Studies on flocculation of fine mineral tailings using novel polyacrylamide based polymer

One of the important features in managing or treating sulfide fine tailings is separating solids from liquid by settling test. This thesis presents results of studied conducted on flocculation of Kaolin suspensions (a model tailings) and sulfide mineral tailings. Two polymers (PAM and Al-PAM) were tested as flocculants. The zeta potential value of slurries was measured by Nano Zetasizer device. Al-PAM was found to be more effective for flocculation of kaolinite samples and also sulfide samples while PAM with used concentration was not. This study represents the power of flocculation as a possible solution to deal with industrial tailings --Abstract, page iii

Current state of fine mineral tailings treatment: A critical review on theory and practice

The mining industry produces fluid fine mineral tailings on the order of millions of tonnes each year, with billions of tonnes already stored globally. This trend is expected to escalate as demand for mineral products continues to grow with increasingly lower grade ores being more commonly exploited by hydrometallurgy. Ubiquitous presence and enrichment of fine solids such as silt and clays in fluid fine mineral tailings prevent efficient solid-liquid separation and timely re-use of valuable process water. Long-term storage of such fluid waste materials not only incurs a huge operating cost, but also creates substantial environmental liabilities of tailings ponds for mining operators. This review broadly examines current theoretical understandings and prevalent industrial practices on treating fine mineral tailings for greater water recovery and reduced environmental footprint of mining operations

Impact of fugitive bitumen on polymer-based flocculation of mature fine tailings

In bitumen recovery from oil sands, a percentage of the bitumen is lost to tailings. The effect of fugitive bitumen on fines settling and consolidation in tailings ponds remains controversial. In the current study, the settling performance of mature fine tailings (MFT) in response to flocculant addition was considered by studying MFT of varying bitumen content. Bitumen content in the MFT was adjusted by controlled removal of bitumen using a Denver flotation cell. The initial settling rate of flocculated MFT was observed to increase with decreasing bitumen content from 0.45 to 0.18wt%. A further reduction in bitumen content was found to dramatically decrease the settling rate of flocculated MFT. Such behaviour seems counterintuitive since the polymer flocculant was found to have a greater affinity for 'clean' surfaces (Al2O3) than for bitumen contaminated surfaces, as measured by quartz crystal microbalance with dissipation (QCM-D), which would predict a further increase in settling rate of flocculated MFT with decreasing bitumen content. The reduction in settling rate below a critical bitumen content is thought to result from selective removal of hydrophobic solids, since washing of untreated MFT with toluene is shown to significantly improve settling of flocculated solids. The current study confirms the use of flotation as a viable option to control MFT bitumen content and improve the settling rate of flocculated MFT

Application of Rhamnolipid and Microbial Activities for Improving the Sedimentation of Oil Sand Tailings

