Hydroxyapatite Synthesis

Andronescu, Ecaterina; Ştefan, Ella; Dinu, Elena; Ghiţulică, Cristina

doi:10.4028/www.scientific.net/kem.206-213.1595

Cited by 16 publications

(11 citation statements)

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“…Phosphate adsorption is slow (hours) so rapid infiltration can result in deeper phosphate mass at depth. Citrate is needed to keep Ca in solution long enough (days) to inject into the subsurface; a solution containing Ca 2+ and phosphate only will rapidly form mono-and di-calcium phosphate [Ca(H 2 PO 4 ) 2 , CaHPO 4 *2H 2 O], but not apatite (Andronescu et al 2002;Elliot et al 1973;Papargyris et al 2002). Relatively slow biodegradation of the Ca-citrate complex (days) allows sufficient time for injection and transport of the reagents to the areas of the aquifer where treatment is required Williams et al 2008).…”

Section: Subsurface Apatite Placement By Solution Injection/infiltrationmentioning

confidence: 99%

Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

Szecsody¹,

Rockhold²,

Oostrom³

et al. 2009

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SummaryThe objective of this project is to develop a method to emplace apatite precipitate in the 100-N Area vadose zone, resulting in sorption and ultimately incorporation of Sr-90 into the apatite structure. The Ca-citrate-phosphate (Ca-citrate-PO 4 ) solution can be infiltrated into unsaturated sediments to result in apatite precipitate to provide effective treatment of Sr-90 contamination. Microbial redistribution during solution infiltration and a high rate of citrate biodegradation for river water microbes (water used for solution infiltration) produces a relatively even spatial distribution of the citrate biodegradation rate and ultimately, apatite precipitate in the sediment. Manipulation of the Ca-citrate-PO 4 solution infiltration strategy can be used to induce apatite precipitation in the lower half of the vadose zone (where most of the Sr-90 is located) and within low-K layers (which may have higher Sr-90 concentrations):• infiltration rate: more rapid Ca-citrate-PO 4 solution infiltration resulted in greater depth of apatite precipitate, but less lateral spreading• decrease in infiltration rate: rapid then slow solution infiltration resulted in greater lateral spreading of the apatite precipitate at depth• sequential solution then water infiltration: water infiltration after solution infiltration effectively moved the apatite mass to depth in homogeneous sediment systems• solution concentration: infiltration of higher Ca-citrate-PO 4 solution concentrations resulted in a greater depth of apatite precipitate• infiltration cycles: repeated infiltration of the Ca-citrate-PO 4 solution with time between cycles to allow for water drainage increased depth and greater lateral spread of apatite• low-K zones had a higher apatite precipitate due to higher residual water content• solution then water infiltration into a complex heterogeneous system with low-K and high-K discontinuous zones (8 ft high) showed high apatite precipitate in low-K and medium-grained sediment, but low treatment in high-K zones due to low water contentThe most effective infiltration strategy to precipitate apatite at depth (and with sufficient lateral spread) was to infiltrate a high concentration solution (6 mM Ca, 15 mM citrate, 60 mM PO 4 ) at a rapid rate (near ponded conditions), followed by rapid, then slow water infiltration. Repeated infiltration events, with sufficient time between events to allow water drainage in the sediment profile can be used to build up the mass of apatite precipitate at greater depth. Low-K heterogeneities were effectively treated, as the higher residual water content maintained in these zones resulted in higher apatite precipitate concentration. High-K zones did not receive sufficient treatment by infiltration, although an alternative strategy of air/surfactant (foam) was demonstrated effective for targeting high-K zones. The flow rate manipulation used in this study to treat specific depths and heterogeneities is not as easy to implement at field scale due to the lack of characterization of heterogene...

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Section: Subsurface Apatite Placement By Solution Injection/infiltrationmentioning

confidence: 99%

Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

Szecsody¹,

Rockhold²,

Oostrom³

et al. 2009

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show abstract

“…Citrate is needed to keep calcium in solution long enough (days) to inject into the subsurface because a solution containing Ca 2+ and phosphate only will rapidly form mono-and di-calcium phosphate, but not apatite (Andronescu et al 2002, Elliot et al 1973, Papargyris et al 2002. Relatively slow biodegradation of the Ca-citrate complex (days) allows sufficient time for the reagents to be injected and transported to the areas of the aquifer where treatment is required.…”

Section: Apatite Placement In the Subsurfacementioning

confidence: 99%

100-NR-2 Apatite Treatability Test: High-Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization

