Remediation of Uranium-contaminated Groundwater by Sorption onto Hydroxyapatite Derived from Catfish Bones

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1 Water Air Soil Pollut (2013) 224:1429 DOI /s Remediation of Uranium-contaminated Groundwater by Sorption onto Hydroxyapatite Derived from Catfish Bones S. A. Chattanathan & T. P. Clement & S. R. Kanel & M. O. Barnett & N. Chatakondi Received: 19 June 2012 / Accepted: 18 December 2012 / Published online: 23 January 2013 # Springer Science+Business Media Dordrecht 2013 Abstract Hydroxyapatite (HA) was prepared from catfish bones, identified as catfish HA (CFHA), using mechanical and chemical treatment methods. CFHA was characterized by x-ray diffraction (XRD) and scanning electron microscope (SEM) techniques to confirm the presence of HA. The ability of CFHA to remove uranium (U(VI)) from aqueous phase was investigated using both batch and column experiments. Adsorption experiments in batch experiments were carried by varying ph, preparation temperature, and particle size. The data shows that the maximum adsorption occurred between ph5.5 and 7. The adsorption of U(VI) on CFHA was greater at 300 C than at 100 C. Batch data shows that the smallest particles, with maximum surface area, exhibited significant U (VI) removal efficiency. Column experiments were conducted using the smallest CFHA particles at different flow rates and breakthrough profiles were S. A. Chattanathan : T. P. Clement : S. R. Kanel : M. O. Barnett Department of Civil and Environmental Engineering, Auburn University, Auburn, AL 36849, USA S. R. Kanel (*) Air Force Institute of Technology, Wright Patterson AFB, OH , USA sushil.kanel.ctr@afit.edu N. Chatakondi USDA ARS Catfish Genetics Research Unit, Mississippi State University, Mississippi State, MS 39762, USA obtained. The scalability of the U(VI) removal process was tested by comparing the performances of columns packed with different CFHA. The results indicated that the reaction scales to the mass concentration of the reactants (CFHA and U(VI)). We also found that at ph7, the CFHA packed in the column has the potential to remove about 3.9 mg of U(VI) per gram. Our study shows that CFHA may be used in permeable reactive barriers for remediating U(VI)-contaminated groundwater plumes. Keywords U(VI). Hydroxyapatite. Permeable reactive barrier. Groundwater remediation 1 Introduction The development of nuclear technologies has led to the increase of nuclear wastes containing radionuclides being released into the environment. Pollution caused by radionuclides is a serious problem throughout the world (Das 2012). In the United States, groundwater aquifers in several Department of Energy (DOE) sites have been severely contaminated with radionuclides. Due to its chemical and radiological toxicity, migration of U(VI) from these sites can pose considerable health and environmental hazard. The United States Environmental Protection Agency (USEPA) has set the maximum contaminant level (MCL) for U(VI) in drinking water as 30 μg/l since December 2003 (Han et al. 2007).

2 1429, Page 2 of 9 Water Air Soil Pollut (2013) 224:1429 Permeable reactive barrier (PRB) is one of the most promising technologies that has the potential to treat subsurface U(VI) plumes (Fuller et al. 2003). Various types of sorbent materials have been used within the PRB to remove U(VI) from groundwater. These materials include reactive sorption media such as activated carbon, zero-valent iron (ZVI), zeolites, phosphate rocks, and hydroxyapatites (HAs) (Han et al. 2007; Phillips et al. 2008; Raicevic et al. 2006b; Saxena et al. 2006). Among these alternatives, HA has received considerable attention in recent years for treating metal-contaminated groundwater (Thakur et al. 2005). This is because HA can react with heavy metals and radionuclides forming minerals that are stable across a wide range of geological conditions (Nriagu 1974; Raicevic et al. 2006a). For example, the solubility product of unreacted apatite is K sp =10 20 (Raicevic et al. 2006a), whereas reacted U (VI)-apatite minerals such as autonite have a very low K sp value of (Raicevic et al. 2006a) and chernikovite around (Raicevic et al. 2006b). It has also been observed that sedimentary and/or biogenic apatites deposited by seawater can sequester metals and radionuclides into their apatite structure for many years (Wright et al. 1987). These sequestered metals are difficult to remove via desorption, leaching, or ion exchange processes, even under extreme diagenetic