Adsorption of nickel (II) ions from wastewater using glutaraldehyde cross-linked magnetic chitosan beads: isotherm, kinetics and thermodynamics.

ABSTRACT

Magnetic chitosan beads (MCSB), prepared from solution by using an external magnet, and the adsorption of Ni(II) ions from wastewater by MCSB and its cross-linked derivative with glutaraldehyde (GLU-MCSB) was investigated in an adsorption system. The GLU-MCSB sorbents are insoluble in aqueous acidic solution and improve adsorption capacity. The adsorption process was carried out by considering various parameters, viz. adsorbent dose, contact time, pH and temperature. Thermogravimetric analysis of beads shows that degradation takes place in two stages. Fourier transform infra-red spectra of magnetic beads exhibit an absorption band at 606 cm-1 for Fe-O. The elemental analysis (energy dispersive X-ray analysis) and scanning electron microscopy were used to analyze the structure and characteristics of MCSB and GLU-MCSB. The Ni(II) removal efficiency attains a highest value of 95.12% with cross-linked GLU-MCSB in comparison to 79.5% with MCSB. Adsorption processes follow the pseudo-second-order rate kinetics model, which suggested that the rate-limiting step may be the chemical adsorption rather than the mass transport. The experimental data of adsorption fitted well with the Langmuir and Freundlich isotherms with a high correlation coefficient (R2 > 0.9), showing that monolayer adsorption took place on the surface of GLU-MCSB absorbents. The negative values of entropy change, -175.64 and -163.30 J/(mol·K), and enthalpy change, -54.75 and -49.58 kJ/mol, for MCSB and GLU-MCSB suggest that the process is spontaneous and exothermic in nature.