Synergistic Enhancement of Lead and Selenate Uptake at the Barite (001)–Water Interface

The interactions of heavy metals with minerals influence the mobility and bioavailability of toxic elements in natural aqueous environments. The sorption of heavy metals on covalently bonded minerals is generally well described by surface complexation models (SCMs). However, understanding sorption on sparingly soluble minerals is challenging because of the dynamically evolving chemistry of sorbent surfaces. The interpretation can be even more complicated when multiple metal ions compete for sorption. In the present study, we observed synergistically enhanced uptake of lead and selenate on the barite (001) surface through two sorption mechanisms: lattice incorporation that dominates at lower coverages and two-dimensional monolayer growth that dominates at higher coverages. We also observed a systematic increase in the sorption affinity with increasing co-sorbed ion coverages, different from the assumption of invariant binding constants for individual adsorption processes in classical SCMs. Computational simulations showed thermodynamically favorable co-incorporation of lead and selenate by simultaneously substituting for barium and sulfate in neighboring sites, resulting in the formation of molecular clusters that locally match the net dimension of the substrate lattice. These results emphasize the importance of ion–ion interactions at mineral–water interfaces that control the fate and transport of contaminants in the environment.

重金属与矿物的相互作用，可影响天然水环境中有毒元素的迁移性与生物有效性。重金属在共价键合矿物表面的吸附行为，通常可借助表面络合模型（surface complexation models, SCMs）得到较好的描述。然而，由于吸附剂表面的化学性质处于动态演化过程中，理解难溶性矿物表面的吸附机制颇具挑战。当多种金属离子竞争吸附位点时，吸附过程的解析难度会进一步提升。本研究观测到，铅与硒酸根在重晶石（barite）（001）晶面的吸附量呈现协同增强效应，其吸附机制包含两种路径：低覆盖度下占主导的晶格嵌入，以及高覆盖度下占主导的二维单层生长。同时，我们发现吸附亲和力随共吸附离子覆盖度的升高呈系统性提升，这与经典表面络合模型中单个吸附过程结合常数恒定的预设相悖。计算模拟结果显示，铅与硒酸根可通过同时替代相邻位点中的钡与硫酸根，实现热力学有利的共嵌入，最终形成局部尺寸与基底晶格净尺寸匹配的分子团簇。上述研究结果凸显了矿物-水界面处离子间相互作用的重要性——这类相互作用直接控制着环境中污染物的归趋与迁移过程。