conditions such as changes in pore water chemistry, ph, temperature variations (of more than 500 C), and/or under tectonic disruptions (Wright 1990; Wright et al. 1987). Researchers have used both natural and synthetic HA to remove U(VI) from contaminated water. Natural HA can be derived from bones and phosphate-rich rocks. Synthetic HA can be prepared by chemically reacting a hydroxide source such as calcium hydroxide and phosphoric acid (Bouyer et al. 2000). The efficiency of synthetic HA for treating U(VI) has been studied previously (Arey et al. 1999; Fuller et al. 2002; Krestou et al. 2004; Simon et al. 2008; Wellman et al. 2008). Cheaper alternative to HA is highly desirable for the remediation of actinides as synthetic HA is expensive while practically applying for large-scale remediation. Thomson et al. (2003) compared the efficiencies of different sorbents (synthetic apatites, tricalcium phosphate bones char, and activated magnetite) in batch for removing dissolved metals and radionuclides (As, Am, Pu, Se, Tc, and U) (Thomson et al. 2003). However, the sorption capacity estimated from batch experiments might not be applicable for the PRB system where the contact time might not be sufficient to reach equilibrium. Hence, the efficiency of commercially viable natural HA should be studied through column experiments. In this study, we provide feasibility data for using natural HA obtained from farmed catfish (a cross between the channel catfish, Ictalurus punctatus (female) blue catfish, Ictalurus furcatus (male)) bones to treat uranium plumes. Catfish farming is one of the major agricultural industries in the southeastern regions of the United States, and reusing the fish bones from the industry offers both economic and environmental benefits (Chatakondi et al. 2005). The goal of this research is to study the feasibility of using HA derived from these catfish bones (identified as catfish HA (CFHA)) to remove U(VI) from contaminated groundwater. The specific objectives are to: (1) prepare and characterize the HA materials derived from the catfish bones, (2) conduct batch experiments to study the influence of various chemical conditions (ph, preparation temperature, and initial concentrations) on CFHA and U(VI) interaction, and (3) perform column experiments to investigate U(VI) removal by CFHA under dynamic flowing conditions. 2 Material and Methods 2.1 Materials All the chemicals used in the experiments were of reagent grade. Several chemicals including sodium nitrate, sodium bicarbonate, sodium hydroxide and nitric acid were purchased from Fisher Scientific (Fairlawn, NJ, USA). Commercial HA (CHA) was purchased from Sigma-Aldrich (St. Louis, MO, USA). American Chemical Society (ACS) reagent-grade chemicals such as hydrogen peroxide were purchased from Sigma-Aldrich (St. Louis, MO, USA). All reagents were used as received without further alteration. Ultrapure water (Millipore, 18.2 MΩ cm) was used to prepare all solutions. The acids were of trace-metal grade. The U (VI) solution was prepared from plasma-grade U(VI) standard made using depleted U(VI). Catfish bones were collected from a catfish processing plant near Selma, AL, USA and were boiled for about an hour in a pressure cooker. The cooked bones were washed in a flowing stream of water to remove flesh and fat materials. The remaining bones were soaked in 30 % hydrogen peroxide for a day to

3 Water Air Soil Pollut (2013) 224:1429 Page 3 of 9, 1429 remove all residual organic matter. The peroxidetreated bones were air dried for 2 days and then crushed into smaller pieces and heated in an oven for 3 days at 100 C unless otherwise specified. In order to investigate the effects of heat treatment, two types of fish bones were prepared by heating the bones at 100 C and 300 C. Also, to study the size effects, the fish bones prepared at 100 C were mechanically crushed and sieved to yield samples having large (>2,000 μm), medium (300 2,000 μm), and small (<300 μm) particle sizes. 