Densification of oil sand tailings deposited in the tailing ponds and recovering water from them are two major challenges issues in the oil sands surface mining industry. A small increase in the tailing settlement rate (which normally is very slow) can improve the densification of tailings and significantly, reduce water consumption and the volume of tailing ponds. Currently most of the industrial methods for consolidation of oil sand tailings are based on clay particle flocculation methods which use different kinds of agents such as calcium sulfate (gypsum), and polymeric flocculants. In this work, rhamnolipid (JBR 425) was investigated as a flocculating agent and microbial activities by performing the sedimentation experiments to increase the sedimentation of fine tailing particles. It has been found that rhamnolipid increased sedimentation by improving the hydrophobic interaction between the particles. The feasibility of in situ biosurfactant production by indigenous microorganisms, Bacillus subtilis strain and two microbial strains isolated from weathered oil was investigated and it was found that all strains could produce very low amounts of biosurfactant. A mixed culture of two microbial strains isolated from weathered oil increased the sedimentation. Different concentrations of rhamnolipid together with these two microbial strains at 23 ºC ºC could lead to significant increases in sedimentation (by a maximum factor of 3.04), increases in the concentration of larger particles (by a maximum factor of 1.9), particle mean diameter (by a maximum factor of 2.11) and flocculation in the tailings samples amended with them compared to the control. Rhamnolipid (0.5%) together with these two microbial strains at 15 ºC ºC showed significant increases in sedimentation (by a factor of 5.1), the concentration of larger particles (by a factor of 2.63), particle mean diameter (by a factor of 2.70) and flocculation in the tailings samples compared to the control. while the zeta potential is still negative. According to the pH measurements (during the 50 days) increase in the ionic strength (I) of the pore water and reduction in the thickness of the DDL of clay particles is not responsible for increasing the sedimentation as dissolution of MFT carbonate minerals and releasing divalent cations could not occur at pH higher than 7.5. However there might be a small amount of CH4 production at 15 ºC oC in the deeper layer of mud. This means that the mechanism of flocculation in these cases could be probably due to increasing the hydrophobicity of the particles, due to the interaction of biosurfactant and high molecular weight microbial organic compounds through a bridging mechanism with clay particles, and to due to forming transient canals from small amounts of CH4 production. Using rhamnolipid as a flocculating agent could bring the remaining oil and also a small amount of insoluble heavy metals from the tailing sediment into the water. Dissolved heavy metal ions and rhamnolipid in water could be removed through micellar- enhanced ultrafiltration (MEUF) process (between 30% for Cd and 100% for V, and 97.5% for rhamnolipid). This work shows the potential of using rhamnolipid and microbial culture in order to increase the oil sand sedimentation through flocculation and microbial activity in a more environmental friendly and densification process

Application of Rhamnolipid and Microbial Activities for Improving the Sedimentation of Oil Sand Tailings

Densification of oil sand tailings deposited in the tailing ponds and recovering water from them are two major challenges issues in the oil sands surface mining industry. A small increase in the tailing settlement rate (which normally is very slow) can improve the densification of tailings and significantly, reduce water consumption and the volume of tailing ponds. Currently most of the industrial methods for consolidation of oil sand tailings are based on clay particle flocculation methods which use different kinds of agents such as calcium sulfate (gypsum), and polymeric flocculants. In this work, rhamnolipid (JBR 425) was investigated as a flocculating agent and microbial activities by performing the sedimentation experiments to increase the sedimentation of fine tailing particles. It has been found that rhamnolipid increased sedimentation by improving the hydrophobic interaction between the particles. The feasibility of in situ biosurfactant production by indigenous microorganisms, Bacillus subtilis strain and two microbial strains isolated from weathered oil was investigated and it was found that all strains could produce very low amounts of biosurfactant. A mixed culture of two microbial strains isolated from weathered oil increased the sedimentation. Different concentrations of rhamnolipid together with these two microbial strains at 23 ºC ºC could lead to significant increases in sedimentation (by a maximum factor of 3.04), increases in the concentration of larger particles (by a maximum factor of 1.9), particle mean diameter (by a maximum factor of 2.11) and flocculation in the tailings samples amended with them compared to the control. Rhamnolipid (0.5%) together with these two microbial strains at 15 ºC ºC showed significant increases in sedimentation (by a factor of 5.1), the concentration of larger particles (by a factor of 2.63), particle mean diameter (by a factor of 2.70) and flocculation in the tailings samples compared to the control. while the zeta potential is still negative. According to the pH measurements (during the 50 days) increase in the ionic strength (I) of the pore water and reduction in the thickness of the DDL of clay particles is not responsible for increasing the sedimentation as dissolution of MFT carbonate minerals and releasing divalent cations could not occur at pH higher than 7.5. However there might be a small amount of CH4 production at 15 ºC oC in the deeper layer of mud. This means that the mechanism of flocculation in these cases could be probably due to increasing the hydrophobicity of the particles, due to the interaction of biosurfactant and high molecular weight microbial organic compounds through a bridging mechanism with clay particles, and to due to forming transient canals from small amounts of CH4 production. Using rhamnolipid as a flocculating agent could bring the remaining oil and also a small amount of insoluble heavy metals from the tailing sediment into the water. Dissolved heavy metal ions and rhamnolipid in water could be removed through micellar- enhanced ultrafiltration (MEUF) process (between 30% for Cd and 100% for V, and 97.5% for rhamnolipid). This work shows the potential of using rhamnolipid and microbial culture in order to increase the oil sand sedimentation through flocculation and microbial activity in a more environmental friendly and densification process

