Removal of metal impurities in rice husk and characterization of rice husk ash under simplified acid pretreatment process

Acid pretreatment plays an important role in the preparation of amorphous silica with high activity and high specific surface area before combustion process. However, some limitations and problems exist in the pretreatment process of previous literatures. On the basis of this, this work is aimed at simplifying the acid pretreatment process and combustion condition, which could present a more advantageous process for practical industrial applications. Then the removal percentage and behavior of metal impurities in rice husk is studied by ICP-OES, and effects of acid pretreatment on properties of rice husk ash (RHA) at various combustion temperatures are comprehensively investigated in comparison with previous results by scanning electron microscope (SEM), X-ray fluorescence (XRF), X-ray diffractometer (XRD), and surface analyzer. The results suggest that the removal degree of each metal is various due to each chemical form in rice husk, of which removal percentage of K is especially remarkable. The contributions of simplified acid pretreatment to the properties of RHA are equally prominent: smaller nanoscale particles, higher purity, and specific surface area of above 200 m2/g. In addition, the pretreatment can also eliminate the crystallization and keep the high activity of RHA in combustion temperature range of 600–900°C. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 830–837, 2017