Abstract

The rice husk ash (RHA) waste from biomass power plant in Thailand is still underutilized leaving disposal problems. Indeed, this material content high silica inside it has a possibility to become a potential zeolites precursor. In this study, small particle of RHA has been reused to prepare a Na-A and Na-X zeolites with high purity using two step method hydrothermal treatments. First, RHA was submitted to a chemical pre-treatment using NaOH powder and then adjusting the Si/Al molar ratio by adding sodium aluminate solutions, and maintaining the mixture at different temperature and heating time. Pure zeolites used to remove cadmium from aqueous solution concentration ranging from 30 to 500 mg/L and at the temperature of 20, 30 and 40oC using batch technique. The effect of time, initial concentration, pH and temperature on removal process was investigated. The results showed that kinetic data were followed more closely the pseudo-second order model than the pseudo-first order by both zeolites. The adsorption isotherms were described by Langmuir and Freundlich isotherm models, and both model fitted well with both zeolites. The thermodynamic parameters such as, Gibbs free energy changes (#x394;Go), standard enthalpy change (#x394;Ho) and standard entropy change (#x394;So) had been determined. The results show that cadmium ion removed onto Na-A and Na-X zeolites are an endothermic and spontaneous in nature.