Modeling of the fractal-like adsorption systems based on the diffusion limited aggregation model

The modeling of the fractal-like adsorption systems, such as the sludge-, algae-, and nanoparticle aggregation-pollutants systems, is of vital significance to understand the mechanisms involved and to connect the mechanisms with the isotherms. But it has not been studied yet. In this paper, a three-dimensional DLA (diffusion limited aggregation) model was modified and used to investigate the fractal-like adsorption systems which were dominated by the physical, chemical, ion exchange and multi-mechanisms. The connection between the adsorption isotherms and the adsorption mechanisms was established. The results showed that the shape and filling degree of the modified DLA model was improved. The adsorption capacity of the fractal-like adsorption system increases with the increase of the fractional dimension of the DLA model. The chemical adsorption capacity is directly proportional to the adsorption active sites. In the ion exchange system, the structure of the DLA model did not change before and after adsorption. The BET, Sips, and ion exchange isotherms could adequately represent the physical, chemical, and ion exchange adsorption. For the multi-system, the adsorption isotherm was C-shaped with the fractal dimensions of the DLA model of 2.28 and 2.42. When the fractal dimensions increase, the isotherm was S-shaped and linear. (C) 2020 Elsevier B.V. All rights reserved.