Effects of hydration and hardening of calcium sulfate on muscovite dissolution during pressure acid leaching of black shale

In the conventional process of oxygen pressure acid leaching of black shale, vanadium extraction depends on acid attack to muscovite, resulting in high acid consumption and a long leaching time. The two problems significantly reduce equipment life, increase production costs, and decrease production efficiency. To solve these problems, hydration and hardening of calcium sulfate were introduced to promote muscovite cracking, increasing the exchange reaction rate of hydrogen ion to aluminum ion. This paper investigated the effect of hydration and hardening of calcium sulfate on calcium sulfate growth and muscovite dissolution, exploring interactions between calcium sulfate and muscovite. Results indicate that in stress-damaged muscovite structure, propagation of ductile cracks in muscovite particles increases their specific surface area and weakens muscovite structural strength. These effects allow muscovite to dissolve much more easily during the pressure acid leaching process. The hydration and hardening of calcium sulfate crystals can thus facilitate muscovite dissolution.