Method for remediating arsenic-contaminated soil

A method for remediating arsenic-contaminated soil, comprising:

• a washing step of adding a first type of arsenic contaminant, with which arsenic was co-precipitated, and a second type of arsenic contaminant to which arsenic was electrically adsorbed, to a washing solution in an acidic and reducing conditions, to dissolve the first and second types of arsenic contaminants, thereby releasing arsenic ions, in which the washing solution is maintained at a pH of 5.5-7.5 and an Eh of −200 to −400 mV at a time point when the dissolution is completed, wherein the washing solution is prepared by mixing a 0.01 N aqueous solution of hydrochloric acid with 2% sodium dithionite;
• a solid-liquid separation step of separating the soil and the washing solution from each other after the washing step;
• and
• a post-treatment step of adding an oxidizing agent to the washing solution, which was separated in the solid-liquid separation step, to modify the arsenic into a form including the first or second type, and removing the arsenic from the washing solution by solid-liquid separation.