Shi Zhenqing, Liu Chongxuan, Zachara John M, Wang Zheming, Deng Baolin
Pacific Northwest National Laboratory, Richland, Washington 99354, USA.
Environ Sci Technol. 2009 Nov 1;43(21):8344-9. doi: 10.1021/es9021359.
The inhibitory effect of phosphate mineral precipitation on diffusion-limited uranium release was evaluated using a U(VI)-contaminated sediment collected from the U.S. Department of Energy Hanford site. The sediment contained U(VI) that was associated with diffusion-limited intragrain regions within its millimeter-sized granitic lithic fragments. The sediment was first treated to promote phosphate mineral precipitation in batch suspensions spiked with 1 and 50 mM aqueous phosphate and calcium in the stoichiometric ratio of the mineral hydroxyapatite. The phosphate-treated sediment was then leached to solubilize contaminant U(VI) in a column system using a synthetic groundwater solution with chemical components representative of Hanford groundwater. Phosphate treatment significantly decreased the extent of U(VI) release from the sediment. Within the experimental duration of about 200 pore volumes, the effluent U(VI) concentrations were consistently lower by over 1 and 2 orders of magnitude after the sediment was treated with 1 and 50 mM of phosphate, respectively. Measurements of solid-phase U(VI) using laser-induced fluorescence spectroscopy, scanning electron microscopy, and chemical extraction of the sediment collectively indicated that the inhibition of U(VI) release from the sediment was caused by (1) U(VI) adsorption to the secondary phosphate precipitates and (2) the transformation of original U(VI) mineral phases to less soluble forms.
利用从美国能源部汉福德场地采集的受U(VI)污染的沉积物，评估了磷酸盐矿物沉淀对扩散受限的铀释放的抑制作用。该沉积物中的U(VI)与毫米大小的花岗岩岩屑碎片内扩散受限的颗粒内部区域有关。首先对沉积物进行处理，以促进在添加了化学计量比的矿物羟基磷灰石的1 mM和50 mM磷酸盐水溶液和钙的分批悬浮液中形成磷酸盐矿物沉淀。然后使用具有代表汉福德地下水化学成分的合成地下水溶液，在柱系统中浸出经磷酸盐处理的沉积物，以溶解污染物U(VI)。磷酸盐处理显著降低了沉积物中U(VI)的释放程度。在约200个孔隙体积的实验持续时间内，在用1 mM和50 mM磷酸盐处理沉积物后，流出液中U(VI)的浓度分别持续降低了超过1个和2个数量级。使用激光诱导荧光光谱法、扫描电子显微镜和沉积物的化学萃取对固相U(VI)进行的测量共同表明，沉积物中U(VI)释放的抑制是由(1) U(VI)吸附到次生磷酸盐沉淀物上以及(2) 原始U(VI)矿物相转变为溶解度较低的形式引起的。
