Radium-226 Removal from Simulated Produced ... - ACS Publications

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Radium-226 Removal from Simulated Produced Water Using Natural Zeolite and Ion-Exchange Resin Wen Fan, Blake Liberati, Meagan Novak, Mira Cooper, Natalie Kruse, David Young, and Jason P Trembly Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03230 • Publication Date (Web): 09 Nov 2016 Downloaded from http://pubs.acs.org on November 15, 2016

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Industrial & Engineering Chemistry Research

Radium-226 Removal from Simulated Produced Water Using Natural Zeolite and Ion-Exchange Resin Wen Fan1, Blake Liberati1, Meagan Novak1, Mira Cooper1, Natalie Kruse2, David Young3, and Jason Trembly1,* 1. Institute for Sustainable Energy and the Environment, Russ College of Engineering and Technology, Ohio University, Athens, OH, 45701. 2. Environmental Studies Program, Voinovich School of Leadership and Public Affairs, Ohio University, Athens, OH, 45701. 3. Institute for Corrosion & Multiphase Technology, Department of Chemical & Biomolecular Engineering, Ohio University, Athens, OH, 45701. KEYWORDS: clinoptilolite, radium, produced water, ion-exchange, cation selectivities ABSTRACT: Large volumes of produced water with high dissolved solids content are generated by the oil and gas industry. The presence of naturally occurring radioactive materials (NORM), such as radium, in this flowback water adds to costs associated with its handling, treatment, and disposal. In this research, clinoptilolite was tested for radium removal and its performance compared to an ion-exchange resin. The natural zeolite showed excellent stability in high chloride environments; its capacity and selectivity for radium outperformed the ionexchange resin.

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INTRODUCTION During oil and gas production large volumes of produced water are generated that contain many constituents that are harmful to humans, including naturally occurring radioactive materials (NORM), such as radium, and high levels of dissolved inorganics 1. Due to its prevalence in oil/gas produced water, NORM elements are deposited in scale and sludges contaminating tubulars, equipment, and components. Moreover, NORM creates additional produced water treatment and reuse complexities caused by process and product contamination concerns. To effectively mitigate NORM process/product contamination, a unit operation allowing for selective NORM removal before further produced water handling is needed. In this process, solids filtration (such as a sock filter) would be first implemented to capture suspended solids, followed by a selective NORM removal step to prepare the produced water for further processing. Natural zeolites are aluminosilicate minerals which have long been used for treating water containing radioactive effluents. Clinoptilolite (Clino), a natural microporous zeolite, is especially of interest because of its high cation-exchange capacities and high selectivities for Cs+, Ba2+, and Sr2+ 2. Clino has been used to treat drinking water, mine water 3, 4, produced water from coalbed natural gas operations 5, and wastewater associated with the nuclear energy industry 2. Interestingly, there has been little research evaluating the use of clino to remove radioactive materials from produced water generated by oil/gas wells. Clino’s reported cation selectivity with associated ionic radii is as follows 6, 7 181 pm 166 pm 152 pm 148 pm 135 pm 118 pm 116 pm 114 pm 72 pm > > > > > > > > 2+ NH4 + Na+ Cs+ K+ Rb+ Ba2+ Sr2+ Ca2+ Mg


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Clino’s preference for larger cations make it potentially capable of NORM remediation, since the ionic radius of 226Ra2+ is 148 pm, which is greater than the radii of major 226Ra2+ produced water constituents including Ba2+, Sr2+, Na+, Ca2+, Fe2+, Mn2+, and Mg2+. The dissolved solids content of produced water makes selective removal of radium difficult. As a result, current technologies used in radium removal including reverse osmosis 8, barium sulfate co-precipitation 9, 10, ion exchange 9, and ultrafiltration 8 all involve high cost. In this paper, clino is evaluated as a cheaper alternative for its efficiency and selectivity in removing radium in simulated produced water in the presence of barium, and the results are directly compared to a standard ion exchange resin - Dowex® G-26. Clino showed greater overall performance and shows promise as a candidate for NORM remediation from produced water. MATERIALS AND METHODS One ion-exchange resin (Dowex® G-26, Dow Chemical Company) and two different mesh sizes of clino (Bear River Zeolite, Preston, ID) were tested and compared for radium removal from both deionized (DI) water and simulated produced water. Forty (40) mesh clino is referred to as powered clino (P-Clino), and ~4-8 mesh clino as granulated clino (G-Clino). Solid form salts of NaCl, CaCl2, BaCl2, MgCl2, and SrCl2 were purchased from Fisher Scientific; and 100 nCi/L 226

Ra2+ was purchased from Eckert & Ziegler (Atlanta, GA). Radioactive materials were

analyzed on stainless steel trays in a dried form using a portable RadEye HEC scintillator (ThermoScientific). Increased solution ionic strength significantly reduced the sensitivity of the RadEye HEC, thus 226

Ra2+ removal results from only DI water and a solution ionic strength of ~0.5 M are presented.

