A systematic research study was carried out in order to characterize the rheology of concentrated slurries prepared from eight nickel laterites. The experiments were carried out using a rotational viscometer, and the behavior of the laterites was evaluated in terms of the apparent viscosity and yield stress obtained through flow curve modeling. An attempt was made to correlate the results obtained for the laterite samples with data obtained for model single mineral systems as well as for model mixed mineral systems. In combination with detailed mineralogical characterization of the laterite samples, all the rheological results allowed a rheology-based laterite classification system to be proposed. Accordingly, the laterite samples gave the following responses: the SAPSIL samples (high-quartz) generally producedl ow yield stress values, the SAPFE samples (high-iron) were characterized by intermediate to high yield stress values, while the SAP samples (saprolite) gave the highest yield stress values. Interestingly, these dominant rheological responses of laterites could actually be predicted based on rheological tests carried out on model mineral suspensions (particularly goethite and quartz). Since the rheology of fine mineral suspensions is largely determined by the surface properties (surface charge) of the particles, a series of electro-acoustic measurements were also performed on model minerals and laterite samples to analyze the surface charge characteristics of the tested samples. It was demonstrated that the current electro-acoustic theory developed for single mineral systems can readily be used for modeling the behavior of mixed mineral systems. The modeling and experimental data agreed exceptionally well when constituent minerals were of the same surface charge under given pH. Clear but rather small deviations between experiment and theory were observed under conditions when the minerals were oppositely charged. This observation strongly suggested that inter-particle aggregation was most likely responsible for the observed discrepancies. Overall, the results of this thesis show that laterite slurries exhibit a wide range of rheological responses due to highly variable mineralogy, differences in particle size distributions, and difference in the surface properties of the many constituent minerals. It also shows that the surface properties of the minerals relates to rheology.

Nickeliferous laterite ores are currently processed using complex energy intensive flowsheets. Limited mineral upgrading can be achieved by low-cost mineral processing as the nickel is not found as a separable mineral phase but finely disseminated throughout the host goethite mineral. Whole ore extraction processes are required which result in intrinsically higher capital and operating costs. Market pressure has provided incentives to develop alternative upgrading techniques that can produce a nickel concentrate and reduce the material input to downstream processing facilities. Thermal upgrading through a selective reduction mechanism to produce a ferronickel concentrate has been studied extensively and has shown promising potential. In this research, a two stage selective reduction of nickeliferous laterite ore was investigated at 600oC and 1000 – 1100oC with varying coal and sulphur additions. Experiments showed that the limonite ore could be selectively reduced using a coal additive to a ferronickel and wustite phase. A combination of XRD and bromine/methanol diagnostic leach tests confirmed the presence of metallic nickel and iron in the calcine. Higher degrees of metallization corresponded with higher sulphur additions and growth zone temperatures. Sulphur was added to improve particle growth through the establishment of a Fe-O-S liquid phase, which was found to improve Ni recovery from 13.8% to 75.8% over the range of 0 – 4 wt% S. Ferronickel particles ranging in size from 20 – 60 microns were shown to be present but highly dispersed throughout the upgraded ore. Particle growth improved with higher growth zone temperatures and longer retention times. Magnetic separation of the calcine showed maximum upgrading of grades to 3 – 4 wt% nickel with recoveries ranging from 83.7 – 93.2%. Partial oxidation of wustite particles to magnetite caused the particles to be magnetic and resulted in recovery of unwanted iron oxides. The presence of iron oxide fines was believed to allow for rapid oxidation of wustite phase and also produce slimes that hindered physical separation of the upgraded ore. / Thesis (Master, Mining Engineering) -- Queen's University, 2013-12-29 22:34:20.417

No description available.

No description available.

A systematic research study was carried out in order to characterize the rheology of concentrated slurries prepared from eight nickel laterites. The experiments were carried out using a rotational viscometer, and the behavior of the laterites was evaluated in terms of the apparent viscosity and yield stress obtained through flow curve modeling. An attempt was made to correlate the results obtained for the laterite samples with data obtained for model single mineral systems as well as for model mixed mineral systems. In combination with detailed mineralogical characterization of the laterite samples, all the rheological results allowed a rheology-based laterite classification system to be proposed. Accordingly, the laterite samples gave the following responses: the SAPSIL samples (high-quartz) generally producedl ow yield stress values, the SAPFE samples (high-iron) were characterized by intermediate to high yield stress values, while the SAP samples (saprolite) gave the highest yield stress values. Interestingly, these dominant rheological responses of laterites could actually be predicted based on rheological tests carried out on model mineral suspensions (particularly goethite and quartz). Since the rheology of fine mineral suspensions is largely determined by the surface properties (surface charge) of the particles, a series of electro-acoustic measurements were also performed on model minerals and laterite samples to analyze the surface charge characteristics of the tested samples. It was demonstrated that the current electro-acoustic theory developed for single mineral systems can readily be used for modeling the behavior of mixed mineral systems. The modeling and experimental data agreed exceptionally well when constituent minerals were of the same surface charge under given pH. Clear but rather small deviations between experiment and theory were observed under conditions when the minerals were oppositely charged. This observation strongly suggested that inter-particle aggregation was most likely responsible for the observed discrepancies. Overall, the results of this thesis show that laterite slurries exhibit a wide range of rheological responses due to highly variable mineralogy, differences in particle size distributions, and difference in the surface properties of the many constituent minerals. It also shows that the surface properties of the minerals relates to rheology.

