Chemical Characteristics of Leachate in Low-Level Radioactive Waste Disposal Facilities

Tian, Kuo; Benson, Craig H.; Tinjum, James M.

doi:10.1061/(asce)hz.2153-5515.0000361

Cited by 6 publications

(3 citation statements)

References 19 publications

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“…CaCl 2 solutions with concentrations ranging from 20 to 500 mM were used to represent conditions ranging from dilute leachate to high-concentration leachate. The 20 mM CaCl 2 solution was considered a dilute permeant solution, the 50 and 100 mM CaCl 2 solutions were considered modest-concentration solutions, and the 200 and 500 mM CaCl 2 solutions were considered highconcentration solutions based on municipal solid waste leachate data reported in Bradshaw and Benson (2014), low-level radioactive waste leachate data in Tian et al (2017), and coal combustion product leachate data in Chen et al (2019). The BPC GCLs were anticipated to have lower hydraulic conductivity than NaB GCLs to some, if not all, of these solutions.…”

Section: Test Liquidsmentioning

confidence: 99%

Polymer Elution and Hydraulic Conductivity of Bentonite–Polymer Composite Geosynthetic Clay Liners

Tian

Likos

Benson

2019

J. Geotech. Geoenviron. Eng.

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Hydraulic conductivity tests were conducted on two commercially available bentonite-polymer composite (BPC) geosynthetic clay liners (GCLs) containing the same dry blend of sodium bentonite (NaB) and polymer sandwiched between two nonwoven geotextiles (GTs) bound by needlepunching: a bentonite-polymer GCL (BP GCL) and bentonite-polymer GCL with silt film (BPS GCL). The GCLs were essentially identical except that the BPS GCL contained a woven slit-film GT to constrain polymer elution. The slit-film GT was located inside the GCL adjacent to the downstream nonwoven GT. The test liquids were deionized (DI) water and 20-500 mM CaCl 2 representing dilute to high-concentration permeant solutions. Effluent from the hydraulic conductivity tests was analyzed for total organic carbon (TOC) to quantify polymer elution. Scanning electron microscopy (SEM) was used to capture how the solution chemistry affected the fabric of the BPC and how hydraulic conductivity was related to pore-scale features in the fabric. Both BPC GCLs were approximately one to four orders of magnitude less permeable than a conventional NaB GCL permeated with the same solutions. Polymer elution data and SEM images of polymer structure suggest that polymer retention in the pore space and pore clogging by polymer hydrogel are responsible for the lower hydraulic conductivity of BPC GCLs. The BPS GCL had less polymer elution and hydraulic conductivity three orders of magnitude lower than the BP GCLs when permeated with 50 and 100 mM CaCl 2 solutions because the slit-film GT reduced polymer elution from the bentonite. A conceptual framework is proposed relating solution chemistry, pore-scale fabric, and hydraulic conductivity of dry-blended BPC GCLs.

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Section: Test Liquidsmentioning

confidence: 99%

Polymer Elution and Hydraulic Conductivity of Bentonite–Polymer Composite Geosynthetic Clay Liners

Tian

Likos

Benson

2019

J. Geotech. Geoenviron. Eng.

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“…The heavy metal desorption process is affected by the pH of the pore fluid solution [42]. Even waste soils with neutral pH values exhibit significant levels of heavy metal sorption [92]. Harter [93] examined the effects of soil pH on heavy metal adsorption and stated that the degree to which metal ions hydrolyze at a specific extractant pH (leading to their release from the host soil) is unknown.…”

Section: Retention In Soilsmentioning

confidence: 99%

Efficacy of Enzymatically Induced Calcium Carbonate Precipitation in the Retention of Heavy Metal Ions

