Bioleaching could be applied to remove metal impurities fron clay.Some research papers regarding to this topic are attached,would help in this direction.
It is dependent to Fe and Ti phases. If these elements are in sulfide or oxide form, the most simple way to remove iron is using Iron and Sulfur oxidizing micro-organisms such as acidithiobacillus ferrooxidans and acidithiobacillus thiooxidans. These microorganisms produce sulfuric acid and dissolve the Fe by providing an oxidizing environment.
However, if Fe and Ti are in silicate phase using fungi (Such as aspergillus niger) can be better. These microorganisms decompose the silicate structures by producing organic acids which results to Fe dissolution.