- Title
- Characterisation, beneficiation, and modelling of gold ore for gravity pre-concentration in a REFLUX™ Classifier
- Creator
- Lowes, Callan Phillip
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Pre-concentration of low grade ores can improve the economics and environmental sustainability of a mining operation significantly, though the performance of the separations may vary depending on the characteristics of the ore. This study was concerned with the application of the REFLUX™ Classifier, which is a gravity separation technology consisting of a vertical section below a system of parallel inclined channels, to pre-concentration of low grade, gold-bearing ores. The aim was to investigate the performance of the system for continuous gravity separation on these poorly liberated feeds, ultimately producing a robust partition surface for the separator which could be used to model the amenability of a given feed to pre-concentration. Continuous steady-state separations were conducted on a porphyry copper-gold ore of nominal top size 1.0 mm using a REFLUX™ Classifier with a 3 mm inclined channel spacing. At a solids throughput of 13.0 t/(m² h), the set point was varied to examine the effect of mass rejection on the recovery of gold. An 85 % overall gold recovery was achieved on the +90 µm portion of the feed through a 40 wt. % rejection of the initial feed mass. This is considered a promising result given the narrow density distribution and broad size range of the feed. Samples of the feed, underflow and overflow were collected from the continuous separations for the purpose of determining the density distributions and deriving the partition surface of the REFLUX™ Classifier. Recognising the issues associated with the sink/float fractionation technique, the approach was taken to determine the density distributions through hydrodynamic fractionation in another REFLUX™ Classifier operating in semi-batch mode. A dense liquid, namely an aqueous solution of lithium heteropolytungstates (LST), was used for the first time as a fluidising medium to provide a stronger buoyancy force compared to water or a 70 wt. % glycerol solution. Theoretical analysis demonstrated that the dense liquid reduces the net particle weight force and hence the terminal settling velocity of the particles, thus promoting shear-induced inertial lift at much lower shear rates compared to the other fluids. This significantly improved the density-based fractionation produced by the inclined channels, amplifying the significance of the particle density. Fractionation data that aligned very closely with sink/float data on different samples over the size ranges −2.0 + 0.090, −1.0 + 0.25 and −0.5 + 0.090 mm was produced in separate investigations using 6, 3 and 1.8 mm channel spacing systems, respectively. Conversely, the water and 70 wt. % glycerol solutions were found to perform poorly, as expected. The validation of the LST flow fractionation method also helped to reaffirm the hydrodynamics of the laminar-shear mechanism (Galvin & Liu, 2011). The focus of the work then shifted to examining the partition surface of the continuous REFLUX™ Classifier with a 3 mm inclined channel spacing. Based on sink/float data for a chromite ore separation, the density cut point, ρ₅₀, decreased as a function of particle size, d, to the power −0.22, while the Ecart Probable, Ep, remained relatively constant at 325 kg/m³ across the −300 + 38 µm size range. The following model then described the variation in the ρ₅₀ as a function of particle size in dimensionless form by introducing the reference particle density and size, ρ₀ and d₀, respectively: (ρ₅₀-1000)/(ρ₀-1000)=(d/d₀ )^-0.28 The partition curves extracted based on the LST flow fractionation technique were then validated against the sink/float data, demonstrating the ρ₅₀ values were determined with remarkable accuracy across the entire size range, while the Ep values were in close agreement above 75 µm. In the context of this study, where the performance of the REFLUX™ Classifier for pre-concentration was assessed to a lower particle size limit of 90 µm, there was confidence in the partition curves extracted using the LST flow fractionation technique. Applied to samples from one of the earlier porphyry copper-gold ore separations over the size range −1.0 + 0.090 mm, the variation in ρ₅₀ was well-described by the above model, adjusted only by ρ₀, despite differences in the ore type and particle size range. The partition surface was then applied to the feed density distribution generated through LST flow fractionation to simulate separations at a range of density cut points. Gold recovery modelled as a function of mass rejection agreed closely with the experimental separations. The final part of this study was focused on pre-concentration of a gold-bearing sulfide ore of nominal top size 0.5 mm. A 3 mm inclined channel spacing was used and the solids throughput increased covering the range 13.0-39.4 t/(m² h). Despite being constrained by the mineralogy and poor liberation characteristics of the feed, the efficiency of the REFLUX™ Classifier was shown to be very high in relation to the theoretical optimum. The partition curves for the −0.5 + 0.090 mm separations at 13.0 and 39.4 t/(m² h) were then quantified using LST flow fractionation. Increasing the solids throughput resulted in an increase in the ρ₅₀ and Ep values, though the variation in ρ₅₀ with particle size was consistent with the above model. Combining the complete set of partition data then showed that the REFLUX™ Classifier was described by a universal partition surface adjusted by only ρ₀ to describe the range of feed conditions and process parameters examined in the study.
- Subject
- gravity separation; pre-concentration; REFLUX™ Classifier
- Identifier
- http://hdl.handle.net/1959.13/1453039
- Identifier
- uon:44577
- Rights
- Copyright 2021 Callan Phillip Lowes
- Language
- eng
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