2.2 Batch Experiments Batch adsorption experiments were conducted at room temperature (22 C) in 50-mL polycarbonate centrifuge tubes as reported previously (Loganathan et al. 2009). All of the experiments were completed in duplicates. The samples were prepared by mixing appropriate amount of HA, ionic strength adjuster (0.01 M NaNO 3 ), NaHCO 3 (0.01 M), and acidified U(VI) stock solution [UO 2 (NO 3 ) 2 ] in deionized water. The vials were capped quickly (to minimize CO 2 exchange) and were shaken for about 72 h (from the kinetic data, this time was found to be adequate for the attainment of equilibrium). The ph values were recorded before and after the reaction. The reacted samples were opened, and an aliquot of the supernatant was withdrawn and immediately filtered with a 0.45-μm syringe filter. The filtrate was used to measure the aqueous U(VI) concentrations. The U(VI) concentrations in our study were maintained at 1 mg/ L for both batch and column experiments. The batch experiments were conducted at both ph7 and 8.5, and the ph of the solution was adjusted using 1 M NaOH or HNO 3. The equilibrium aqueous U(VI) concentrations in both kinetic and isotherm experiments were M, which is within the range of U(VI) concentrations used by others (Cheng et al. 2006). 2.3 Column Experiments About 1.5 g of CFHA and 7.5 g of Ottawa sand ( μm) (unless otherwise mentioned) were mixed thoroughly and was dry packed into a glass column (length 10 cm and diameter 1 cm). The column was tapped at regular intervals while packing to ensure uniformity. The column was run in a vertical mode with the feed solution being injected into the bottom of the column directed upwards and the effluent was sampled from the top, either manually or by using a fraction collector. A large volume of U(VI) feed solution, with a known U(IV) concentration, was prepared. A sufficient amount of ionic strength adjuster and buffer solutions was added to the stock solution. The final ph was adjusted to the desired value and the solution was pumped at different rates into the column using an highperformance liquid chromatography (HPLC) pump. Glass wool was placed at the end of the column to prevent washout of the solid material as reported previously (Kanel and Al-Abed 2011). When manual sampling was employed, the U(VI) solution from the outlet was collected at regular time intervals in 50-mL polycarbonate centrifuge tubes. After each experiment, the column was emptied and washed with concentrated HNO 3 and water. The experiments were repeated at least twice to verify reproducibility. 2.4 Analysis and Characterizations The U(VI) concentration was measured using a kinetic phosphorescence analyzer (KPA-11, Chemchek Instruments, Richland, WA, USA). The filtered samples were acidified to lower the ph value close to 1.5. The uncertainty in detection limit of the U(VI) analysis was ±3 % (Cheng et al. 2004). The total calcium concentration was analyzed using a flame atomic absorption spectrophotometer (AAS 220FS, Varian, Palo Alto, CA, USA). Samples of CHA and CHFA were prepared by dropping a small prepared sample on a mica substrate and air drying it overnight. These samples were then coated with a thin layer of gold (~10 nm) and imaged using a JEOL JSM-7000F field emission scanning electron microscope (SEM) equipped with an energy dispersive X-ray analyzer (JEOL USA). X-ray diffraction (XRD) data were collected using a Rigaku Mini- Flex diffractometer using Cu Kα radiation. 3 Results and Discussion 3.1 Solid-Phase Characterizations of HA The SEM images (Fig. 1a) and CFHA (Fig. 1b) show that the average sizes of CHA and CFHA particles are about 100 nm and 50 nm, respectively. The data also shows that the XRD pattern of CFHA matches (the

4 1429, Page 4 of 9 Water Air Soil Pollut (2013) 224:1429 Fig. 1 SEM image of a commercial hydroxyapatite, b fish bones, and c comparison of XRD data of catfish bones and commercial hydroxapatite figure on the top) well with the XRD pattern of CHA (bottom figure), confirming that the material derived from catfish bones was indeed HA (Fig. 1c). particles are more efficient in removing U(VI) than larger particles. For particle size less than 300 μm, the percentage sorption of U(VI) were 40, 61, 75, 3.2 Influence of Particle Size The CFHA prepared at 100 C was crushed in a blender to prepare samples with different particle sizes. Particles of three different sizes (>2,000 μm, between 2,000 μm and 300 μm, and <300 μm) were obtained by sieving the crushed CFHA. A digital picture of these samples is shown in Fig. 3 (inset). Surface area plays an important role in controlling the sorption mechanism. When the particles are crushed into smaller particles, a new area is created, which results in an increase in net surface area. Since U(VI) interaction with HA is a surface reaction, increase in surface area should increase the rate of removal. As expected, smaller CFHA Fig. 2 Effects of CFHA particle size on the kinetics of uranium removal process. Experimental conditions: 1 mg/l of initial U (VI), 0.5 g/l of CFHA, 0.01 M NaNO 3, 0.01 M NaHCO 3,pH7, and room temperature

