<p>A method for removing one or more substances from a starting material comprising a metal, a semi-metal, a metal compound or a semi-metal compound comprises the steps of mixing fine particles of said starting material with a reagent Y and heating the starting material so as to effect a diffucion interface between the starting material and the reagent Y such that the one or more substances migrate from the nanoparticle to reagent Y. Purified metal or semi-metal particles are thereby produced. The method can be used for the production of photovoltaic grade silicon.</p>
