The principal objectives of the work described in this thesis were: 1. To develop an improved multiphase CFD model for classifying cyclones and further improve understanding of the separation mechanism based on fluid flow and turbulence inside the cyclone. 2. To develop an improved Empirical model of classifying cyclones, covering a wide range of design and operating conditions. The multi-phase CFD model developed in this work is based on the approach reported by Brennan et al (2002) and Brennan (2003) using Fluent, and involves individual models for the air-core, turbulence, and particle classification. Two-phase VOF and mixture models for an air/water system were used to predict the air-core and the pressure and flow fields on 3D fitted fine grids. The turbulence was resolved using both DRSM (QPS) and LES turbulence models. The predicted mean and turbulent flow field from the LES and DRSM turbulence models were compared with the LDA measurements of Hsieh (1988). The LES model predicts the experimental data more accurately than the DRSM model. The standard mixture model (Manninnen et al, 1996) and the modified mixture model for a water/air/solids system were used to predict cyclone performance. The standard mixture model was able to predict classification efficiency reasonably at low solids concentrations, but under-predicts the recovery of coarse size fractions to underflow. To improve the predictions at moderate to high feed solids, the author modified the slip velocity with additional Bagnold dispersive forces, Saffman lift forces, and a hindered settling correction for particle drag in the mixture model superimposed on an LES turbulence model. Several cyclone geometries were used for validating the multiphase CFD model. The modified mixture model improves prediction of the separation of coarse size particles, and the predicted closely matches the experimental in various cyclones. The particle classification mechanism has been further elucidated using the simulated particle concentration distributions. At high solids concentrations, the modified CFD model predicts the efficiency curve reasonably well, especially the cut-size of the cyclone, but prediction of fine particle recovery to overflow is poor compared to the experimental data. It appears that the fines are significantly affected by turbulent dispersion and the flow resistance due to the high viscosity of the slurry at the apex is not sufficiently accounted for in the modified Mixture model. The improved multi-phase CFD model was validated against two sets of experimental data available in the literature: particle concentrations measured by gamma ray tomography data in a dense medium cyclone (Subramanian, 2002), and particle size distribution inside a hydrocyclone (Renner, 1976). Large eddy simulation (LES) with the modified Mixture model, including medium with a feed size distribution appears to be promising in predicting medium segregation inside a dense medium cyclone. The CFD predicted sample size distributions at different positions are reasonably comparable with Renner’s (1976) experimental data near the wall and in the bottom cone, but differ considerably near the forced vortex region, and also near the tip of the vortex finder wall. The CFD model shows no air-core formation at the low operating pressure used by Renner, which suggests his experiments involved an unusual/unstable forced vortex based cyclone separation. The effect of turbulence on fluid and solid particle motion was also studied in this thesis. The resolved turbulent fluctuations from LES of the hydrocyclone at steady flow were analysed using ensemble averaging. The ratio of the effective turbulent acceleration of each particle size to the centrifugal acceleration was calculated for various cyclones, which showed that turbulent mixing becomes less important with larger particles. The trends in this ratio correlate with the equilibrium positions of the particles from the multiphase LES. The analysis indicates that the short-circuiting might be aggravated by turbulent mixing across the locus of zero vertical velocity (LZVV) against the classification force, and along the vortex finder wall into the inner upflow region of the cyclone. An experimental study of the “fish-hook” effect was pursued in various industrial scale cyclones to evaluate the effect of various cyclone parameters. The observed diameter at which fine particle recovery starts to increase is mainly affected by feed solids content and spigot diameter, but less influenced by feed pressure. The observed particle recovery to the underflow at the fishhook dip size, the bypass, is always higher than the underflow water split. Any cyclone variable that affects the underflow water split, will also affect the bypass value. CFD studies showing high particle Reynolds numbers for coarse particles were used to provide a qualitative mechanism for fines reporting to the underflow in the wakes behind the larger particles (Tang et all. 1992). The Frachon and Cilliers (1999) model was used to fit and evaluate the fishhook parameters. The variations of these fishhook parameters were quantified for changes in cyclone design and operating conditions. The development of an improved empirical hydrocyclone model was attempted by collecting extensive historical data covering a wide range of cyclones. Additional experiments on 10 and 20 inch Krebs cyclones were performed to fill the gaps in the database, especially at low to moderate feed solids concentration and with different cone sections. Tangential velocity, turbulent diffusion, slurry viscosity and particle hindered settling correlations were identified from CFD as the key inputs to the particle classification mechanism for the empirical model. A new cyclone model structure based on a dimensionless approach has been developed. The model for , , Q gives a very good fit to the data, while the model for separation sharpness gave reasonable correlations with the cyclone design and operating conditions. 208 additional data sets were used to validate the new hydrocyclone model.

