Factors Controlling Chromium Release from Chromate Containing Soils

Chromium (Cr) release pattern in contaminated factory ruins soils and standard mixed soils (JSO-1: JSO-2 = 1: 4) provided by the Geological Survey of Japan were studied to determine the factors controlling the Cr release in contaminated soils which is imperative to elucidate Cr behavior in soils and groundwater. The contaminated soil was collected from factory ruins in Chiba prefecture of Japan. Among the standard soils, the JSO-1 is uncontaminated loam soil and JSO-2 is contaminated soil. One thousand (1000) μg g⁻¹ Cr were added in the contaminated soils and standard mixed soils in the form of K2CrO4 (potassium chromate). Chromium concentration in alkaline solution was high (i.e. 33.9 μg ⁻¹) for contaminated soil but low ℓ (i.e. 11.1 μg ⁻¹) for JSO-1: JSO-2 mixed soil. After the experiment, Cr ℓ concentration in the solution for the JSO-1: JSO-2 mixed soil lies in Cr(OH)3 region close to Cr(OH)3/CrO4^2- boundary in neutral to alkaline region in EhpH diagram, while that for the contaminated soil in CrO4^2- region in alkaline solution. The lower Cr concentration for the JSO-1: JSO-2 mixed soils is probably due to the efficient reduction of Cr⁶⁺ to Cr³⁺ by iron oxides (FeO) present in basaltic glass and adsorption of Cr³⁺ by weathering product (e.g. allophone, iron hydroxide) in the soil.