Cao Hua, Liu Xinmin, Feng Bo, Sun Jiaqi, Ma Deyuan, Chen Xijing, Li Hang
Chongqing Key Laboratory of Soil Multi-Scale Interfacial Process, College of Resources and Environment, Southwest University, Chongqing, 400715, China.
Sci Rep. 2024 Oct 5;14(1):23169. doi: 10.1038/s41598-024-74563-6.
Traditionally, the surface charge number (SCN) of permanently charged soils/clay minerals is believed to be unaffected by environmental pH. However, recent studies have revealed the occurrence of polarization-induced covalent bonding between H and the surface O atoms of permanently charged clay minerals. This discovery challenges the traditional notions of "permanently charged soil" and "permanently charged clay mineral". The purpose of this study is to confirm that there are no true "permanently charged clay" or "permanently charged soil". In this study, the SCNs of two permanently charged clay minerals, two variably charged clay minerals, five permanently charged soils (temperate soils), and four variably charged soils (tropical or subtropical soils) were measured at different pH values using the universal determination method of SCN. The results showed that: (1) The SCNs of the permanently/variably charged soils and clay minerals decreased significantly with decreasing pH; (2) the SCN of montmorillonite decreased less with decreasing pH than the SCNs of variably charged minerals, whereas the SCN of illite decreased to nearly the same extent, indicating strong polarization-induced covalent bonding between H and the surface O atoms of illite; (3) the SCNs of permanently charged soils decreased to a similar extent as those of variably charged soils with decreasing pH. This study demonstrated that the concepts, "permanently charged clay mineral" or "permanently charged soil", are questionable because of the polarization-induced covalent bonding between H and the surface O atoms of clay minerals.
传统上，人们认为永久带电土壤/粘土矿物的表面电荷数（SCN）不受环境pH值的影响。然而，最近的研究揭示了H与永久带电粘土矿物的表面O原子之间存在极化诱导的共价键。这一发现挑战了“永久带电土壤”和“永久带电粘土矿物”的传统概念。本研究的目的是证实不存在真正的“永久带电粘土”或“永久带电土壤”。在本研究中，使用SCN的通用测定方法，在不同pH值下测量了两种永久带电粘土矿物、两种可变带电粘土矿物、五种永久带电土壤（温带土壤）和四种可变带电土壤（热带或亚热带土壤）的SCN。结果表明：（1）永久/可变带电土壤和粘土矿物的SCN随pH值降低而显著降低；（2）蒙脱石的SCN随pH值降低的幅度小于可变带电矿物的SCN，而伊利石的SCN降低幅度几乎相同，表明H与伊利石的表面O原子之间存在强烈的极化诱导共价键；（3）随着pH值降低，永久带电土壤的SCN降低幅度与可变带电土壤的相似。本研究表明，由于粘土矿物的H与表面O原子之间存在极化诱导共价键，“永久带电粘土矿物”或“永久带电土壤”的概念值得怀疑。
