Study On The Adsorption Mechanism Of Ni²⁺ On Layered Double Hydroxides

In this paper, ZnAl-LDHs and MgAl-LDHs intercalated with CO32-, NO3-, EDTA were synthesized by coprecipitation method. XRD, IR, BET, and SEM were used to characterize the structure and morphology of LDHs. The samples were added to the solution of Ni(NO3)2·6H2O in order to study the adsorption properties. The concentration of Ni2+ was examined at real-time by ICP analysis. The adsorption kinetics were studied.The XRD patterns are characteristic of a layered phase with the basal diffraction due to planes (003), (006) and (110). FT-IR spectra indicate that CO32-, NO3- and EDTA were intercalated between the layers respectively. As the specific surface of the LDHs increase, the saturated adsorptive capacity increases. ZnAl-CO3-LDHs (Zn/Al molar ratio=2) has the maximum capacity, up to 19 mg/g, that is about 96% Ni2+ in the solution. The Pseudo second equation can perfectly fit the Ni2+ adsorption process on LDHs, indicates a chemispoption mechanism being the rate-determining step.Mg-Al LDHs have a characteristic layered structure, and CO32-, NO3- and EDTA were intercalated between the layers respectively. CO3-LDHs with the molar ratio of (3:1) which has the maximum adsorptive capacity about 84 mg/g.As An adsorptive material of Ni2+, the LDHs with big specific surface have favourable properties. Especially the MgAl-CO3-LDHs can reduce the Ni2+ concentration to 0.0087 mg/L which is much less than the standard 0.5mg/L of GB8978-2002. Obviously, LDHs can be expected to put in fact in the treatment of Ni2+ contained in the wastewater.