Simulated produced water was synthesized in the lab and the composition is shown in Table 1.


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Known amounts of

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226

Ra2+ were added to either DI water or simulated produced water to reach

final concentration levels of 0.25, 1.0, 2.0, 5.0, 6.7, 10 nCi/L. Triplicates were analyzed using a 30 min counting time once samples were dried in an oven set at 105 °C. Table 1. Simulated produced water composition Ionic (M)

Strength

0.47

pH

Na+ (mg/L)

Ca2+ (mg/L)

Ba2+ (mg/L)

Mg2+ (mg/L)

Sr2+ (mg/L)

Cl(mg/L)

6.5

8,300

3,300

750

350

500

20501

Note: All cations present as chlorides. Two mesh sizes of clino were first tested for their hydrothermal stability in a saline environment. In each test, 1 gram of clino was exposed to a 280 g/L brine solution containing NaCl, CaCl2, BaCl2, MgCl2, and SrCl2 for 25 days at 120 °C in 45 mL PTFE-lined Parr autoclave. Once the materials were removed and dried, they were analyzed by X-ray diffraction (XRD) (Ultima IV, Rigaku, Japan). Sorbent capacity was evaluated in batch testing conditions. Varying amounts of sorbents ranging from 0.01 g to 1 g were added into 50 mL centrifuge tubes where 10 mL of radioactive solution containing 10 nCi/L of

226

Ra2+ was then added to the sorbent. The mixtures were agitated on a

shaker plate overnight. Once sorbents settled in centrifuge tubes, supernatant was pipetted out for analysis using the RadEye HEC. Clino samples were also analyzed using a scanning electron microscope (SEM) (JSM-6390, JEOL) with an energy dispersive spectrometer (EDS) attachment (Genesis, EDAX). Following batch tests, column tests were used to observe breakthrough for two sorbents: P-Clino and Dowex® resin. A solution containing 10 nCi/L

226

Ra2+ was passed through a lightly packed


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column at a flowrate of 10 mL/min. Samples were taken every 15 to 20 min and analyzed on the RadEye HEC. In addition, sorbent selectivity was also evaluated and compared using inductively coupled plasma – optical emission spectroscopy (ICP-OES) (iCAP 6000, Thermo Scientific). Na+, Ca2+, Ba2+, Mg2+, and Sr2+ concentrations were determined for pre- and post-sorbent absorption, and the results were compared to find the most efficient sorbent for removing 226Ra2+. RESULTS AND DISCUSSIONS Stability Test The structure of clino was found to be stable after hydrothermal treatment in a high dissolved solids content solution containing ~168,000 ppm Cl-, as shown in Figure 1. The XRD pattern of the P-Clino was found to be exactly the same after the treatment. Three additional peaks found in G-Clino were identified as NaCl crystals which could be unevenly distributed in the clino sample during the grinding process for XRD analysis. The remainder of the peaks are associated with the clinoptilolite structure.


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Figure 1. XRD pattern of clino before and after brine treatment at 120 °C for 25 days Sorbent Capacities Both ion-exchange resin and natural zeolite are not exclusive in removing

226

Ra2+, thus it is

important to find the sorbent capacities in both DI water and high dissolved solids content solutions. In DI water, 1g of G-Clino, P-Clino, and Dowex® resin was able to remove 100 pCi of added 226

Ra2+ to below detectable limits. To determine

226

Ra2+ capacity of the materials, additional

trials were completed by lowering sorbent addition to the solution so that detectable amounts of activity could be measured allowing capacities to be quantified. The capacities were found to be 2.0 nCi/g, 19.3 nCi/g, and 14.8 nCi/g for G-Clino, P-Clino, and Dowex® resin, respectively. Clearly, G-Clino was the least efficient in removing

226

Ra2+ in the DI water while P-Clino

showed the best efficiency. P-Clino has a higher surface area and pore volume (70.21 m2/g and


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0.026 cm3/g) compared to G-Clino (25.49 m2/g and 0.008cm3/g), which is believed to be the likely factor for P-Clino’s increased radium removal efficiency. With addition of dissolved solids, sorbent capacities dropped significantly for all three materials due to competition for sorption and/or ion-exchange sites. For G-Clino, 1 g of sorbent was unable to remove the 100 pCi of

