Preparation of Fe-Zr bimetallic modified biochar based on response surface methodology and optimization of key parameters for removing sulfate ions from mine water

As an unconventional water resource, the utilization of mine water resources in the Yellow River Basin is the key to ecological protection and high-quality development of the Yellow River Basin. At present, the various indicators of the discharged mine water from major coal enterprises in the upper and middle reaches of the Yellow River can basically meet the surface III standard, but the majority of the drainage contains excessive sulfate ions (SO₄²⁻) (≈300 mg/L). In response to the above issues, Fe-Zr bimetallic modified Ginkgo biloba leaf biochar (Fe-Zr@GBC) was prepared, and the key parameters in the preparation process (pyrolysis temperature, pyrolysis time, Fe and Zr ratio, etc.) were optimized using response surface methodology. Box Behnken design was used to explore the effects of multiple factors and their interactions. Finally, the adsorption and removal efficiency of SO₄²⁻ in mine water was tested through static adsorption experiments. The results showed that under the conditions of pyrolysis temperature of 700 ℃, pyrolysis time of 4.0 hours, Zr∶Fe mass ratio of 7∶3, and ball milling time of 2.0 hours Fe-Zr@GBC The best removal effect for SO₄²⁻ in mine water; The results are very close to the Design Expert optimization results (pyrolysis time of 5.45 h, pyrolysis temperature of 601.9 ℃, ball milling time of 1.75 h). Compared with the predicted removal rate of SO₄²⁻ (92.36%), the static adsorption experiment verified that the removal rate of SO₄²⁻ was 88.38%, and the difference between the model value and the verification value was only 4.3%, indicating that the Design Expert optimization results have strong reliability. On this basis, the adsorption kinetic and thermodynamic characteristics were investigated. The results show that the adsorption process of SO₄²⁻ by Fe-Zr@GBC is mainly monolayer adsorption, and the pseudo-second-order kinetic model can well simulate the diffusion of SO₄²⁻ in Fe-Zr@GBC particles, indicating that the adsorption reaction of Fe-Zr@GBC is more consistent with chemical adsorption. In summary, the prepared Fe-Zr@GBC and its efficient removal effect on SO₄²⁻ provide a green, efficient, and stable new solution for addressing the problem of excessive SO₄²⁻ in mine drainage of the Yellow River Basin, and offer technical support for the ecological protection and high-quality development of the Yellow River Basin.