Two ombrotrophic peat bogs (NC2 and BL2) from North Stradbroke Island, Australia, were precisely dated using 210Pb and analyzed by scanning electron microscopy. Sub-samples were total digested and sequentially leached for trace and major elements concentrations using ICP-MS and ICP-OES. Total Pb concentrations in both profiles increased with the time. PAAS normalized REE patterns were characterized by relatively flat patterns, with slight enrichment in LREE, and a significant negative Eu anomaly. The temporal changes in metal concentrations, 206Pb/207Pb ratios, REEs, and ash content observed in the two profiles suggest three different periods with distinct conditions in terms of dust provenance and atmospheric pollution: (1) Pre-anthropogenic (pre-1842); (2) Early industrial (from 1840s to 1920s); (3) Industrial (post-1930s). Ombrotrophic peat bogs may be reliable archives of environmental pollution, but also shows that adjacent sites may provide contrasting evidence. Despite their close proximity, the two sites show different trends in metal deposition. Metals in NC appear to be largely bound to minerals and inorganic materials, while in BL they are mainly organic-related. Indeed the peculiar behaviour of Pb in the BL profile suggests that biological process may cause Pb isotopic fractionation. Ash contents, texture, Pb isotopic compositions, Sb/Pb values, patterns of selected trace elements (Pb, Cu, Zn, Cd, Cr, Co, Sb, Ni, Se, As, Be and Mo), and their leaching behaviours suggests that NC and BL are chemically different types of peat bogs. NC peat bog is an open sink for elements, and can be used to define regional anthropogenic impacts. In contrast, the BL site appears to be influenced by local natural and anthropogenic processes and activities, such as changes in land use. Furthermore, it demonstrated that only some of the environmental-related trace elements preserve their original depositional record. Arsenic, Be, Co, and Zn are highly mobile under weak acid conditions, and are therefore not suitable for assessing temporal trends of pollution. Cadmium, Ni, and V may also be highly mobile under certain conditions. In contrast, Pb, Cu, Cr, Mo, and Sb are not subject to vertical migration, and are useful for establishing the pollution record of ombrotrophic peat bogs.

Various organic compounds, including graphitic carbon, can be formed abiotically in hydrothermal systems, such that evidence for early life must necessarily combine geological, morphological and geochemical data to be compelling. Carbonaceous materials (CM) have been isolated from three rock packages of mid to early Archaean age from the Pilbara Craton of Western Australia. This CM has been subjected to a multidisciplinary approach utilising a variety of analytical and observational techniques, in an attempt to establish the occurrence, associations, mineral affinities, historical environments of growth, and the metamorphic/thermal history experienced by what may be some of the earliest, relatively pristine record of 3500 million year old life on this planet. CM isolated from drillcore obtained from the first of these localities, the 3.24 Ga Sulphur Springs volcanic hosted massive sulphide (VHMS) deposit, occurs as isotopically light (δ13C values of −34.0 ‰ to −26.8 δ13C) finely striated, lenticular to banded material emplaced parallel to original sedimentary bedding planes within the fine-grained silicified epiclastic hanging wall sediments. Petrological and transmission electron microscopy (TEM) observations have revealed well-preserved bundles of filamentous and tubular structured microbial remains closely resembling both modern-day and more ancient microbial forms documented from sea floor hydrothermal environments. Total organic carbon (TOC) has a range of <1.0 to 2.3 %, while the thermal maturity (%Ro) of the filamentous bundles points to maximum temperatures since deposition of around 90–100 °C, a factor that has enabled the preservation of their morphology. These results are suggestive of a well-developed Archaean sediment-hosted microbial community, situated within a basinal environment associated with an active centre of seafloor hydrothermal activity. The majority of the CM isolated from drillcore samples of the second locality, the 3.46 Ga Salgash Subgroup, a lower member of the Apex Basalt, also appears as in situ, bedding parallel bands intercalated with foliated altered argillaceous sandstone beds. TOC of the samples ranges from 1.25 to 11.48 %, while carbon content varies from 2.05 to 32.17 %. δ13C results are relatively heavy, varying from -30.4 to -22.5 ‰. Thermal maturity indicators of 10-13 %Ro suggest the CM having been subjected to temperatures greater than normally obtained from processes associated with burial. Electron paramagnetic resonance (EPR) results showed this CM