Dissertations / Theses on the topic 'Fine tailings'

Mature fine tailings (MFT), as a mixture of residual bitumen, sand, silt, fine clay particles and water, are a byproduct of oil sands extraction. The large volume, and poor consolidation and water release ability of MFT have been causing significant economic and environmental concerns. Therefore, several studies have been implemented on finding innovative dewatering/disposal techniques. As a result, different methods have been introduced and tested at a laboratory or a field scale, yet very few of these are commercially used in the oil sands industries. Despite the extensive research, an optimal solution has not been found due to the lack of technical or economic feasibility. In the present study, a novel approach that consists of the rapid dewatering of MFT by using a super absorbent polymer (SAP) to produce dense MFT is proposed. A comprehensive laboratory investigation on the geotechnical characteristics and behavior before and after treatment of MFT is conducted. The effects of SAP based dewatering and freeze/thaw cycles on the undrained shear strength of dewatered MFT by using a vane shear apparatus are studied. Furthermore, the ability of recycled SAP to dewater and densify MFT is assessed. Finally, this study provides the results of consolidation and hydraulic conductivity testing to evaluate the void ratio versus effective stress and hydraulic conductivity of MFT. The effects on the behavior and characteristics of MFT after amendment with usage of recycled SAP are also investigated. The results indicate that SAP has the ability to significantly dewater, densify and increase the undrained shear strength of MFT. Furthermore, when subjected to freeze/thaw cycles, the MFT dewatered with SAP shows an additional increase in strength and solid content. It is also found to be possible to regenerate the polymer (still within sachets) through light thermal drying, and the regenerated SAP can still significantly dewater and thus increase the shear strength and solid content of the MFT. In addition, the obtained high solid content affects and improves the compressibility of the material, thus resulting in low initial void ratios. On the other hand, low hydraulic permeability that is derived from low initial void ratios and consolidation is improved by the freeze/thaw process due to the interconnected voids created during the freezing process.

Managing oil sand slurry tailings waste is a significant issue in the oil sands industry and thus accurate characterization of the tailings is required. Conventional soil characterization tests usually involve one or more limiting assumptions such as small strains and constant coefficients of consolidation and hydraulic conductivity. These limitations are significant when testing low density slurries such as dredged soils and mining waste. One unconventional test in particular, the Seepage Induced Consolidation Test (SICT) has been shown to accurately determine compressibility and permeability relations for low density slurries. The SICT was first constructed at the Colorado University (CU) in Boulder, Colorado and has been used for the past two decades to characterize phosphate slurry tailings. Over the last two years a SICT was constructed at the University of British Columbia to provide accurate consolidation characterization of oil sand waste, in particular, mature fine tailings (MFT). Benchmark testing was initially performed on kaolinite clay at the UBC laboratory and results showed the test was repeatable and comparable to results obtained at CU. Test results on MFT at UBC also proved to be in agreement with published data from CU. The use of the SICT helps in the understanding of MFT and the characterization results can be directly used in into large strain consolidation modeling such as CONDES0 1D and SoilVision’s SVOffice 1D, 2D, and 3D software programs. These and other similar models, which are dependent on the compressibility and permeability relations from the SICT, can be used in the design of waste disposal strategies at every stage of a mining project.

The South African economy is an energy-driven economy which relies on coal to meet most of its energy demands. Coal mining has resulted in the generation of coal waste over 60 million tonnes, annually. Apart from the huge footprint of this waste, the sulphide minerals contained in the waste have resulted in the generation of acid rock drainage (ARD). A lot of techniques have been developed to prevent and mitigate ARD, however most of these techniques have fallen short in terms of meeting their desired objectives due to the long-term nature of ARD generation which can persist for hundreds of years after mine closure. This has resulted in emphasis being put on long-term prevention techniques that remove ARD risk over treatment techniques. One prevention technique which has shown good technical potential is the two-stage flotation method developed for desulphurisation of hard rock tailings and coal fines, developed at the University of Cape Town. On desulphurising coal, the first stage produces an upgraded coal product that may be sold, with the second stage used to separate the tailings from the first stage into targeted high-sulphide and low-sulphide fractions which may then be appropriately used or disposed of. An economic assessment of the process showed across a wide range of coal wastes the high cost of oleic acid used in the first stage of the process as a collector was a major contributor to the operating costs. The investigation undertaken in this thesis looked at the potential of algal lipids and their derivatives as biocollectors to replace the oleic acid collector in the desulphurisation process at the laboratory scale. A review of cost was carried out for a process that used raw algal lipids (RALs) or fatty acid methyl esters (FAMEs), which are derived from RALs through transesterification. Batch flotation experiments were used to assess the performance of the two bioflotation reagents in comparison to oleic acid and dodecane, an alternative but less successful chemical collector. The algal lipids cost review was a desktop study which was done by adapting literature data from Davis et al. (2014) which focused on economic evaluation of algal lipid biofuels production pathways. Results from laboratory experiments for two different coal waste feed samples showed that the performance of RALs and FAMEs was similar to that of oleic acid for the sample that was high in ash and sulphur, and better than oleic acid for the sample that was low in ash and sulphur. For example, the product from Site 1 discards from Waterberg had 24.37% ash and 2.76% sulphur using FAMEs, 26.13% ash and 2.56% sulphur with RALs, and 23.48% ash and 2.41% using oleic acid, at a reagent dose of 2.8 kg/t for all reagents. For Site 2 waste tailings from the Witbank area, the product had 23.17% ash and 0.72% sulphur when FAMEs were used as collector, 22.75% ash and 0.75% sulphur with RALs, and 20.18% ash and 0.74% sulphur using oleic acid, at the same reagent dose. Discards from Site 1 had an initial ash and sulphur content of 47.61% and 5.71%, respectively. Site 2 waste tailings had 25.56% ash and 0.91% sulphur before flotation. Increasing biocollector dosage resulted in higher yields with a compromise on the upgraded coal quality. The pH tests showed that the performance of the two bioflotation reagents was best at pH 4 in terms of yield. However, increasing the pH of the process from the natural pH of the sample (pH 2.7) to 7 resulted in collection of more ash and sulphur, thus reducing the product quality. The algal lipids cost review showed that RALs and FAMEs were potentially 20 to 21% cheaper than oleic acid, with more room for improvement. Both the laboratory experiments and the technical evaluation showed that algal lipids and their derivatives have the potential to replace oleic acid in the two-stage desulphurisation process for coal waste to obtain a saleable quality coal product while simultaneously decreasing the impact of ARD from coal waste.

