Next Generation Solvent Performance in the Modular Caustic Side Solvent Extraction Process- 15495 PDF Download

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Changes to the Modular Caustic Side Solvent Extraction Unit (MCU) flow-sheet were implemented in the facility. Implementation included changing the scrub and strip chemicals and concentrations, modifying the O/A ratios for the strip, scrub, and extraction contactor banks, and blending the current BoBCalixC6 extractant based solvent in MCU with clean MaxCalix extractant based solvent. During the successful demonstration period, the MCU process was subject to rigorous oversight to ensure hydraulic stability and chemical/radionuclide analysis of the key process tanks (caustic wash tank, solvent hold tank, strip effluent hold tank, and decontaminated salt solution hold tank) to evaluate solvent carryover to downstream facilities and the effectiveness of cesium removal from the liquid salt waste. Results indicated the extraction of cesium was significantly more effective with an average Decontamination Factor (DF) of 1,129 (range was 107 to 1,824) and that stripping was effective. The contactor hydraulic performance was stable and satisfactory, as indicated by contactor vibration, contactor rotational speed, and flow stability; all of which remained at or near target values. Furthermore, the Solvent Hold Tank (SHT) level and specific gravity was as expected, indicating that solvent integrity and organic hydraulic stability were maintained. The coalescer performances were in the range of processing results under the BOBCalixC6 flow sheet, indicating negligible adverse impact of NGS deployment. After the Demonstration period, MCU began processing via routine operations. Results to date reiterate the enhanced cesium extraction and stripping capability of the Next Generation Solvent (NGS) flow sheet. This paper presents process performance results of the NGS Demonstration and continued operations of MCU utilizing the blended BobCalixC6-MaxCalix solvent under the NGS flowsheet.

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Languages : en
Pages : 239

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This report summarizes the FY 2010 and 2011 accomplishments at Oak Ridge National Laboratory (ORNL) in developing the Next Generation Caustic-Side Solvent Extraction (NG-CSSX) process, referred to commonly as the Next Generation Solvent (NGS), under funding from the U.S. Department of Energy, Office of Environmental Management (DOE-EM), Office of Technology Innovation and Development. The primary product of this effort is a process solvent and preliminary flowsheet capable of meeting a target decontamination factor (DF) of 40,000 for worst-case Savannah River Site (SRS) waste with a concentration factor of 15 or higher in the 18-stage equipment configuration of the SRS Modular Caustic-Side Solvent Extraction Unit (MCU). In addition, the NG-CSSX process may be readily adapted for use in the SRS Salt Waste Processing Facility (SWPF) or in supplemental tank-waste treatment at Hanford upon appropriate solvent or flowsheet modifications. Efforts in FY 2010 focused on developing a solvent composition and process flowsheet for MCU implementation. In FY 2011 accomplishments at ORNL involved a wide array of chemical-development activities and testing up through single-stage hydraulic and mass-transfer tests in 5-cm centrifugal contactors. Under subcontract from ORNL, Argonne National Laboratory (ANL) designed a preliminary flowsheet using ORNL cesium distribution data, and Tennessee Technological University confirmed a chemical model for cesium distribution ratios (DCs) as a function of feed composition. Inter laboratory efforts were coordinated with complementary engineering tests carried out (and reported separately) by personnel at Savannah River National Laboratory (SRNL) and Savannah River Remediation (SRR) with helpful advice by Parsons Engineering and General Atomics on aspects of possible SWPF implementation.

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This report summarizes the FY 2010 and 2011 accomplishments at Oak Ridge National Laboratory (ORNL) in developing the Next Generation Caustic-Side Solvent Extraction (NG-CSSX) process, referred to commonly as the Next Generation Solvent (NGS), under funding from the U.S. Department of Energy, Office of Environmental Management (DOE-EM), Office of Technology Innovation and Development. The primary product of this effort is a process solvent and preliminary flowsheet capable of meeting a target decontamination factor (DF) of 40,000 for worst-case Savannah River Site (SRS) waste with a concentration factor of 15 or higher in the 18-stage equipment configuration of the SRS Modular Caustic-Side Solvent Extraction Unit (MCU). In addition, the NG-CSSX process may be readily adapted for use in the SRS Salt Waste Processing Facility (SWPF) or in supplemental tank-waste treatment at Hanford upon appropriate solvent or flowsheet modifications. Efforts in FY 2010 focused on developing a solvent composition and process flowsheet for MCU implementation. In FY 2011 accomplishments at ORNL involved a wide array of chemical-development activities and testing up through single-stage hydraulic and mass-transfer tests in 5-cm centrifugal contactors. Under subcontract from ORNL, Argonne National Laboratory (ANL) designed a preliminary flowsheet using ORNL cesium distribution data, and Tennessee Technological University developed a chemical model for cesium distribution ratios (DCs) as a function of feed composition. Inter Laboratory efforts were coordinated in complementary fashion with engineering tests carried out (and reported separately) by personnel at Savannah River National Laboratory (SRNL) and Savannah River Remediation (SRR) with helpful advice by Parsons Engineering and General Atomics on aspects of possible SWPF implementation.

