METHOD FOR TREATING DUST EXTRACTED FROM CEMENT KILN

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PROBLEM TO BE SOLVED : To provide a treatment method wherein dust extracted from a cement kiln is washed with water, the solid content is re-used as a cement raw material, the resulting selenium-containing washing solution that cannot be treated with general trivalent iron ions is discharged after being reduced to a wastewater emission control level or lower by the Water Pollution Control Law. SOLUTION : The method for treating dust extracted from a cement kiln comprises : (1) the first step of adding water to dust extracted from a cement kiln gas to make it slurry so as to carry out solid-liquid separation; (2) the second step of adjusting pH of the liquid phase (original water) obtained after solid-liquid separation in the first step at 5 to 10, adding a chelating agent for removing heavy metals, adding a ferric salt compound, further re-adjusting pH of the liquid phase at 5 to 10, and then adding a flocculant, thereby carrying out solid-liquid separation; (3) the third step of adding a ferrous salt compound to the liquid phase obtained after solid-liquid separation in the second step, adjusting pH at 8 to 12, and adding a flocculant, thereby carrying out solid-liquid separation; and (4) the fourth step of adding a ferric salt compound to the liquid phase obtained after solid-liquid separation in the third step, adjusting pH at 8 to 12, and adding a flocculant, thereby carrying out solid-liquid separation.