Physically it is meaningless. Please try to do non-linear fit (Qe vs Ce). Many a times, linear fit results in such absurd values. And, please try to define such a region for adsorption isotherm fit, where the extent of adsorption started from very beginning and gradually it reached the equilibrium.
In my view , it depend on your adsorbent . You can check the zero point charge of the adsorbent then compare there is attraction or replusion i guess it is replusion case. also the entropy of the sorption reaction if entropy negative it means the adsorbent has no affinity for sorption reaction Good Luck