The adsorption of palmytic acid on rice husk ash chemically modified with Al(III) ion using the sol-gel technique

Silica-incorporated aluminum (RHA-A1) was synthesized from rice husk ash (RHA) using the sol-gel technique. RHA-Al was calcined at 500 degreesC for 5 h to yield RHA-A1(C). The ratio of silica to alumina was found to be 4:1. The BET analysis of RHA-A1(C) showed an increase in total pore Volume and specific Surface area compared to RHA-Al. SEM and XRD showed that RHA-A1 and RHA-A1(C) were composed of microcrystals and the surface of both samples had a Porous structure. Adsorption studies of palmytic acid on RHA-A1 and RHA-A1(C) at 30, 40, and 50 degreesC conformed to the Langmuir isotherm. The equilibrium parameter, R, revealed that both are good adsorbents for palmytic acid. The Gibbs free energy of adsorption, DeltaG(ads)(0), was determined to be between -21.0 and -26.0 kJ mol(-1). DeltaH(ads)(0) and DeltaS(ads)(0) for RHA-A1 were found to be 26.2 kJ mol(-1) and 158 J mol(-1), respectively. Corresponding Values for RHA-A1(C) were 31.7 kJ mol(-1) and 178 J mol(-1). The adsorption of fatty acid on RHA-A1 and RHA-A1(C) was an endothermic process, which occurred spontaneously. An FTIR Study on the adsorbed material was used to determine the possible adsorbed complex on the surface of the adsorbent. (C) 2004 Elsevier Inc. All rights reserved.