Deeper Insights into the Bohart–Adams Model in a Fixed-Bed Column

The Bohart–Adams model was one of the most widely used breakthrough models in column experiments. However, it usually provided a poor fit for the modeling of an asymmetric breakthrough curve. This work proposed the n-order Bohart–Adams and fractal-like Bohart–Adams models. The former indicated a nonlinear decay process of the concentration of the adsorbate or residual capacity of the adsorbent, while the latter reflected a diffusion-limited process on the heterogeneous surfaces. The Bohart–Adams and modified Bohart–Adams models were mathematically equivalent. The applicability of the n-order Bohart–Adams and fractal-like Bohart–Adams models was validated by norfloxacin and Cu(II) adsorption in a fixed-bed column. Compared with the Bohart–Adams model, the two new models had better fitting performance with higher R2 and lower χ2 values, and all of the residuals were randomly distributed. The fractal-like Bohart–Adams and modified dose–response models provided the best fitting quality for the adsorption of Cu(II) (R2 = 0.9956 and χ2 = 7.56 × 10–4) and norfloxacin (R2 = 0.9991 and χ2 = 1.37 × 10–4), respectively. This work may provide a practical method for the modeling of the asymmetric breakthrough curves.