Granulated activated carbon modified with hydrophobic silica aerogel-potential composite materials for the removal of uranium from aqueous solutions

Aqueous solutions of 100 parts per billion (ppb) uranium at pH 7 were treated with granulated activated carbon (GAC) that had been modified with various formulations of hydrophobic aerogels. The composite materials were found to be superior in removing uranium from a stock solution compared to GAC alone evaluated by a modified ASTM D 3860-98 method for batch testing. The testing results were evaluated using a Freundlich adsorption model. The best performing material has parameters of n = 2.87 and K-f = 1169 compared to n = 1.00, and K-f = 20 for GAC alone. The composite materials were formed by mixing (CH3O)(4)Si with the hydrophobic sol-gel precursor, (CH3O)(3)SiCH2CH2CF3 and with specified modifiers, such as H3PO4, Ca(NO3)(2), and (C2H5O)(3)SiCH2CH2P(O)(OC2H5)(2), gelation catalysts, and GAC in a supercritical reactor system. After gelation, supercritical extraction, and sieving, the composites were tested. Characterization by FTIR and P-31 NMR indicate the formation of phosphate in the case of the H3PO4 and Ca(NO3)(2) composites and phosphonic acid related compounds in the phosphonate composite. These composite materials have potential application in the clean up of groundwater at DOE and other facilities.