed that alunite forms more easily than natroalunite, and the reaction rate increases with increasing temperature, and the precipitation is controlled by the chemical reaction. Vanadium loss increases as the pH value increases. It can be deduced that the ion state of tetravalent vanadium (VO2+) was transformed into the ion state of pentavalent vanadium (VO2+) in the hydrothermal environment. The VO2+ can be adsorbed on the alunite or natroalunite as a result of their negative surface charges, ultimately leading to vanadium loss.
Highlights
Black shale is an important and abundant vanadium-bearing resource in China, and has attracted much attention from researchers [1,2,3]
The main distribution of vanadium grade in black shale deposits is in the range 0.1–1.0%; only 2.8% of black shale possesses a vanadium grade over 1.0%
In the alkaline leaching process, the silica present in black shale can react with alkali to form colloidal silica, which makes it difficult to separate vanadium-bearing alkali leachate from residue
Summary
Black shale is an important and abundant vanadium-bearing resource in China, and has attracted much attention from researchers [1,2,3]. In vanadium-bearing black shale, vanadium (V) mainly exists as low-valence V(III) in the crystal lattice of the muscovite, replacing aluminum (Al) due to their isomorphism [4,5]. The mica structure needs to be destroyed in order to release vanadium from the black shale. In the alkaline leaching process, the silica present in black shale can react with alkali to form colloidal silica, which makes it difficult to separate vanadium-bearing alkali leachate from residue. Acid leaching is usually adopted for the extraction of vanadium from black shale [6,7]. The separation of vanadium over aluminum has become the core scientific problem in the purification and concentration of high-aluminum vanadium-bearing leachate
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