الفهرس 
Water pollutionOnly 14 pages are availabe for public view
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Abstract
The present investigation was carried out to evaluate detoxification of heavy metals such as Pb (II), Cu (II) and Co (II) from wastewater by using by product material such as rice straw. Also evaluate the effect of gamma radiation on rice straw as sorbent material.
The obtained results could be summarized in the following points:
1. characterization of Rice Straw:
Rice straw has good physical Properties and chemical stability. where its moisture content (%), bulk density (g/ml) and apparent density (g/ml) were 4.62, 0.285 and 0.154 respectively.
Also its solubility in Hcl (6 M), Solubility in HNO3 (6 M), solubility in KOH (1 M) and solubility in NaOH (1 M) were 17, 18.45, 13, 11 % respectively.
The FTIR spectra showed the functional groups of modified (Gamma irriadted) and unmodified rice straw the results represented the information about the functional groups on the surface of the cell wall of the rice straw where the cell wall of rice straw compromise of OH groups, –CH2 groups and glycoside group at adsorption bands 3401.58, 2918.31 and 1104.29 cm−1 respectively. These sorption bands indicated in the presence of cellulose unit in rice straw. Furthermore absorption at 1514.85 cm−1 can be attributed to the vibration of aromatic units in lignin of rice straw. And the band that appeared at 1644.15 cm-1 represents C=O stretching of carbonyl. The peak displayed at 1372 cm -1 is possibly due to carboxylate group –COO stretching. Also, the band at 867.78 cm-1 is characteristics of out of plane deformation, vibration of the C–H in aromatic structure. The peak at 784.89 cm-1 is considered to be the bonding between C and Si, or the overlapping of the Si–O and Si–OH. The bands at 668 and 467 cm-1 are assigned, respectively, to Si–O–Al and Si–O–Si bending vibrations.
The (FT-IR) results of modified rice straw with exposure to 5 and 10 (kGy) gamma radiation showed that no considerable difference in rice straw poly functional nature by using radiation to modify. where didn’t happen any considerable stretch in main functional groups.
Scanning electron micrographs of rice straw show that the external surface of rice straw is full of cavities and the morphology of this material can facilitate the adsorption of metals, due to the irregular surface of rice straw, thus makes possible the adsorption of metals in different parts of this material. So, based on the morphology, it can be concluded that this material presents an adequate morphological profile to retain metal ions. Also, scanning electron micrographs represented that the radiation modify, destroy the surface cavities and make the surface more regular, thus reduced the adsorption of metal ions on the rice straw surface.
2. Batch experiments
Effect of the initial concentration on adsorption process: Percent removal efficiency decreased from 88.46, 73.32 and 77.44% to 51.60, 34.53 and 39.73% for Pb (II),Cu (II) and Co (II) respectively. Also values of sorbed metal ions per unit weight to adsorbent ”qe” increased from 4.423, 3.666 and 3.872 mg g-1 to 30.96, 20.718 and 23.83 mg g-1 for Pb (II), Cu (II) and Co (II) respectively, due to concentration increase from 50 to 600 mg L-1.
Effect of metal ion solution pH on adsorption process: percente removal was 78.26, 44.78 and 26.86 % for Pb (II), Cu (II) and Co (II) respectively, when pH=1.5 and increased until it reached the maximum value (88.46, 73.32 and 70.44 %) for Pb(II), Cu(II) and Co(II), respectively at pH 6.5.
Effect of agitation time on adsorption process: The results indicated that with increasing agitation time from 5 to 240 min, percent removal increased until equilibrium adsorption. Equilibrium adsorptions were established within 25 min, this hold is true for removal studied metal ions, whereas the removal percentages were 91.2, 74.2 and 78.2%, for Pb (II), Cu (II) and Co (II) respectively. And the results showed the percent removal efficiency stay nearly constant for both metal ions with no considerable increasing above 25 min. up to 240 min.Effect of sorbent amount on adsorption process: The results show that with increase rice straw dose from 4 g L-1 to 40 g L-1, the removal percentage increased from 65.05 57.42 and 65.14% at 4 g.L-1 to 89.9 75.52 and 77.54% at 10 g.L-1 for Pb (II), Cu (II) and Co (II), respectively. And the results showed the removal efficiency stay nearly constant for both metal ions with no considerable increasing above 10 g L-1 up to 40 g L-1.
3. Comparison between the radiated rice straw and unmodified rice straw:
The results illustrated the radiation negative effect on rice straw as adsorbent, where the Pb (II) percent removal decreased from 88.46% to 80.21% To 76.15% for non-radiated rice straw, radiated rice straw by 5 and 10 (kGy) respectively at 50 mg l-1 .Also the Cu (II) percent removal decreased from 73.32% to70.24% to 65.52% for non-radiated rice straw, radiated rice straw by 5 and 10 (kGy) respectively at 50 mg l-1 and decreased from 77.44% to 73.98% to 71.35% for non-radiated rice straw, radiated rice straw by 5 and 10 (kGy) respectively at 50 mg l-1.
4. Sorption Isotherm Models:
The Langmuir constants ”Qo” and ”b” increased with temperature where ”Qo” increased from 31.18 to 33.06 to 33.15 mg g-1 for Pb (II) , from 25 to 28.32 to 29.04 mg g-1 For Cu (II) and from 5.6 to 6.09 to 10.93 mg g-1 for Co (II) by increasing temperature 289,318 and 388K.
