This study introduces Fraxinustree leaves as a new, efficient biosorbent for of As(III). A suitable response surface was achieved by running a central composite design (CCD). Simultaneous optimization of both responses (R% and q) was carried out and 67% of the goal of desirability function was attained. The results obtained for simultaneous optimization are: R=70 % and q = 80.6 mgg-1 with 67 % desirability in m = 600 mgL-1 where s = 0.10 g and pH = 3.9. Langmuir and Freundlich isotherms model were applied in explaining the sorbent-sorbate equilibrium study, and maximum capacity uptake equals 99.97 mg g-1and KL= 0.05 L mg-1 has been obtained. FT-IR and kinetic results were considered to examine the functional groups involved and the adsorption mechanism.
