Simultaneous Methylene Blue Adsorption and pH Neutralization of Contaminated Water by Rice Husk Ash

[Image: see text] In this study, the potential of rice husk ash (RHA) to act as an adsorbent for treating dye-containing wastewater was demonstrated. The RHA used in this study contained 91.7% silica, which was composed of crystalline (cristobalite and tridymite) and amorphous phases. The mechanochemical treatment of RHA led to an increase in its specific surface area from 6.2 to 14.6 m(2)/g in 15 min and dramatically improved its methylene blue (MB) adsorption ability. Langmuir adsorption isotherms revealed that the maximum adsorption capacity of the treated RHA was 8.59 mg/g, which is 2.45 times higher than that of raw RHA. pH-dependent adsorption studies on the RHA revealed that MB was adsorbed on the deprotonated Q(3) silanol through electrostatic interactions. Moreover, the RHA adsorbent showed pH buffering at a pH value of approximately 7; thus, the pH of the solution could be neutralized simultaneously with the adsorptive removal of MB.