Efficient removal of mercury from the exhaust gases of an industrial process or combustion process can be achieved using an adsorbent that can be regenerated by a simple and efficient method. A cutting tool for forming the recess is held by a moving apparatus at a prescribed angle relative to the work. A plurality of ink supply conduits extending through the wafer from a second side of the wafer to the array of drop ejection apparatuses on the first side. A positioning member is formed as a member separate from the elastic member and positioning the elastic member with respect to the frame. Therefore, the thorium never reaches break-through and the column can be used continuously without regeneration.