Study on the transport law of characteristic pollutants in red mud leachate in saturated sand

In order to reveal the pollution mechanism of red mud to groundwater and prevent the pollution, the water quality of leachate from a red mud pile site of an aluminium refinery in northern China was analyzed. Three characteristic pollutants severely exceeding standards were identified: F⁻, SO₄ ²⁻, Al³⁺. Through a one-dimensional sand column experiment, the migration law of the characteristic pollutions in saturated medium sand, fine sand and silt sand was studied. The results showed that the greater the migration distance of characteristic pollutants in the sand column, the smaller the concentration of the pollutants; the smaller the sand particle size, the smaller the permeability coefficient, which means the stronger retention capacity of pollutants and the longer complete penetration time of characteristic pollutants in the sand column. Using Hydrus-1D software to simulate the migration process of the three characteristic pollutants in saturated sand, the dispersion degree （$\alpha$） of the medium sand, fine sand and silty sand was 1.76, 0.95 and 0.58 cm, respectively. The solute reaction parameters K_d and N_u of F⁻ in the three different sands were 2.10, 1.00, 4.10 mg/mL and 24, 28, 30 mL/mg; SO₄ ²⁻ were 1.78, 0.99, 5.00 mg/mL and 12, 20, 32 mL/mg; Al³⁺ were 1.44, 1.65, 4.44 mg/mL and 18, 17, 45 mL/mg, respectively. It was displayed that the smaller the grain of sand, the stronger the adsorption capacity (larger K_d) and the faster the adsorption speed (larger N_u). In order to prevent the pollution of red mud, it was recommended to use silt soil or finer-grained clay as the pollution impermeable layer according to the principle of economy and convenience.