This study focuses on the use of novel Enteromorpha sp. macroalgal biomass (EMAB), for the biosorption of hexavalent chromium from aqueous solutions. The biosorbent was characterized by Fourier transformer infrared spectroscopy, energy dispersive spectroscopy, and scanning electron microscopy techniques. The effect of experimental parameters such as pH, initial concentration of Cr(VI) ions, biosorbent dosage, and temperature were evaluated. The maximum biosorption capacity for Cr(VI) was observed at pH 2.0. The modeling of the experimental data at equilibrium was performed using two parameter isotherm models. Both Langmuir and Freundlich isotherm equations better fitted the equilibrium data. A contact time of different initial Cr(VI) concentrations was about 160 min to attain biosorption equilibrium. The kinetic data were fitted by models including pseudo-first-order, pseudo-second-order, and intraparticle diffusion. The pseudo-second-order and intraparticle diffusion kinetic models adequately described the kinetic data. Moreover, the thermodynamic parameters indicated that the biosorption process was spontaneous, endothermic, and increased randomness in nature. The results showed that EMAB could be used as an effective biosorbent for the removal of Cr(VI) from aqueous solution. List of symbols A TTemkin isotherm equilibrium binding constant (L mg -1 ) b T Temkin isotherm constant (J mol -1 ) b L Langmuir isotherm constant (L mg -1 ) C 0 Initial Cr(VI) concentration (mg L -1 ) C e Cr(VI) concentration in solution at equilibrium (mg L -1 ) E Mean biosorption energy E (kJ mol -1 ) K F Freundlich constant (L g -1 ) K Dubinin-Radushkevich model constant (mol 2 kJ -2 ) K j Jovanovic isotherm constant (L g -1 ) k 1Pseudo-first-order rate constant (min -1 ) k 2 Pseudo-second-order rate constant (g mg -1 min -1 ) k id Intraparticle diffusion rate constant (mg g -1 min -1/2 ) k c Equilibrium constant m Amount of biosorbent (g) n F Freundlich exponent Q 0 Monolayer coverage capacity (mg g -1 ) Q m Maximum adsorption capacity (mg g -1 ) in Dubinin-Radushkevich model q mj Maximum adsorption capacity in Jovanovic model (mg g -1 ) q e Amount of Cr(VI) ions adsorbed per unit mass of biosorbent (mg g -1 ) R Gas constant (8.314 J mol -1 K -1 ) R L Separation factor V Volume of the solution (L) DG°Gibbs free energy (kJ mol -1 ) DH°Enthalpy (kJ mol -1 ) DS°Entropy (J mol -1 K -1 ) ePolanyi potential

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