Weiksnar Kate D, Lott Dreyton J, Townsend Timothy G
Department of Environmental Engineering Sciences, University of Florida, P. O. Box 116450, Gainesville, FL 32611-6450, USA.
Department of Environmental Engineering Sciences, University of Florida, P. O. Box 116450, Gainesville, FL 32611-6450, USA.
Sci Total Environ. 2024 Dec 1;954:176628. doi: 10.1016/j.scitotenv.2024.176628. Epub 2024 Sep 30.
Production of phosphoric acid generates a calcium sulfate byproduct known as phosphogypsum (PG). PG is not considered a suitable standalone road base material because of concerns such as strength and presence of radionuclides. This paper investigates the latter, specifically the influence of blending PG with common alkaline road base aggregates - limerock (LR) and recycled concrete aggregate (RCA) - on radionuclide leaching. Radionuclide leaching from several PG sources was assessed for gross alpha, gross beta, uranium, and combined radium (226 + 228). Solution pH affected Ra mobility, with minimum concentrations exhibited at a pH in the range of 6 to 8. Mobile Ra concentrations in RCA blends decreased compared to original PG; Ra mobility initially increased at low LR replacements but decreased with increasing mass of LR (50 %-75 %). The data suggest an additional mechanism beyond pH alone impacted Ra mobility from the blends, possibly the binding or substitution of radium by elevated concentrations of Ba, Sr, or Ca. Blending with RCA resulted in radionuclide concentrations below respective drinking water thresholds, mitigating leaching concern from PG-RCA road base blends. PG-LR blends can meet regulatory limits when incorporating appropriate PG sources, providing an avenue for PG-amended road base materials. The blending approach reduced Ra mobility from PG-amended base, accommodating more PG use, serving as an alternative scenario to end-of-life stacking.
磷酸生产会产生一种硫酸钙副产品，称为磷石膏（PG）。由于强度和放射性核素的存在等问题，PG不被认为是一种合适的独立道路基层材料。本文研究了后者，具体而言，研究了将PG与常见的碱性道路基层骨料——石灰岩（LR）和再生混凝土骨料（RCA）混合对放射性核素浸出的影响。评估了几种PG来源的放射性核素总α、总β、铀和镭（226 + 228）的浸出情况。溶液pH值影响镭的迁移率，在pH值为6至8的范围内呈现出最低浓度。与原始PG相比，RCA混合物中的可移动镭浓度降低；在低LR替代量时，镭的迁移率最初增加，但随着LR质量的增加（50%-75%）而降低。数据表明，除了pH值之外，还有一种额外的机制影响了混合物中镭的迁移率，可能是高浓度的钡、锶或钙对镭的结合或替代。与RCA混合导致放射性核素浓度低于各自的饮用水阈值，减轻了PG-RCA道路基层混合物的浸出问题。当使用合适的PG来源时，PG-LR混合物可以满足监管限制，为PG改良道路基层材料提供了一条途径。混合方法降低了PG改良基层中镭的迁移率，允许更多地使用PG，作为一种替代方案来取代废弃堆放。
