الفهرس 
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Abstract
In the present study, guava leaves were used as low cost adsorbent for the removal of heavy metals (cadmium ions). Guava leaves have been used as raw material (GL) for the preparation of different activated adsorbents. Activated adsorbents were prepared from guava leaves by chemical activation(GLl) and (GL2).All adsorbents were characterized by Fourier Transform Infrared spectroscopy ”FTIR”, Energy Dispersive X¬ray ”EDX”, Scanning Electron Microscope ”SEM”, and Brunauer, Emmett, and Teller ”BET”. Batch adsorption experiments were conducted to study the effect of different parameters such as: contact time, adsorbent dose, pH, initial concentration of cadmium ions and temperature on removal of cadmium ions.
The adsorption kinetic data were fitted with first order, second order and Elvoich kinetic models. It was found that the cadmium adsorption kinetic onto guava leaves was well fitted by second order kinetic model rather than first order model for GL, GLl and GL2 respectively. Three adsorption isotherm models namely, Langmuir, Freundlich and Dubinin-Radushkevich were used to analyze the equilibrium data. The Freundlish isotherm provided the best correlation for Cd2+ adsorption onto GL & GLl adsorbents but for GL2 adsorbent was fitted to D-R isotherm, the maximum adsorption capacity was found equal to 19.696 , 17.966 & 24.236 mg g’ for GL , GLl & GL2 adsorbents respectively. Thermodynamic parameters were evaluated and the adsorption process was an exothermic process.
Also, response surface methodology was employed for the removal of cadmium 1I1 order to study the combined effect of operational parameters; experiments were performed for different combinations of some parameters using statistically designed experiments using Design Expert 8.0.6.1 with four variables at three levels. Experiments were carried out as per Box-Behnken surface statistical design with four input parameters namely adsorbent dose (0.1- q.•5g), initial concentration (20 -100 mg L-’), temperature (30 - 70°C) and pH (3.5 - 6.7). Contact time (120 min) was taken as a fixed input parameter. A non-linear regression method was used to fit the second order polynomial equation to the experimental data and to identify the relevant model tem1S. Regression analysis
II showed good fit of the experimental data to the second-order polynomial model with the coefficient of-determination (R2) value of 0.9845,0.9570 & 0.9810 for GL, GLI & GL2 adsorbents. ivlethod of the desirability function was applied to optimize operationalconditions. ,,\pplying the method of the desirability function, gave a maximum adsorption capacity 19.4J54 mg/g of cadmium with desirability of 1 by guava leaves (GL) , 21.788 mg/g of cadmium with desirability of I by guava leaves (GLl) and 42.7105 mg/g of cadmium with desirability of 0.982 by guava leaves (GL2The results suggest that guava leaves have high possibility to be used as an effective and economicaladsorbent for Cd2+ removal