Leach of the weathering crust elution-deposited rare earth ore for low environmental pollution with a combination of (NH4)2SO4 and EDTA

Abstract

High concentration of ammonium sulfate, a typical leaching agent, was often used in the mining process of the weathering crust elution-deposited rare earth ore. After mining, a lot of ammonia nitrogen and labile heavy metal fractions were residual in tailings, which may result in a huge potential risk to the environment. In this study, in order to achieve the maximum extraction of rare earth elements and reduce the labile heavy metal, extraction effect and fraction changes of lanthanum (La) and lead (Pb) in the weathering crust elution-deposited rare earth ore were studied by using a compound agent of (NH₄)₂SO₄-EDTA. The extraction efficiency of La was more than 90% by using 0.2% (NH₄)₂SO₄-0.005 M EDTA, which was almost same with that by using 2.0% (NH₄)₂SO₄ solution. In contrast, the extraction efficiency of Pb was 62.3% when use 0.2% (NH₄)₂SO₄-0.005 M EDTA, which is much higher than that (16.16%) achieved by using 2.0% (NH₄)₂SO₄ solution. The released Pb fractions were mainly acid extractable and reducible fractions, and the content of reducible fraction being leached accounted for 70.45% of the total reducible fraction. Therefore, the use of 0.2% (NH₄)₂SO₄-0.005 M EDTA can not only reduce the amount of (NH₄)₂SO₄, but also decrease the labile heavy metal residues in soil, which provides a new way for efficient La extraction with effective preventing and controlling environmental pollution in the process of mining the weathering crust elution-deposited rare earth ore.

Keywords: Ammonium sulfate; EDTA; Fraction; Lanthanum; Lead; Rare earth.