Lateritisation is associated with tropical climates and geomorphic conditions of peneplanation where hydromorphic processes of weathering predominate. Laterites are products of relative (residual) and absolute(chemical) accumulation after leaching of mobile constituents. Their major element chemistry is controlled by the aluminous character of bedrock and drainage. Bauxitisation is characterised by residual gibbsite neoformation and lateritisation, by both residual accumulation and hydromorphic precipitation of goethite controlled by the redox front at the water table. The laterite forms part of a weathering profile that is underlain by saprock, saprolite, the mottled zone and overlain by a soil horizon. The secondary gold in laterites has its source invariably with mineralised bedrock. The distribution of secondary gold is controlled by mechanical eluviation and hydromorphic processes governed by organic, thiosulphate and chloride complexing. The precipitation of secondary gold is controlled by pH conditions, stability of the complexing agent and ferrolysis. Gold-bearing laterites are Cainozoic in age and are best developed on stable Archean and Proterozoic cratons that have suffered epeirogenesis since lateritisation. Mechanical eluviation increases in influence at the expense of hydromorphic processes as a positive function of topographic slope and degradation rate. Gradients greater than 10⁰ are not conducive for lateritisation, with latosols forming instead. High vertical degradation rates may lead to the development of stone lines. In the Western Australian case, post-laterite aridification has controlled the redistribution of secondary gold at levels marked by stabilisation of the receding palaeowater table. Mineable reserves of lateritic ore are located at Boddington, Westonia and Gibson toward the south-west of the Yilgarn Block. A significant controlling variable appears to be the concentration of chloride in the regolith. Based on the Boddington model, the laterite concentrates the following elements from bedrock gold lodes: i) Mo, Sb, W, Hg, Bi and Au as mobile constituents. ii) As and Pb as immobile constituents. Geochemical sampling of ferruginous lag after bedrock and laterite has provided dispersed anomalies that are easily identifiable. "Chalcophile corridors" up to 150 km in length are defined broadly by As and Sb but contain more discrete anomalies of Bi, Mo, Ag, Sn, W, Se or Au, in the Yilgarn Block. The nature of the weathered bedrock, the tabular distribution of secondary gold ore deposition and the infrastructural environment lends the lateritic regolith to low cost, open-cut mining. The western Australian lateritic-gold model perhaps can be adapted and modified for use elsewhere in the world.

A systematic research study was carried out in order to characterize the rheology of concentrated slurries prepared from eight nickel laterites. The experiments were carried out using a rotational viscometer, and the behavior of the laterites was evaluated in terms of the apparent viscosity and yield stress obtained through flow curve modeling. An attempt was made to correlate the results obtained for the laterite samples with data obtained for model single mineral systems as well as for model mixed mineral systems. In combination with detailed mineralogical characterization of the laterite samples, all the rheological results allowed a rheology-based laterite classification system to be proposed. Accordingly, the laterite samples gave the following responses: the SAPSIL samples (high-quartz) generally producedl ow yield stress values, the SAPFE samples (high-iron) were characterized by intermediate to high yield stress values, while the SAP samples (saprolite) gave the highest yield stress values. Interestingly, these dominant rheological responses of laterites could actually be predicted based on rheological tests carried out on model mineral suspensions (particularly goethite and quartz). Since the rheology of fine mineral suspensions is largely determined by the surface properties (surface charge) of the particles, a series of electro-acoustic measurements were also performed on model minerals and laterite samples to analyze the surface charge characteristics of the tested samples. It was demonstrated that the current electro-acoustic theory developed for single mineral systems can readily be used for modeling the behavior of mixed mineral systems. The modeling and experimental data agreed exceptionally well when constituent minerals were of the same surface charge under given pH. Clear but rather small deviations between experiment and theory were observed under conditions when the minerals were oppositely charged. This observation strongly suggested that inter-particle aggregation was most likely responsible for the observed discrepancies. Overall, the results of this thesis show that laterite slurries exhibit a wide range of rheological responses due to highly variable mineralogy, differences in particle size distributions, and difference in the surface properties of the many constituent minerals. It also shows that the surface properties of the minerals relates to rheology. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

