Magnetic resonance imaging methods to reveal the real‐time distribution of nickel in porous media

Abstract

Direct and non-destructive measurement of the sorption, diffusion and mobility of ions and molecules in porous media has applications in industry and environmental science. We used magnetic resonance imaging (MRI) to visualize the dynamic distribution of paramagnetic nickel (Ni þ2 ) ions in porous media. Various MRI sequences were tested to image Ni 2þ at small concentrations. Noisy gradient echo images had poor contrast between samples containing various Ni 2þ concentrations. Turbo spin echo and spoiled gradient echo images showed a linear relation between Ni 2þ concentrations and signal intensity over a wide range of concentrations. Spoiled gradient echo images resolved Ni 2þ concentrations (down to 30 mg litre À1 ) better than turbo spin echo images. However, for smaller concentrations, uncertainty in intensity values increased. A T 1 measurement, obtained using an inversion recovery sequence, showed a linear correlation between T 1 and Ni 2þ concentration down to 1.5 mg litre À1 . In a glass bead medium with an ion exchange resin as an Ni sink, the real-time development of the Ni 2þ depletion zone around the resin, as Ni was sorbed into the resin, was imaged by T 1 mapping. A spatial resolution of 0.58 mm and a temporal resolution of less than a minute were achieved. The two-dimensional Ni 2þ gradient that was determined from MRI agreed well with geochemical modelling results. The results of this study showed that MRI, in particular T 1 mapping, can quantify microscale behaviour of paramagnetic species in porous media. However, ferromagnetic components that naturally occur in most soils can easily disturb the MRI signal.

Magnetic resonance microscopy of iron transport in methanogenic granules

“…In situ metal concentrations can be measured by microelectrodes, but these microelectrodes are poorly developed [7]. Magnetic Resonance Imaging (MRI) can measure metal transport in porous matrixes non-destructively and non-invasively based on changes in spin-lattice (T 1 ) or spin-spin (T 2 ) relaxation times due to the presence of paramagnetic metal ions [8][9][10][11][12][13]. Although MRI measurements have often been applied to reveal structural and diffusional properties of microbial biofilms [14][15][16][17][18][19], only a few studies have focused on metal-biofilm interactions [20][21][22][23][24].…”

“…Single methanogenic granules were exposed to an [FeEDTA] 2À solution and the consequent penetration of iron into the granule was followed in time using T 1 weighted 3D Turbo Spin Echo (TSE) methods [9,26,27]. Using 3D TSE, a spatial resolution of 109 Â 109 Â 218 lm 3 and a temporal resolution of 11 min was achieved.…”

Analysis of nickel concentration profiles around the roots of the hyperaccumulator plant Berkheya coddii using MRI and numerical simulations

“…In a previous study we developed a MRI method to study the temporal and spatial distribution of dissolved Ni 2+ ions in a porous medium under the influence of absorption by an exchange resin (Moradi et al 2008). Here we showed that MRI can detect concentration profiles and thus can be used to investigate Ni 2+ uptake by hyperaccumulator plants in a more complex system.…”

“…Among other new techniques, Magnetic Resonance Imaging (MRI) has been proposed to assess the spatial distribution of water and metal ions in porous media (Herrmann et al 2002;Pierret et al 2003;Moradi et al 2008). The presence of paramagnetic ions and molecules in a solution affects the spin vector relaxation times (longitudinal relaxation time T 1 and transverse relaxation time T 2 ) of water protons ( 1 H).…”

Iron, Cobalt, and Gadolinium Transport in Methanogenic Granules Measured by 3D Magnetic Resonance Imaging

“…Transport of various metals and their various chemical species has been measured using MRI in many different porous media such us sandy aquifers (Nestle et al, 2003;Moradi et al, 2008) or various biomatrixes (Donahue et al, 1994;Nestle and Kimmich, 1996;Bartacek et al, 2009). In a previous paper (Bartacek et al, 2009), we described the methodology for MRI measurements in single anaerobic granules using a mixture of Fe 2+ and [FeEDTA] 2− .…”