Document Details
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Document Type |
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Thesis |
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Document Title |
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Natural lignocellulosic materials and its potential as adsorbents for metal cations removal from aqueous solutions المواد الليجنوسيليولوزية الطبيعية و إستخدامها كممتزات للتخلص من الملوثات الكاتيونية فى المحاليل المائية |
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Subject |
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Faculty of Sciences > Chemistry department |
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Document Language |
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Arabic |
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Abstract |
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Re-use of agricultural wastes is one of the adopted strategies in different countries to close the gap between natural sources and increased water demand. Drainage and industrial wastewater contain varieties of toxic heavy metals that can potentially cause hazard on humans and environment. Although adsorption technique is considered one of the proper methods for the wastewater treatments, economic aspect is a crucial factor for the broad application of such technique.
This thesis is dedicated to the re-use of agricultural wastes (or lignocellulosic materials) to remove cadmium and lead ions from aqueous solution. Watermelon and mallow wastes as cheap materials were used to prepare modified adsorbents. This work is divided into three parts.
Part one is dedicated to remove cadmium ions by using watermelon wastes. From watermelon rinds, four adsorbents were prepared. Beside the native watermelon rind (WM), three modifications are performed. The modification was done by using microwave radiation in the presence of water (WMW), NaOH (WMA) and H2O2 (WMH). The prepared adsorbents in addition to the native one were utilized for the removal of Cd(II) from aqueous solution. The four adsorbents were then characterized by FTIR. The FTIR spectra of the raw and modified watermelon reflected the modification that has been done to the native material. Effect of some parameters such as contact time, cadmium concentration, adsorbent dose, temperature and pH were examined. With increasing the pH, the adsorption of cadmium ions increased and then showed a decreasing trend when the pH was higher than 9.2. This decreasing trend in adsorption capacity is due to the formation of soluble hydroxyl complexes which result in the precipitation of Cd(II) as Cd(OH)2. Regarding dosage effect, it was observed that the percentage of adsorption increased as the adsorbent dosage was increased over the range 1 g to 5 g/L. This is due to the fact that an increase in adsorbent dosage increases the number of active sites available for adsorption process.
Effect of cadmium ions concentration on watermelon was also studied. The study revealed that the adsorption capacities of the four watermelon adsorbents increased with increasing cadmium concentration while the adsorption yields of cadmium showed the opposite trend. The equilibrium uptake and adsorption yield were highest for both WMW and WMH, the two lines almost coincide together, but one can barely see that the removal capacity of WMW is the highest. This may be due to the greater micro porous structure and therefore less crystallinity of cellulose in hot water treated watermelon under microwave radiation. This was also confirmed by what was conducted by the adsorbent dosage effect.
Adsorption isotherm models were also applied. On comparing the values of the correlation coefficient, R2, for the four tested isotherms, it can be observed that the removal data of Cd(II) onto watermelon rind fitted well with the Langmuir isotherm followed by Temkin, Freundlich isotherm and least in Dubinin-Radushkevich isotherm. Also, by comparing the maximum adsorption capacities of cadmium (II) on watermelon, WMW have great potential for the removal of Cd(II) ions from aqueous solutions.
Kinetic studies conducted showed that the adsorption process followed the pseudo second order kinetic model. The values of the thermodynamic quantities, ΔH°, ΔG° and ΔS° were negative. The thermodynamic results obtained in this study was the normal consequence of the combination of physical adsorption, which takes place through electrostatic interactions and is confirmed by the mean free energy, E, that was conducted by using Dubinin-Radushkevich constants.
The second part of this thesis was to examine the use of mallow wastes as valuable and cheap adsorbent to remove lead from aqueous solutions. Three modified adsorbents were prepared from mallow wastes. MW was obtained when mallow was subjected to microwave radiation in the presence of water, while MC was obtained from the radiation of mallow via microwave radiation (dry). MS was obtained when mallow were sonicated. The three mallow adsorbents were characterized using FTIR. FTIR analysis showed the success of mallow modification. By comparing the fresh mallow adsorbents and Pb(II) loaded adsorbents, shifts in the wave numbers of dominant peaks associated with the Pb(II) loaded in the FTIR spectra are detected. The three prepared adsorbents, MW, MS and MC were subjected to lead ions in aqueous solutions to evaluate the efficiency of mallow as cheap adsorbent material. The effects of five variables, initial solution pH, adsorbent dosage, concentration of Pb(II)ions, time and temperature on the removal efficiency for Pb(II) ions were evaluated. Effect of pH indicates that the lead removal efficiency increased with increasing the pH. However, At pH higher than 6, lead precipitation (Pb(OH)2) occurred due to the existence of OH- ions in the adsorption medium.
The impact of mallow dosage on the removal efficiency was also determined. As the mallow dosage increased from 1 g/ L to 5 g/L, the removal efficiency of lead increased significantly as previously predicted.
Changing lead ions concentration had different effects on capacity and removal efficiency of mallow. The study revealed that as the lead concentration increased the removal efficiency of mallow decreased. On the other hand, adsorption capacity showed a reverse trend.
Application of different adsorption isotherms to the experimental data showed that the applicability of the four isotherms models for the present study for mallow adsorbents followed the following order: Langmuir>Dubinin-Radushkevich>Temkin>Fruendlich. The maximum adsorption capacity (qL) from Langmuir model was calculated as 66.67, 64.94 and 250.00 mg/g for MW, MS and MC, respectively.
The obtained statistical data and kinetic constants in the current investigation proved that the adsorption process of lead ions onto mallow was controlled by the Pseudo second-order model.
Lead adsorption as a function of contact time in four different temperatures showed that the uptake capacities of lead ions decreased as the temperature increased. This is mainly due to the decreased surface activity, suggesting that adsorption between lead and mallow is an exothermic process. Thermodynamic parameters that was obtained in this work revealed that the negative values of ΔH° confirmed the exothermic nature of lead sorption onto MW, MS and MC process. The negative values of ΔS° showed the decreased randomness at the Pb(II)/mallow surface. The negative value of ΔG° decreases with an increase in temperature, indicating that the spontaneous nature of adsorption is inversely proportional to the temperature.
Therefore, upon treatment of watermelon and mallow with different treatment methods, WMW and MC are the most efficient methods for the removal of cadmium(II) and lead(II) ions from aqueous solutions, respectively.
The third part of this study was dedicated to application of the prepared mallow and watermelon adsorbents to three real environmental samples, Red sea water, Al-Arbaien lake water and tap water. The adsorption of Cd(II) and Pb(II) onto watermelon and mallow adsorbents from Red sea water and Al-Arbaien lake water was slightly low compared with tap water. This may be due to the high concentration of Na+, K+, Ca2+ and Mg2+ in sea water sample, which compete with Cd(II) and Pb(II) adsorption on watermelon and mallow binding sites. This confirms the applicability of watermelon and mallow for environmental treatment, especially with regard to cadmium and lead ions. |
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Supervisor |
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Prof. Elham Shafik Aazam |
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Thesis Type |
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Master Thesis |
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Publishing Year |
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1437 AH
2016 AD |
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Co-Supervisor |
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Dr. Dalal Zein El-Abdeen Husein |
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Added Date |
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Sunday, April 17, 2016 |
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Researchers
| مرام عبد الله باعطية | Ba-attia, Maram Abdullah | Researcher | Master | |
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