Water treatment agent prepared by blast furnace slag and preparation method thereof

The invention relates to a water treatment agent prepared by utilizing blast furnace slag, and the agent is obtained by treating blast furnace slag by alkaline solution. The blast furnace slag comprises: 25-30% of SiO2, 40-45% of CaO, 15-20% of Al2O3, 10-20% of MgO, 1.08-1.5 of (CaO+MgO)/(Al2O3+SiO2). The alkaline solution with pH of more than 11 are mixed with the blast furnace slag as per 1 : 1-5 of the solid-to-liquid ratio, dried for 24-48h at 50-120 DEG C after filtration, and the outcome is taken out, smashed and passes through a standard filter of 6-80 m. The improved blast furnace slag is used as the water treatment agent and can treat the sewage with high efficiency and large amount, especially for the sewage containing the ions such as Ni(II), Pb (II), Cu(II), Zn(II), Mn(II), Fe(III), Al(III), Cr(III), etc.