Application of Rhamnolipid and Microbial Activities for Improving the Sedimentation of Oil Sand Tailings

Densification of oil sand tailings deposited in the tailing ponds and recovering water from them are two major challenges issues in the oil sands surface mining industry. A small increase in the tailing settlement rate (which normally is very slow) can improve the densification of tailings and significantly, reduce water consumption and the volume of tailing ponds. Currently most of the industrial methods for consolidation of oil sand tailings are based on clay particle flocculation methods which use different kinds of agents such as calcium sulfate (gypsum), and polymeric flocculants. In this work, rhamnolipid (JBR 425) was investigated as a flocculating agent and microbial activities by performing the sedimentation experiments to increase the sedimentation of fine tailing particles. It has been found that rhamnolipid increased sedimentation by improving the hydrophobic interaction between the particles. The feasibility of in situ biosurfactant production by indigenous microorganisms, Bacillus subtilis strain and two microbial strains isolated from weathered oil was investigated and it was found that all strains could produce very low amounts of biosurfactant. A mixed culture of two microbial strains isolated from weathered oil increased the sedimentation. Different concentrations of rhamnolipid together with these two microbial strains at 23 ºC ºC could lead to significant increases in sedimentation (by a maximum factor of 3.04), increases in the concentration of larger particles (by a maximum factor of 1.9), particle mean diameter (by a maximum factor of 2.11) and flocculation in the tailings samples amended with them compared to the control. Rhamnolipid (0.5%) together with these two microbial strains at 15 ºC ºC showed significant increases in sedimentation (by a factor of 5.1), the concentration of larger particles (by a factor of 2.63), particle mean diameter (by a factor of 2.70) and flocculation in the tailings samples compared to the control. while the zeta potential is still negative. According to the pH measurements (during the 50 days) increase in the ionic strength (I) of the pore water and reduction in the thickness of the DDL of clay particles is not responsible for increasing the sedimentation as dissolution of MFT carbonate minerals and releasing divalent cations could not occur at pH higher than 7.5. However there might be a small amount of CH4 production at 15 ºC oC in the deeper layer of mud. This means that the mechanism of flocculation in these cases could be probably due to increasing the hydrophobicity of the particles, due to the interaction of biosurfactant and high molecular weight microbial organic compounds through a bridging mechanism with clay particles, and to due to forming transient canals from small amounts of CH4 production. Using rhamnolipid as a flocculating agent could bring the remaining oil and also a small amount of insoluble heavy metals from the tailing sediment into the water. Dissolved heavy metal ions and rhamnolipid in water could be removed through micellar- enhanced ultrafiltration (MEUF) process (between 30% for Cd and 100% for V, and 97.5% for rhamnolipid). This work shows the potential of using rhamnolipid and microbial culture in order to increase the oil sand sedimentation through flocculation and microbial activity in a more environmental friendly and densification process

Starch-based Polymers as Flocculants of Oil Sands Mature Fine Tailings and for Extraction of Bitumen from Oil Sands