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Researchers successfully demonstrated the chemistry and process equipment of the Caustic-Side Solvent Extraction (CSSX) flowsheet using MaxCalix for the decontamination of high level waste (HLW). The demonstration was completed using a 12-stage, 2-cm centrifugal contactor apparatus at the Savannah River National Laboratory (SRNL). This represents the first CSSX process demonstration of the MaxCalix solvent system with Savannah River Site (SRS) HLW. Two tests lasting 24 and 27 hours processed non-radioactive simulated Tank 49H waste and actual Tank 49H HLW, respectively. A solvent extraction system for removal of cesium from alkaline solutions was developed utilizing a novel solvent invented at the Oak Ridge National Laboratory (ORNL). This solvent consists of a calix[4]arene-crown-6 extractant dissolved in an inert hydrocarbon matrix. A modifier is added to the solvent to enhance the extraction power of the calixarene and to prevent the formation of a third phase. An additional additive is used to improve stripping performance and to mitigate the effects of any surfactants present in the feed stream. The process that deploys this solvent system is known as Caustic Side Solvent Extraction (CSSX). The solvent system has been deployed at the Savannah River Site (SRS) in the Modular CSSX Unit (MCU) since 2008.

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Researchers successfully demonstrated the chemistry and process equipment of the Caustic-Side Solvent Extraction (CSSX) flowsheet using MaxCalix for the decontamination of high level waste (HLW). The demonstration was completed using a 12-stage, 2-cm centrifugal contactor apparatus at the Savannah River National Laboratory (SRNL). This represents the first CSSX process demonstration of the MaxCalix solvent system with Savannah River Site (SRS) HLW. Two tests lasting 24 and 27 hours processed non-radioactive simulated Tank 49H waste and actual Tank 49H HLW, respectively. Conclusions from this work include the following. The CSSX process is capable of reducing 137Cs in high level radioactive waste by a factor of more than 40,000 using five extraction, two scrub, and five strip stages. Tests demonstrated extraction and strip section stage efficiencies of greater than 93% for the Tank 49H waste test and greater than 88% for the simulant waste test. During a test with HLW, researchers processed 39 liters of Tank 49H solution and the waste raffinate had an average decontamination factor (DF) of 6.78E+04, with a maximum of 1.08E+05. A simulant waste solution (≈34.5 liters) with an initial Cs concentration of 83.1 mg/L was processed and had an average DF greater than 5.9E+03, with a maximum DF of greater than 6.6E+03. The difference may be attributable to differences in contactor stage efficiencies. Test results showed the solvent can be stripped of cesium and recycled for ≈25 solvent turnovers without the occurrence of any measurable solvent degradation or negative effects from minor components. Based on the performance of the 12-stage 2-cm apparatus with the Tank 49H HLW, the projected DF for MCU with seven extraction, two scrub, and seven strip stages operating at a nominal efficiency of 90% is ≈388,000. At 95% stage efficiency, the DF in MCU would be ≈3.2 million. Carryover of organic solvent in aqueous streams (and aqueous in organic streams) was less than 0.1% when processing Tank 49H HLW. The entrained solvent concentration measured in the decontaminated salt solution (DSS) was as much as ≈140 mg/L, although that value may be overstated by as much as 50% due to modifier solubility in the DSS. The entrained solvent concentration was measured in the strip effluent (SE) and the results are pending. A steady-state concentration factor (CF) of 15.9 was achieved with Tank 49H HLW. Cesium distribution ratios [D(Cs)] were measured with non-radioactive Tank 49H waste simulant and actual Tank 49H waste. Below is a comparison of D(Cs) values of ESS and 2-cm tests. Batch Extraction-Strip-Scrub (ESS) tests yielded D(Cs) values for extraction of ≈81-88 for tests with Tank 49H waste and waste simulant. The results from the 2-cm contactor tests were in agreement with values of 58-92 for the Tank 49H HLW test and 54-83 for the simulant waste test. These values are consistent with the reference D(Cs) for extraction of ≈60. In tests with Tank 49H waste and waste simulant, batch ESS tests measured D(Cs) values for the two scrub stages as ≈3.5-5.0 for the first scrub stage and ≈1.0-3.0 for the second scrub stage. In the Tank 49H test, the D(Cs) values for the 2-cm test were far from the ESS values. A D(Cs) value of 161 was measured for the first scrub stage and 10.8 for the second scrub stage. The data suggest that the scrub stage is not operating as effectively as intended. For the simulant test, a D(Cs) value of 1.9 was measured for the first scrub stage; the sample from the second scrub stage was compromised. Measurements of the pH of all stage samples for the Tank 49H test showed that the pH for extraction and scrub stages was 14 and the pH for the strip stages was ≈7. It is expected that the pH of the second scrub stage would be ≈12-13. Batch ESS tests measured D(Cs) values for the strip stages to be ≈0.002-0.010. A high value in Strip No.3 of a test with simulant solution has been attributed to issues associated with the limits of detection for the analytical method. In the 2-cm contactor tests, the first four strip stages of the Tank 49H waste test and all five strip stages in the simulant waste test had higher values than the ESS tests. Only the fifth strip stage D(Cs) value of the Tank 49H waste test matched that of the ESS tests. It is speculated that the less-than-optimal performance of the strip section is caused by inefficiencies in the scrub section. Because strip is sensitive to pH, the elevated pH value in the second scrub stage may be the cause of strip performance. In spite of the D(Cs) values obtained in the scrub and strip sections, testing showed that the solvent system is robust. Average DFs for the process far exceeded targets even though the scrub and strip stages did not function optimally. Correction of the issue in the scrub and strip stages is expected to yield even higher waste DFs.

