Comparative evaluation of chitosan and natural marly clay for Co2⁺ and Ni2⁺ removal from aqueous solutions: kinetic, selectivity, and pH studies
摘要
Chitosan and natural marly clay were investigated as low-cost and environmentally friendly adsorbents for the removal of Ni2⁺ and Co2⁺ ions from aqueous solutions. X-ray diffraction (XRD) analysis revealed the predominantly amorphous structure of chitosan, while natural marly clay exhibited several crystalline peaks associated with mineral phases. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of functional groups and mineral surface site. Kinetic experiments showed that equilibrium was reached after 180 min for both adsorbents. Chitosan exhibited the highest adsorption performance, with adsorption capacities of 30 mg g⁻1 for Co2⁺ and 19.38 mg g⁻1 for Ni2⁺. Natural marly clay also showed significant adsorption capacities, reaching 25.66 mg g⁻1 for Co2⁺ and 15.78 mg g⁻1 for Ni2⁺. In binary systems, chitosan maintained high adsorption capacities for both metals. The kinetic data were well fitted by the applied exponential model, with high correlation coefficients ranging from 0.979 to 0.991. The effect of initial pH revealed that Ni2⁺ adsorption onto chitosan remained nearly constant over the studied pH range, whereas Co2⁺ adsorption slightly decreased with increasing pH. For natural marly clay, the optimum removal efficiencies were obtained at pH 4 for Co2⁺ and pH 5 for Ni2⁺. Overall, these findings demonstrate that both chitosan and natural marly clay are effective adsorbents for heavy metal removal, with chitosan showing superior adsorption performance and stronger affinity toward Co2⁺ and Ni2⁺ ions.