5 Water Air Soil Pollut (2013) 224:1429 Page 5 of 9, 1429 and 87 % in 1, 3, 12, and 72 h, respectively (Fig. 2). While for particle sizes greater than 2,000 μm and those between 2,000 μm and 300 μm, the percentage U(VI) sorption at the end of 72 h were only 60 % and 55 %, respectively. Hence, smaller CFHA particles with size less than 300 μm were used in all subsequent experiments. 3.3 Influence of CFHA Preparation Temperature CFHA calcined at 100 C and 300 C for 24 h were prepared. U(VI) sorption experiments with CFHA were performed to study the effect of surface area changes resulting from heating (Fig. 3). Particle size of less than 300 μm was chosen as higher particle size had less sorption capacity. The results show that increasing the preparation temperature slightly decreased the sorption of the U(VI) onto CFHA (Fig. 3). Similar observations were reported by Ozawa and Suzuku (2002) in which three preparation temperatures, 600 C, 800 C, and 1,000 C, were used to prepare fish bones. They found that the surface area of the particles decreased with increases in the oven temperature. In their study, the preparation temperature of 600 C yielded material with a maximum surface area of 10.5 m 2 /g, while 800 C and 1,000 C had surface areas of 4 and 1.6 m 2 /g, respectively. Similarly, Ozawa et al. (2003) demonstrated that fishbone apatite prepared at 600 C was more effective in removing chromium than those prepared at 900 C. Therefore, CFHA prepared at 100 C was used in all subsequent experiments. 3.4 Influence of ph The effect of ph (ranging from 2 to 9) on U(VI) sorption onto CHA and CFHA are presented in Fig. 4. For CHA, the extent of U(VI) removal was mg/g in the ph range 3 5 and it decreased sharply at ph below 4 and above 9. A similar trend was observed for CFHA. Maximum U(VI) adsorption occurred within the ph range of 5 to 8.5. The phdependent sorption effect is due to the ionization of both the adsorbate and the adsorbent causing repulsion at the surface and decreasing the net U(VI) adsorption. The point of zero charge of HA is negative for ph values higher than 7.7 (Krestou et al. 2004). This point of zero charge will be shifted to 7.13 when the solution is in equilibrium with atmospheric carbon dioxide (Wu et al. 1991). Below ph7.7, HA remains positively charged and it will be negatively charged above ph 7.7. When the ph is above 7.13, HA surface becomes negatively charged and as the solution ph increases, the U(VI) species becomes negatively charged [UO 2 (CO 3 ) 2 2 ] by equilibrating with atmospheric CO 2 present in the vial head space (Krestou et al. 2004). When the ph is above 9, UO 2 (CO 3 ) is the predominant U(VI) species and since the isoelectric point of HA is near ph=7.7, the HA product surface also becomes negative (Korte and Fernando 1991) and hence, there will be an electrostatic repulsion. Between ph3.5 and 5.5 U(VI) exist in the form of uranyl ion that are repelled by the positive surface charge of HA. Between ph5.5 and 7, the uranyl ion is replaced by positive or neutral U(VI) mononuclear and polynuclear hydroxocomplexes ((UO 2 ) 3 (OH) 5 +,UO 2 (OH) 2 0. CHA CFHA Fig. 3 Effects of CFHA preparation temperature on the kinetics of uranium removal process (experimental conditions: 1 mg/l of initial U(VI), 0.5 g/l of CFH A, 0.01 M NaNO 3, 0.01 M NaHCO 3, ph7, and room temperature). Inset Image of fish bone hydroxyapatite with different particle sizes Fig. 4 Influence of ph on sorption of U(VI) onto commercial hydroxyapatite and fish bones (experimental conditions: 1 mg/l of initial U(VI), 0.5 g/l of HA, 0.01 M NaNO 3,0.01M NaHCO 3, and ph ~2 10 at ~295 K)

6 1429, Page 6 of 9 Water Air Soil Pollut (2013) 224:1429 The negative sites on HA attract the positive-charged U(VI) species. Therefore, speciation can greatly impact U(VI) sorption Comparison of CFHA and CHA Sorption Kinetics at Two Different ph Kinetic experiments were conducted to compare the removal efficiency of U(VI) on CHA and CFHA at ph values of 7 and 8.5 (Fig. 5) and the curve fitting has been done using power trend line. The results indicate that the treatment efficiency is considerably higher at neutral ph. The data shows that at ph8.5, about 60 % of dissolved U(VI) was removed, whereas at neutral ph, over 90 % of U (VI) was removed in 72 h (Fig. 5). The removal efficiency of CHA at ph8.5 was about 80 % in 72 h, which was slightly higher than CFHA removal efficiency at a similar ph. The data also shows that