in a highly ordered graphitic state. Optically, the graphite lacks the typical pronounced anisotropy characterising graphites in metamorphic terranes. Graphitisation therefore, is likely the result of rapid heating at very high temperature. HRTEM of this material revealed an extremely high level of molecular ordering contemporaneous with the presence of the C60 fullerene molecules within carbon nanotubes. These forms are a key to the distinction between biologically and abiotically synthesized CM, both by their small size and their resistance to thermal degradation. The occurrence of these carbon forms in terrestrial deposits is rare, and usually associated with wildfires, lighting strike or meteoritic impact. In the case of the Salgash CM, the formation of these molecules and the isotropic graphitised state of the CM is interpreted as a result of emplacement under pressure of very high temperature (komatiitic/ peridotite) lavas. The thermal overprint of the CM by such a high temperature process resulted in the volatilisation of the organic material, destruction of any primary biological morphology and the subsequent reorganisation of the residual CM, resulting in increased molecular ordering. In the third part of the study, CM isolated from drillcore samples of the ca. 3.5 Ga Dresser Formation bedded black chert-barite units, occurs in both dispersed and layered forms, interlayered with fine-grained silica. The intimate association of the CM and silica strongly resembles silicified microbial colonies from active hydrothermal systems, which have been previously proposed as analogues of Archaean hydrothermal sites. Isotopically light δ13C values from -38.2 to -32.1 ‰, and the association of C, H, and N, are highly indicative of a biological origin for the material. Palaeotemperatures calculated from δ18O isotope analysis of quartz chips indicate a depositional temperature for the hydrothermal veins ranging from ~120 °C to ~200 °C. 207Pb-206Pb isotope analyses conducted on pyrites extracted from the interbedded barite units reveal a dual MORB and Erosion mix source for the Pb, which gives an average 207Pb/206Pb age of 3531±42 Ma for the deposit. Ro measurements reveal four distinct CM populations, defined as ACM, A1CM, BCM, and CCM, which represent temperatures ranging from 170 °C to potentially >400 °C. TEM and HRTEM observations of the lower temperature CM population show morphological entities strongly suggestive of microbial remains, including possible cell wall remnants. Higher Ro rank CM commonly fills or coats mineral grains and lacks distinguishable structures, which is consistent with an increased thermal degradation /hydrothermal overprint. The geological setting and mineralogy of the Dresser Formation endorse its formational history as a silica-barite dominated seafloor hydrothermal deposit, most likely analogous to modern “white smokers”. The occurrence of the predominant CM (type ACM) in more or less continuous bands and laminae within the sedimentary rocks suggest an in situ, syndepositional source for the majority of this material, whereas the dispersed nature of type BCM particles indicates a recycled nature. The occurrence of type CCM within fluid inclusions gives an insight into the primary morphology of the non-degraded original microbial cells that may have existed at that time. These observations, combined with the carbon isotopic heterogeneity and fractionations are suggestive of chemosynthetic microbes occupying a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the CM. Finally, in an effort to further understand the CM structures observed in the rocks of the Dresser Formation in the context of present day microbial colonies in similar environments, a comparative morphological study was conducted using a potential modern analogue derived from an active seafloor hydrothermal environment. Such methodology utilises the standard classification used in biological species identification, which is initially based on visual identification of specific features, whether by the naked eye, light microscopy or electron microscopy. The extant hyperthermophilic microbe Methanocaldococcus jannaschii was cultured under conditions similar to the Archaean seafloor, simulating an increased thermal maturity by artificially induced autoclaving at 100 °C (1 atm) and 132 °C (2 atm). A striking resemblance to the early Archaean forms observed in the Dresser CM was evident in both wall structure and thermal degradation mode of the cultured microbe. Cell disintegration of the cultures occurred at 100 °C marking the limits of life, whereas complete disintegration, deformation and shrinkage of the cells occurred at 132 °C. These comparative observations present as a feasible way of understanding the structural features in CM identified in Archaean sedimentary packages.

