Abstract :
[en] Heavy metals discharged by industrial wastewater to the environment has become a major public health and environmental concern [1]. For example, heavy metals ions such as Ni (II) and Cu (II) are known to be toxic and must be removed from wastewater. However, Ni (II) and Cu (II) ions also have paramagnetic properties which previously allowed the use of Magnetic Resonance Imaging (MRI) and Nuclear Magnetic Resonance (NMR) relaxometry to follow their migration and their adsorption on different media [2-3]. The purpose of this study is to monitor the removal of Ni (II) and Cu (II) from water by amberlite IR120 with T1 and T2 relaxometry. In order to obtain the adsorption isotherms, different samples containing the same amount of Amberlite IR120 resin was put in contact with aqueous solutions containing Ni (II) or Cu (II) ions at different concentrations, before being shaken by a vortex mixer. Once the equilibrium reached, the longitudinal and transversal relaxation time (T1, T2) of the solution was measured which allowed the determination of the amount of adsorbed metal. Study of the loaded resin was afterwards carried out using a larger amount of resin which was dried and rehydrated before being analyzed. The equilibrium adsorption behavior of Ni (II) or Cu (II) can be satisfactorily described by the Langmuir model, with maximum adsorption capacity of 81.5 mg g-1 and 78.3 mg g-1 for Cu (II) and Ni (II) respectively whereas the sorption equilibrium constants are 0.98 mM-1 (Cu (II)) and 1.8 L mM-1 (Ni (II)). The longitudinal and transverse relaxation of the wet resin are shown to be biexponential. The relaxation rate of the fast relaxing water fraction of the wet resin can be correlated with metal contents obtained by Atomic Emission Spectroscopy (ICP-AES). The next step will be to reproduce these experiments for other adsorbents and paramagnetic ions at different magnetic fields. With this methodology, the adsorption could be followed with low-cost portable NMR device. In the future, it will also be interesting to carry out a so-called NMR column experiment in order to investigate the adsorption within the resin in real-time.
References: [1] Tchounwou, P. B., Yedjou, C. G., Patlolla, A. K., & Sutton, D. J., Molecular, Clinical and Environmental Toxicology. Experientia Supplementum, 2021, 101, 133-164. [2] Gossuin, Y., Hantson, A.-L., & Vuong, Q. L, Journal of Water Process Engineering, 2020, 33, 101024. [3] Gossuin, Y., & Vuong, Q. L., Separation and Purification Technology, 2018, 202, 138-143.
