Preparation Of Composite Adsorbent And Application In Coexisting Arsenate And Fluoride Removal

An effective adsorbent, TLA, for simultaneous arsenate [As(V)] and fluoride (F) removal from drinking water was prepared by loading titanium and lanthanum on activated carbon. The adsorption isotherms, kinetics, and adsorption envelops for As(V) and F on TLA were investigated and compared with that onE33p and activated alumina (AA). The X-ray diffraction (XRD) and scanning electron microscopy -Energy dispersive X-ray spectroscopy (SEM-EDX) were employed to determine the TLA characterization.The EDX analysis showed that the titanium and lanthanum contents on TLA were increased significantly. TLA has a good adsorption capacity for As(V) and F. XRD patterns confirmed that anatase TiO₂ was presented in TLA. The EDX and XRD result indicated that lanthanum species in TLA was in an amorphous lanthanum oxide form with high more adsorption sites.The As(V) and F adsorption on TLA can be described using Langmuir adsorption isotherm equation which is eatablished on the basis of the monolayer chemical adsorption. The results show that TLA has a significantly higher adsorption capacity than E33p and AA. The adsorption capacities of TLA, E33p and AA determined using Langmuir isotherm at neutral pH were 30.3 mg/g, 18.0 mg/g and 7.2 mg/g for single As(V), and 27.8 mg/g, 2.3 mg/g, 4.8 mg/g for single F, respectively. Their adsorption capacities were reduced to 25.1 mg/g, 17.9 mg/g and 6.7 mg/g for As(V), and 17.0 mg/g, 0.9 mg/g, 3.6 mg/g for F, respectively, under a coexisting anion scenario. TLA has a good adsorption performance for As(V) and F. E33p is effective for As(V) removal but has nearly no adsorption capacity for F. The adsorption of As(V) and F on AA were extremely low.In the initial stage of adsorption, the rate was very quick and the adsorption capacities were increased rapidly. Then the adsorption rate reduced gradually. The adsorption equilibrium can be achieved after 15 minutes. The adsorption follows second-order kinetics. The results indicated that the chemical bond between TLA and As(V)/F which was formed by sharing the common electrons or exchanging electrons is the foundamental constraint to limit the adsorption rate. With the increase of the initial concentration, the adsorption capacity was also enhanced. It indicated that the concentration gradient between bulk solution and adsorbent surface was increased as a consequence of increasing initial concentrations, which is a benefit to adsorption process.The charge-distribution multisite complexation model can be used to precisely describe the As(V) and F adsorption behaviors. The experiment phenomena and the model simulated results indicated that the As(V) and F adsorption exhibit obvious characteristics of anion adsorption. The As(V) and F removal efficiency was significantly influenced by the solution pH. When pH was 5.1～7.3, the As(V) adsorption efficiency was greater than 97%. The As(V) adsorption efficiency was decreased to 21. 1% as pH was increased to 12.2. When pH was 4.8～6.8, the F adsorption efficiency was greater than 87%. The F adsorption efficiency was decreased to 15.3% as pH was increased to 11.1. Under a coexisting anion scenario, the As(V) adsorption efficiency was still higher than 99% in the pH range 6.0～7.2. With the pH increased to 12.0, the As(V) adsorption efficiency was decreased to 21.1%, and F adsorption efficiency was decreased from 78.3% to 5.1% while pH was increased from 5.0 to 12.0. The As(V) adsorption on TLA formed bidentate binuclear coordination and F surface complexes on TLA was monodentate structure. The As(V) adsorption has a higer priority than F adsorption .