A device comprises a contact reaction chamber, a circulating water inlet, a clear water basin, a circulating pump, a circulating water outlet, a solid phase extractant collecting tank, a magnetic holder, an electromagnet, a solid-liquid separation area, a drain valve, a wall sprinkling water inlet, and a wall sprinkling pipe, wherein, the contact reaction chamber is in a conical shape, and utilizes hydraulic power to perform stir to ensure no dead corner exists during contact stir; the obconical solid-liquid separation area increases the action area between a magnetic solid phase extractant and the electromagnet; the solid phase extractant collecting tank is in a downwards protruding dish shape to prevent the solid phase extractant from losing.