Moghal

Lateef²,

Mohammed³

et al. 2020

Sustainability

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This study evaluated the efficacy of enzyme induced calcite precipitation (EICP) in restricting the mobility of heavy metals in soils. EICP is an environmentally friendly method that has wide ranging applications in the sustainable development of civil infrastructure. The study examined the desorption of three heavy metals from treated and untreated soils using ethylene diamine tetra-acetic acid (EDTA) and citric acid (C6H8O7) extractants under harsh conditions. Two natural soils spiked with cadmium (Cd), nickel (Ni), and lead (Pb) were studied in this research. The soils were treated with three types of enzyme solutions (ESs) to achieve EICP. A combination of urea of one molarity (M), 0.67 M calcium chloride, and urease enzyme (3 g/L) was mixed in deionized (DI) water to prepare enzyme solution 1 (ES1); non-fat milk powder (4 g/L) was added to ES1 to prepare enzyme solution 2 (ES2); and 0.37 M urea, 0.25 M calcium chloride, 0.85 g/L urease enzyme, and 4 g/L non-fat milk powder were mixed in DI water to prepare enzyme solution 3 (ES3). Ni, Cd, and Pb were added with load ratios of 50 and 100 mg/kg to both untreated and treated soils to study the effect of EICP on desorption rates of the heavy metals from soil. Desorption studies were performed after a curing period of 40 days. The curing period started after the soil samples were spiked with heavy metals. Soils treated with ESs were spiked with heavy metals after a curing period of 21 days and then further cured for 40 days. The amount of CaCO3 precipitated in the soil by the ESs was quantified using a gravimetric acid digestion test, which related the desorption of heavy metals to the amount of precipitated CaCO3. The order of desorption was as follows: Cd > Ni > Pb. It was observed that the average maximum removal efficiency of the untreated soil samples (irrespective of the load ratio and contaminants) was approximately 48% when extracted by EDTA and 46% when extracted by citric acid. The soil samples treated with ES2 exhibited average maximum removal efficiencies of 19% and 10% when extracted by EDTA and citric acid, respectively. It was observed that ES2 precipitated a maximum amount of calcium carbonate (CaCO3) when compared to ES1 and ES3 and retained the maximum amount of heavy metals in the soil by forming a CaCO3 shield on the heavy metals, thus decreasing their mobility. An approximate improvement of 30% in the retention of heavy metal ions was observed in soils treated with ESs when compared to untreated soil samples. Therefore, the study suggests that ESs can be an effective alternative in the remediation of soils contaminated with heavy metal ions.

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“…Abiotic factors that also impact the rate of APCA degradation include photolytic [20], radiolytic [21] and chemical degradation pathways [22]. The latter are facilitated by a high ionic strength of disposed waste [23] and a high pH environment caused by the grouting cement [24].…”

Section: Introductionmentioning

confidence: 99%

Quantification of common aminopolycarboxylic acids in trench leachate from the Low Level Waste Repository

O’Hanlon

Chapman

Taylor³

et al. 2019

J Radioanal Nucl Chem

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The aminopolycarboxylic acids (APCAs), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NTA), are used as decontamination agents throughout the nuclear industry; therefore, APCAs are often found in radioactive waste. Limits of acceptance on APCAs are imposed on wastes consigned to the Low Level Waste Repository (LLWR) because, when present in the waste, the ligands have the potential to mobilise otherwise surface-bound or solid radionuclides, making them available for transport to groundwater and ultimately to the bio-sphere. A selective and sensitive methodology to detect and quantify these ligands in a range of complex matrices is advantageous in supporting waste acceptance processes. A reversed-phase high-performance liquid chromatography (HPLC) procedure has been applied for quantification of EDTA, DTPA and NTA in their Fe(III)-complex form. Method validation results show linearity (r 2 > 0.999), precision (intra/inter-day %RSD ≤ 10%), accuracy (recovery = 100 ± 3%), sensitivity (minimum limits of detection = 0.31, 0.38 and 4.3 μM for EDTA, DTPA and NTA, respectively) and selectivity (simultaneous determination of the three APCA complexes achieved with baseline resolution) for Fe(III)-APCAs in aqueous solution. Chromatographic peak overlap is observed for samples containing Fe(III)-and Co(III)-EDTA; two deconvolution methods (2D least-squares fitting vs. PARAFAC) were applied to resolve the peaks and the performances compared. The optimised HPLC method was applied to trench leachate samples from the LLWR site. EDTA was detected with 0.4 μM < concentrations < 1 μM in samples from four of the six sampling locations tested. The levels are not considered sufficient to increase the risk of radionuclide mobilisation. The technique is considered to be robust and will be considered further in informing limits of acceptance on APCAs.

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Chemical Characteristics of Leachate in Low-Level Radioactive Waste Disposal Facilities

Cited by 6 publications

References 19 publications

Polymer Elution and Hydraulic Conductivity of Bentonite–Polymer Composite Geosynthetic Clay Liners

Polymer Elution and Hydraulic Conductivity of Bentonite–Polymer Composite Geosynthetic Clay Liners

Efficacy of Enzymatically Induced Calcium Carbonate Precipitation in the Retention of Heavy Metal Ions

Quantification of common aminopolycarboxylic acids in trench leachate from the Low Level Waste Repository

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