the reaction reaches equilibrium within 72 h. A similar observation was also made in all other kinetic experiments and hence, all subsequent batch experiments were designed to run for 72 h (or 3 days). in the batch system was 0.5 g/l and the ph was adjusted to 7. The batch reactors were kept on a shaker and allowed to equibriate for 3 days. From the intial and final concentration measurements, the amount of U(VI) partioned to CFHA was calculated and these solid-phase concentrations are plotted against the final aqueous-phase equilibrium concentrations (Fig. 6a). The isotherm data showed that the adsorption mechanism follows a linear trend at low liquid concentration values (until about 1 mg/ L). Beyond 1 mg/l, the removal process appeared to reach a saturation level and the data indicated a maximum capacity (saturation level) of about 18 mg of unit per gram of CFHA at ph7. Two additional isotherm experiments were also completed to evaluate the sensitivity of the isotherm data to ph changes. Figure 6b shows the isotherm data for ph8.5 and 9. At higher ph values, the isotherm is 3.5 Adsorption Isotherms Adsorption isotherm experiments were performed by reacting a fixed amount of CFHA ( g) with U(VI) solutions with intial concentrations varying from 1 to 10 mg/l. The solid solution ratio Fig. 5 Comparison of uranium removal kinetics using CFHA and CHA. Experimental conditions: 1 mg/l of initial U(VI), 0.5 g/l of CFHA, 0.01 M NaNO 3, 0.01 M NaHCO 3, ph7 and 8.5, and room temperature Fig. 6 a Isotherm data for fish bone hydroxyapatite at ph7. Experimental conditions: 1 to 10 mg/l of initial U(VI), 0.5 g/l of CFHA, 0.01 M NaNO 3, 0.01 M NaHCO 3, and room temperature. b Isotherm data for fish bone hydroxyapatite at ph8.5 and 9. Experimental conditions: 1 to 30 mg/l of initial U(VI), 0.5 g/ L of CFHA, 0.01 M NaNO 3, 0.01 M NaHCO 3, and room temperature

7 Water Air Soil Pollut (2013) 224:1429 Page 7 of 9, 1429 linear until an equlibrium U(VI) concentration value of 8 mg/l; beyond this limit, the system appears to reach a saturation level. The data indicates that the maximum capacity of 12 mg of U(VI) per gram of CFHA at the ph value of 8.5 and a maximum capacity value of about 5 mg of U(VI) per gram of CFHA at ph9. The results are consistent with ph edge data (Fig. 4) that indicates a sharp drop in sorption between the ph values 8.5 and 9.5. Similar results were reported while studying U(VI) adsorption using CHA. However, the maxium U(VI) adsorption reported was about mg U(VI)/g HA (Jeanjean et al. 1995). This is much higher compared to fish bones that may be due to the fact that it is pure chemical HA. Phosphate rock has also been used to remove U(VI) ion and the maximum adsorption capacity was reported between 9.92 and mg U (VI)/phosphate rock depending on initial concentration of U(V) ion (Saxena et al. 2006) (Table 1). 3.6 Influence of Flow Rate on Sorption of U(VI) in Column Packed with CFHA Column experiments were conducted to investigate U(VI) removal efficiency at different flow rates (2, 5 and 10 mlmin 1 ). All the columns were filled with a mixture of 1.5 g of CFHA (size less than 300 μm) and 7.5 g of sand. The influent U(VI) concentration was 1 mg/l and the initial ph value was adjusted to 8.5. U(VI) feed solution was supplied at the following three distinct flow rates: 2 mlmin 1, 5 mlmin 1, and 10 mlmin 1. The breakthrough data from all three columns along with a control data (column with clean sand) are shown in Fig. 7. The results show that at high flow rates (of 10 ml/min), the transport is influenced by kinetics. On the other hand, the effluent breakthrough data from lower flow rates (of 2 and 5 ml/min) are almost the same and the breakthrough pattern is relatively sharp. 3.7 Testing the Scalability of U(VI) Removal Process We hypothesized that under similar transport conditions, adsorption of U(VI) should exclusively depend on the amount of sorbent (CFHA) in the system and hence, the performance of the column can be predicted based on the mass of the sorbent. In order to test this scaling hypothesis, we designed a column experiment with a flow rate of 5 ml/min, doubled the amount of CFHA in the system to 3 g, and simultaneously doubled the concentration of U(VI) in the influent solution. If our scaling hypothesis is true, then the effluent data from this experiment should be similar to the 5 ml/min data presented in Fig. 7. Figure 8 compares data from the two-column experiments. The results show that both datasets are almost identical, thus proving the adsorption of U(VI) directly scales to the amount of CFHA used in the system. The data also indicates that it took about 2,400 pore volumes to fully breakthrough, when the effluent concentration was equal to the influent concentration. By integrating the area under the breakthrough curve by using the trapezoidal rule, we estimated that about 3.9 mg of U (VI) was removed by the column containing 1.5 g of CFHA. This implies the fish bone material had a treatment capacity of about 2.6 mg U(VI)/g CFHA at ph value of 8.5, under dynamic transport conditions. 