RESUMO
Toxic As(â ¢) and Cd(â ¡) ions in water can be transferred and enriched into human bodies through the food chain, causing serious health damage at excessive levels. In this study, fulvic acid (FA) was selected as the modifier of iron-manganese-nickel layered double hydroxide (FeMnNi-LDH), and a stable layered composite (FA@FeMnNi-LDH) was prepared using the co-precipitation method, which could adsorb As(â ¢) anions and Cd(â ¡) cations simultaneously, especially with the higher adsorption capacity of the cation Cd(â ¡). Its structure was characterized by XRD, TEM, FT-IR, and XPS, and the adsorption capacity and mechanisms of As(â ¢) and Cd(â ¡) in water by the composite were also investigated. The results showed that with typical characteristic peaks of layered double hydroxides, the synthesized composite possessed a stable structure, maximum FA loading capacity, and optimal adsorption performance. The adsorption kinetics of As(â ¢) and Cd(â ¡) conformed to the pseudo-second-order kinetic model, and the adsorption isotherms well-followed the Langmuir model, with the maximum adsorption capacity at 25â being 249.60 mg·g-1 for As(â ¢) and 156.50 mg·g-1 for Cd(â ¡), respectively. The composite exhibited a good adsorption performance on As(â ¢) and Cd(â ¡) in the range of pH 2-7 and pH 4-7, respectively. The competitive adsorption effect of co-existed anions on As(â ¢) showed a sequence of PO43->CO32->NO3-, and that of co-existed cations on Cd(â ¡) was Pb2+>Cu2+>K+. The adsorption capacity of As(â ¢) and Cd(â ¡) decreased with the increase in the concentration of competing ions. The main adsorption mechanism for As(â ¢) was ion-exchange occurring in the interlayers of LDH, and that for Cd(â ¡) was coordination complexation occurring with the loaded FA, respectively. In conclusion, the prepared FA@FeMnNi-LDH composite material posed a good application prospect for adsorption removal of As(â ¢) and Cd(â ¡) in water and their toxicity control.