Feasibility of using ammonium iron (II) sulphate to passivate hexavalent chromium in polluted soil

ABSTRACTThe use of ammonium iron (II) sulphate ((NH₄)₂Fe(SO₄)₂) to remediate soil contaminated with Cr (VI) was assessed. (NH₄)₂Fe(SO₄)₂ effectively remediated soil contaminated with Cr (VI) and, acted as a fertilizer by supplying nitrogen because it contains ammonium. The effects of the (NH₄)₂Fe(SO₄)₂ dose, water content, pH of the soil and the contact time were investigated. The amount of Cr (VI) leached from the most-polluted soil, determined using a leaching toxicity procedure using optimized conditions, was 347.64 mg kg^-1 when the soil was untreated and 6.74 mg kg^-1 when the soil was treated with (NH₄)₂Fe(SO₄)₂. Bio-utilizable Cr contributed 59.44% and 0.16% of the total Cr contents of the untreated and treated soil, respectively. The relatively stable Cr species contributed 24.92% and 98.38% of the total Cr contents of the untreated and treated soil, respectively. The results indicated that adding (NH₄)₂Fe(SO₄)₂ markedly decreased the risk of Cr being released from heavily contaminated soil by decreasing the availability of Cr in the soil. Overall, the results indicated that adding (NH₄)₂Fe(SO₄)₂ causes some Cr (VI) in contaminated soil to be reduced to Cr (III), and to form a precipitate, which decreases the risk of Cr being released. (NH₄)₂Fe(SO₄)₂ can be applied to soil contaminated with Cr (VI) on a large scale because it is cheap and simple to achieve.