Removal of cyanide from the gold cyanidation plant tailings using graphene-based magnetic nanocomposites

Cyanides are widely used as depressants in the selective flotation of sulphide minerals and as gold solvents in the gold cyanidation process. Despite widespread application of cyanide compounds in the mineral processing industry, they are highly toxic to humans and aquatic organisms. In this research study, two novel and efficient graphene-based magnetic nanocomposite adsorebnts namely magnetic chitosan graphene oxide (MCGO) and magnetic chitosan nitrogen-doped graphene oxide (MCNGO) were synthesized for cyanide removal from aqueous solutions. The prepared adsorbents were characterized by XRF (X-ray florescence), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy), VSM (vibrating sample magnetometer) and FTIR (Fourier transform infrared spectroscopy) techniques. The adsorption experiments showed that at optimum conditions (adsorbent dosage: 1 mg/mL; cyanide concentration: 260 mg/L; pH = 9.5; contact time = 120 min) more than 93 and 98% of cyanide was removed by MCGO and MCNGO, respectively. The relationship between the process variables and the cyanide removal was modelled using the artificial neural networks (ANNs). The kinetic studies revealed that the cyanide adsorption process on the both adsorbents followed the pseudo-second-order kinetic model. The equilibrium data fitted best to the Langmuir model, confirming monolayer adsorption of cyanide on homogeneous surface of the adsorbents. The maximum adsorption capacities of MCGO and MCNGO were found to be 405.3 and 483.74 mg/g, respectively. The thermodynamic analysis indicated that the adsorption process was spontaneous ( increment G(o) < 0), endothermic ( increment H-MChGO(o) = 13.04 kJ/mol; increment H-MChNGO(o) = 15 kJ/mol) and entropy-driven ( increment S-MChGO(o) = 51.48 k J/K.mol; increment S-MChNGO(o) = 58.50 kJ/K.mol). The adsorption experiments on the tailings of a gold cyanidation plant showed that the developed adsorbents were capable of removing more than 90% of cyanide from the real sample.