Absorption Characteristics of Cd²⁺ by Sludge Incineration Ashes

The sludge incineration ashes were obtained by burning the sludge from urban sewage treatment plant. Based on the characterization of sludge incineration ashes, their adsorption of Cd²⁺ from water was studied. The results showed that the adsorption efficiency increased with the adsorption time, the amount of sludge incineration ash, and the initial pH, while the temperature had little effect. Under the optimal conditions of the adsorption time of 80 min, the sludge incineration ash amount of 10 g/L, the initial pH of 5-7 and the temperature of 30 ℃, the removal efficiency could reach more than 99% when the concentration of Cd²⁺ was below 10 mg/L. The Cu²⁺ in water had inhibition on the adsorption of Cd²⁺, while the Cr⁶⁺ had little effect. The adsorption process obeyed the Langmuir isotherm model and the physical adsorption was the main mechanism and the adsorption amount could reach 17.94 mg/g.