الفهرس 
AbstractOnly 14 pages are availabe for public view
 |  | from | 286 |  |  |
| | | from | 286 | | |
Abstract
Rice husks, a locally available agricultural byproduct, were investigated with the aim of producing good adsorbing materials suitable for remediating water pollution. Raw lignocellulose was treated through various procedures: simple carbonization to high temperature, pyrolysis under flowing steam at moderate temperatures and chemical activation with H3PO4 followed by pyrolysis at moderate temperatures. A partially deashed precursor was obtained by boiling in alkali solution, thereafter botanical residue was steam activated at a single temperature, and leachate acidified whereby silica was precipitated. Many types of adsorbents were thus derived: chars, activated carbon and silica. The obtained various categories of sorbents were characterized by different techniques to asses their physicochemical and adsorptive properties. This involved: ash content, thermogravimetry, FTIR, electron microscopy, N2 gas adsorption at 77K and adsorption capacity from solution using probe molecules.The obtained various categories of sorbents were characterized by different techniques to asses their physicochemical and adsorptive properties. This involved: ash content, thermogravimetry, FTIR, electron microscopy, N2 gas adsorption at 77K and adsorption capacity from solution using probe molecules. Adsorbents with high ash contents (reaching up to 60%) were obtained indicating the formation of mixedtype materials with carboninorganic composition. Lowporosity adsorbents are formed with maximum surface area of 480 m2/g and total pore volume attaining 0.430 ml/g, which is ascribed to the considerable inorganic content of insignificant porosity. Chars with poorly developed porosity exhibit high adsorption capacity for iodine and methylene blue that does not correspond to their N2surface area. Steamactivated raw husks and some presilicated material produced nearly similar microporous carbons. Silica gels derived by leaching with increasing alkali concentrations, followed by precipitation, are good adsorbents with low similar porosity (N2surface area ?100m2/g). H3PO4 activated carbons present low to moderate adsorbing products essentially with mesoporosity character and their porous characteristics are not regular function of conditions of preparation: activant concentration or temperature of treatment. The capacity of removing: iodine, phenol, pnitrophenol, mehtylene blue and acid greendye, were function of the adsorbent type and degree of micro/mesoporosity. Selected samples were tested as to their capacity for removing specific water pollutants including organic and inorganic species. In the former, adsorption of humic acid, herbicides (simazine and atrazine) and acid green dye, were determined as function of contact time, initial concentration, temperature and type of adsorbent. Removal capacity of three radionuclides was followed under same abovementioned variables. The monovalent cations of cesium137 and silver110 as well as the hexavalent cations of uranium238 were investigated. Besides, a sample of polluted water from drain branch of the Nile was tested for the capacity of decontamination of heavy metals by a prepared adsorbent, which attained 100% efficiency. Adsorbents derived from rice husks proved to be with good adsorbing capacity in the many, referred to, preliminary removals which recommends this cheap raw material as suitable and promising feedstock for their preparation.