| DOI: | 10.2172/1240616
|
| 报告号: | DOE-WUSTL--0006857
|
| 报告题名: | Final Report: Dominant Mechanisms of Uranium-Phosphate Reactions in Subsurface Sediments |
| 作者: | Catalano, Jeffrey G.; Giammar, Daniel E.; Wang, Zheming
|
| 出版年: | 2016
|
| 发表日期: | 2016-03-08
|
| 总页数: | 7
|
| 国家: | 美国
|
| 语种: | 英语
|
| 中文主题词: | 钙
; 降水
; 沉积物
; PH
; 磷酸盐
; 扩散
; 铁
; 矿物
; PH值
|
| 主题词: | CALCIUM
; PRECIPITATION
; SEDIMENTS
; PH
; PHOSPHATE
; DIFFUSION
; IRON
; MINERALS
|
| 英文摘要: | Phosphate addition is an in situ remediation approach that may enhance the sequestration of uranium without requiring sustained reducing conditions. However, the geochemical factors that determine the dominant immobilization mechanisms upon phosphate addition are insufficiently understood to design efficient remediation strategies or accurately predict U(VI) transport. The overall objective of our project is to determine the dominant mechanisms of U(VI)-phosphate reactions in subsurface environments. Our research approach seeks to determine the U(VI)-phosphate solid that form in the presence of different groundwater cations, characterize the effects of phosphate on U(VI) adsorption and precipitation on smectite and iron oxide minerals, examples of two major reactive mineral phases in contaminated sediments, and investigate how phosphate affects U(VI) speciation and fate during water flow through sediments from contaminated sites. The research activities conducted for this project have generated a series of major findings. U(VI) phosphate solids from the autunite mineral family are the sole phases to form during precipitation, with uranyl orthophosphate not occurring despite its predicted greater stability. Calcium phosphates may take up substantial quantities of U(VI) through three different removal processes (adsorption, coprecipitation, and precipitation) but the dominance of each process varies with the pathway of reaction. Phosphate co-adsorbs with U(VI) onto smectite mineral surfaces, forming a mixed uranium-phosphate surface complex over a wide range of conditions. However, this molecular-scale association of uranium and phosphate has not effect on the overall extent of uptake. In contrast, phosphate enhanced U(VI) adsorption to iron oxide minerals at acidic pH conditions but suppresses such adsorption at neutral and alkaline pH, despite forming mixed uranium-phosphate surface complexes during adsorption. Nucleation barriers exist that inhibit U(VI) phosphate solids from precipitating in the presence of smectite and iron oxide minerals as well as sediments from contaminated sites. Phosphate addition enhances retention of U(VI) by sediments from the Rifle, CO and Hanford, WA field research sites, areas containing substantial uranium contamination of groundwater. This enhanced retention is through adsorption processes. Both fast and slow uptake and release behavior is observed, indicating that diffusion of uranium between sediment grains has a substantial effect of U(VI) fate in flowing groundwater systems. This project has revealed the complexity of U(VI)-phosphate reactions in subsurface systems. Distinct chemical processes occur in acidic and alkaline groundwater systems. For the latter, calcium phosphate formation, solution complexation, and competition between phosphate and uranium for adsorption sites may serve to either enhance or inhibit U(VI) removal from groundwater. Under the groundwater conditions present at many contaminated sites in the U.S., phosphate appears to general enhance U(VI) retention and limit transport. However, formation of low-solubility uranium phosphate solids does not occur under field-relevant conditions, despite this being the desired product of phosphate-based remediation approaches. In addition, simple equilibrium approaches fail to well-predict uranium fate in contaminated sediments amended with phosphate, with reactive transport models that include reaction rates and mass transport through occluded domains needed to properly describe the system. Phosphate addition faces challenges to being effective as a stand-alone groundwater treatment approach but would prove beneficial as an add-on to other treatment methods that will further limit uranium migration in the subsurface. |
| URL: | http://www.osti.gov/scitech/servlets/purl/1240616
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| Citation statistics: |
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| 资源类型: | 研究报告
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/42204
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| Appears in Collections: | 过去全球变化的重建
影响、适应和脆弱性
科学计划与规划
气候变化与战略
全球变化的国际研究计划
气候减缓与适应
气候变化事实与影响
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Content Type |
Version |
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| 1240616.pdf（234KB） | 研究报告 | -- | 开放获取 | | View
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| Recommended Citation: | |
Catalano, Jeffrey G.,Giammar, Daniel E.,Wang, Zheming. Final Report: Dominant Mechanisms of Uranium-Phosphate Reactions in Subsurface Sediments. 2016-01-01.
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