226

Ra2+ present in the simulated produced water, leading to a

capacity of approximately 0.08 nCi/g. Similarly, the higher ionic strength solution reduced capacity of both P-Clino and Dowex® to 0.69 nCi/g and 0.48 nCi/g, respectively. Table 2 provides a comparison for the three sorbents in the test solutions. Under both aqueous environments, P-Clino was found to be the most efficient in removing

226

Ra2+ from water, even

at high dissolved solids content. Compared to Dowex® resin, P-Clino’s greater efficiency is most likely contributed to by its selectivity towards larger diameter cations. Table 2. Compiled capacity results for clino and Dowex® resin

DI water Simulated produced water

G-Clino 2.0 ± 0.15

Capacity (nCi/g) P-Clino 19.3 ± 0.91

Dowex® Resin 14.8 ± 0.73

0.08 ± 0.006

0.69 ± 0.06

0.48 ± 0.04

Selectivity Test To test for selectivity, one (1) gram of the sorbents were added to simulated produced water and the supernatant was analyzed after the same treatment in batch tests. The elemental absorption profiles for the sorbent materials are provided in Figure 2, including

226

Ra2+ absorption

percentage calculated from batch tests under the same condition. Dowex® resin had minimal


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selectivity for

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226

Ra2+ as the percentages of all cations absorbed were very similar including for

the most abundant species in produced water (Na+, Ca2+, and Mg2+). However, both G-Clino and P-Clino demonstrated better selectivity towards larger size cations (Ra2+ 148 pm > Ba2+ 135 pm> Sr2+ 118 pm >Na+ 116 pm > Ca2+ 114 pm > Mg2+ 72 pm) 7 and low preference to the other more abundant species. For P-Clino, removal efficiency was greatest for

226

Ra2+, followed by Ba2+;

barium is immediately above radium in the periodic table. Thus, when salts are present in solutions, clino is a better choice to selectively removal radioactive materials compared to Dowex® resin. However, when Ba2+ is a major cation species found in wastewater, competition between the two species could significantly, and adversely impact, the performance of clinoptilolite for radium removal.

Figure 2. Percentage of cations absorbed on three different sorbents In addition, the particular clino used in this study was determined to have the approximate chemical formula of (Ca0.67K1.44)(Al2.50Si15.50O36), based upon scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). This approximate formula was confirmed at several locations of the clino material, the negative charge of the aluminosilicate


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lattice is balanced by the cations present within the zeolitic pore structure. Upon exposure of clino to the simulated produced water, Ca2+ and Mg2+ (likely also present in quantities below the EDS detectable limit) were replaced with larger elements including Na+ and Ba2+, as indicated by the SEM and EDS results shown in Figure 3, agreeing with previously reported clinoptilolite selectivity data 7. The carbon and Pd content of the material is related to the conductive carbon tape and Pd sputter coating used to mount and prepare the samples for SEM analysis.

Figure 3. Clino pre- and post-exposure to simulated produced water a) representative SEM image and b) representative EDS analysis results (“-” indicated below limits of detection) Column Test Due to the low radium capacity found for G-Clino, only P-Clino and Dowex® resin were used in column tests. Approximately 3 L of DI water-based radioactive solution (3.2 L containing 11.07 nCi/L for P-Clino and 3.4 L containing 11.06 nCi/L for Dowex® resin) or 1.65 L of simulated produced water (containing 12.08 nCi/L for P-Clino and 11.69 nCi/L for Dowex® resin) was passed through ¼-in columns packed with 1 g of powered clino or 1 g of Dowex® resin.


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In the case of DI water based solution, it was discernable that there was no breakthrough point (Figure 4). P-Clino’s efficiency did reduce as more solution eluted from the column; while removal efficiency remained the same for Dowex® resin. Accounting for radioactivity in the eluted solution, 27.81 nCi 226Ra2+ (78.5 %) was retained in the P-Clino column, while 34.65 nCi 226

Ra2+ (92.2 %) was retained in the Dowex® resin column. Even though both sorbents had

higher capacities than their batch test results, Dowex® resin presented better efficiency than PClino. However, because the breakthrough wasn’t observed, the true capacity could be even higher than the reported value here. The increased capacity could be the result of breaking stationary barriers on the sorbents through continuous flow and thus more efficient exchange. Dinca, et al., also reported an increased capacity when one column was split into two columns with the same amount of sorbent present 3.

