**4. Conclusions**

A direct acid leaching process and a calcium-roasting acid leaching process on HCVS were conducted. The following conclusions were obtained:


**Author Contributions:** Methodology, B.L.; supervision, W.S. and Z.L.; other contributions were made by H.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Chongqing Science and Technology Commission (No. cstc2021jcyj-msxmX0129) and the Science and Technology Research Program of Chongqing Municipal Education Commission (No. CXQT20026).

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