Vermeul¹,

Fritz²,

Fruchter³

et al. 2010

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SummaryFollowing an evaluation of potential strontium-90 ( 90 Sr) treatment technologies and their applicability under 100-NR-2 hydrogeologic conditions, the U.S. Department of Energy (DOE), Fluor Hanford, Inc. (now CH2M Hill Plateau Remediation Company [CHPRC]), Pacific Northwest National Laboratory, and the Washington State Department of Ecology agreed that the long-term strategy for groundwater remediation at the 100-N Area should include apatite as the primary treatment technology. This agreement was based on results from an evaluation of remedial alternatives that identified the apatite permeable reactive barrier (PRB) technology as the approach showing the greatest promise for reducing 90 Sr flux to the Columbia River at a reasonable cost. This report documents work completed to date on developing a high-concentration amendment formulation and initial field-scale testing of this amendment solution.The general approach for developing an in situ remedial technology for sequestering 90 Sr in groundwater through the formation of calcium-phosphate mineral phases (i.e., apatite) was documented in a project-specific treatability test plan that provides a detailed discussion of test objectives and outlines the technical approach for developing and deploying the technology. Activities completed to date in support of the 100-NR-2 apatite treatability test that have been reported in previous documents include 1) laboratory-scale studies, 2) pilot-scale field testing with a low-concentration solution, 3) initial treatment of a 91-m (300-ft) -long PRB section with the low-concentration formulation, and 4) analysis of sediment samples collected following low-concentration treatment to determine whether any apatite had formed. A high-concentration amendment solution was formulated to maximize apatite formation within the targeted treatment zone while minimizing the short-term increases in 90 Sr concentration associated with injecting high-ionic-strength solutions.The original concept for field-scale deployment of the apatite PRB technology involved injecting a low-concentration, apatite-forming solution, followed by higher concentration injections as required to emplace sufficient treatment capacity to meet remedial objectives. The low-concentration injections were designed to provide a small amount of treatment capacity, thus stabilizing the 90 Sr residing within the treatment zone while minimizing 90 Sr mobilization because of the injection of high-ionic-strength solutions. In theory, this approach would act to minimize 90 Sr mobilization during subsequent highconcentration injections. However, results from the low-concentration field testing with a formulation containing stoichiometric calcium and phosphate concentrations for apatite precipitation and subsequent laboratory studies aimed at optimizing the amendment formulation determined that modifying the solution to a calcium-poor formulation was a better approach for maximizing apatite formation while minimizing short-term increases in 90 Sr concentration. This m...

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“…Citrate is needed to keep calcium in solution long enough (days) to inject into the subsurface; a solution containing Ca 2+ and phosphate only will rapidly form mono-and di-calcium phosphate, but not apatite (Andronescu et al 2002;Elliott et al 1973, Papargyris et al 2002. Relatively slow biodegradation of the Ca-citrate complex (days) allows sufficient time for injection and transport of the reagents to the areas of the aquifer where treatment is required.…”

Section: Subsurface Apatite Placement By Solution Injectionmentioning

confidence: 99%

Interim Report: 100-NR-2 Apatite Treatability Test: Low Concentration Calcium Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization

Williams¹,

Fritz²,

Mendoza³

et al. 2008

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SummaryEfforts to reduce the flux of strontium-90 ( 90 Sr) to the Columbia River from past-practice liquid waste disposal sites have been underway since the early 1990s in the 100-N Area at the Hanford Site. Termination of all liquid discharges to the ground in 1993 was a major step toward meeting this goal. However, 90 Sr adsorbed on aquifer solids beneath the liquid waste disposal sites and extending beneath the near-shore riverbed remains a continuing source to groundwater and the Columbia River. Researchers realized from the onset that the initial pump-and-treat system was unlikely to be an effective long-term solution because of the geochemical characteristics of 90 Sr; subsequent performance monitoring has substantiated this theory. Accordingly, the first Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) 5-year review re-emphasized the need to pursue alternative methods to reduce impacts on the Columbia River. 1Following an evaluation of potential 90 Sr treatment technologies and their applicability under 100-NR-2 hydrogeologic conditions, U.S. Department of Energy, Fluor Hanford, Inc. (FH), Pacific Northwest National Laboratory, and the Washington State Department of Ecology agreed the long-term strategy for groundwater remediation at the 100-N Area will include apatite sequestration as the primary treatment, followed by a secondary treatment⎯or polishing step⎯if necessary (most likely phytoremediation). Since then, the agencies have worked together to agree on which apatite-sequestration technology has the greatest chance of reducing 90 Sr flux to the Columbia River at a reasonable cost. In July 2005, aqueous injection, (i.e., the introduction of apatite-forming chemicals into the subsurface) was endorsed as the interim remedy and selected for field testing. Studies are in progress to assess the efficacy of in situ apatite formation by aqueous solution injection to address both the vadose zone and the shallow aquifer along the 91 m (300 ft) of shoreline where 90 Sr concentrations are highest. This report describes the field testing of the shallow aquifer treatment that was funded by FH.A low-concentration, apatite-forming solution was injected into the shallow aquifer in 10 injection wells during fiscal years 2006 and 2007, and performance monitoring is underway. The lowconcentration, apatite-forming solution consists primarily of calcium chloride, trisodium citrate, and sodium phosphate. The objective of the low-concentration Ca-citrate-PO 4 injections is to stabilize the 90 Sr in the aquifer at the test site, to be followed by high-concentration injections to provide for long-term 90 Sr treatment. Two pilot test sites at the east and west ends of the barrier, which are equipped with extensive monitoring well networks, were used for the initial injections to develop the injection design for the remaining portions of the barrier. Based on a comparison of hydraulic and transport response data at the two pilot test sites, it was determined the apparent permeability ...

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Hydroxyapatite Synthesis

Cited by 16 publications

References 0 publications

Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

Sequestration of Sr-90 Subsurface Contamination in the Hanford 100-N Area by Surface Infiltration of a Ca-Citrate-Phosphate Solution

100-NR-2 Apatite Treatability Test: High-Concentration Calcium-Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization

Interim Report: 100-NR-2 Apatite Treatability Test: Low Concentration Calcium Citrate-Phosphate Solution Injection for In Situ Strontium-90 Immobilization

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