الفهرس 
UraniumOnly 14 pages are availabe for public view
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Abstract
This investigation was conducted to study the effect of using the natural modified clay minerals deposits (smectite and kaolinite) as low-cost materials to remove and/ or reduce uranium from contaminated sediments and/ or soil at Wadi Um Hamad area - southwest of Sinai.
Factors affecting adsorption and desorption of uranium were studied such as (different pH, temperatures, quantities of adsorbents, contact time and different uranium initial concentrations).
An incubation experiment was performed using different concentrations of clay minerals which are 1% and 2.5% of both modified mineral. After incubation for a period of 28 days, uranium was extracted with DTPA solution. Different forms of uranium were extracted before and after the experiment.
Pots experiment was carried out under greenhouse conditions to study the ability of sunflower plants to reduce uranium pollution in the sandy loam soil of Um Hamad region in the greenhouse of Nuclear Materials Authority station. Each pot (capacity 4 kilos) was planted by four seeds. The plants were tested after various growing periods to investigate the phytoremediation efficiency after 3, 6 and 9 weeks. The experiment was designed in a completely randomized design with three replicates for each treatment as follows:
- 4 Kgs washed sand U0: Zero U approximately.
- 3 Kgs washed sand + 1 Kg Um Hamad soil U1: 65 mg.kg U ˶.
- 2 Kgs washed sand + 2 Kgs Um Hamad soil U2: 130 mg.kg U ˶.
- 1 Kg washed sand + 3 Kgs Um Hamad soil U3: 195 mg.kg U ˶.
- 4 Kgs Um Hamad soil U4: 260 mg.kg U ˶.
The obtained results are summarized in the following:
- The results of the mineralogical analysis by XRD of the chemically modified smectite and kaolinite clays showed the destruction of their characteristic diffraction peaks by both treatments (acidification and calcination) with hydrochloric acid has broken its lattice structure.
- The study showed that the efficiency of uranium adsorption was maximum at pH 5 and 6 for smectite and kaolinite, respectively.
- Contact time affected the uranium adsorption by both modified clay minerals (smectite and kaolinite) by three stages. The first stage of U adsorption increased rapidly in the first 45 min almost for smectite and kaolinite then it slowed down from 45 to 60 min. After 60 min equilibrium stage was attained and uranium adsorption became almost constant, till the end of experiment time. It is worth to mention that the adsorption capacities of the two minerals after 90 min are almost similar.
- Adsorption of uranium by calcinated smectite increased by increasing U concentration in solution, and maxiumum adsorption efficiency (90%) was attained to 600 mg/l. This means that smectite mineral can adsorbe U more than the concentration used in this experiement. In other was this accertain the superiority of smectite in another kaolinite in removing and /or decreasing U pollution. For kaolinite different result was obtained, as maxiumum U adsorption efficiency was near 90%, after which it decreased. At equilibrium, adsorbed U by smectite and kaolinite was 22.7 and 16.2 mg.g, respectively.
- The results indicated that the effect of adsorption temperature on the uranium adsorption efficiency is constant with increasing temperature.
- U removed from both minerals general increased by increase weight of used clay minerals. However at any specific weight, uranium removed from smectite is much higher than that removed from kaolinite special at lower doses. Both mineral behaved similary at higher doses.
- The obtained data were fitted to the Langmuir adsorption equation. The maximum adsorption value obtained in accordance to Langmuir isotherm was 27.4 mg/g for smectite and 18.68 mg/g for kaolinite. The values of correlation coefficient (R2) were 0.99 and 0.98 for smectite and kaolinite, respectively.
- The kinetics studies showed the uranium adsorption on smectite and kaolinite expressed well by pseudo-second order kinetics model. One mole from sodium acetate solution is the best eluent for uranium desorption from loaded adsorbent. The obtained results of recovery percentage (desorbed U %) from loaded adsorbent as affected by 1.0 M CH3COONa were 86% and 80% for smectite and kaolinite, respectively. The non extractable U was considered retained and represents 14 and 20% from the adsorbed U.
- The concentration of uranium extracted with DTPA decreased with the use of a quantity of clay at concentrations of 1.0 and 2.5%. The results obtained using DTPA can be arranged as follows: smectite 2.5%> smectite 1.0%> Kaolinite 2.5%> Kaolinite 1. 0%, respectively.
- Results of sequential extraction of uranium (from Um Hamad deposits) is arranged as follows in decreasing order: residue (RES) > organically bound (ORG) > carbonate bound (CAB) ≈ bounded to oxides (OXD) > interchangeable (EXC), respectively.
- Dry weight of plant parts (shoots or roots) increased by increasing ratio of soil (Um Hamad) to pure sand: In other words (U4) represent 4 kgs of Um Hamad soil in the pot while (U0) contain 4 kgs of pure sand/ pot. This increase in the dry weight of plant parts is due to quantity of the sand loam soil of Um Hamad while U0 the pot contains 4 kgs of pure sand. All pot received no nutrient solution. For all tratment U accumulated more in the roots than the shoots of sunflower in this experiement.
Finally, it could be concluded that the application of the modified clay minerals- both smectite and kaolinite- behaved similary concerning U adsorption. The increase noticed in adsorption capacities was due to increase in surface area of both minerals due to their breakdown by acid treatment. The uranium adsorption follow Langmuir isotherm with a capacity 18.68 mg/g for modified kaolinite and 27.4 mg/g for modified smectite. However, the adsorbed U amounts were the adsorbed U as 86 and 80 %, for smectite and kaolinite, respectively. So, the retained U amounts represented 14 and 20%, respectively. The kinetics studies of uranium adsorption on smectite and kaolinite follows pseudo-second order model. The optimum conditions for uranium adsorption by the used clay minerals seemed economic process. The adsorption of uranium (VI) onto modified clays was more favorable at higher initial U concentrations than at lower concentrations. Kaolinite and smectite clays caused a considerable decrease in Exch. fraction (the most mobile fraction) of uranium in the studied soil sample while CAB- U, OXD- U, ORG- U and RES fractions seemed to be not affected with the tested clay minerals (kaolinite and smectite).
Application of phyto-remediation to reduce uranium in soil using sunflower plants (Helianthus annuus L.) was useful and effective. Uranium accumulated in roots more than shoots.