Activated alumina as special sorbents

Activated alumina is a versatile sorbent that can be tailored for many special applications. New applications continue to be developed, mainly by the aluminum companies. Little is disclosed on the details of their modifications. However, the modifications follow simple general principles of surface chemistry, such as acid-base chemistry. Two methods are used for tailoring (1) variation of the activation process, and (2) use of dopants. The following are proven applications of various tailored aluminas  

Acid Gas Removal. The aluminas that are used for acid gas removal obviously contain relatively high soda contents. Sodium is always contained in aluminas because Na(OH) is used in the Bayer process for extraction of alumina from bauxite. The typical content of Na20 in activated aluminas is 0.3% (wt). The soda content can vary considerably. The soda content in the alkalized alumina is typically 1%. The BET (Brunauer-Emmett-Teller) surface areas of activated aluminas are generally in the range 200-500 m /g, with total pore volumes near 0.5 cc/g. 

Water Treatment. Water treatment is a useful application for alumina. Many studies have been performed for the removal of arsenic and fluoride from water. Alumina is particularly effective for adsorption of As , which is in the form of anionic H2ASO4 in the aqueous solution. In aqueous media, the zero point 

Alkalized Alumina. Activated alumina can be alkalized by impregnation with alkali oxides, such as K2O, Na20, or NH4OH. Alkalized alumina is a conuner-cial sorbent for flue gas desulfurization, developed since the early 1970s (e.g., Emerson et al., 1971). Alkalized alumina also has other interesting applications two will be discussed here CO2 removal and NOx removal. 

The alkalized aluminas are prepared by impregnation with solutions of alkali salts, for example, alkali bicarbonates. The salts are typically decomposed by heat-treatment to 500 °C. The alkali oxide contents are typically 5% (wt), but a range of 1-10% has been reported. The surface areas are reduced 

---