Why is calcite a strong phosphorus sink in freshwater? Investigating the adsorption mechanism using batch experiments and surface complexation modeling
Why is calcite a strong phosphorus sink in freshwater? Investigating the adsorption mechanism using batch experiments and surface complexation modeling
复制标题
为什么方解石在淡水中具有很强的磷沉降作用？
DOI：
10.1016/j.chemosphere.2021.131596
复制
发表时间：
2022
期刊：
影响因子：
8.8
通讯作者：
Dalton, Robert
中科院分区：
文献类型：
--
作者：
Flower, Hilary;Rains, Mark;Taşcı, Yasemin;Zhang, Jia-Zhong;Trout, Kenneth;Lewis, David;Das, Arundhati;Dalton, Robert
沉积物对磷的吸附是水体磷限制的主要驱动因素之一。与其他天然溶液相比，沉积物在淡水中吸附更多的P，但驱动这种差异的机制知之甚少。为了深入了解这一机制，我们进行了淡水和海水中方解石对磷吸附的批量实验，并使用计算机软件开发络合模型。我们的模拟揭示了三个主要原因，结合在一起，可以解释更大的P吸附在淡水与海水中的方解石。首先，水的P形态的差异。离子对CaPO 4 −在淡水中更丰富;虽然海水中有更多的Ca 2+离子，但MgHPO 40和NaHPO 40更受欢迎。第二，磷的吸附形态不同。离子对CaPO 4 −（淡水中的首选吸附质）能够进入HPO 42 −（海水中的首选吸附质）无法获得的吸附位点，从而提高了淡水中可以吸附到方解石表面的P的最大浓度。第三，水化学影响离子之间对表面位置的竞争。其他离子（包括P）在浸入淡水和海水中时更有效地与CO 32 −竞争，即使HCO 3 −/CO 32 −的浓度在淡水和海水中更高。此外，我们发现，在贫营养条件下，磷吸附是由较高的能量吸附网站，和较低的能量网站在富营养条件下。这项研究是第一次模拟磷吸附机制，以方解石在淡水和海水中。
One of the primary drivers of Phosphorus (P) limitation in aquatic systems is P adsorption to sediments. Sediments adsorb more P in freshwater compared to other natural solutions, but the mechanism driving this difference is poorly understood. To provide insights into the mechanism, we conducted batch experiments of P adsorption to calcite in freshwater and seawater, and used computer software to develop complexation models. Our simulations revealed three main reasons that, combining together, may explain the greater P adsorption to calcite in freshwater vs. seawater. First, aqueous speciation of P makes a difference. The ion pair CaPO4−is much more abundant in freshwater; although seawater has more Ca2+ions, MgHPO40and NaHPO40are more thermodynamically favored. Second, the adsorbing species of P make a difference. The ion pair CaPO4−(the preferred adsorbate in freshwater) is able to access adsorption sites that are not available to HPO42−(the preferred adsorbate in seawater), thereby raising the maximum concentration of P that can adsorb to the calcite surface in freshwater. Third, water chemistry affects the competition among ions for surface sites. Other ions (including P) compete more effectively against CO32−when immersed in freshwater vs. seawater, even when the concentration of HCO3−/CO32−is higher in freshwater vs. seawater. In addition, we found that under oligotrophic conditions, P adsorption is driven by the higher energy adsorption sites, and by the lower energy sites in eutrophic conditions. This study is the first to model P adsorption mechanisms to calcite in freshwater and seawater.