Mature fine tailings (MFT) generated by oil sands extraction operations in Alberta pose significant environmental challenges. Polymeric flocculants are often needed to accelerate the consolidation and dewatering of MFT. A number of starch-based flocculants were synthesized and examined as flocculants for MFT. Thermoresponsive hydroxybutyl (HB) corn starch (HB-CS) and potato starch (HB-PS) were shown to flocculate 2 and 10 wt % MFT and their thermoresponsive behavior was absolutely required for optimal performance in that they were considerably more effective, in terms of initial settling rates (ISR) and supernatant turbidity (ST), for settling tests conducted at temperatures above their lower critical solution temperatures (LCSTs) than below. Cationic corn starch (Cat-CS) and potato starch (Cat-PS) were prepared by incorporating cationic moieties, N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC), on CS or PS in basic conditions. It was shown that both Cat-CS and Cat-PS exhibited excellent performance, in terms of ISR and ST, for flocculating 2 wt % MFT. A novel starch-based dual polymer flocculation process was proposed in that the dual polymer flocculants consisting of HB-CS and Cat-CS or HB-PS and Cat-PS were used to flocculate 2 and 10 wt % MFT. The dual polymer flocculants were in all aspects superior to the single polymer flocculant. An ISR as high as 52 m/h and a ST as low as 16 nephelometric turbidity units (NTU) can be achieved with the use of a dual polymer flocculant for the settling of 10 wt % MFT. Processing aids are generally required to improve the recovery of bitumen from poor processing oil sands ores that contain a relatively high amount of divalent cations and fine and clay solids. In this thesis, starch-based polymers were examined as processing aids in an aqueous-solvent hybrid bitumen extraction process, in which toluene was added to oil sands slurry to facilitate bitumen liberation. The highest bitumen recovery, at 86 %, was achieved using thermoresponsive starch nanoparticles (TRSNPs) with an LCST of 32 oC at 1 gram per liter of the oil sands slurry and 50 mg of toluene when the extractions were conducted at 45 oC. When the extraction was conducted under the same conditions without the TRSNP, bitumen recovery from the poor processing ores was only 31 %. Moreover, cationic hydrophobically modified SNPs were shown to be a good demulsifier, which significantly enhanced bitumen recovery during the extraction process. The use of the cationic hydrophobically modified SNPs at 1 g/L along with 50 mg of toluene also improved bitumen recovery from aged oil sands ores and a bitumen recovery as high as 81 % was obtained. Without the starch-based polymers, a poor bitumen recovery of 28 % was achieved with 50 mg of toluene for the aged ores

Master of Science

thesisDespite their many uses, fine clay particles such as kaolinite are a nuisance in management of tailings in various industries such as the oil sands and phosphate processing industry. The effective flocculation, sedimentation, and consolidation of these fine particles are a major challenge. In industries, polymers are added to tailings suspension to facilitate formation and eventual sedimentation of flocs. The structure of floc and the water entrapped within the floc determine floc behavior and settling characteristics. The quantification of water entrapped within the kaolinite flocs has not been reported before. The information on kaolinite floc size and shape is also limited due to the challenges in experimental procedures for these delicate structures. In this thesis research, operating conditions for kaolinite flocculation were determined and a suitable polymer was chosen by settling experiments. Further investigation of the floc formed was done in suspended state as well as in sedimented state. The flocs were analyzed for their size, shape, water content, and microstructure. A pool of analytical techniques like the Particle Vision & Measurement (PVM), Dynamic Image Analysis (DIA), Scanning Electron Microscopy (SEM), High Resolution X-ray Microtomography (HRXMT), and image processing software like Fiji, Medical Image Processing Analysis & Visualization (MIPAV), and Drishti were used. The analysis of suspended flocs by PVM and DIA revealed a mean floc size of about 225 µm for high molecular weight, 5% anionic polyacrylamide-induced flocs. The low molecular weight, 70% cationic polymer-induced flocs were found to be smaller in size (145 µm). DIA was used to analyze the flocs at different solid concentration. It was found that the increase in solid concentration leads to increase in floc size. Floc circularity was also analyzed by using both these methods. Most flocs were irregular in shape with circularity ranging between 0.2-0.3. However, the circularity results from both these methods do not agree well due to the difference in methods of detection and different definitions used for circularity/sphericity. Major contribution of this thesis work includes development of a new technique for water content and size analysis of sedimented kaolinite flocs. The sediment bed was segmented into about 13 thousand individual flocs and each floc was analyzed for its size and water content. The results suggest a normal distribution of water content for these flocs, with mean water content of 53.9% and standard deviation of 11.8%. About 98% of the flocs have water content in the range 30-80%. The size analysis revealed that about 90% of the flocs are less than 1.5 mm in size. The water content was found to decrease with increase in size of the floc. The flocs were found to be fairly irregular, with sphericity values around 0.1. The floc shape analysis was also done but limited to 10 flocs. In addition to macroscopic analysis of individual flocs, flocs were also analyzed for their microstructure. Visualization of floc microstructure and polymer chain was done with the help of SEM. Microstructures of up to 10 µm in size were revealed along with the web formed by polymer chain

