To provide an admixture for controlling elution of hexavalent chromium in soil and sludge contaminated with heavy metals, used in combination with a cement solidification agent, and a method for controlling elution thereof.

The admixture for fixing hexavalent chromium, produced by mixing sodium silicate with liquid containing a chloride and ferrous sulfate as main components, is mixed with treated soil and sludge containing hexavalent chromium in combination with the cement solidification agent so as to fix hexavalent chromium and to control elution thereof. In solidifying contaminated soil and sludge of which the elution of various heavy metals is not controlled so as to meet the environmental standards by a conventional cement solidification agent, the method remarkably reduces the elution of heavy metals or the like without damaging exertion of strength of cement and controls the elution thereof to meet the environmental standards.