Robustness of the CSSX Process to Feed Variation: Efficient Cesium Removal from the High Potassium Wastes at Hanford

Abstract

This contribution finds the Caustic-Side Solvent Extraction (CSSX) process to be effective for the removal of cesium from the Hanford tank-waste supernatant solutions. The Hanford waste types are more challenging than those at the Savannah River Site (SRS) in that they contain significantly higher levels of potassium, the chief competing ion in the extraction of cesium. By use of a computerized CSSX thermodynamic model, it was calculated that the higher levels of potassium depress the cesium distribution ratio (D Cs ), as validated to within ¡11% by the measurement of D Cs values on various Hanford wastesimulant compositions. A simple analog model equation that can be readily applied in a spreadsheet for estimating the D Cs values for the varying waste compositions was developed and shown to yield nearly identical estimates as the computerized CSSX model. It is concluded from the batch distribution experiments, the physical-property measurements, the equilibrium modeling, the flowsheet calculations, and the contactor sizing that the CSSX process as currently formulated for cesium removal from alkaline salt waste at the SRS is capable of treating similar Hanford tank feeds, albeit with more stages. For the most challenging Hanford waste composition tested, 31 stages would be required to provide a cesium decontamination factor (DF) of 5000 and a concentration factor (CF) of 2. Commercial contacting equipment with rotor diameters of 10 in. for extraction and 5 in. for stripping should have the capacity to meet throughput requirements, but testing will be required to confirm that the needed efficiency and hydraulic performance are actually obtainable. Markedly improved flowsheet performance was calculated based on experimental distribution ratios determined for an improved solvent formulation employing the more soluble cesium extractant BEHBCalixC6 used with alternative scrub and strip solutions, respectively 0.1 M NaOH and 0.010 M boric acid. The improved solvent and flowsheet can meet minimum requirements (DF 5 5000 and CF 5 2) with 15 stages or more ambitious goals (DF 5 40,000 and CF 5 15) with 19 stages. Thus, a modular CSSX application for the Hanford waste seems readily obtainable with further short-term development.

Macrocyclic Pyridone Pentamers for Highly Selective High‐Capacity Removal of Caesium Ions from Radioactive High‐Salinity Waste

“…There has been widespread improvement of different extractive materials, mainly focusing on separation and isolation of Cs + from aquatic ecosystems. For instance, inorganic (crystalline silicotitanates, [7] metal thiophosphate, [8] sulfide clusters, [9] zeolitic [23–29] chalcogenides, [23] Prussian blue, [30] etc) and organic (phenolic resins, [31] polysaccharides, [32] resorcinol‐formaldehyde, [33] etc) ion exchangers are the major treatment methods for removal of Cs + from liquid waste. Additionally, organic extractants based on functionalised calixarenes, [3–5,22] cucurbit[n]urils, [12] uranyl organic framework, [14] isoguanosine tetramer [24] or pentamer, [25] and carbon nanotubes have been recently reported as suitable host molecules for selective binding with Cs + .…”

“…Additionally, organic extractants based on functionalised calixarenes, [3–5,22] cucurbit[n]urils, [12] uranyl organic framework, [14] isoguanosine tetramer [24] or pentamer, [25] and carbon nanotubes have been recently reported as suitable host molecules for selective binding with Cs + . Among these, 1,3‐dialkoxycalix[4]arene‐crowns‐6 in the 1,3‐alternate conformation (BOBcalixC6, [26] MAXCalix [27] and BEHBCalixC6, [28,29] etc) have gained particular interest due to their very high selectivity in separating Cs + from other metal ions [3–5] . Nevertheless, most of these separation methods require large quantities of materials to achieve effective separation of Cs + ions, [10] a high cost or difficulties in separating Cs + ‐bound materials from wastes after Cs + sorption, leaving ample scopes for further improvement in cost‐effective removal of Cs + with high selectivity.…”

Recommended Guanidine Suppressor for the Next-Generation Caustic-Side Solvent Extraction Process

“…The NG-CSSX process [1,2] was designed to provide a step-jump improvement in waste decontamination factor (DF) and waste throughput vs. the CSSX process [3,4,5] in the removal of cesium from legacy high-level salt waste stored in underground storage tanks in the U.S. Department of Energy (DOE) complex. Following initial results pointing to its feasibility [6,7,8] , the NG-CSSX process has been under development since 2010 under funding from the DOE Office of Environmental Management, Office of Technology Innovation and Development. To reach the target cesium decontamination and concentration factors (DF = 40,000…”

Demonstration of the Next-Generation Caustic-Side Solvent Extraction Solvent With 2-Cm Centrigugal Contractors Using Tank 49h Waste and Waste Simulant

“…This is reflected in the high 137 Cs activity of the sample (1.44E+08 dpm/mL). Potassium (K) ion (505 mg/L) and rubidium (Rb) ion (0.476 mg/L), which compete with Cs during extraction, [5] are also present. To date, studies have not been completed to evaluate the effect of Rb on Cs removal.…”