How iron `(III)` catalyses the reaction between iodide & persulphate ?

Explanation

`{:(2Fe^(3+)+2I^(-),to,2Fe^(2+),+I_(2)),(2Fe^(2+)+S_(2)O_(8)^(2-),to,2Fe^(3+),2SO_(4)^(2-)),(2I^(-)+S_(2)O_(8)^(2-),overset(Fe(III))to,I_(2),+2SO_(4)^(2-)):}`