The diffuse layer model (DLM) is one of the most frequently used surface complexation models (SCM) for predicting cation adsorption onto ferrihydrite. However, the DLM with its existing database sometimes fails to predict cation adsorption, especially in multi-solute systems. Notably, the failure is often attributed to inaccurate selection of the surface complexes and/or underestimation of the site density for DLM formulation. DLM simulations of batch adsorption data conducted with cadmium, copper, lead, and zinc on ferrihydrite in CO₂ free systems demonstrates the ability of the DLM to fit single-solute data reasonably well but highlights its limitations with respect to predicting bi-solute data. Modifications to the DLM were made in two steps. First, spectroscopic evidence was used to guide cation complexation reactions at the ferrihydrite surface. Second, surface characteristics (reactive site density, specific surface area, and acidity constants) of ferrihydrite were updated according to recent literature. Results from this study suggest that when spectroscopic verification is employed and surface site density is increased, a simple two-site DLM can predict cation adsorption on ferrihydrite in single-solute systems for pH data above 3.5 and in most of the bi-solute systems tested.

扩散层模型（DLM）是最常用的表面络合模型（SCM）之一，用于预测阳离子吸附到三水铝石上。但是，DLM及其现有数据库有时无法预测阳离子吸附，尤其是在多溶质系统中。值得注意的是，失效通常归因于表面复合物的选择不正确和/或DLM配方的位点密度低估。用镉，铜，铅和锌在CO _2中的亚铁酸盐上进行批量吸附数据的DLM模拟自由系统演示了DLM合理地拟合单溶质数据的能力，但强调了其在预测双溶质数据方面的局限性。对DLM的修改分两个步骤进行。首先，光谱学证据被用于指导在水铁矿表面的阳离子络合反应。其次，根据最近的文献更新了水铁矿的表面特性（反应部位密度，比表面积和酸度常数）。这项研究的结果表明，当使用光谱验证并增加表面位点密度时，简单的两点DLM可以预测单溶质系统中pH值高于3.5的双溶质系统和大多数双溶质系统中亚铁酸盐上的阳离子吸附。 。