Effect of Cu²⁺ on the saturated coefficient of permeability of remolded loess

The coefficient of permeability is an important index to evaluate the migration and diffusion of heavy metal polluted liquid in remodeled loess. At present, the existing studies have shown that there is a certain correlation among the pH value, the value of electrical conductivity, ion content and saturated coefficient of permeability of the polluted liquid, but the geochemical reaction mechanism during the infiltration process has not been clarified. Therefore, the Qp loess in the Bailuyuan area of Xi’an is collected, and the Cu²⁺ solution is selected as the infiltration solution to carry out the saturated infiltration test of the reshaped loess, and the geochemical inversion model based on the Netpath software is established. The results show that the saturated coefficient of permeability decreases significantly from the first day during the test, and has a larger decrease compared with the deionized test group, with a range of 5.57×10⁻⁵ cm/s. The ion source analysis proves that the geochemical reaction occurs, including mineral dissolution, precipitation and cation exchange. The geochemical inversion simulation results show that the presence of Cu²⁺ aggravates the mineral dissolution and produces a large amount of Ca²⁺, which promotes the leftward shift of the carbonate mineral dissolution balance, starting from the first day continual calcite and dolomite precipitation, and the precipitation amounts are 1.912 mmol and 0.958 mmol, respectively, which blocked the seepage pores and reduced the coefficient of permeability of the soil. The results are helpful in understanding the change of the saturated the permeability coefficient of the remodeled loess during the intrusion of heavy metal ions, and are of important theoretical significance for further clarifying the geochemical mechanism affecting the change of the permeability coefficient.