My project is about the absorption of a colored pollutant (Rhodamine B) with a concentration of about 5ppm from an aqueous solution with the help of a polymer adsorbent.
In this regard, I encountered a problem in calculating absorption isotherms:
In the Langmuir model, the value of the intercept in its linear equation becomes negative, and as a result, the Langmuir constant becomes negative.
In the Freundlich model, the slope value in its linear equation is negative, which causes the "n" value in the Freundlich equation to become negative.
Langmuir equation: y = 0.0927x - 0.0102 with R² = 0.9989
Freundlich equation: y = -0.1716x + 2.4921 with R² = 0.9877
I would be grateful if you could guide me
Mohammad Tajik Ijdani, Presumbly you perform equilibrium test in too narrow a range of changes in Co, so the dependence of qe vs Ce is close to stright line with a slight deviation to the left. Besides it is worth noting, that any nonlinear transformation , here function inversion or taking logarithm, can cause various surprises. But is just a guess.
The very high concentration of another ion that can compete with the adsorbate in the adsorption process can cause this problem. I am also trying to decipher the reason.
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