Removal of trace levels of arsenic and selenium from aqueous solutions by calcined and uncalcined layered double hydroxides (LDH).

摘要

The adsorption of As and Se from dilute aqueous solutions, representing model power plant effluent streams, by calcined and uncalcined layered double hydroxide (LDH) adsorbents has been investigated. The adsorption isotherms obey the Freundlich model. The adsorption capacities of As(V), As(III), Se(VI) and Se(IV) on the calcined and Uncalcined LDH has been compared with each other. The influence of starting solution pH on adsorption of As and Se has been investigated. Competing ions have a greater effect on Se(IV) than on As(V) uptake. Desorption of As(V) and Se(IV) from the LDH depends on the type of ion species, and their concentration in the desorbing solutions.; The third chapter describes As(V) adsorption on appropriately conditioned calcined layered double hydroxide (LDH) adsorbents. Conditioning the adsorbent significantly reduced the dissolution previously observed with uncalcined and calcined LDH. The adsorption rates and isotherms have been investigated in batch experiments. The As(V) adsorption rate on conditioned LDH increases with decreasing adsorbent particle size; the adsorption capacity of As(V) on conditioned LDH, on the other hand, is independent of particle size. A homogenous surface diffusion model was used to describe the experimental kinetic data. The estimated diffusivity values are shown to depend on the particle size.