Author: Kofi Adu-Wusu
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Category : Chemical engineering
Languages : en
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Languages : en
Pages : 16

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As part of the ongoing development of the Next-Generation Caustic-Side Solvent Extraction (NGS) process, the thermal stability of the process solvent was investigated and shown to be adequate for industrial application. The solvent was thermally treated at 35 C over a period of 13 months whilst in dynamic contact with each of the aqueous phases of the current NGS process, namely SRS 15 (a highly caustic waste simulant), sodium hydroxide scrub solution (0.025 M), and boric acid strip solution (0.01 M). The effect of thermal treatment was evaluated by assessing batch extract/scrub/strip performance as a function of time, by monitoring the sodium extraction capacity of the solvent, and by analysis of the solvent using electrospray mass spectrometry. Current studies indicate that the NGS solvent should be thermally robust for a period of XXX months at the Modular Caustic-Side Solvent Extraction Unit (MCU) pilot plant located at Savannah River Site. Furthermore, the guanidine suppressor appears to be the solvent component most significantly impacted by thermal treatment of the solvent, showing significant degradation over time.

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Languages : en
Pages : 26

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A new solvent system referred to as Next Generation Solvent or NGS, has been developed at Oak Ridge National Laboratory for the removal of cesium from alkaline solutions in the Caustic Side Solvent Extraction process. The NGS is proposed for deployment at MCU{sup a} and at the Salt Waste Processing Facility. This work investigated the chemical compatibility between NGS and 16 M, 8 M, and 3 M nitric acid from contact that may occur in handling of analytical samples from MCU or, for 3 M acid, which may occur during contactor cleaning operations at MCU. This work shows that reactions occurred between NGS components and the high molarity nitric acid. Reaction rates are much faster in 8 M and 16 M nitric acid than in 3 M nitric acid. In the case of 16 M and 8 M nitric acid, the nitric acid reacts with the extractant to produce initially organo-nitrate species. The reaction also releases soluble fluorinated alcohols such as tetrafluoropropanol. With longer contact time, the modifier reacts to produce a tarry substance with evolved gases (NOx and possibly CO). Calorimetric analysis of the reaction product mixtures revealed that the organo-nitrates reaction products are not explosive and will not deflagrate.

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Languages : en
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The Modular Caustic-Side Solvent Extraction Unit (MCU) is the first, production-scale Caustic-Side Solvent Extraction process for cesium separation to be constructed. The process utilizes an engineered solvent to remove cesium from waste alkaline salt solution resulting from nuclear processes. While the application of this solvent extraction process is unique, the process uses commercially available centrifugal contactors for the primary unit operation as well as other common methods of physical separation of immiscible liquids. The fission product, cesium-137, is the primary focus of the process due to the hazards associated with its decay. The cesium is extracted from the waste, concentrated, and stripped out of the solvent resulting in a low-level waste salt solution and a concentrated cesium nitrate stream. The concentrated cesium stream can be vitrified into borosilicate glass with almost no increase in glass volume, and the salt solution can be dispositioned as a low-level grout. The unit is deployed as an interim process to disposition waste prior to start-up of the Salt Waste Processing Facility. The Salt Waste Processing Facility utilizes the same cesium removal technology, but will treat more contaminated waste. The MCU is not only fulfilling a critical need, it is the first demonstration of the process at production-scale.