The possible utilization of rice husk ash as an adsorbent for methylene blue dye from aqueous solutions has been investigated by Chandrasekhar and Pramada [101]. The highest adsorption capacity was found to be approximately 690 mg/g. Rice husk ash as an adsorbent was also tested for Indigo Carmine dye removal from aqueous solution by Lakshmi et al. [102]. An adsorption capacity in the range of 29.3–65.9 mg/g was reported at different temperatures (293–323 K).