Abstract
Rice husks chemically modified with three different treatment methods; sodium hydroxide, nitric acid, and distilled water, were investigated to compare their color removal efficiencies for two dyes; Basic Red 4G (a cationic dye) and Direct Supra Red BWS (an anionic dye). The results revealed that the basic dye was adsorbed by these adsorbents better than the direct dye. The modified rice husk prepared using sodium hydroxide treatment showed the highest color removal efficiency (97% for Basic Red 4G) among the three modified rice husks. This modified rice husk was selected for further study of the adsorption equilibrium and adsorption isotherm. The results of adsorption equilibrium investigation fitted well with Langmuir model indicating that the dye adsorption takes place as a monolayer adsorption, based on the assumptions of the Langmuir model. The maximum adsorption capacity calculated from the Langmuir model was calculated to be 6.2 mg/g and 2.6 mg/g for Basic Red 4G and Direct Supra Red BWS, respectively. While the 1/ n values from Freundlich model were calculated as 0.2702 and 0.5841 for Basic Red 4G and Direct Supra Red BWS, respectively, indicating favorable dye adsorption. This modified rice husk is a potential alternative adsorbent for color removal in the wastewater from dyeing process using cationic dyes.
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