Figure 4. Column test 226Ra2+ removal results in DI water at 25 °C With simulated produced water, breakthrough was quickly observed as shown in Figure 5 for both sorbents. After 80 minutes, radioactivity in eluted solution was the same as the initial solution which meant absorption had ceased. Similarly, accounting for radioactivity in the eluted


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solution, 3.02 nCi

226

Ra2+ (15.2%) was retained in the P-Clino column, with 1.84 nCi

226

Ra2+

(9.5%) retained in the Dowex® resin in from the simulated produced water. Sorbent capacity in the simulated produced water column tests also increased compared to the batch test results which were achieved overnight on a shaker plate (P-Clino with a capacity of 0.69 nCi/g and Dowex® resin with a capacity of 0.48 nCi/g). P-Clino showed better performance in the column tests in the presence of simulated produced water due to its high selectivity towards 226Ra2+ over other constituent cations (particularly Ba2+).

Figure 5. Column test 226Ra2+ removal results in simulated produced water at 25 °C CONCLUSIONS Clinoptilolite is a promising candidate for treating wastewater from hydraulic fracturing operations. First, the structure shows stability after being exposed to high chloride content solutions at 120 °C for 25 days. Second, the capacity for removing 226Ra2+ in simulated produced water was as high as 3.02 nCi/g, which is an equivalent to 0.1 GBq/ton. This value was determined in the presence of Ba2+, a strong competitor for clino absorption sites. Using the


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reported experimental data and commercial bulk pricing, the NORM removal costs were determined to be 0.002 ¢/nCi for P-Clino and 4.713 ¢/nCi for Dowex® resin. These results indicate the natural zeolite is more economical, yet highly selective, for removal of

226

Ra2+ and

Ba2+, while remaining less sensitive to uptake of Na+ and Sr2+ and insensitive to Ca2+ and Mg2+, which are major produced water co-constituents. AUTHOR INFORMATION Corresponding Author *Tel.:740-566-7046. Fax: 740-593-0476. E-mail: [email protected] ACKNOWLEDGMENTS This work was sponsored under Research Partnership to Secure Energy for America (RPSEA) contract number 11122-60. In addition, the authors would like to thank Ken Redlin for materials analysis. In addition, the authors would like to thank the Center for Electrochemical Engineering for use of their XRD. Finally, the authors would like to thank the Bear River Zeolite Company, Inc. of Preston Idaho for providing clinoptilolite samples for use in this study. REFERENCES 1.

Ferrer, I.; Thurman, E. M., Chemical constituents and analytical approaches for hydraulic

fracturing waters. Trends in Environmental Analytical Chemistry 2015, 5, 18-25. 2.

Bish, D. L., Natural Zeolites and Nuclear-Waste Management: The Case of Yucca

Mountain, Nevada, USA. In Natural Microporous Materials in Environmental Technology, Misaelides, P.; Macášek, F.; Pinnavaia, T. J.; Colella, C., Eds. Springer Netherlands: Dordrecht, 1999; pp 177-191.


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3.

Dinca, G.; Dutu, I.; Sandor, G.; Peic, T. In Removal of 226 Ra from waste waters resulted

from mining and processing of uranium ores with natural zeolites, IRPA9: 1996 international congress on radiation protection. Proceedings. Volume 3, 1996; 1996. 4.

Chałupnik, S.; Franus, W.; Wysocka, M.; Gzyl, G., Application of zeolites for radium

removal from mine water. Environmental Science and Pollution Research 2013, 20, (11), 79007906. 5.

Zhao, H.; Vance, G. F.; Urynowicz, M. A.; Gregory, R. W., Integrated treatment process

using a natural Wyoming clinoptilolite for remediating produced waters from coalbed natural gas operations. Applied Clay Science 2009, 42, (3–4), 379-385. 6.

Mumpton, F. A., La roca magica: Uses of natural zeolites in agriculture and industry.

Proceedings of the National Academy of Sciences 1999, 96, (7), 3463-3470. 7.

Shannon, R., Revised effective ionic radii and systematic studies of interatomic distances

in halides and chalcogenides. Acta Crystallographica Section A 1976, 32, (5), 751-767. 8.

Kosarek, L., Radionuclide removal from water. Environmental Science & Technology

1979, 13, (5), 522-525. 9.

Arthur, J. D.; Langhus, B. G.; Patel, C., Technical summary of oil & gas produced water

treatment technologies. All Consulting, LLC, Tulsa, OK 2005. 10. Igunnu, E. T.; Chen, G. Z., Produced water treatment technologies. International Journal of Low-Carbon Technologies 2012.


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Ra2+ Removal from Produced Water Using Natural Zeolite Materials


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