Utilization of groundwater treatment plant (GWTP) sludge for nickel removal from aqueous solutions: Isotherm and kinetic studies

In this study, the potential of groundwater treatment sludge reuse in the adsorption of nickel ions from aqueous solutions was evaluated. The effects of varying solution pH (4.5, 5.5, 6.5, 7.5), initial nickel concentrations (10, 50, 100, 200 mg L-1) and contact time (10, 30, 60 120 min) on Ni(II) removal were investigated. Results showed that the pH level had no significant effect on the Ni(II) removal. At all pH levels, the amount of nickel adsorbed increased from 1.3 mg g(-1) to a maximum of 11.6 mg g(-1) as the initial Ni(II) concentration was increased from 10 to 200 mg L-1. The nickel adsorption on the sludge at all pH levels was described by the Freundlich model, as implied by the high coefficient of determination (R-2) values of 0.9890 to 0.9977 for this model. The adsorption affinity constant (n value) obtained from the Freundlich equation, which ranged from 2.98 to 3.10, suggests chemical adsorption of nickel on the sludge. The kinetic data of nickel adsorption on the sludge at pH 6.5 and initial Ni(II) concentrations of 50, 100 and 200 mg L-1 was best described by the pseudo-second order adsorption kinetic rate model, with coefficient of determination values ranging from 0.9945 to 0.9995, indicating that chemisorption between the sludge binding sites and Ni(II) governs the adsorption process. The results of the study confirm the applicability of the groundwater treatment sludge as a low-cost alternative for nickel removal from wastewater.