Enhancing pozzolanic properties of rice husk ash using acid leaching treatment

Rice husk ash (RHA) is one of the major agricultural wastes in rice producing countries. Approximate 20% of the total amount of paddy is rice husk (RH) which will be generating 120 Mtons annually. This causes a serious disposal problem due to low commercial interest. The presence of metallic impurities (Na₂O and K₂O) in non-treated RHA can trigger alkali reaction in hardened concrete. Acid leaching treatment prior to combustion is proposed in this study as an effective approach to remove the metallic impurities. HCl acid solutions with different concentrations, namely 1.0M, 0.1M and 0.01M were prepared to leach RH for 2 hours at constant temperature of 80°C. The rice husk was then dried in room temperature and combusted at 800°C for 2 hours using electrical furnace. The characterization studies of the acid leached rice husk ash (ATRHA) were done by x-ray fluorescent (XRF), x-ray diffraction (XRD) and loss on ignition (LOI). Result shows that RHA leached with 1.0M of HCl at 80°C for 2 hours followed by the controlled combustion process at 800°C for 2 hours (ATRHA3) effectively removed impurities and produced RHA which contained > 98% of pure amorphous silica. In addition, the LOI result shows that there is a 5.24% reduction of un-burnt carbon content inATHRA3 sample compared to control specimen.