Cationic Cellulose Nanocrystals for the Flocculation of Mature Fine Oil Sands Tailings

As the volume of oil sands tailings continues to increase each year with a concurrent need for better flocculants to replace the inorganic electrolytes and synthetic polymers, natural polymers are being considered as good substitutes. Cellulose nanocrystals (CNCs) possess interesting properties such as high specific area, biodegradability, surface functionalization capabilities and their large scale availability. This thesis explores the development of CNC-based flocculants for bentonite clay removal. Cationic and thermo-responsive CNC-based copolymers were prepared via the free radical polymerization technique. The thermo-responsive characterization of the CNC-gpoly( oligo(ethylene glycol) methyl ether methacrylate) (CNC-POEGMA) indicated that the LCST could be tuned by adjusting the poly(2-methacryloyloxyethyl) trimethyl ammonium chloride (PDMC) content. The cloud point measurements revealed that the LCST of CNC-POEGMA decreased in the presence of salt following a typical salting-out effect. Additionally, CNCPOEGMA- PDMC displayed two salt-responsiveness behaviors depending on the DMC content. CNC-POEGMA-PDMC with low DMC ratio displayed salting-in effect at low salt concentrations due to the extension of adsorbed PDMC caused by the screening of negative charges on CNCs by sodium cations. On the other hand, higher salt concentrations led to salting-out effect due to the strong ion-pair formation that removed the hydration shell around PDMC along with the polarization of water around POEGMA. The flocculation results of CNC-POEGMA-PDMC revealed that the thermo-responsive property could facilitate the formation of compact flocs at low dosage. The use of CNC-PDMCs cationic copolymers synthesized via the Activators ReGenerated by Electron Transfer polymerization (ARGET-ATRP) as flocculants for bentonite removal was also investigated. CNC-PDMC with different chain length demonstrated pH and salt-responsiveness. The hydration and conformation of the CNC-PDMC were more sensitive in the presence of salt due to the higher hydrophobicity of the ion-pair formed between the chloride ions and the quaternary ammonium groups. The flocculation results indicated that CNC-PDMCs had better performance compared to inorganic electrolytes at low dosage. The flocculation performance of the CNC-PDMCs and inorganic electrolytes after 5 min settling followed the Hofmeister series, and the flocculation behavior after 24 h settling agreed with DLVO theory. Three cationic-biopolymers were synthesized: CNC-g-PDMC, PDADMAC-coated-CNC and PDADMAC-coated-CNF. The CNC-g-PDMC prepared via the ARGET-ATRP possessed a branched-cationic structure while the other two polymers prepared via physical adsorption had a flat-cationic structure. The effect of cationic charge distribution of three cationic-biopolymer based flocculants on bentonite removal was evaluated. The flocculation results indicated that the cationic charge distribution affected the performance of the flocculants. The extended-cationic brushes of CNC-PDMC possessed better approachability toward bentonite particles compared to the coatedcationic layer of PDADMAC-CNC and PDADMAC-CNF. These findings are in agreement with the Singh’s model on the dependence of flocculation efficiency on the conformation of the flocculants. The microscopic images showed that the flocs formed with CNC-PDMC were more compact compared to flocs formed with the PDADMAC-CNC and PDADMAC-CNF. The effect of brush sequence, charge density and salt concentration on the thermo-responsive behavior of cationic and thermos-responsive CNC-based copolymers was studied. The LCST of CNC-PMEO2MA was found to be 24.5 °C, and after grafting with two different ratios of PDMC brushes on PMEO2MA brushes, the LCST could be tuned by adjusting the PDMC content. The CNC-PMEO2MA-PDMC with a relatively low PDMC content exhibited a broad phase transition and the LCST increased to 28.5 °C. However, the CNC-PMEO2MA-PDMC with higher PDMC content, resulted in a sharp transition behavior similar to the CNC-PMEO2MA and the LCST was 25 °C. The observed trend was due to steric hindrance of the polymer brushes. The higher the grafting density yielded brushes with lower hydration and the stronger hydrophobic interactions between the polymethacrylate backbone of the chains being densely grafted on the CNC substrate. For the copolymers with the opposite sequence, CNC-PDMC-PMEO2MA, the LCST was very close to CNC-PMEO2MA indicating that the presence of PDMC brushes on the inner layer had no effect on its thermo-responsive property. The addition of salt tuned the LCST of the CNCPMEO2MA leading to a typical salting-out effect as the chloride ions polarized the water molecules around the polar groups of PMEO2MA. On the other hand, the CNC-PMEO2MAPDMC and CNC-PDMC-PMEO2MA displayed similar salt-responsiveness behavior; displaying a salting-out effect at low salt concentrations and salting-in effect at high salt concentrations

