Efficacy and Mechanism of Copper Removal from Electroplating Wastewater by Schwertmannite-like Mineral

To explore the key influencing factors of copper removal by schwertmannite-like mineral and its mechanism of action, a shake flask method was used to synthesize schwertmannite-like mineral by adding Na2SiO3 and CaCl2 in the synthesis process of schwertmannite. The results showed that increasing the initial pH value from 2.0 to 5.0 increased the copper removal rate by 30.18%, indicating that high pH value effectively promoted copper removal. However, increasing the complexing agent concentration from 0.7 to 1.5 mmol/L decreased the copper removal rate by 27.51%, implying that high complexing agent concentration significantly inhibited copper removal. At a temperature of 40 °C, pH of 5.0, coexisting ion concentration (Mg2+, K+, Na+) of 1.5 mmol/L, complexing agent concentration (EDTA-Na2) of 0.5 mmol/L, and copper content of 50 mg/L, the removal of copper was achieved with the addition of 0.5 g/L FeSO4·7H2O, 1.01 mL/L H2O2, 0.58 g/L Na2SiO3, and 3.25 g/L CaCl2. Under these conditions, the removal of copper reached the highest level of 97.99%, which was 85.01% higher than that of schwertmannite. When the schwertmannite-like mineral was dissolved in 1 L of ultrapure water, the highest copper dissolving rate was 1.98%, which was 19.06% less than that of schwertmannite. Due to the synergy of several mechanisms, including adsorption and CaSiO3 co-precipitation, the schwertmannite-like mineral has better removal efficiency and stability than schwertmannite.