The monotonic, cyclic and post-cyclic shear response of gold tailings was investigated using constant-volume direct simple shear test device. The reconstituted gold tailings specimens normally consolidated to vertical effective stress levels ranging from 50 kPa to 400 kPa initially exhibited contractive behaviour followed by a dilative response under monotonic loading, with their shear stiffness and strength increasing with increasing initial effective confining stress. Overconsolidated specimens developed negative excess pore pressures during monotonic shear, with increasing dilative response, shear resistance, and stiffness displayed with increasing overconsolidation ratio (OCR). Overall, the monotonic behaviour of normally consolidated reconstituted gold tailings specimens is similar to the typical monotonic behaviour of normally consolidated clays and low-plastic silts; similarly, the behaviour of overconsolidated reconstituted gold tailings specimens is similar to the typical monotonic behaviour of overconsolidated clays. During cyclic loading, the tailings exhibited cumulative decrease in effective stress (or increase in equivalent excess pore-water pressure) with increasing number of loading cycles, resulting in progressive degradation of shear stiffness. The cyclic shear resistance increased with increasing OCR. The findings on the cyclic shear response of normally consolidated reconstituted gold tailings are in general agreement with those available published data on the cyclic response of different tailings, obtained from tests carried out on cyclic triaxial (TX) and DSS devices. The CRR of the gold tailings from this study, however, was found to be higher than that observed in Fraser river sand and Quartz rock powder, but in the same range as natural Fraser river silt. The post-cyclic monotonic shearing response, obtained from DSS tests, carried out on normally consolidated and overconsolidated reconstituted gold tailings specimens was also studied as a part of the current research work. The post-cyclic shear strength of normally and overconsolidated specimens, normalized to the initial effective confining stress, were observed to increase with increasing OCR. The post-cyclic consolidation volume changes experienced by the gold tailings specimens were in agreement with previously published results suggesting that post-cyclic volumetric strains would increase with increasing maximum excess pore water pressure ratio developed during cyclic loading.

Fine tailings exhibit extremely poor dewatering characteristics. The research presented here deals with two closely related projects. The first project concentrated on finding an efficient treatment method for already existing fine tailings. The second project was to evaluate process modifications aimed at fine tailings reduction and to develop an understanding of the effect of electrolyte in the process water of the characteristics of fine tailings. The behavior of ultrafines separated from fine tailings was further investigated. A $\sp2$H NMR technique was applied to determine the gelation rates for ultrafines at different electrolyte concentrations. The gelation concentration was determined using ultrafines suspensions diluted with salt solutions. Results indicate, that while gelation time varies from minutes to weeks, the gelation concentration is always about 3-4 wt%, even at an extremely high salt concentrations further floc densification (dewatering) is impossible. Although adequate floc densification could not be achieved using chemical treatment, dewatering was increased markedly using freeze-thaw (a physical method). To evaluate process modifications, samples of different process streams produced during comparison pilot plant runs performed at Syncrude Canada Ltd. were investigated. The aggregation state and distribution of ultrafines were determined in all stream samples. In conjunction with the characteristics of parent oil sand ores, results prove that the settling rate was different only up to the point where the gelation onset concentration of the ultrafines fraction was reached, regardless of the ionic composition of water. Modifications to the extraction process resulted only in marginal differences in the characteristics of the discharge streams. The final volume of fine tailings depends on the ultrafine content in the oil sand ore, and not on the type and concentration of the electrolyte in th process water. Although modified extraction processes resulted in faster settling, the modification produced "dirtier" (containing more clay) secondary froths, thus bringing about other process problems.

Oil sand processing to extract bitumen generates large volumes of slurry comprising water, silt, sand, clay, unrecovered bitumen, and residual chemical aides and solvents added during the extraction process. The by-product stream of the bitumen extraction is pumped into constructed tailings ponds. Managing these tailings is one of the most difficult environmental challenges for the oil sand industry. This study aims to develop a novel technique to assist in the assessment of the technologies for managing mature fine tailings (MFT) in oil sands. Innovative application of a superabsorbent polymer in the oil sands industry may provide a new method for tailings management. However, thus far, no study has addressed this research gap. In fact, fundamental knowledge of the behavior of MFTs pre-dewatered with the superabsorbent polymer could provide an important way to positively affect the speed of reclamation. To this end, comprehensive instrumentation, geo-environmental, and geotechnical analyses are carried out to obtain essential knowledge on the behavior of MFTs pre-dewatered with the polymer. The results of this study reveal that the mechanical, hydraulic, and thermal properties of the MFTs are related. Evaporation and drying shrinkage can affect the hydro-mechanical properties of the tailings and have a significant influence on the developed shear strength of the MFTs. In addition, the process-affected water includes a high concentration of the dissolved ions and organic chemicals that stem from ore extraction chemicals and tailings treatments, or that may be released from oil sands ores. Through the application of a superabsorbent polymer in the dewatering of oil sand MFTs, the chemical components are entrapped in the polymer chains, thus limiting the mobility of the major ions and trace metals in water bodies beneath the oil sand tailings pond. Results show that the application of the superabsorbent polymer considerably reduces the rate of drainage from the oil sand MFTs into water bodies, which can help mitigate the risk of seepage. The author believes that the superabsorbent polymer dewatering technique can be considered as an environmentally friendly promising approach for management of oil sands MFTs. This new technique can accelerate the pace of reclamation and thus minimize the footprint of the oil industry in Canada.

