Sulfate migration and transformation characteristics in paddy soil profile affected by acid mine drainage

SO₄^2-, a major component of acid mine drainage (AMD), plays an important role in study environment of AMD. We investigated the distribution and adsorption-desorption mechanisms of SO₄^2- and the variation of stable isotope of sulfur (δ³⁴S) values in the soil profile polluted by AMD. Results showed that the species and ³⁴S values of SO₄^2- differed significantly among different soil depths. In the surface soil (0-20 cm), native water-soluble SO₄^2- (WSS) in the range ~85 % total SO₄^2- was the dominant species. There was a peak of adsorption, which correlated significantly with amorphous oxide Fe, indicating that iron oxides and pH was fundamentally proportional to SO₄^2- forms. The high concentrations of Cu²⁺ and Pb²⁺ also played important roles in form of SO₄^2- in soil profile. Desorption kinetics of explained three SO₄^2--bound forms. The trend mean δ³⁴S values of WSS and AS in soil vertical profile was very similar with increasing from surface to subsurface, and have lower δ³⁴S values than those of total sulfur, indicating that mineralization of organic sulfur should produce SO₄^2- that was more depleted in δ³⁴S. SO₄^2- desorbed and trend δ³⁴S values could provide reasonable explanation for the migration of SO₄^2-. In the AMD irrigation scope, the higher SO₄^2- concentration was reserved by immobilized as organic sulfur, and then main approach of SO₄^2- migration was desorption and organic sulfur mineralize in now stage.