Abstract :
[en] Heavy metals discharged by industrial wastewater to the environment has become a major public
health and environmental concern [1]. In this context, adsorption of metal present in wastewater
by ion exchange resins or adsorbents is one of the most used methods. However, current
techniques to study the adsorption efficiency are indirect and destructive.
In this research, the paramagnetic properties of Ni (II), Mn (II) present in wastewater are used.
Indeed, it is well known that paramagnetic ions affect the Nuclear Magnetic Resonance (NMR)
relaxation times of water protons, which can be measured by benchtop NMR relaxometry [2-3].
Therefore, the purpose of this study is to prove the abilities of direct and non-destructive NMR
relaxometry to monitor the removal of paramagnetic heavy metals.
In order to study the adsorption kinetics, a sample containing a small amount of resin (Amberlite
IR120) was put in contact with aqueous solutions containing the paramagnetic ion of interest
before being shaken by a vortex mixer. The transverse relaxation time (T2) was measured at
different time intervals which allowed the monitoring of the amount of adsorbed metal. Repeating
the same experiment with different metal concentrations provided the adsorption isotherms.
The equilibrium adsorption behavior of all metal ions can be satisfactorily described by the
Langmuir model, with maximum adsorption capacity of 84.1 mg g-1 and 50.3 mg g-1
for Ni (II) and
Mn (II) respectively whereas the sorption equilibrium constant are 1.55 L mg-1
(Ni (II)) and 40.2 L
mg-1
(Mn (II)). Experimental kinetic data fitted well with the pseudo-second-order kinetic model.
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,101, 133-164 (2012).
[2] Gossuin, Y., Hantson, A.-L., & Vuong, Q. L, Journal of Water Process Engineering, 33, 101024 (2020).
[3] Gossuin, Y., & Vuong, Q. L., Separation and Purification Technology, 202, 138-143 (2018).
