Abstract:Recebido em 15/4/09; aceito em 29/10/09; publicado na web em 10/3/10 Many routes for extracting silica from rice hulls are based on direct calcining. These methods, though, often produce silica contaminated with inorganic impurities. This work presents the study of a strategy for obtaining silica from rice hulls with a purity level adequate for applications in electronics. The technique is based on two leaching steps, using respectively aqua regia and Piranha solutions, which extract the organic matrix and ino… Show more
Contaminated sediments provide the main source of mercury for methylation by bacteria in lakes and waterways. In situ capping has been used to remediate these sediments, but traditional reactive materials have very low affinity for Hg(II). This study investigated the mercury uptake by biogenic silica modified with L-cysteine, as a potential material to be used for in situ remediation technologies. The adsorbent was obtained from rice hull ash by extraction as sodium silicate and acid hydrolysis through the sol-gel process; it was then modified with L-cysteine by impregnation from aqueous solution. The unmodified and modified biogenic silica showed structural and chemical properties suitable for mercury sorption from aqueous medium. The cysteine affected the structural properties of the unmodified silica, decreasing the specific surface area and pore volume by eightfold. On the other hand, cysteine increased the silica adsorption capacity, resulting in mercury uptake similar to that of the unmodified silica. The Hg(ll) specific adsorption by unmodified and modified silica was 0.20 mmol/g and 0.19 mmol/g SiO2, respectively, from an aqueous solution of 1 mmol/L Hg(II). The pH range of 3-7did not have an effect on Hg(II) adsorption. However, the presence of chlorine, added as HgCl2, seems to have limited the mercury adsorption, especially at high concentrations of Hg(II). The mercury adsorbed on the silica surface could not be recovered using HCl even from concentrated solutions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.