الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
SUMMARY
urrently, water is one of the most vital human resources and has economic, social, political and environmental importance throughout the world. Water pollution has become a serious environmental problem and has attracted global concern in recent years, particularly since various pollutants are entering aquatic systems as a result of rapid industrialization and urbanization. The most important treatment processes for metals ions and dyes contaminated waste streams include chemical precipitation, membrane separation, filtration, ion exchange, adsorption and coprecipitation/adsorption. However, all these techniques have their inherent advantages and limitations in applications. These processes usually need expensive facilities and high maintenance cost. Therefore, there is a need for more economical alternative technologies for the treatment of metals and dyes contaminated waste streams.
The aim of present work is to study the treatment of aqueous solution containing hazardous substances such as heavy metals ions (lead and cobalt) and organic pollutants (methyl orange and humic acid) using adsorbents prepared form local agricultural by product wastes. The experimental part deals with the collection of raw samples and discussing the different procedures of treatment aimed to modify the sorption capability and describing the methods used for characterization of both the raw and new converted adsorbents. In this concern all apparatus and techniques employed are described.
Pine sawdust (PSD) was used as precursor for preparing 14 samples of activated carbons by either physical or chemical activation methods. In this concern, activated carbons were prepared as follows: (i) physical activation was preformed using either steam, CO2 or N2 gas (ii) chemical activation was done either by mineral acids (HCl, HNO3, H2SO4 or H3PO4), organic acids (ascorbic acid or oxalic acid) or strong alkalies (KOH or NaOH) .
Rice husk (RH) or rice husk ash (RHA) were used as precursors for preparation of 12 samples of silica gel after extraction with NaOH followed by precipitation either by mineral acids (HCl, HNO3 and H2SO4) or organic acids (oxalic acid, citric acid, and acetic acid).
The results of the first part of this study describes the physicochemical and adsorption properties of both raw precursors, the 14-activated carbons derived from sawdust and the 12 silica gel samples prepared from rice husk or rice husk ash. In this concern, characterization of the adsorbents selected to be used in the following adsorption applications exhibited bulk. Density greater than 0.25 g/cc. i.e. the value of density reported by American Water Works Association (AWWA) as the lower limit of the bulk density to be of practical use. The activated carbons prepared from sawdust have high ash content compared to the starting sawdust. This indicates that during the process of chemical activation using H3PO4 a substantial amount of carbon was consumed leading to an increase of ash content. Natural precursor rice husk has ash content of 17%. However, the silica gel that made from rice husk and rice husk ash have always higher ash content due to their high specific mineral content, especially their richness in silica
from N2 isotherms, the chemically activated sawdust carbon PSDP5 has the highest surface area (991.14 m2/g) and the physically activated sawdust carbon, PSDC8 has the highest surface area (361.28 m2/g). Silica gel were prepared from rice husk ash has surface area lower than activated sawdust carbons.
The scanning electron microscopy (SEM) images of sawdust samples before and after activation, showed that pine sawdust particle has fibrous structure. The changes in pretreated sawdust can be explained by the removal of the hemicelluloses that gave the look to the smooth particle surface, and the appearance of the naked cellulose-lignin complex which has a more similar look to lignin. The changed surface of the pretreated sawdust explains the enhanced adsorption properties and the higher BET surface area values.
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The surface of RH was characterized by ridges. The surface appeared highly undulated due to the presence of regularly spaced conical protrusions and bright spots which can be attributed to silica which is more highly concentrated in regions corresponding to dome-shaped protrusions and adjoining sloping areas. Si-Cl-RHA sample extracted with alkaline treatment (4%) NaOH followed by HCl, look like collection of flowers or tree leaves and some needle or rods can be seen. This shape is acceptable as Si-Cl-RHA is mainly amorphous silica surface.
In order to gain the property of raw materials, prepared silica and carbon surfaces, the FTIR spectra have been studied in addition to the EDX (Energy dispersive x-ray) and elemental analysis. On the basis of pH measurement, the prepared carbons from sawdust show according to activation procedure basic and acidic surfaces (pH = 4.5 - 9) while the prepared silica gel from rice husk and rice husk ash show basic surfaces (pH = 8.2 -10.1).
In the second part of this investigation, raw materials, prepared silica and activated carbons were tested for removal of lead and cobalt ions from aqueous solution. Si-Cl-RHA and PSDC8 adsorbents were found to be the most effective in removal of cobalt and lead respectively. Therefore, the following adsorption experiments were done using these two adsorbents. Factors affecting adsorption process proved that the reaction rate was fast, requiring only a short contact time for the two metal ions under investigation, followed by a relatively slow rate stage the equilibrium steady state was reached within 90 min for both lead and cobalt.
The pseudo-first and second order kinetic models were applied For lead and cobalt. The calculated qe (equilibrium adsorption capacity) values obtained from pseudo-second order rate expression are in good agreement with the experimental data (qe,exp) indicating the chemisorption control.
The linear portion of the curves of qt vs. t0.5 plots for the two studied sorption systems do not pass through the origin point. This
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proved that the intra-particle diffusion was not the only rate-controlling step. The sorption mechanism of these sorption systems from aqueous solution is rather a complex process, probably a combination of external mass transfer and intraparticle diffusion which contribute to the rate determining step.
The adsorption edge for Pb (II) was found at pH 5, While that of Co (II) was found at pH 6.