Liquefaction is a major challenge in geotechnical engineering in which soil strength and stiffness are compromised due to earthquake activity. Understanding and predicting the behaviour and liquefaction susceptibility of soils under cyclic loading is a critical issue in civil engineering, mining and protective engineering. Numerous earthquake-induced ground failure events (e.g., substantial ground deformation, reduced bearing capacity) or liquefaction in natural fine-grained soils or manmade fine-grained soils (i.e., fine tailings) produced by mining activities have been observed and reported in the literature. Tailings are manmade soils that remain following the extraction of metals and minerals from mined ore in a mine processing plant. Traditionally, such tailings are stored in surface tailings impoundments at the mine’s surface. However, geotechnical and environmental risks and consequences related to conventional tailings impoundments have attracted the attention of the engineering community to develop novel methods of tailings disposal and management to minimize geotechnical and environmental risks. Thus, engineers have introduced and implemented innovative tailings technologies—thickened tailings and paste tailings—as cost-effective means for tailings management in mining operations. As both thickened tailings and paste tailings have lower water content and higher solid content than tailings in conventional impoundments, these tailings may be more resistant to liquefaction. However, it should be noted that the seismic or cyclic behaviour of these thickened and paste tailings, with and without heavy rainfall effects, are not fully understood. There is little technical information or data about the behaviour and liquefaction of thickened and paste tailings under seismic or cyclic loading conditions. The objective of the present PhD research is to investigate the response of layered thickened and paste tailings deposits, with and without heavy rainfall effects, to cyclic loads by conducting shaking table tests. To simulate the field deposition of thickened and paste tailings, tailings were deposited in three thin layers in a flexible laminar shear box (FLSB) attached to the shaking table equipment. A sinusoidal seismic loading at a frequency of 1 Hz and peak horizontal acceleration of 0.13g was applied at the bottom of the layered tailings deposits. Acceleration, displacement and pore water pressure responses to the cyclic loading were monitored at the middle depth of each layer of the tailings deposits. Regarding the acceleration response of these thickened and paste tailings deposits (without the effect of heavy rainfall), there was no difference between the middle of the bottom and middle layers or at the base of the shaking table. However, the acceleration at the middle of the top layer differed from the acceleration at the base of the shaking table. Throughout shaking, the layered tailings deposits (with and without the effect of heavy rainfall) exhibited contraction and dilation responses. The excess pore water pressure ratios of the layered thickened tailings deposit that was not exposed to heavy rainfall prior to shaking were found to exceed 1.0 during shaking. However, for the layered paste tailings deposit that was not exposed to the effect of heavy rainfall prior to shaking, the excess pore water pressure ratios were found to be lower than 0.85 during shaking. This reveals that without the effect of heavy rainfall, the layered thickened tailings deposit was susceptible to liquefaction, whereas the layered paste tailings deposit was resistant to liquefaction during shaking. The excess pore water ratios of the layered thickened and the paste tailings deposits that were exposed to heavy rainfall prior to shaking were found to be lower than 0.8 during shaking. This reveals that with the effect of heavy rainfall, the layered thickened and paste tailings deposits were resistant to liquefaction during shaking. The results and findings of this PhD research thus provide valuable information for the implementation of tailings in earthquake-prone areas.

Management and reclamation of large inventories of legacy and fresh mature fine tailings (MFT) represent a continuing and significant challenge to surface mine operators in the Alberta Oil Sands because of the complex chemical and physical behavior of these tailings. Suncor’s tailings recovery operations (TRO™) and Shell Canada’s atmospheric fines drying (AFD) use anionic polymers to flocculate MFT to remove fine tailings solids from aqueous suspension. Addition of anionic polyacrylamide polymer to MFT results in the creation of a complex synthetic material, polymer-amended MFT (PA-MFT). This research investigates the fundamental properties and characteristics governing PA-MFT dewatering in an effort to better understand how these factors contribute to overall material behavior including strength development and consolidation. This work confirms that the addition of anionic polyacrylamide polymer does little to change the zeta potential of the input raw MFT as the resulting material is colloidally stable. The work also indicates how residual bitumen and fabric act independently and in combination to reduce the permeability of PA-MFT and enable retention of water within the material’s fabric especially when it is stored in lifts that exceed the depth at which the combination of evaporative drying and underdrainage are effective. It is concluded that PA-MFT fabric includes abundant micropores with tortuous flow paths with little connectivity between pores. The size and configuration of the pores effectively traps water within the PA-MFT fabric. Residual bitumen may also block pore throats or form a hydrophobic barrier that limits both the effectiveness of evaporation for material deposited below a depth of 15 cm in thick lift deposits. Residual bitumen may also prevent diffusion of trapped water upward through deposited material and contributes to the plasticity and compressibility exhibited by PA-MFT when it is deposited in lifts thicker than 20 cm.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

