Rapid elimination of copper (II), nickel (II) and chromium (VI) ions from aqueous solutions by charcoal modified with phosphoric acid used as a green biosorbent

Activated carbon modified by phosphoric acid noted CAa was successfully used as a new low-cost adsorbent for removing Cu2+, Ni2+ and Cr6+ metal ions from artificially contaminated aqueous solutions. Experiments were performed in batches for adsorption kinetics and isotherms. Scanning electron microscope (SEM) observations as well as a nitrogen adsorption-desorption BET surface area measurement showed the formation of mesoporous CAa with an average pore size of 3.1 nm and a surface area of ABET = 678.74 m(2) g(-1). The adsorption data for Cu2+, Ni2+ and Cr6+ fitted well with Langmuir adsorption model with maximum adsorbed amount of 238.10 mg g(-1) for Cu(II), 80.64 mg g(-1) for Ni(II) and 125 mg g(-1) of Cr(VI) with the maximal amount measured by N-2 adsorption of 231.5337 cm(3) g(-1) STP. The experimental variables studied were pH, temperature, amount of biomass and initial ion concentration. Maximum biosorption was observed for pH = 2. The adsorption capacity seems to be optimized by increasing the temperature, the amount of biosorbent and the initial concentration. Isotherm adsorptions are in agreement with Langmuir models. The calculated changes in adsorption free energy (Delta G degrees), enthalpy (Delta H degrees) and entropy (Delta S degrees) confirm that the present adsorption process is a favorable, endothermic and spontaneous phenomenon.