The adsorption isotherm models namely Langmuir (L), Freundlich (F) and Dubinin-Radushkevich (DR) were used to represent experimental data. By comparing the calculated correlation coefficients, R2, for each model it can be concluded that the experimental data fit the Langmuir model better than the Freundlich model. from the Langmuir isotherm parameters, The maximum capacity qo of lead and cobalt were found to be 91.6 and 75.7 mg/g respectively.
from the Freundlich isotherm parameters, the magnitude of K and n; the Freundlich constants, showed easy uptake of both cobalt and lead. Values of n between 1 and 10 represent good and favorable adsorption and higher value of K indicates high affinity.
from the DR isotherm parameters, the mean free energy values (E) obtained in case of cobalt and lead adsorption are in the energy range of an ion-exchange reaction i.e., 8-16 kJ/mol.
The thermodynamic parameters of lead and cobalt were calculated. The data indicate those lead and cobalt sorptions are better occurred at higher temperature.
The presence of PO43- ion, in exception of all the studied anions and cations increases the sorption capacity of PSDC8 by 14.58%. Therefore, the PO43- could be added through the sorption of Pb(II) to increase the sorption capacity of prepared PSDC8.
The presence of PO43- and SO42- ions, in exception of the studied other anions and cations increases the sorption capacity of Si-Cl-RHA by 0.83% and 14.09% respectively. Therefore, the PO43- and SO42-could be
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added through the sorption of Co(II) to increase the sorption capacity of prepared Si-Cl-RHA.
Recovery of the biosorbed lead and cobalt onto PSDC8 and Si-Cl-RHA respectively was carried out using various eluting agents containing organic acids, salt solutions, mineral acids and distilled water. 3M HNO3 and 0.5M H2SO4 was found to be the most efficient desorbent agent in case of Pb(II):PSDC8 and Co(II):Si-Cl-RHA systems respectively.
In The third part of this investigation, raw martial, all prepared silica and the activated carbons were tested for removal methyl orange and humic acid from aqueous solution. PSDP5 carbon sample exhibited the highest removal capacity for both methyl orange and humic acid compared to the other adsorbents. Factors affecting adsorption process proved that the reaction rate was fast, requiring only a short contact time for methyl orange but, for humic acid the rate was slow, requiring long contact time. In case of methyl orange the equilibrium was attained after shaking for about 40 min, while in case of humic acid, about 48 hrs were required to attain equilibrium.
The kinetic data of the methyl orange and humic acid adsorption can be described well by pseudo-second order rate equation due to the high values of correlation coefficient R2 compared to that of pseudo-first order model. The calculated equilibrium adsorption capacities (qe,cal) from pseudo-second order model agree well with the experimental values (qe,exp). These results suggest that there sorption systems are not first order reaction and the rate-limiting step may be chemical sorption.
from the Langmuir isotherm parameters, it is clear that the adsorptive capacity (qo) of PSDP5 towards methyl orange is higher than that toward humic acid. This result was confirmed by the higher value of b (adsorption affinity) for methyl orange, than that of humic acid.
from the Freundlich isotherm parameters, the values of 1/n were found in the range 0.1 to 0.5, indicating that: (a) the adsorption capabilities of methyl orange and humic acid towards PSDP5 increased as the temperature increased and (b) surface structure of sorbent PSDP5
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is heterogenous. The values of the Freundlich exponent “n” are greater than one, indicating that the adsorption of methyl orange and humic acid by PSDP5 carbon is favorable. However, it is further clear that adsorption of methyl orange is more favorable than that of the humic acid as indicated by higher K and n values, and higher capacity at the same equilibrium concentration.
The thermodynamic parameters of methyl orange and humic acid were calculated. The data indicate that methyl orange and humic acid sorption is better occurred at higher temperature.
After establishing the applicability of the proposed method for cobalt removal from aqueous solutions, the next objective was to test the effectiveness of the process for treatment of radioactive liquid wastes. For this purpose, removal of cobalt from simulates of: low level liquid waste (LLLW) generated by Nuclear Research Center at Inshas, Egypt and process wastewater (PWW) that might arise in research laboratories in the same Center, was performed under the optimal experimental conditions. Results indicated that % removal of 60Co and 137Cs in low level liquid waste are 99.5% and 93% respectively and % removal of 60Co in process wastewater is 98.5%.
The fourth part of the investigation, the data obtained in batch mode studies is not applicable to wastewater treatment plants where contact time is not sufficiently long for attainment of equilibrium. Therefore, it becomes necessary to determine the capacity of any biosorbent in continuous operation before its application in wastewater treatment plant at industrial scale, continuous flow fixed – bed columns studies are required. A packed bed column is an effective process for cyclic sorption/desorption and this investigation is concerned with the uptake of Co(II) by Si-Cl-RHA adsorbent through a fixed-bed column at three different bed depths, influent Co(II) concentrations and flow rates. Results indicated that the adsorption capacity increased with increasing bed depth, but decreased with increasing the influent concentration and flow rate. The column sorption process was found to perform better at lower influent Co(II) concentration, lower flow rate and higher bed depth. Thomas,Yoon-Nelson, Clark, Adams–Bohart, Wolborska, Dose-
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Response and BSDT models were successfully used to predict the breakthrough curves, indicating that Thomas and Yoon-Nelson were very suitable for Si-Cl-RHA column design.
The study concluded that sawdust and rice husks which as agricultural solid wastes have a negative impact on the environment can be converted to different types of valuable activated carbons and silica and can act as useful adsorbates that can be qualified for use in waste water treatment processes that contain inorganic, organic pollutants and low level liquid radioactive wast