Study Of Cadmium And Arsenate Co-adsorption On TiO₂

Anatase(As(V)) and cadmium(Cd) are widely used industrial materials with a variety of applications, including pigments, cosmetics, ceramics, solar cells, and metal smelting in recent years, leading to the greatly increase of As(V) and Cd concentrations in natural waters, which is harmful to human heathy. A number of traditional heavy metal removal methods, for example, precipitation, ion exchange, neutralization, and film filtration, but they all have the shortcomings like low removal, difficult to recycle, expensive, and generates lots of sluge. Adsorption overcomes these shortcomings and becomes a widely used heavy metal removal method. A zero sluge and As remediation technolygy for acidic metallurgical industry wastewater was developed by TiO₂ adsorption.The effect of cadmium (Cd) and arsenate (As) co-adsorption on the titanium dioxide (TiO₂) surface was investigated. Multiple complimentary techniques including batch adsorption experiments, surface-enhanced Raman scattering spectroscopy, Zeta potential measurements, Fourier transform infrared spectroscopy, and charge-distribution multisite complexation model were used for the quantitative analysis and the determination of the structure of surface complexes. The results are as follows.The TiO₂ adsorption results show that exist of As(V) will promote Cd removal. The Cd removal inctrased from 334.0 mg/g TiO₂ and 661.9 mg/g TiO₂ to 458.2 mg/g TiO₂ and 848.7 mg/g TiO₂ and pH 5 and pH 7. The Cd removal increase as the increase of As(V) concentration at pH 3-8. At the same time, the exist of Cd will promote As(V) removal at pH 3^-10.The adsorption kinetics show that both single As and Cd adsorption on TiO₂ followed pseudo second-order kinetics and reached equilibrium within 15 and 40 min. When Cd and As co-adsorbed on TiO₂, the adsorption kinetics followed pseudo first-order and required much longer time to reach equilibrium.The adsorption mechanism study show that As(V) and Cd will not form complexation in solution at low As concentrations (As=10 mg·L^-1,Cd=75 mg·L^-1), both As and Cd formed bidentate binuclear inner-sphere surface complexes on TiO₂ surfaces; when at higer As(V) concentration (As>150 mg·L^-1,Cd=350 mg·L^-1), precipitation will be formed when pH values are higher than 5, the removal mechanism is precipitation, and when pH values are lower than 5, the removal mechanism is the formation of [Ti₂O₂AsO₂Cd^1/3] at TiO₂ surface.