Cemented paste backfill (CPB) is a novel technology developed in the past few decades to better manage mining wastes (such as tailings) in environmentally friendly way. It has received prominent interest in the mining industry around the world. In this technology, up to 60% of the total amount of tailings is reused and converted into cemented construction material that can be used for secondary support in underground mine openings (stopes) and to maximize the recovery of ore from pillars. CPB is an engineered mixture of tailings, water, and hydraulic binder (such as cement), that is mixed in the paste plant and delivered into the mine stopes either by gravity or pumping. During and after placing it into the mine stopes, the performance of CPB mainly depends on the role of the hydraulic binder, which increases the mechanical strength of the mixture through the process of cement hydration. Similar to other fine-grained soils undergoing cementations, CPB’s behavior is affected by several conditions or factors, such as cement hydration progress (curing time), chemistry of pore water, mixing and curing temperature, and filling strategy. Also, it has been found that fresh CPB placed in the mine stopes can be susceptible to many geotechnical issues, such as liquefaction under ground shaking conditions. Liquefaction-induced failure of CPB structure may cause injuries and fatalities, as well as significant environmental and economic damages. Many researches studied the effect of the aforementioned conditions on the static mechanical behavior of CPB. Other researches have evaluated the liquefaction behavior of natural soils and tailings (without cement) during cyclic loadings using shaking table test technique. Only few studies investigated the CPB liquefaction during dynamic loading events using the triaxial tests. Yet, there are currently no studies that addressed the liquefaction behavior of CPB under the previous conditions by using the shaking table technique. In this Ph.D. study, a series of shaking table tests were conducted on fresh CPB samples (75 cm × 75 cm ×70 cm), which were mixed and poured into a flexible laminar shear box (that was designed and build for the purpose of this research). Some of these shaking table tests were performed at different maturity ages of 2.5 hrs, 4.0 hrs, and 10.0 hrs, to investigate the effect of cement hydration progress on the liquefaction potential of CPB. Another set of tests were conducted to assess the effect of the chemistry (sulphate content) of the pore-water on the cyclic response of fresh CPB by exposing cyclic loads on couple of CPB models that contain different concertation of sulphate ions of 0.0 ppm and 5000 ppm. Moreover, as part of this study, series of shaking table test was conducted on CPB samples that were prepared and cured at different temperatures of 20oC and 35oC, to evaluate the effect of temperature of the cyclic behavior of CPB. Furthermore, the effect of filling strategy on the cyclic behavior of fresh CPB was assessed by conducting set of shaking tables tests on CPB models that were prepared at different filling strategies of continuous filling, and sequential or discontinuous (layered) filling. The results obtained show that CPB has different cyclic behavior and performance under these different conditions. It is observed that the progress of cement hydration (longer curing time) enhances the liquefaction resistance of CPB, while the presence of sulphate ions diminishes it. It is also found that CPB mixed and cured in low temperature is more prone to liquefaction than those prepared at higher temperatures. Moreover, the obtained results show that adopting the discontinuous (layered) filling strategy will improve the liquefaction resistance of CPB. The finding presented in this thesis will contribute to efficient, cost effective and safer design of CPB structures in the mine areas, and will help in minimizing the risks of liquefaction-induced failure of CPB structures.

Thesis (MScIng)--University of Stellenbosch, 2007.
ENGLISH ABSTRACT: Due to economic and environmental constraints mining operations are placed under increasing pressure to effectively manage and operate tailings disposal operations. Restrictions imposed on water usage and tailings operations footprint have led to higher density and wider particle size distribution slurries conveyed to tailings areas. One means of efficiently disposing the tailings is co-disposal. In this method a concentrated fine vehicle slurry is used to convey a coarser fraction. This produces a higher density of tailings, with a number of advantages both upstream and downstream of the tailings process. Limited research has been conducted on the effect of coarse particles on the non-Newtonian rheological properties of these slurries. This lack of information complicates the design and reliable operation of these systems. This project aims at gaining a clearer understanding as to the mechanisms involved in the addition of coarse particles to a fine clay slurry vehicle; and to provide a means of estimating the measured slurry rheological properties. A number of experiments were designed to test the slurry (both Kaolin only, and Kaolin-coarse particle mixtures) rheological properties using a Couette viscometer (for the dynamic flow properties of yield stress and plastic viscosity) and a vane instrument (for the static yield stress measurements). The slurries were prepared in varying Kaolin clay solids concentrations with reverse osmosis water. Glass beads and two types of industrial sand were used as the coarse fractions. All of the coarse particles had a similar size but varied significantly in shape. Slurry pH and temperature readings were monitored throughout the tests. Tests were done initially on clay only slurries. The rheological properties of these slurries were repeatable, and no noticeable variations of properties with time were observed. The yield stress (both static and dynamic) and plastic viscosity data were well correlated with established relationships. Coarse particles were added to the clay only slurries, and then removed. The remaining clay only slurry exhibited the same rheological properties as the initial clay only slurry. The presence of coarse particles increased all the measured rheological properties (i.e. dynamic yield stress, Bingham viscosity, and static vane yield stress) in a fashion resembling the effect of adding clay to a clay only slurry. In addition, the change in measured rheological property by addition of coarse particle was independent of the clay fraction in the clay slurry. Furthermore, with both the clay only slurries and clay and coarse sand slurries, a constant linear relationship existed between the static and dynamic yield stress. Several correlations from the literature were found to provide reasonable prediction of the rheological property variations observed. These empirical and semi-empirical models however did little to explain the mechanisms involved in coarse particle addition. A new correlation has been proposed, Residual Clay Concentration, which predicts the change in rheological property based on an additional clay concentration, which in turn is a linear function of the coarse particle concentration. The accuracy of this model further strengthens the belief that the coarse particle acts in a similar fashion to a floc. By means of a case study example the importance of selecting an appropriate model for design was illustrated. The Residual Clay Concentration method provided the most conservative results. This combined with its theoretical basis strengthens the models recommendation for use in design.
AFRIKAANSE OPSOMMING: As gevolg van ekonomiese en omgewings beperkinge word mynwese nywerhede onder toenemende druk geplaas om doeltreffende afvalstroom bestuur en operasie toe te pas. Beperkinge geplaas op water gebruik en afvalstroom area-groote ly tot hoër digthede en wyer partikel-grooteverspreidings van flodders vervoer na afval areas. Een manier om van die afval doeltreffend ontslae te raak en te berg is deur medeberging. In die metode word ‘n gekonsentreerde fyn flodder gebruik as draer van ‘n growwer partikel-fraksie. Dit ly tot ‘n hoër digtheid flodder, met verskeie voordele in beide die op – en afstroom prosesse. Beperkte navorsing is gedoen op die effek van growwe partikels op die nie-Newoniese rheolgiese eienskappe van hierdie flodders. Hierdie tekort aan informasie maak die effektiewe, betroubare bedryf en operasie van die sisteme meer ingewikkeld. Hierdie projek is daarheen gemik om ‘n beter begrip te ontwikkel met betrekking tot die meganismes betrokke in die byvoeging van growwe partikels aan ‘n fyn klei-agtige flodder draer; en om ‘n manier te voorsien wat die rheologiese eienskappe kan beraam. Verskeie eksperimente was ontwerp om die flodders (beide slegs Kaolien, en Kaoliengrowwe partikel mengsels) se rheologiese eienskappe te toets deur die gebruik van ‘n Couette-viskometer. Die Couette viskometer was gebruik om die dinamiese eienskappe (van grens-spanning, en plastiese viskositet) te meet. ‘n Vaan apparaat is gebruik om die eienskap van statiese grens-spanning te meet. Die flodders was voorberei in verskeie Kaolien konsentrasies met tru-osmosis water. Glas krale en twee tipes industriële sand is gebruik as die growwe fraksies. Al die growwe partikels het soortgelyke groottes gehad, maar het grootliks verskil in vorm. Die flodder pH en temperatuur lesings is deurentyd nagegaan. Toetse was aanvanklik gedoen op die klei-alleenlike flodders. Die gemete reologiese eienskappe van die flodders was herhaalbaar, en geen opmerkbare veranderinge van die eienskappe met betrekking tot tyd is gemeet nie. Die grens-spanning (beide statiese en dinamiese) en plastiese viskositeit is goed gekorrelleer met gevestigde verhoudinge. Growwe partikels is aan die klei-alleenlike flodders bygevoeg, en daarnae verwyder. Die oorblywende klei-alleenlike flodder het dieselfde gemete rheologiese eienskappe getoon as die oorspronklike klei-allenlike flodder. Die teenwoordigheid van growwe partikels het na ‘n toename van al die gamete rheologiese eienskappe gelei wat fisies baie soortgelyk is aan die byvoeging van klei tot ‘n klei-alleenlike flodder. Verder, met beide die klei-alleenlike en klei-growwe partikel flodders het ‘n konstante liniëre funksie tussen die statiese en dinamiese grens-spannings bestaan. Verskeie verhoudings uit die literatuur het goeie korrelasie bewerkstellig met die waargenome rheologie veranderinge. Hierdie empiriese en semi-empiriese modelle doen egter min om die megansimes betrokke in die toevoeging van growwe partikels te verduidelik. ‘n Nuwe korrelasie is voorgestel, naamlik die Residu Klei Konsentrasie. Hierdie model voorspel die verandering in reologiese eienskappe gebaseer op ‘n addisionele klei konsentrasie, wat ‘n liniëre funkise is van die growwe partikel konsentrasie. Die goeie korrelasie gesien met die model versterk die idée dat die growwe partikel in ‘n soortgelyke manier as ‘n flok gedra in die teenwoordigheid van ander flokke. Deur middel van ‘n tipiese industriële voorbeeld is die belangrikheid in die keuse van die regte korrelasie geillustreer. Die Residu Klei Konsentrasie metode het die mees konservatiewe resultate gelewer. Hierdie feit gekombineerd met die model se soliede teoreitiese beginsels versterk dit as voorgestelde korrelasie vir ontwerp.

