Fig. 4. Adsorption behaviors of Cr(iii) on GH (A) and GA-GH (B) at pH 3.0 and 3.8, respectively. Adsorption isotherm plots and curves were fitted by Langmuir (dot line) and Freundlich (solid line) models, with the equations given as q_e = q_maxK_LC_e/(1 + K_LC_e) and q_e = K_FC_e^1/n, respectively, where q_e is the amount (mg g⁻¹) of Cr³⁺ ions adsorbed at equilibrium, C_e is the equilibrium concentration (mg L⁻¹) of Cr³⁺ ions, K_L and q_max (maximum adsorption capacity) are the Langmuir constants of adsorption, and K_F and n are the Freundlich constants of adsorption.