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With large populations living in tropical regions of the world with volcanic substrates, understanding basalt weathering processes is vital. The Hawaiian Islands are an excellent natural analogue to study chemical weathering rates due to a uniform bedrock (basalt), large variations in rainfall, and varying ages across the islands. Laterite weathering profiles (LWP) develop over time through chemical weathering, where LWP thickness is influenced by many factors, including precipitation and time. Using the rapid, non-invasive horizontal-to-vertical spectral ratio (HVSR) method, LWP thicknesses can be estimated to constrain chemical weathering rates. Studying the laterite weathering profiles developed from basaltic bedrock of varying ages on Oahu (~2 Ma), Molokai (~1 Ma) and Kohala, Hawaii (~0.3 Ma) reveals three profiles in varying developmental stages. Over 200 HVSR soundings were collected on Oahu, Molokai, and Kohala. Shear wave velocity values of LWPs were determined by MASW (multichannel analysis of surface waves), and LWP thicknesses verified from geologic logs and outcrop. Oahu has thick LWPs compared to the other islands and shows a trend of increasing thickness with increasing precipitation across the island. The Molokai LWP follows a trend similar to Oahu, with a noticeable difference of thicknesses (20-40 m) at similar precipitation thresholds. Molokai presented a unique case, where the shear-wave velocity (Vs) boundaries between laterite and basalt were gradational for ~43% of HVSR datapoints, resulting in featureless frequency spectra that could not reliably model laterite-basalt boundary depths. The gradational nature of the LWP of Molokai is attributed to the young age of the island, and primary permeability properties of the thick, post-shield alkalic lavas. Molokai has an aerially average weathering rate of 0.02 to 0.04 m/ka. Kohala HVSR data show a newly developed LWP with varying LWP thickness within the same precipitation isohyet. LWPs on Kohala show a unique trend where LWP is thickest along the coast and is wedge shaped thinning out towards higher elevations. Each island differs in age and has its own unique LWP trends, with older islands tending to have deeper, more developed LWPs at similar precipitation ranges.

Pas de résumé en français disponible / Locally available building materials are proven energy efficient and eco-friendly, making them a sustainable building material. In the last two decades, use of raw earth as building material is augmented, owing to the environmental concerns construction industry is also reconsidering the use of raw earth, researchers on the other hand are working to understand the mechanical and dynamic behaviour of earthen buildings, yet the study of mechanical parameters possess multiple challenges due to material inert properties exposing the need of new experimental approaches to extract accurate mechanical parameters. Building techniques such as adobe, compressed earth blocks, rammed earth, and laterite building stones are on a verge of reclaiming elite position in construction industry. In this study, experimental investigation on two naturally available building materials, unstabilised rammed earth (USRE) and laterite building stones (LBS) are carried out. The work focuses on the parameters that need to be considered in the experimental procedures, which influences the mechanical properties of USRE and LBS are seen. The locally available soils in the region of Rhone-alps, France and laterite building stones from Burkina Faso are used in this experimental campaign. Rammed earth walls are constructed by compacting moist soil in layers, due to manufacturing technique there is a density gradient within the layer that leads to heterogeneity. On the other hand, the manufacturing parameters of the USRE such as compaction energy and manufacturing water content have a direct influence on the dry density of the material and therefore the strength. The manufacturing parameters and specimens replicating the in-situ condition are very important to understand the behaviour of USRE wall. Hence an experimental procedure to study the unconfined compressive strength, considering the influence of manufacturing parameters and specimens replicating in-situ conditions are performed along with the cyclic loading and unloading to study the elasto-plastic property of the USRE. The test procedure is performed on two different soils that are used to build USRE structures. Along with the compressive strength of USRE, the tensile strength and flexural strength are also presented by subjecting specimens under split tensile test and four point bending test. Another important parameter is the mechanical strength properties of USRE layer interface under lateral loads. A novel experimental procedure to study the interface strength properties are discussed in this study. The experimental procedure is simple and xii compact that can be performed using a simple uniaxial press using inclined metallic wedges that allows rectangular prism to undergo bi-axial loading. With the help of inclined metallic wedges, shear stress and normal stress can be induced on the specimen interface allowing to obtain coulomb’s failure criteria and hence the strength properties of the interface. Laterite building stones (LBS) which are mainly used in tropical countries are porous in nature. The moisture retention capacity of porous building material will bring indoor comfort, but the presence of water molecules within the material and their variation to the outdoor environment is responsible for complex mechanical behaviour. Hence an experimental investigation to analyse the moisture ingress of LBS and their influence on mechanical strength is designed. The moisture ingress is studied by subjecting LBS for moisture sorption and desorption test and moisture buffering test. Then the influence of moisture ingress on mechanical strength (flexure and compression) are investigated using three point bending test and unconfined compression test with loading and unloading cycles. This experimental investigation allows studying the moisture ingress and their influence on strength along with elasto-plastic behaviour of LBS.