Estimation of Paramagnetic Ion Concentrations in mine waters by Time Domain NMR

Theme 1. Environmental protection
Session Name 1.8 Modelling and control of water and wastewater treatment in the Arctic conditions
Presentation Type Oral
Author(s) Ekaterina Nikolskaya (South-Eastern Finland University of Applied Sciences, Finland), Mika Liukkonen (University of Eastern Finland, Finland), Yrjö Hiltunen (South-Eastern Finland University of Applied Sciences, Finland)
Abstract text

Tightening requirements for the environmental quality of mining waters necessitate the development of more efficient purification methods. However, today’s commercially available water quality measurements are not able to cope with certain significant contaminants like metal ions in real time. The objects of the study were paramagnetic ions such as Mn2+,Fe2+, Fe3+, Cu2+ and Zn2+, which are the principal metal components in mine waters.

In this paper, the spin-spin relaxation rates R2 of mine waters were measured using a Time Domain Nuclear Magnetic Resonance (TD-NMR) device, which has been modified for online measurements. The pH and R2 data were collected by varying the amounts of metals, nitric acid and sodium hydroxide. The reference concentrations of the metals were measured by X-ray fluorescence spectroscopy (XRF).

First, the relaxation rates for several metal ions were measured at the low pH as a function of concentrations of the ions, and using this data the relaxivities r2 of the metals were determined. Then, experimental relaxation rates R2exp were measured for  mine water during precipitation. The relaxation rate R2calc values were modelled using the concentrations measured by XRF and the relaxivity values of the metals. The experimental and calculated relaxation values have a strong correlation. Finally, the measuring system based on online TD-NMR for determining metal ion concentrations was tested and demonstrated in laboratory conditions.

The presented results show the potential of the TD-NMR method for monitoring the concentrations of metal ions in mine waters.​

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