Phase distribution identification in the column leaching of low grade ores using MRI

Abstract

Heap bioleaching is gaining importance as an approach for the recovery of valuable metals (e.g. Cu 2+ ) from low grade ores. In this process iron and/or sulfur oxidising microorganisms are used to aid the oxidation of base metal sulfides in the ore, thereby liberating the metal ions into solution. Leach performance is strongly influenced by the contacting of the leach solution and the ore particles. In order to better understand the distribution of the leaching solution on the pore scale in these heaps, MagneticResonance Imaging (MRI) was used to acquire images non-invasively of a section of an irrigated ore bed. This was made possible by the use of specialist MRI acquisition sequences suited to the magnetically heterogeneous environment as presented by the ore material. From the images we were able to determine the pore-occupancy of the liquid and gas phases and to provide novel measurement of the interfacial area between air, leach solution and ore.

MRI and gravimetric studies of hydrology in drip irrigated heaps and its effect on the propagation of bioleaching micro-organisms

“…In the first instance, a specialist magnetic resonance imaging (MRI) method which is insensitive to the metal content of the ore (Fagan et al, 2013;Fagan et al, 2012) is used to examine the liquid flow in the immediate vicinity of the irrigation point where the signal in an MRI acquisition is directly proportional to the liquid volume. The liquid distribution is subsequently monitored using gravimetric techniques in a long-term bioleach of a 132 kg "slice" of agglomerated ore, the results of which are related to the microbial colonisation and mineral recovery in the heap.…”

Magnetic resonance imaging characterisation of the influence of flowrate on liquid distribution in drip irrigated heap leaching

“…The distributions of the different phases (gas, liquid and solid) in the column were mapped and analysed using the methodology developed by Fagan et al (2013). This required the acquisition of images of the unsaturated flowing column at the different flowrates as well as a 3D image of the flooded column.…”

“…The binary flowing images were combined with that of the flooded column to produce phase maps which show the gas, liquid and solid positions within the column. A detailed description of this procedure, how partial volume elements are accounted for in it and hence its accuracy may be found in Fagan et al (2013).…”

“…We have shown in a previous study that maps of the liquid distribution in representative leaching systems can be acquired using a specialist magnetic resonance imaging (MRI) technique called spin echo single point imaging (SESPI) which is immune to the detrimental influence of para-and ferromagnetic species in the ore (Fagan et al, 2013;Fagan et al, 2012) and is able to detect liquid both external and internal to the ore. This technique may be used to determine the liquid distribution and position relative to the solid ore and through analysis of temporal changes in signal magnitude, changes in the flow patterns in the bed may be projected.…”

“…The aim of this paper is to use this approach to quantify the effect of flowrate changes on liquid distribution in representative drip irrigated heap leaching systems, applying the techniques developed in Fagan et al (2013). Two aspects are considered: the liquid flow in a leaching column at steady state and the transient liquid distribution in the immediate vicinity of the drip irrigation point source using a setup with a greater ore bed breadth.…”