A vertical autoclave according to an embodiment of the present disclosure is a vertical autoclave including an inlet port through which a process solution is introduced, an outlet port through which the process solution is discharged, an oxygen inlet port through which oxygen is supplied to the process solution, an agitator configured to mix the process solution, an inner wall, an acid-resistant brick layer lined on a lower portion and a side portion of the inner wall, and an acid-resistant metal layer lined on an upper portion of the inner wall. A method of removing salt from an autoclave includes raising a surface level of a solution in the autoclave from a first level to a second level such that salt in the autoclave is immersed in the solution, and maintaining the surface level of the solution at the second level. The salt is dissolved in the solution while the surface level of the solution is maintained at the second level.