Adsorption by activated carbon is an effective method of dye removal. However, due to high production and regeneration costs of activated carbon, various studies on low-cost adsorbents have been conducted. Agricultural waste such as rice husk (RH) is seen to be a good adsorbent for dye removal. Moreover, rice husk is readily available. In this study, rice husk-based adsorbents were prepared by chemical and thermal treatments. Standard curve (colour vs absorbance) for Direct Blue 86 (DB 86) was prepared to determine the concentration of dye before and after adsorption. The adsorption potential of the adsorbent for textile dye DB 86 was evaluated by batch adsorption tests. The most effective adsorbent, RH6, was selected and its DB 86 adsorption capacity was determined and compared with that of commercial powdered activated carbon (PAC). The optimum pH for DB 86 removal was pH 2 for both adsorbents. The optimum contact time was observed to be 180 min for both RH6 and PAC. The optimum adsorbent dosage was 4 g/L for RH6 and 3 g/L for PAC. Both Langmuir and Freundlich isotherm models provided high correlation coefficients R2 (>0.97); with Langmuir isotherm R2 > 0.99. The adsorption capacity obtained was 34.4828 mg/g and 47.6190 mg/g for RH6 and PAC, respectively. Pseudo second order kinetic model yielded high R2 values (>0.99) and much closer values of qe,exp and qe,cal (amounts of solute adsorbed determined experimentally and using the model equation) to show that the model describes the adsorption mechanism better than the pseudo first order kinetic model. RH6 has potential to be used as adsorbent for dye removal from wastewater.
