Adsorptive removal of Ni2+ and Cd2+ from wastewater using a green longan hull adsorbent

The adsorptive removal of Ni2+ and Cd2+ at concentrations of approximately 50mgL(-1) in wastewater is investigated using an agricultural adsorbent, longan hull, and the adsorptive mechanism is characterized. The maximum adsorption capacity of approximately 4.19mg g(-1) Cd2+ was obtained under the optimized conditions of room temperature, pH 5.0, and a solid-to-liquid ratio of 1:30 in approximately 15min. For Ni2+, the maximum adsorption capacity of approximately 3.96mg g(-1) was obtained at pH 4.7 in approximately 20min. The adsorption kinetics for both metal ions on the longan hull can be described by a pseudo second-order rate model and are well fitted to the Langmuir adsorption isotherm. The adsorption mechanism of the longan hull to Ni2+ and Cd2+ ions is shown to be a monolayer adsorption of metal ions onto the absorbent surface. Thereinto, the longan hull adsorbent contains N-H, C-H, C=O, and C=C functional groups that can form ligands when loaded with Ni2+ and Cd2+, which reduces the fluorescence of the dried longan hull material.