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Performance evaluation of adsorptive removal of Ni(II) by treated waste granular-activated carbon and new granular-activated carbon

Granular-activated carbon is a commonly used adsorbent in water treatment. It can be reused by regeneration when saturated, but there are limits to the number of regenerations in actual engineering. This study created a simple and economical treatment method allowing for the reuse of waste granular-activated carbon (WGAC) that approaches the regeneration limit. The adsorption kinetics, equilibrium, and thermodynamics of Ni(II) onto the treated waste granular-activated carbon (TWGAC) and the new granular-activated carbon (NGAC) were studied. The N2 adsorption/ desorption isotherms, zeta potential, SEM, energy-dispersive spectrometry and FTIR spectra were used to characterize and compare the NGAC and TWGAC. Analysis revealed that the structure of WGAC was severely damaged, but the adsorption capacity and adsorption mechanism after treatment were similar to those of NGAC. Experimental data showed that the pseudo-second-order kinetic model and the Freundlich isothermal model had high correlation coefficients (R2 > 0.99). The maximum adsorption capacity of TWGAC and NGAC was 138.9 and 123.5 mg g–1. Thermodynamic parameters, including the negative values ΔG, positive values ΔH, and positive value ΔS, indicated that the current adsorption processes of TWGAC and NGAC were feasible, spontaneous and endothermic. After three cycles, TWGAC’s removal rate for Ni(II) remained as high as 95.3%.