3.8 Column Performance at Neutral ph Batch experiment data has already indicated that the removal capacity of the CFHA is higher at ph 7 when compared to its capacity at ph 8.5. We completed a column experiment at ph 7 to quantify the ability of CFHA for treating dissolved U(VI) at neutral ph. In order to minimize the kinetic effect and allow high residence time, a lower flow rate was chosen (1 ml/ min). Figure 9 provides the breakthrough data obtained from a column containing 1.5 g of CFHA treating 1 mg/ L of U(VI)-contaminated water. The data show that it Table 1 A comparison of adsorption capacity of hydroxyapatite to uranium ion Adsorbent Adsorption capacity mg of U(VI)/g adsorbent Experiment Reference Commercial HA Batch Jeanjean et al. (1995) Rock phosphate 9.92 to Batch Saxena et al. (2006) Catfish bone HA 12 (ph8.5) and 5 (ph9) Batch Our study Catfish bone HA 3.9 Column Our study

8 1429, Page 8 of 9 Water Air Soil Pollut (2013) 224:1429 Fig. 7 Influence of flow rates (2, 5, and 10 ml/min) on U(VI) sorption onto sand and CFHA (or catfish apatite (CFA)) mixed sand packed column. Experimental condition: influent U(VI) concentration: 1 mg/l, CFHA: 1.5 g, sand: 7.5 g, 0.01 M NaNO 3, 0.01 M NaHCO 3, ph 8.5, and room temperature took about 2,500 pore volumes to fully saturate the column (when the effluent concentration was equal to the influent concentration). By integrating the area under the breakthrough curve, we estimated that the fish bone material had a treatment capacity of 3.9 mg U(VI)/g CFHA at ph7. This is approximately twice the value of the capacity observed at ph 8.5. Mibus and Brendler (2006) conducted column experiments with CHA and U(VI) stock solution. The column results indicated a retardation factor varying in the range of 27 to 45 for soils containing 0.1 % of pure HA at a solution ph of 7.83 (Mibus and Brendler 2006). Our column experiment was completed with 16 % CFHA and the computed value of retardation factor was 2,250, which is comparable to the value of 4,300, estimated by directly scaling Mibus and Brendler's data. This could be Fig. 9 Breakthrough data at ph7. Experimental condition: influent U(VI) concentration 1 mg/l, CFHA 1.5 g, 0.01 M NaNO 3, 0.01 M NaHCO 3, ph7, flow rate 1 ml/min, and room temperature attributed to the usage of pure HA, which, indeed, is expected to perform better than natural fish bones. 4 Conclusions In the literature, there are only a few remediation alternatives available for treating U(VI)-contaminated groundwater systems. Among available options, the use of natural HA in a PRB appears to be a promising method. In this study, we investigated the feasibility of using natural HA derived from catfish bones as a sorbent material in a PRB to treat uranium plumes. The finding of this study shows that the heat-treated fish bones derived from catfish wastes is a promising reactive barrier material for treating U(VI)-contaminated groundwater plumes. However, further pilot studies are needed to scale up this technology to treat large groundwater plumes in fieldscale systems. Furthermore, physicochemical interferences due to variations in anion, cation, and organic matter naturally present in groundwater should also be evaluated. Acknowledgments This work was supported by the US Department of Energy Grant No. DE-FG02-06ER64213 at Auburn University. References Fig. 8 Scalability of observed breakthrough data at ph8.5. Experimental condition: influent U(VI) concentration 1 and 2 mg/l, CFHA 1.5 and 3 g, 0.01 M NaNO 3, 0.01 M NaHCO 3, ph8.5, flow rate 5 ml/min, and room temperature Arey, J., Seaman, J., & Bertsch, P. (1999). Immobilization of U (VI) in contaminated sediments by hydroxyapatite addition. Environmental Science and Technology, 33, Bouyer, E., Gitzhofer, F., & Boulos, M. (2000). Morphological study of hydroxyapatite nanocrystal suspension. Journal of Materials Science. Materials in Medicine, 11,

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