Two ombrotrophic peat bogs (NC2 and BL2) from North Stradbroke Island, Australia, were precisely dated using 210Pb and analyzed by scanning electron microscopy. Sub-samples were total digested and sequentially leached for trace and major elements concentrations using ICP-MS and ICP-OES. Total Pb concentrations in both profiles increased with the time. PAAS normalized REE patterns were characterized by relatively flat patterns, with slight enrichment in LREE, and a significant negative Eu anomaly. The temporal changes in metal concentrations, 206Pb/207Pb ratios, REEs, and ash content observed in the two profiles suggest three different periods with distinct conditions in terms of dust provenance and atmospheric pollution: (1) Pre-anthropogenic (pre-1842); (2) Early industrial (from 1840s to 1920s); (3) Industrial (post-1930s). Ombrotrophic peat bogs may be reliable archives of environmental pollution, but also shows that adjacent sites may provide contrasting evidence. Despite their close proximity, the two sites show different trends in metal deposition. Metals in NC appear to be largely bound to minerals and inorganic materials, while in BL they are mainly organic-related. Indeed the peculiar behaviour of Pb in the BL profile suggests that biological process may cause Pb isotopic fractionation. Ash contents, texture, Pb isotopic compositions, Sb/Pb values, patterns of selected trace elements (Pb, Cu, Zn, Cd, Cr, Co, Sb, Ni, Se, As, Be and Mo), and their leaching behaviours suggests that NC and BL are chemically different types of peat bogs. NC peat bog is an open sink for elements, and can be used to define regional anthropogenic impacts. In contrast, the BL site appears to be influenced by local natural and anthropogenic processes and activities, such as changes in land use. Furthermore, it demonstrated that only some of the environmental-related trace elements preserve their original depositional record. Arsenic, Be, Co, and Zn are highly mobile under weak acid conditions, and are therefore not suitable for assessing temporal trends of pollution. Cadmium, Ni, and V may also be highly mobile under certain conditions. In contrast, Pb, Cu, Cr, Mo, and Sb are not subject to vertical migration, and are useful for establishing the pollution record of ombrotrophic peat bogs.

Abstract In the existing JKMRC breakage testing method for AG/SAG mill modelling, ore is characterised using mainly high energy single impact tests. However, recent DEM studies have suggested that breakage in AG/SAG mills is mainly due to low energy repetitive (or multiple) collisions rather than single high energy impacts. Furthermore, several of the published AG/SAG ore hardness tests developed outside the JKMRC use laboratory tumbling mills to quantify the specific power required to grind the ore to a set product size. Comprehensive experiments were carefully designed using two mill diameters of 1.1 and 0.6 m to mimic the reported low energy repetitive impact breakage under low load conditions. The ore breakage characterisation parameters derived from high energy single impact tests were used to predict the low energy repetitive impact breakage behaviour. Significant bias has been shown to be associated with the traditional high energy single impact characterisation approach, suggesting an alternative method was required. An extensive experimental program with more than 1400 tests was conducted using a newly developed JKRBT (JKMRC Rotary Breakage Tester) device, gravity drop test and laboratory tumbling mills. Comprehensive data were collected and analysed to provide an understanding of low energy repetitive impact breakage of particles and high energy single impact breakage. Details of the experimental study and findings are presented in Chapter 5. A breakage characterisation model has been developed, which takes into account the various impact energy classes and their associated body breakage and surface breakage responses. The breakage conditions were analysed and used to derive two sets of impact breakage parameters (body breakage and surface breakage). These parameters were then combined using a procedure believed to account for the two key breakage modes in tumbling, and successfully applied to predict the breakage in the two laboratory tumbling mills. Chapter 6 presents the breakage modelling approach and results. Based on the understanding of different breakage modes, a novel particle breakage characterisation method for AG/SAG mill modelling has been proposed and validated. Different from the prior-art JKMRC approach in which the breakage tests are conducted at high energy single impact, the proposed method incorporates high energy single impact, low energy multiple impacts and a simplified tumbling test. Both breakage probability and degree of breakage are used to characterise the breakage behaviour of ores. The details of the new characterisation method can be found in Chapter 7. The studies conclude that • The JKRBT can be used to investigate rock breakage characteristics under single and repetitive impacts; • The breakage of rocks in tumbling mills (under very low load conditions) can be likened to the low energy JKRBT repetitive impact breakage. • The behaviour of particle breakage as observed in AG/SAG milling can be modelled using a combination of JKRBT and tumbling ore breakage characterization; • A methodology for ore breakage characterization for AG/SAG mill modelling has been proposed and validated using independent sets of ores samples.