Nitrate and Nitrite Ion Removal from Aqueous Solutions by Activated Carbon Prepared from Olive Stones (Supervisor)

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Hiba Nassar
Nitrate and Nitrite Ion Removal from Aqueous Solutions by Activated Carbon Prepared from Olive Stones2.61 MB
Many different parts of the world have been facing the problem of nitrate and nitrite contamination of surface and ground water. Excessive use of nitrate-based chemical fertilizers is considered to be the main reason for this contamination. Therefore a simple, practical and economic process to reduce nitrate and nitrite concentrations in aqueous solutions was the major objective of this research. To achieve this goal, bench-scale nitrate and nitrite adsorption experiments were conducted using activated carbon as adsorbent. Two research methods were used to minimize the cost of activated carbon production. The first one is by choosing a cheap available starting material (Jift), the other one is by a good choice of the production method. Moreover, by choosing Jift as starting material, we may reduce solid waste pollution, while reducing the cost of raw material for the production of activated carbon. In this study, activated carbon was produced from olive stones by chemical activation technique using different activating agents such as ZnCl2, H3PO4 and NaHCO3. The precursor/activating agent weight ratio was 1:1. Different impregnation methods and different carbonization temperatures 450 -750°C were used. Scanning electron microscopy (SEM) images revealed that the carbon prepared by ZnCl2 activation involved higher cavities than other counterparts. The highest surface area calculated by acetic acid adsorption method for carbon activated by ZnCl2 activation (AC No.7) was 1482.57 m2 g-1. Activated carbon prepared by the chemical activation of olive stone was examined for the adsorption of nitrite and nitrate ions from aqueous solutions. Carbon activated by ZnCl2 was found to be the most effective adsorbent for nitrate and nitrite removal. Commercial activated carbon (CAC) was used for comparison purposes. The adsorptive properties of CAC and activated carbon prepared from olive stone were investigated in terms of adsorbent dose, pH, temperature, contact time and contaminant concentration in a batch system. Results indicate that the adsorption effectiveness for OSC/ZnCl2C/450 (AC No. 7) was higher than for CAC. The total sorption capacities were found to be 7.00 and 5.53 mg/g for nitrite and nitrate, respectively. Lowering pH led to a significant increase in nitrite and nitrate adsorption. The effect of temperature on adsorption by AC No.7 and CAC has also been investigated in the range of 10-40°C. The results indicate that the temperature slightly affected effectiveness of AC No. 7 adsorption. This fact indicates that AC No. 7 can be used for in situ treatment of nitrite and nitrate in underground and surface water. The equilibrium adsorption data were interpreted using Langmuir and Freundlich models. The adsorption of nitrite on AC No.7 at 30°C was better represented by the Freundlich equation. On the other hand, nitrate adsorption on AC No.7 at 20°C was better represented by the Langmuir equation. In order to investigate the adsorption mechanisms, three simplified kinetic models, i.e., pseudo-first-order, pseudo-second-order and intra-particle diffusion were applied to fit the kinetic data obtained by using both adsorbents. The rate constants for the three models were determined and the correlation coefficients were calculated. The kinetic data for both adsorbents supports pseudo-second order model for nitrite adsorption. Adsorption followed pseudo-second-order rate kinetics for nitrate onto AC No.7 and pseudo-first-order rate kinetics onto CAC. Thermodynamic parameters such as standard free energy ΔG°, standard enthalpy ΔH° and standard entropy change ΔS° of the nitrate adsorption process were calculated for both adsorbents.