Abstract: Irrigation with untreated sewage is one of the important causes of heavy metal copper (Cu) pollution in farmland soil in the drylands of Northwest China. Soil pH and the types and concentrations of saline-alkali ions have profound influence on the speciation and mobility of Cu in the saline-alkali soil. We investigated the adsorption behavior and interfacial reaction of Cu at hematite and magnetite/water interface in the presence of four ions including sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), and magnesium (Mg²⁺) based on simulated batch experiments. Scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy were used for characterization. The adsorption capacities of the two iron oxides to Cu increased in the presence of Ca²⁺ but reduced the adsorption rate, indicating that the adsorption affinity between iron oxides and Cu increased in the presence of Ca²⁺. The influence of the four ions on the adsorption capacity of Cu at hematite and magnetite surface varied, with an order of Mg²⁺>Ca²⁺>Na⁺>K⁺, which might be due to the differences of the hydration radius of the four ions. The adsorption capacities of Cu on the surface of the two iron oxides increased with increasing soil pH. The results of XRD, FTIR, and Raman spectroscopy characterization showed that Cu adsorbed on the surface of the two iron oxides could form complicated precipitates through complexation reaction in the coexisting ion system.

Key words: iron oxide, copper, coexisting ion, pH, adsorption