Tailings are a rest product from the extraction of metals and minerals, and is therefore produced in large volumes by all mining companies. One common way to store tailings material is to deposit it as a hydraulic slurry on a tailings impoundment, where the tailings are held in place by tailings dams. Deposit and discharge of tailings, often conducted along the dams, causes a particle segregation which creates different fines contents (percentage of particles smaller than 0,063 mm in the tailings) in the impoundment at various distances from the discharge. Another effect from the discharge is that different densities are created in the deposited layers. Since some tailings dams are constructed on top of old deposited tailings, and if possible with tailings as a construction material, the fines content and density effects on the tailings behaviour are important factors for dam stability. In this thesis, tailings material with different fines contents and different densities have been studied with the purpose to see how the behaviour in strength, compressibility and permeability varies. After an initial case study of sampled tailings from a specific impoundment, the fines content for the three tested materials were determined to be 10, 50 respectively 90%. The behaviour in strength was tested in both triaxial and simple shear tests. Only drained strength was studied for three consolidation stresses in both apparatuses. The result from both tests showed that the strength is increasing with decreasing fines content, and thus evaluated friction angles increases with decreasing fines content. Evaluated friction angles from the simple shear test are though significantly smaller than those from the triaxial tests. Friction angles from triaxial tests are seen as most reliable, since the principal stresses are controlled during the whole test. The difference in friction angles from simple shear and triaxial test is however not a new discovery, it has been found by others before. The results from the triaxial tests indicates that a transitional fines content must exist somewhere between 10 – 50 %, where the behaviour in strength switches from sand dominated to silt dominated. Oedometer tests were conducted to study the compressibility of the three materials. The results showed that the compressibility increased with increasing fines content and with decreased density. In agreement with that conclusion, evaluated oedometer modulus from the normal consolidation curve tended to increase with increasing density and to a smaller extent increase with decreasing fines content. Determination of characteristics in permeability were done by evaluating the hydraulic conductivity from constant head tests. Results from this showed that the hydraulic conductivity increases with decreasing fines content. Furthermore, with increasing density the hydraulic conductivity decreases. Results of both the compressibility and the hydraulic conductivity are of course expected. To develop the relations in compressibility and permeability is considered as hard, since the behaviours are both dependent of fines content and density. However, the results indicate that with different combinations of fines contents and densities similar behaviour in compressibility and permeability can be obtained for different materials.
Anrikningssand (eng. tailings) är en restprodukt från utvinningen av metaller och mineraler. Alla gruvföretag producerar varje år stora volymer anrikningssand som måste förvaras på något sätt. Detta görs ofta genom att anrikningssanden deponeras som en slurry med processvatten på magasin. Anrikningssanden hålls sedan på plats av dammar och ibland i kombination med naturlig topografi. Deponeringen sker ofta från utsläppspunkter längs dammen, vilket resulterar i en sortering av kornstorlekar i magasinet som i sin tur skapar olika finjordshalter (procent av partiklar mindre än 0,063mm) på olika avstånd från utsläppspunkten. Deponeringen skapar också olika lager, som också får olika densiteter. Eftersom en del typer av gruvdammar byggs inåt och grundläggs på tidigare deponerad anrikningssand, samt eftersom anrikningssand ibland används som byggmaterial vid höjningar, är finjordshalten och densitetens effekt på materialbeteendet intressant ur stabilitetssynpunkt för dammarna. I det här arbetet har anrikningssand med olika finjordshalter och densiteter undersökts i laboratorieförsök för att bestämma hållfasthets-, kompressions- och permeabilitetsegenskaper. Först gjordes en case study, med provtagning och klassificering av anrikningssand från en specifik anläggning. Därefter bestämdes att tre stycken material med finjordshalter på 10, 50 och 90 % skulle undersökas. Hållfasthetsegenskaper har undersökts i både triaxial och direkta skjuvförsök. Endast dränerad hållfasthet har studerats för tre stycken konsolideringsspänningar för varje material i både triaxial och direkta skjuvförsök. Resultaten från både triaxialförsök och direkta skjuvförsök visar att hållfastheten ökar med minskad finjordshalt och därför ökar även värdet på utvärderade friktionsvinklar med minskad finjordshalt. Utvärderade friktionsvinklar från direkta skjuvförsök är dock betydligt lägre än friktionsvinklar från triaxialförsök. Friktionsvinklarna från triaxialförsöken är mer trovärdiga eftersom man under hela testet har koll på huvudspänningsriktningarna. Skillnaden i resultatet mellan direkta skjuvförsök och triaxialförsök är inte en ny upptäckt, utan har hittats av andra tidigare. Från resultatet av triaxialförsöken i det här arbetet kan man antyda att det finns ett ”transitional fines content” (TFC) mellan 10 och 50 %, där materialet övergår från sand dominerat beteende till silt dominerat beteende under skjuvning. Ödometerförsök utfördes för att studera kompressionen hos de tre materialen. Resultaten visar att kompressibiliteten ökar med ökad finjordshalt och med lägre densitet. Utvärderade ödometer moduler från normalkonsolideringskurvorna visar att styvheten ökar med ökad densitet, samt en aning till tendens mellan ökad styvhet och minskad finjordshalt. Permeabilitetsegenskaper har studerats genom utvärdering av hydraulisk konduktivitet från constant head test. Det observerades att den hydrauliska konduktiviteten ökar med minskad finjordshalt. Gällande densitetens effekt visar resultaten att med ökad densitet så minskar den hydrauliska konduktiviteten. Både resultat i kompressionsegenskaper och hydraulisk konduktivitet är förstås väntade. Att utveckla sambanden kring kompressions- och permeabilitetsegenskaper anses svårt, eftersom det är beroende av både finjordshalt och densitet. Resultaten indikerar att det med olika kombinationer av finjordshalt och densitet går att uppnå liknande beteende för olika material i både kompression och permeabilitet.

