Abstract
During pressure acid leaching process of black shale-hosted vanadium, increasing the reaction interface of muscovite dissolution can enhance the vanadium release. In this paper, calcium sulfate (CaSO4) deposition behavior and its effect on muscovite under K2SO4 assistance were focused on for demonstrating the function of CaSO4 on vanadium leaching from the black shale. Results showed that as K2SO4 mediated, the apparent activation energy of vanadium leaching and the apparent reaction order of sulfuric acid decreased from 24.37 kJ/mol to 16.63 kJ/mol and 2.7 to 1.9, respectively. The leaching rate and dependence on pH value were modified. The vanadium leaching acceleration owed to CaSO4 deposition on muscovite in the black shale. The ion absorption stimulations found that Ca2+ is confirmed to be easily absorbed on the six-membered ring cavity of silicon-oxygen tetrahedrons in muscovite structure prior to K+ and Na+. Meanwhile, SO42− provides two oxygen atoms to bond with Ca2+ absorbed on muscovite (001) surface. The continuous absorption and bonding create CaSO4 deposition on muscovite (001) surface which also involves the load transmitting. The stress load transmitting correlates to pore formation in muscovite particles. It was proved that massive micropores initiated and proliferated in the existing pores under K2SO4 assistance. The porosity caused by CaSO4 deposition greatly increased the reaction interface of muscovite dissolution and accelerate internal diffusion of H+ to the reaction interface, which can significantly weaken the vanadium leaching dependence on acid.
Highlights
Facing the increasing market demand for vanadium products and environmental problems [1,2,3,4], the efficient and sustainable utilization of vanadium-bearing mineral resources is increasingly necessary and urgent for vanadium industry
The vanadium leaching efficiency can maintain at 85% after calcite in black shale was removed by hydrochloric acid in advance
It was shown that K2 SO4 assistance was the most effective to the vanadium release
Summary
Facing the increasing market demand for vanadium products and environmental problems [1,2,3,4], the efficient and sustainable utilization of vanadium-bearing mineral resources is increasingly necessary and urgent for vanadium industry. Vanadium-bearing black shale has been identified to have enrichments of vanadium, which is distributed in many provinces of China [5,6]. There are vanadium enrichments in black shale elsewhere in the world include United states, Australia, Argentina, and Kazakhstan [7]. The vanadium can exist mostly as low-valence V3+ that replaces Al3+ isomorphically in mica or illite lattice [8], which poses a difficulty for vanadium extraction in a green and high-efficiency way. The roasting–leaching process has become the mainstream technology of vanadium extraction from the black shale in industrial production. It is essential of roasting to activate mica structure and remove the acid-consuming minerals in the black shale, such as pyrite and calcite [9]
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