Chile saltpeter is a natural source of NaNO3; it also contains NaIO3. The NaIO3 can be used as a source of iodine. Iodine is produced from sodium iodate in a two-step process occurring under acidic conditions:
IO3^-(aq) + HSO3^-(aq) --> I^-(aq) + SO_4^{2-}(aq) (not balanced)
I^-(aq) + IO3^-(aq)...