Dissolution of aluminum and titanium during high-temperature acidification of coal gangues and relative kinetics

ABSTRACT

Aluminum (Al) and titanium (Ti) extraction in coal gangues is explored through sulfuric acid extraction to explore a high-value development of abundant coal gangues in Panzhou, Guizhou Province. Results demonstrate that the acid-to-slag ratio slightly affects Al dissolution in high-temperature acidification, and the kinetic study of Al extraction based on high-temperature acidification reveals an acid-to-slag ratio of 1.2:1. However, the acid-to-slag ratio influences significantly Ti dissolution, and the kinetic study of Ti extraction based on high-temperature acidification reveals an acid-to-slag ratio of 1.4:1. Reaction temperature and time remarkably influence Al and Ti dissolution. As reaction temperature and time increase, the Al dissolution rate increases continuously, whereas the Ti dissolution rate initially increases and then remains stable. The dissolution of Al is sensitive to temperature and occurs easily, whereas the dissolution of Ti requires a high temperature. Ti is partially dissolved at low temperatures. The dissolution rate of Ti at 140°C reaches 97.78% at 5 h, but it is only 80.62% at 180°C at 1 h. Therefore, the dissolution kinetics of Al and Ti are discussed through high-temperature acidification. The kinetic study reveals that the activation energies of Al and Ti dissolution in coal gangues and slag acidification are 54.955 and 58.168 kJ/mol (E_aAl < E_aTi), respectively, indicating that Al dissolves more easily than Ti does during the sulfuric acid leaching of coal gangues. The kinetic control type during leaching is chemical reaction and can be described by the following kinetic equation:$1-{\left(1-\mathit{x}\right)}^{\frac{1}{3}}=\mathit{kt}$. The mechanisms of acid leaching of kaolinite and anatase in coal gangues and slag are analyzed through XRD and SEM characterization of solid substances. Our study provides a technological reference and theoretical support for the efficient utilization of coal gangues in industrial production.

KEYWORDS:

• Coal gangue
• acidification
• dissolution
• kinetics
• aluminum
• titanium

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China [No. 21566018]; the Key Research and Development Program of Ningxia, China [No. 2018BEE03021]; and the Foundation of State Key Laboratory of High-efficiency Utilization of Coal and Green Chemical Engineering [No. 2018-K36].