Also Freundlich constants ”1/n” and ”Kf” where ”Kf” increased from 1.91 to 2.1 to 2.33 mg g-1 for Pb (II) , from 1.08 to 1.09 to 1.094 mg g-1 for Cu (II) and from 1.31 to 1.4 to 2.12 mg g-1 for Co(II) by increasing temperature 289,318 and 388K. This increase in sorption capacity with temperature suggested that the active surfaces available for sorption have increased with temperature. Also the numerical values of ”1/n” for the studied metal ions were found to be less than the one ”1/n>1”, It implies heterogeneous surface structure.
The Freundlich regression for Pb (II), Cu (II) and Co (II) sorption where: R2 = 0.97, 0.97 and 0.96 for Pb (II) at 289, 318 and 338 K respectively, R2 = 0.99, 0.99 and 0.99 for Cu (II) at 289, 318 and 338 K respectively, R2 = 0.98741, 0.99303 and 0.99814 for Cu (II) at 289, 318 and 338 K respectively, and the Langmuir regression for Pb (II), Cu (II) and Co (II) sorption where: R2 = 0.92, 0.89 and 0.85for Pb (II) at 289, 318 and 338 K respectively, R2 = 0.99234, 0.9811 and 0.97762 for Cu (II) at 289, 318 and 338 K respectively, R2 = 0.98, 0.98 and 0.96 for Co (II) at 289, 318 and 338 K respectively. Therefore in this study the rice straw is heterogeneous surface structure and this adsorption process favorable to Freundlich adsorption isotherm, also the results confirm occurrence multilayer adsorption on the surface.
Thermodynamic parameters including the enthalpy change ΔHo, kJ mol-1, the Gibbs free energy change (ΔG°, kJ mol-1), and the entropy change ΔSo, J.mol-1.K-1 where the magnitude of ”ΔGo” decreased with rising the temperature, indicating that the adsorption is favorable at high temperatures, also the values of ΔHo were positive, indicating that the adsorption process is endothermic, and the positive values of ”ΔSo” reflect the affinity Pb (II), Cu (II) and Co (II) for adsorbent used. In addition, positive values of ”ΔSo” show the increasing randomness at the solid/liquid interface during the adsorption.from (D-R) adsorption model the adsorption energies were ”E > 8” at all studied temperatures and this result confirmed that the adsorption of the studied metal ions Pb (II), Cu (II) and Co (II) on rice straw is favorable for the Freundlich isotherm more than the other adsorption modules.
5. Sorption Kinetic Models:
The results were fitted by linear regression of two kinetic models, namely: Reaction-based Models, and Diffusion-based Models.
Reaction-based Models: it containing pseudo-first order, pseudo-second order where the results more compatible with pseudo second order its due to the low value of ”R2” and the large difference between the calculated and experimental values of the adsorption capacity of Pb (II), Cu (II) and Co (II) on rice straw at pseudo-first order, also the ”R2” values are more than 0.99 for different temperatures. Moreover, the variations between the calculated ”qe” and experimental ”qe” were minimal for the pseudo-second-order model its indicated to the adsorption depends on both the concentration of metal ions and the adsorbent dose also its referring to presence adsorption layers depends on functional groups. Pseudo-second-order constant ”k2” increased with temperature increasing so that the process is endothermic. The half-adsorption time ”t1/2” was decreased when increasing the reaction temperature. It was be found 9.53, 8.12, 4.55 min. for pb (II) and 30.91, 22.41, 20.44 min. for Cu (II) and 23.75, 22.38 ,19.63 min. for Co (II) at 289,318 and 388 K respectively.
5.Diffusion-based Models: it contains intra particle diffusion to explain the adsorption mechanism where the results show that the plots not pass through the origin and exhibited three regions with three diffusion rates constant. the first, sharper region is the instantaneous adsorption or external surface adsorption which the Pb (II), Cu (II) and Co (II) metal ions diffused quickly with high diffusion rate constant at the beginning of the adsorption process. The second region is the gradual adsorption stage where the intraparticle diffusion is the rate limiting and the diffusion rate becomes slow. The third region exists, which is the final equilibrium state where the intraparticle diffusion starts to slow down due to the extremely low adsorbate concentrations left in the solutions.6. Separation by column chromatography
from column results, it is found that the selectivity of the ions towards rice straw is in the order: Pb (II) > Cu (II) > Co (II)
And observed that when the flow rate increased ”Q0.5” break-through mg g-1 increasing inasmuch increasing interference ions. where Pb (II) break-through ”Q0.5” increasing from 32 to 74 to 140 mg g-1 for 0.5, 3.5, 5 ml min-1. But whenever the flow rate increased affected negatively by percent removal so the minimum flow rate used for increasing percent removal.
The obtained results recommended that rice straw is a good adsorbent to adsorb Pb (II), Cu (II) and Co (II) but it Features with Pb (II)selectivity so when use the rice straw as adsorbent to Cu (II) and Co (II) must make sure absence lead into solution. Also results recommended that when flow rate increase heavy metal removal decreased as well as quality of obtaining water.