A study was conducted to evaluate the properties and processes influencing the rate and magnitude of volume decrease and strength gain for oil sand fine tailings resulting from a change in bitumen extraction process (caustic versus non-caustic) and the effect of adding a coagulant to caustic fine tailings. Laboratory flume deposition tests were carried out with the objective to hydraulically deposit oil sand tailings and compare the effects of extraction processes on the nature of beach deposits in terms of geometry, particle size distribution, and density. A good correlation exists between flume deposition tests results using oil sand tailings and the various other tailings materials. These comparisons show the reliability and effectiveness of flume deposition tests in terms of establishing general relationships and can serve as a guide to predict beach slopes. Fine tailings were collected from the various flume tests and a comprehensive description of physical and chemical characteristics of the different fine tailings was carried out. The characteristics of the fine tailings is presented in terms of index properties, mineralogy, specific surface area, water chemistry, liquid limits, particle size distribution and structure. The influence of these fundamental properties on the compressibility, hydraulic conductivity and shear strength properties of the fine tailings was assessed. Fourteen two meter and one meter high standpipe tests were instrumented to monitor the rate and magnitude of self-weight consolidation of the different fine tailings materials. Consolidation tests using slurry consolidometers were carried out to determine consolidation properties, namely compressibility and hydraulic conductivity, as well as the effect of adding a coagulant (calcium sulphate [CaSO4]) to caustic fine tailings. The thixotropic strength of the fine tailings was examined by measuring shear strength over time using a vane shear apparatus. A difference in water chemistry during bitumen extraction was concluded to be the cause of substantial differences in particle size distributions and degree of dispersion of the comparable caustic and non-caustic fine tailings. The degree of dispersion was consistent with predictions for dispersed clays established by the sodium adsorption ratio (SAR) values for these materials. The biggest advantage of non-caustic fine tailings and treating caustic fine tailings with coagulant is an increased initial settlement rate and slightly increased hydraulic conductivity at higher void ratios. Thereafter, compressibility and hydraulic conductivity are governed by effective stress. The chemical characteristics of fine tailings (water chemistry, degree of dispersion) do not have a significant impact on their compressibility behaviour and have only a small influence at high void ratio (low effective stress). Fine tailings from a caustic based extraction process had relatively higher shear strengths than comparable non-caustic fine tailings at equivalent void ratios. However, shear strength differences were small and the overall impact on consolidation behaviour, which also depends on compressibility and hydraulic conductivity, is not expected to be significant.

Current methods of mine waste disposal have resulted in environmental problems on a global scale. In an effort to circumvent problems inherent to segregated disposal of waste rock and tailings, this thesis examines an alternative mine waste disposal technique where waste rock and tailings are combined as a homogenous mixture. One type of waste rock and one type of tailings were examined individually and as mixtures for volume change, permeability, and soil-water characteristics. Laboratory investigations included compressibility testing in a large diameter consolidation cell, hydraulic conductivity by constant head test alternated with static loading, and soil-water characteristic curve by pressure plate test. Tailings rheology was examined in a cup and bob rotational viscometer. A two-year meso-scale column study of self-weight consolidation was also conducted. The behaviour of mixtures of waste rock and tailings is dependent on mixture design, and mixtures may therefore be designed for specific geotechnical properties. Design variables examined included mixture ratio and initial tailings solids content. Mixture ratio was found to have an optimum value where the tailings slurry just fills the voids between rock particles. Tailings solids content was found to have limits for mixing defined by rheological yield stress. Mixtures had compressive strains similar to waste rock alone and much lower than tailings alone. The finding was attributed to the presence of a load bearing waste rock skeleton. The hydraulic conductivity of mixtures was similar to tailings and much lower than waste rock. The finding was attributed to the presence of a fine-grained tailings matrix. While waste rock alone was observed to remain unsaturated, mixtures remained saturated for long periods of time under conditions of free drainage without access to water. Mixture particle structure was conceptualized through the use of a particle model and described quantitatively by waste rock skeleton void ratio and tailings matrix void ratio. Methods for relating mixture compressibility and hydraulic conductivity to structure are proposed. While exhaustive testing of the range of possible mixtures and behaviours was not possible, this thesis has provided a fundamental theoretical basis for understanding mixture design and behaviour with respect to mixture particle structure.
Applied Science, Faculty of
Mining Engineering, Keevil Institute of
Graduate

Thesis (Ph.D.)--University of Alberta, 2009.
Title from PDF file main screen (viewed on Feb. 19, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geotechnical Engineering, [Department of] Civil and Environmental Engineering, University of Alberta. Includes bibliographical references.

