Author name:
مزهر عبد كاطع
Supervisor name:
غفران فاروق جمعة | رياض حسن الانباري
Key words:
- adsorption
- Adam-Bohart model
- Thomas model
- and Clark model
- Langmuir and Freundlich models
- Cs-137 radionuclides
- batch and fixed bed experiments
- Al-Tuwaitha site
- pumice
- radioactive wastewater
Abstract:
A pure and without modification pumice was extensively studied (for the first time in Iraq) through batch and fixed-bed column processes to decontaminate real liquid radioactive wastes (LRWs) collected from Al-Tuwaitha nuclear site. The radiological characterization by a gamma spectroscopy with a high purity germanium detector (HPGe) showed that LRWs were contaminated with Cs-137 radionuclides. The studied parameters in batch experiments method included pH (2, 5, 7, and 10), pumice weight (0.01, 0.025, 0.05, 0.075, 0.1, 0.2, 0.3, 0.4, and 0.5) g (pumice)/30 mL (radioactive liquid) i.e. (0.33, 0.83, 1.66, 2.5, 3.33, 6.66, 10, 13.33, and 16.66) g/L, mixing time (2, 5, 10, 20, 30, and 60) min, mixing speed (100, 200, 300, 400, and 500) rpm, temperature (20, 30, 35, 40, and 50) ºC, and the initial concentrations of Cs-137 were (250, 842, 1326, 2424) Bq/L. The maximum removal efficiency was 91.75%, occurred at optimal conditions of pumice dose of 3.33 g/L, mixing time of 5 min, mixing speed of 100 rpm, initial Cs-137 concentration of 250 Bq/L, and temperature of 20 ˚C. At optimal conditionings, the isotherm analyses conform closer to Langmuir behavior than Freundlich isotherm. The regression factors (R2) were 0.96 and 0.91 for Langmuir and Freundlich isotherms, respectively. The pseudo-second-order kinetic model was fit for the experimental adsorption data. The thermodynamic model results were ΔS˚ of -155.14 kJ/mol.K, ΔH˚ of 91.45 kJ/mol, and ΔG˚ of -201.54 kJ/mol. The studied parameters of the single-stage, fixed-bed column process are bed thickness (0.2 and 0.4) cm, influent discharge (4 and 6) mL/min, and contaminant concentration (4623.33 and 19013.33) Bq/L. The results demonstrated that the adsorption capacity was 106.47 kBq/g, which was yielded at bed depth of 0.2 cm, influent discharge of 4 mL/min, Cs-137 concentration of 19013.3 Bq/L, and temperature of 20 ˚C. The Thomas and the Clark models were suitable to represent the experimental data where correlation factors R2 were 0.95 and 0.97, respectively. Based on the nature of the suitable models in both the batch and the fixed-bed column, the adsorption process took place on monolayer, heterogeneous surfaces, endothermic nature, less disordered, randomly increased at the interface layer, and was controlled by chemical interactions with active pumice sites.
