Spatial variations in leaching of a low-grade, low-porosity chalcopyrite ore identified using X-ray μCT

Abstract

This study presents an investigation, using 3D X-ray micro computed tomography (μCT), into the effect of sulfide mineral position within an ore particle on leaching efficiency. Three sections of an unsaturated mini-leaching column that had been packed with agglomerated low-grade, low-porosity chalcopyrite ore and leached with an acidified ferric iron solution were imaged at different stages of a 102 day experiment. Image analysis was used to quantify changes in the mineral content and the influence on this of the mineral distance from the ore particle surface, local voidage and radial position within the column. The main factor affecting the mineral recovery was identified to be proximity of the mineral to the ore particle surface, with recovery decreasing with increasing distance from the ore surface. A maximum leaching penetration was observed to exist at 2 mm from the surface, beyond which no recovery was achieved. Higher recoveries at the column wall indicated that preferential flow in this higher voidage had an additional, albeit smaller, impact on leaching efficiency.

Insights into Ferric Leaching of Low Grade Metal Sulfide-Containing ores in an Unsaturated Ore Bed Using X-ray Computed Tomography

“…A qualitative assessment of fragment specific features such as MS distribution, overall MS grain size, occurrence of veins or atypically high porosity also apparently have little influence on the overall reduction in MS volume (Table 2), although full quantification of the features is beyond the scope of this study. Detailed analysis of leaching efficiency with distance from the particle boundary [21], performed on a different agglomerated column from same deposit suggests preferentially leaching of MS grains within a 2 mm annulus of the particle boundary. Fragments with similar MS volume fractions show a greater difference in behaviour within a single column volume (e.g., 5 and 7; Table 2) than they do along the column (variability between V2 and V3 is same as within V1 for all fragments with MS < 1%), and the range of leaching efficacies along the column is also constant (V1: 22.6% to 83.0% reduction, V2: 22.0% to 98.9% reduction, V3: 35.2% to 96.6% reduction).…”

“…The glass tubing of the column was cropped from all images using a cylindrical mask. The study was conducted using a low-grade ore from the Escondida deposit, containing 0.69 wt % copper (primarily as chalcopyrite (0.5 wt %), chalcocite (0.2 wt %), covellite (0.3 wt %) and bornite (0.1 wt %)), 2.95 wt % iron (including that from pyrite (4.0 wt %)), and 2.02 wt % sulfur [21,23]. Detailed analysis of the sulfide chemistry on a grain scale is beyond the scope of this study, and cannot be resolved by non-destructive techniques at this time.…”

“…The ore was acid agglomerated [24], loaded into a glass leaching column (length = 220 mm; internal diameter = 26 mm), and allowed to air dry. Fines were negligible [21]. The leachate solution, containing 0.1 M H 2 SO 4 with 5 g/L ferric iron (emf = 668 mV, Eh = 865 mV, pH = 1.5), was gravity fed into the column at~4 mL/h from a single drip emitter point source.…”

“…However, the more common mineralised veins contain larger more discontinuous, sometimes isolated, sulfide grains (21) and run through the interiors of fragments. Both forms of vein hosted sulfide are found as conjugate pairs in some fragments.…”

“…Samples can be imaged in situ in small scale laboratory experiments, allowing a consistent ore volume to be monitored over the course of a leaching experiment without disturbing the macro-scale configuration of the packed bed of ore fragments or agglomerated material. To date X-ray µCT application to heap leaching research has been successfully demonstrated for the study of bed voidage evolution [13], ore fracturing [14][15][16], mineral liberation [17] and mineral leach kinetics [18][19][20][21].…”