Activated alumina

Abstract: The effects of solution pH and temperature on the adsorption of fluoride onto bone char made from cattle bones were investigated in this work. It was found that the maximum adsorption took place at pH 3 and the adsorption capacity decreased nearly 20 times augmenting the pH from 3 to 12. This behavior was attributed to the electrostatic interactions between the surface of bone char and the fluoride ions in solution. The adsorption capacity was not influenced by temperature in the range from 15 to 35 °C. A comparison of fluoride adsorption capacities among several adsorbents revealed that the adsorption capacity of the bone char was 2.8 and 36 times greater than those of a commercial activated alumina (F-1) and a commercial activated carbon (F-400). The adsorption capacity is considerably dependent upon the physicochemical properties of the bone char surface and the solution pH.

Abstract: Zeolite Y, having composition expressed in oxide-mole-ratios as 0.9\sB0.2 Na2O : Al2O3 - WSiO2 : XH2 wherein W is 3 to 5, X is 0 to 9, and having a specified X-ray powder diffraction pattern, is prepared by crystallization at 20 DEG to 125 DEG C. from an aqueous, sodium aluminosilicate reactant mixture, having a composition within one of the ranges the major silica source being at least one amorphous solid silica having an average particle size of less than 1 micron, e.g. fume silicas, flocculated silica sols, or commercial powdered silicas. Minor proportions of silica gels, or silicic acid, may be employed. A source of alumina may be activated alumina, gamma alumina, alumina trihydrate, sodium aluminate; sodium hydroxide may supply the sodium ion. Zeolite Y crystals may be activated by heating in air or vacuum to as high as 700 DEG C., and may be used as an adsorbent in powder form or pelleted in admixture with a bonding agent such as clay.

Abstract: The removal of Cr(VI) from aqueous solution by batch adsorption technique using different low-cost adsorbents was investigated. Adsorbents such as clarified sludge—a steel industry waste material, rice husk ash, activated alumina, fuller's earth, fly ash, saw dust and neem bark were used to determine the adsorption efficiency. The influence of pH, adsorbent type and concentration, initial Cr(VI) concentration and contact time on the selectivity and sensitivity of the removal process were investigated. Adsorption process was found to be highly pH dependent. The optimum pH range for adsorption of Cr(VI) was found to be between 2 and 3. Kinetics studies were performed to understand the mechanistic steps of the adsorption process and the rate kinetics for the adsorption of Cr(VI) was best fitted with the pseudo-2nd-order kinetic model. Langmuir and Freundlich adsorption isotherms were applicable to the adsorption process and their constants were evaluated. The thermodynamic equilibrium constant and the Gibbs free energy were determined for each system. The adsorption capacity (qmax) calculated from Langmuir isotherm and the Gibbs free energy (ΔGo) value obtained for the different adsorbents showed that clarified sludge was the most effective among the selected adsorbents for the removal of Cr(VI) from aqueous solution. The adsorption efficiencies of rice husk ash and activated alumina were also equally comparable with that of clarified sludge.

Abstract: The health threat of arsenic is well-known, and the U.S. EPA recommends the maximum contaminant level to be 0.01 ppm or less for arsenic in drinking water. Therefore, advanced treatment processes are needed for finished water to meet the required regulations. Adsorption is considered to be a less expensive procedure that is safer to handle than precipitation, ion exchange, and membrane filtration. Activated alumina (AA) is the most commonly used adsorbent for the removal of arsenic from aqueous solutions. However, conventional porous solids including AA have ill-defined pore structures and, typically, low adsorption capacities and act in a kinetically slow manner. An ideal adsorbent should have uniformly accessible pores, an interlinked pore system, a high surface area, and physical and/or chemical stability. To meet this requirement, mesoprous alumina (MA) with a wide surface area (307 m2/g) and uniform pore size (3.5 nm) was prepared, and a spongelike interlinked pore system was developed through a post-hydrolysis method. The resulting MA was insoluble and stable within the range of pH 3-7. The maximum uptake of As(V) by MA was found to be 7 times higher [121 mg of As(V)/g and 47 mg of As(III)/ g] than that of conventional AA, and the kinetics of adsorption were also rapid with complete adsorption in less than 5 h as compared to the conventional AA (about 2 d to reach half of the equilibrium value). A desorption study using sodium hydroxide solutions (0.01-1 M) was conducted, and 0.05 M NaOH was found to be the most suitable desorption agent. More than 85% of the arsenic adsorbed to the MA was desorbed in less than 1 h. Several other activated aluminas with different pore properties were also tested. The results show that the surface area of the adsorbents does not greatly influence on the adsorption capacity. In fact, the key factor is a uniform pore size and an interlinked pore system. These studies show that MA with a wide surface area, uniform pore size, and interlinked pore system can be used as an efficient adsorbent for the removal of arsenic.

Abstract: Equilibrium and kinetic adsorption of tri-valent (arsenite) and penta-valent (arsenate) arsenic to activated alumina is elucidated. The properties of activated alumina, including porosity, specific surface area, and skeleton density were first measured. A batch reactor with temperature control was employed to determine both adsorption capacity and adsorption kinetics for arsenite and arsenate to activated-alumina grains. The Freundlich and Langmuir isotherm equations were then used to describe the partitioning behavior for the system at different pH. A pore diffusion model, coupled with the observed Freundlich or Langmuir isotherm equations, was used to interpret an observed experimental adsorption kinetic curve for arsenite at one specific condition. The model was found to fit with the experimental data fairly well, and pore diffusion coefficients can be extracted. The model, incorporated with the interpreted pore diffusion coefficient, was then employed to predict the experimental data for arsenite and arsenate at various conditions, including different initial arsenic concentrations, grain sizes of activated alumina, and system pHs. The model predictions were found to describe the experimental data fairly well, even though the tested conditions substantially differed from one another. The agreement among the models and experimental data indicated that the adsorption and diffusion of arsenate and arsenite can be simulated by the proposed model.