Electrokinetic Consolidation of Oil Sands Tailings: An Experimental and Numerical Study

The management of fine oil sands tailings, known as mature fine tailings (MFT), is a major challenge for the oil industry in the Northern Alberta, Canada. Dewatering and consolidation of MFT are slow and time consuming due to high water content and low permeability of MFT. The electrokinetic (EK) dewatering treatment has shown to be effective on oil sands tailings based on the results of previous researches. Therefore, this thesis is focusing on experimental and numerical studies of EK dewatering of oil sands tailings. The thesis includes three parts, i.e., EK dewatering of oil sands tailings and kaolinite slurry, EK and chemical (quicklime and Portland cement) combined treatment, and development of a one-dimensional large strain EK consolidation model. In the first part, the EK dewatering experiments are designed and executed on oil sands tailings and slurries of kaolinite, which is the major clay mineral in the Alberta oil sands tailings, with vertically installed electrodes. The analyses are carried to obtain the regression equations of the dewatering trends for the results of oil sands tailings and kaolinite slurries, including the water drainage, water/solid content, energy consumptions, etc. The effects of applied voltage gradient and initial water content on EK dewatering are studied via the regression equations. The material saturation, especially at the anode, is found to be the key factor controlling the water flow generated by electrokinetics. Once the degree of saturation of the material at the anode drops below 80%, the most efficient stage for EK dewatering will end. The effects of EK and chemical combined treatment of MFT are evaluated in the 2nd part in this research. The addition of quicklime or Portland cement minimizes the difference of water content and undrained shear strength of MFT between the anode and cathode, whereas it also reduces EK induced water flow. It is concluded that EK and chemical combined treatment of MFT may be beneficial at a low chemical dosage (1% quicklime or cement). In the 3rd part of this study, a one-dimensional large strain EK consolidation model (LSEK-1D) is developed for oil sands tailings. The model predictions are in consistency with the experimental results in terms of the final settlements and consolidation times. Moreover, the effects of sample initial heights and applied current densities on consolidation times are evaluated via the model. The results indicate that the consolidation times of oil sands tailings are shorter than those based on the conventional small strain consolidation theory, and the application of EK combined with surcharge pressure can significantly reduce the consolidation time of oil sands tailings