 The production of the metals itself is difficult due to their reactivity . The formation of oxides , nitrides and carbides must be avoided to yield workable metals , this is normally achieved by the Kroll process . The oxides ( MO2 ) are reacted with coal and chlorine to form the chlorides ( MCl4 ) .The chlorides of the metals are then reacted with magnesium , yielding magnesium chloride and the metals . 