Continuous accumulation of Mature Fine Tailings (MFT) is a major challenge to oil sands industry. To reduce the inventory of MFT through development of novel tailings treatment technologies, it is essential to understand the stabilization mechanism of fine solids in MFT. This project aims at characterizing fine solids of MFT. A novel method is developed in this study to understand characteristics of fine solids in MFT by studying their response to the changes in water chemistry and chemical treatment. Settling and rheological response of MFT to chemical additives is determined. Combined with solids characterization of the different layers of settled MFT, an enhanced understanding of stabilization of fine solids in MFT is gained. The knowledge generated through this study will provide a scientific basis for technology development of MFT treatment.
Chemical Engineering

Centrifuged fine tailings (CFT) technology was developed to reduce volumes of fluid fine tailings (FFT) stored in tailings ponds at oil sands mines. Increasing FFT inventories in tailings ponds results from slow settlement of clay minerals suspended in oil sands process-affected water (OSPW). High sodium (Na) concentrations in OSPW increase the electrical double layer (EDL) thickness at clay-mineral surfaces, which hinders aggregation and, therefore, settlement. Production of CFT involves dredging FFT from tailings ponds, amending with polyacrylamide and gypsum, and decanter centrifuging. This process promotes aggregation and flocculation, and decreases gravimetric water content from approximately 70 to 55 % (w/w). The resulting CFT is deposited in thin lifts (< 2 m) into sub-aerial containment areas to facilitate further dewatering via freeze-thaw cycling. This research was focused on characterizing the biogeochemical conditions and processes within the CFT deposits. These deposits remain tension-saturated and, similar to tailings ponds, anaerobic redox processes including iron (Fe) reduction, sulfate (SO4) reduction, and methanogenesis likely dominate. The geochemistry, mineralogy, and microbiology of core samples from two field-scale test deposits and two full-scale production deposits were examined. Results were compared with previously published data from FFT deposits to assess impacts of chemical amendments on biogeochemical processes within CFT deposits. Pore-water chemistry within the CFT deposits is affected by evaporative concentration of dissolved ions, which leads to high concentrations of salts (Na, 3000 mg L-1; Cl, 1500 mg L-1; SO4, 5000 mg L-1) and naphthenic acids (NAs 150 mg L-1) near the surface (< 0.3 m) of these deposits. Increases in concentrations of conservative ions (i.e., Cl) indicated that 30 to 40 % of pore water was lost to evaporation at a depth of 0.1 m below surface. Results also suggest that microbially-mediated Fe reduction, SO4 reduction, and methanogenesis are dominant redox processes within the CFT deposits. Microbes related to genera known to use these terminal electron acceptors were identified by high-throughput DNA sequencing data. Increases in dissolved Fe and H2S with depth were also indicative of Fe and SO4 reduction, respectively. These results provide the first insight into biogeochemical conditions and processes within oil sands CFT deposits.

Dissertação de Mestrado em Geociências apresentada à Faculdade de Ciências e Tecnologia
As part of the Europe 2020 strategy, the European Commission identified two constraints that have affected the competitiveness and growth of the European economy: its high dependency on the importation of finished products, and the insecurity of the supply of raw materials. With regards to the latter, the European Commission developed the "Raw Materials Initiative", which promotes an efficient use of resources, as well as encouraging recycling, with particular emphasis on mining waste. This waste must therefore be recognised as a potential source of resources, in particular critical raw materials, which are essential for the production of high-tech equipment, crucial for the competitiveness of the European industry. This use of mining waste as a source of raw materials may also reduce the exploitation of natural resources, which are used for the same purpose, thus introducing the concept of a circular economy.Taking into consideration the relevance of this issue in today’s society, the main goal of this dissertation was to evaluate the potential in critical metals of the mining waste deposited in the fine tailings dams of the Panasqueira mine, located in Portugal, in the municipality of Covilhã, at the Barroca Grande site. From a methodological point of view, the work focused on: (i) surface and borehole sampling; (ii) particle size characterisation of the samples (LDPS); (iii) chemical-mineralogical characterisation of the samples (XRD and SEM); and (iv) elemental characterisation of the samples (XRF).This work allowed us to determine the concentration of critical metals, which are relevant in the context of the national and European economy.The results obtained suggest that in both of the fine tailings dams, which granulometrically range from medium silt to medium sand, and the anomalous concentrations of critical metals, more specifically the semi-metals germanium (Ge) and antimony (Sb), and the metal and light rare earth element cerium (Ce), are significant. In some cases these concentrations are 24 times higher than the natural abundance of these elements in the upper continental crust.
No âmbito da Estratégia Europa 2020, a Comissão Europeia identificou dois constrangimentos que têm condicionado a competitividade e o crescimento da economia europeia: a elevada dependência de importação de produtos acabados e a insegurança no fornecimento de matérias-primas. Relativamente a este último, a Comissão Europeia promoveu a “Iniciativa Matérias-Primas”, estimulando a eficiência no uso de recursos e a circularidade, com destaque para a valorização dos resíduos de extração mineira. Estes resíduos devem, portanto, passar a ser reconhecidos como uma potencial fonte de recursos, nomeadamente de matérias-primas críticas, essenciais para a produção de equipamentos de alta tecnologia, cruciais para a competitividade da indústria europeia. A utilização de resíduos de extração mineira como fonte de matéria-prima pode reduzir a exploração de recursos naturais usados com o mesmo objetivo, introduzindo-se assim o conceito de economia circular.Tendo em consideração a relevância deste tópico para a sociedade de hoje, o objetivo principal desta dissertação consistiu em averiguar o potencial em metais críticos dos resíduos de extração mineira depositados nas células de lamas da mina da Panasqueira, localizadas em Portugal, no concelho da Covilhã, no lugar de Barroca Grande. Do ponto de vista metodológico, o trabalho centrou-se na: (i) recolha de amostras superficiais e em profundidade; (ii) caracterização granulométrica das amostras (LDPS); (iii) caracterização químico-mineralógica das amostras (XRD e SEM); e (iv) caracterização elementar das amostras (XRF).Este trabalho permitiu determinar a concentração de metais críticos relevantes no contexto da economia nacional e europeia. Os resultados obtidos sugerem que em ambas as células de lamas, com granulometria a variar de silte médio a areia média, as concentrações anómalas de metais críticos, nomeadamente dos semi-metais germânio (Ge) e antimónio (Sb), e do metal e terra rara leve cério (Ce), são significativas. Em alguns casos, estas concentrações são 24 vezes superiores à abundância natural destes elementos na crosta continental superior.

Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 m), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water. The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 m) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC. Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23 to 85C). High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work. Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water. The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the companys own electrocoagulation operation. After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT.
Chemical Engineering

Oil sands operators are being faced with the challenge of reclaiming the large volumes of slurry tailings created during oil sands processing. New regulations mandate that operators must minimize fluid tailings by capturing fines in dedicated disposal areas, leading to a ‘trafficable’ or solid deposit. Adding a polyacrylamide polymer to the tailings and thinly spreading them over a sloped disposal area (a process developed by Shell Canada Energy known as the atmospheric fines drying or AFD process) has been shown to enhance the dewatering of tailings which leads to a dry deposit at a much faster rate than traditional methods. Hydroponic experiments using the emergent aquatic macrophytes cattail (Typha latifolia L.) and common reed (Phragmites australis (Cav.) Trin. ex Steud.) were conducted to investigate the phytotoxicity of waters formed during AFD processing. The phytotoxicity of AFD release waters was compared to the phytotoxicity of traditional mature fine tailings (MFT) reclaim water through the monitoring of plant water uptake and whole plant fresh weight over the course of the experiment. It was found that there are no significant differences between the phytotoxicity observed in the MFT and AFD treatments and it was also found that spring runoff melt water from the AFD deposits is less phytotoxic than the original release water. Two additional hydroponic studies using cattail and common reed were also conducted. The first examined the phytotoxic effects attributable solely to the naphthenic acids isolated from Shell’s Muskeg River Mine tailings, and the second evaluated the phytotoxic effects of amending mature fine tailings with gypsum. It was found that the gypsum amended tailings caused greater phytotoxicity in cattail and common reed than tailings without gypsum added. Furthermore, both species were tolerant to growing in nutrient media spiked with naphthenic acids (40 mg/L). The phytotoxicity experiments conducted also demonstrated that common reed is consistently more tolerant to growing in water associated with oil sands tailings and is therefore the more appropriate choice for use in reclamation strategies involving wetland plants. Mass spectrometry was used to determine the naphthenic acid molecular profiles for Shell oil sands tailings. Using low resolution mass spectrometry, no detectable features or changes to the composition of naphthenic acids attributable to Shell processing were found. High-resolution mass spectrometry provided insight into possible plant mediated changes and biodegradation of naphthenic acids. It appears as though, to some extent, cattail is able to dissipate naphthenic acids, which could explain the susceptibility of cattail to the phytotoxic effects of naphthenic acids. Further research is required to determine whether the changes observed in the naphthenic acid mixture are due to microbial degradation and/or a phytotoxic response of the plants studied.

M.Sc.
An estimated 98% of the iron ore exploited in the world is used in the manufacture of pig iron and steel, which are non-substitutable backbones of modern society. The rapid increase of world steel production over the last few years, driven mainly by economic growth in China, have required an equal increase in iron ore production, from 876.8 Mt in 2006 to 948.1 Mt in 2007. The increased rate of exploitation of iron ores has resulted in a rapid depletion of known high-grade iron ore deposits. This, in turn, has led to a dramatic increase of prices, especially for highly thought-after high-grade lumpy iron ores from BIF-hosted deposits. In the absence of any major new discoveries of high-grade iron ore deposits, mining companies have turned to lower-grade materials to assess their beneficiation potential to expand their production base and beneficiation capacity, in order to satisfy future demand. Within this existing framework, this research project was initiated to assess the beneficiation potential of low-grade lumpy stockpiles and high-grade iron ore fines at Beeshoek Iron Ore Mine, owned by Assmang Ltd. The mine is located 7 km West of Postmasburg, in the Northern Cape Province of South-Africa, and processes currently 5.60 million tons of uncontaminated run-of-mine ore per annum. Crushing, washing, classification and jigging are used to produce 2.12 million tons of (37.8% of ROM) of lumpy iron ore product. The balance (3.48 million tons) is currently not used, but is stockpiled or discarded. This includes 0.90 million tons (16.2% of ROM) of ore-grade fines, 0.86 million tons (15% of ROM) of tailings sludge and 1.74 million tons (31% of ROM) of lumpy low grade material. Both ore-grade fines and low-grade lumpy material are discarded separately; they are currently considered as waste. The low-grade lumpy is stockpiled while the fines are used to fill-in mined-out open pits. The evaluation of the beneficiation potential of these two material streams is the main goal of this study. Representative samples were collected from ore-grade fines and the current stockpile for low-grade lumpy material. Hand sorting and lithological categorization of the lumpy material facilitated petrographic and mineralogical studies using light and scanning electron microscopy, as well as X-ray powder diffraction studies. Major and trace element geochemistry were determined using X-ray fluorescence spectrometry and titrimetry (to accurately determine the concentration of iron). Whole rock densities were determined for all lithotypes recognized in the low-grade lumpy material. The grain size distribution was determined for the lumpy materials by actual measurement of the diameter of a representative number of particles, and for fines by sieve analysis. Fines beneficiation tests were conducted using spiral separation and simple classification tests. Washing was used as additional beneficiation method on the fines.