Weng Liping, Van Riemsdijk Willem H, Hiemstra Tjisse
Department of Soil Quality, Wageningen University, P.O. Box 8005, 6700 EC, Wageningen, The Netherlands.
J Colloid Interface Sci. 2007 Oct 1;314(1):107-18. doi: 10.1016/j.jcis.2007.05.039. Epub 2007 Jun 22.
In this paper, the LCD (ligand charge distribution) model is applied to describe the adsorption of (Tongbersven) humic acid (HA) to goethite. The model considers both electrostatic interactions and chemical binding between HA and goethite. The large size of HA particles limits their close access to the surface. Part of the adsorbed HA particles is located in the compact part at the goethite surface (Stern layers) and the rest in the less structured diffuse double layer (DDL). The model can describe the effects of pH, ionic strength, and loading on the adsorption. Compared to fulvic acid (FA), adsorption of HA is stronger and more pH- and ionic-strength-dependent. The larger number of reactive groups on each HA particle than on a FA particle results in the stronger HA adsorption observed. The stronger pH dependency in HA adsorption is related to the larger number of protons that are coadsorbed with HA due to the higher charge carried by a HA particle than by a FA particle. The positive ionic-strength dependency of HA adsorption can be explained by the conformational change of HA particles with ionic strength. At a higher ionic strength, the decrease of the particle size favors closer contact between the particles and the surface, leading to stronger competition with electrolyte ions for surface charge neutralization and therefore leading to more HA adsorption.
在本文中，采用配体电荷分布（LCD）模型来描述（通贝斯芬）腐殖酸（HA）在针铁矿上的吸附。该模型同时考虑了HA与针铁矿之间的静电相互作用和化学结合。HA颗粒的大尺寸限制了它们与表面的紧密接触。部分吸附的HA颗粒位于针铁矿表面的致密部分（斯特恩层），其余的则位于结构较松散的扩散双层（DDL）中。该模型可以描述pH值、离子强度和负载量对吸附的影响。与富里酸（FA）相比，HA的吸附更强，且对pH值和离子强度的依赖性更大。每个HA颗粒上的反应性基团数量比FA颗粒上的多，这导致观察到的HA吸附更强。HA吸附中更强的pH依赖性与由于HA颗粒比FA颗粒携带更高电荷而与HA共吸附的质子数量更多有关。HA吸附的正离子强度依赖性可以通过HA颗粒随离子强度的构象变化来解释。在较高的离子强度下，颗粒尺寸的减小有利于颗粒与表面之间更紧密的接触，导致与电解质离子在表面电荷中和方面的竞争更强，从而导致更多的HA吸附。
