Polyacrylamides revisited: flocculation of kaolin suspensions and mature fine tailings

A series of acrylamide‐based water‐soluble (co)polymers was synthesized and they were investigated as flocculants of model kaolin suspensions and mature fine tailings of oil sands. The effects of molar mass, charge density, and polymer concentration on flocculation efficiency were studied by monitoring the initial settling rate during sedimentation. Hydrolyzed polyacrylamide (HPAM) with high molar mass and intermediate acrylic acid contents (0.14–0.41 mol/mol (14–41 mol%)) performed better in flocculation tests on kaolin suspensions requiring lower dose for maximum initial settling rate than native polyacrylamide (PAM). Surface force measurements showed that at low polymer concentrations (1 ppm), the partially‐adsorbed polymer induced a bridging attraction between the mica surfaces. Increasing the polymer concentration to 10 and 50 ppm caused purely repulsive forces. The presence of anionic groups in HPAM led to stronger repulsion, which was also demonstrated by the higher viscosity and larger hydrodynamic radius of the charged polymer. The charge‐induced increase in the viscosity of polymer solutions was suppressed by the screening effect of salts in a buffer solution and reducing the viscosity is desirable in the injection of flocculants in the industrial process.     

Water soluble polymeric nanofibres for rapid flocculation and enhanced dewatering of mature fine tailings

Water-soluble polymer flocculants have been used to efficiently release entrapped water in oil sands tailings by bridging fine particles to create large heavier flocs which can then settle faster and release water more efficiently. Due to their initial interaction with the fine particles suspended in tailings, polymer nanofibres may perform better than their parent polymers because of the entire surface of the nanofibres being fully accessible to the fine particles. In this work, commercially available poly(acrylamide-co-diallyl dimethylammonium chloride) was chosen as a basis for this study. Initial settling rate, supernatant turbidity, water recovery, capillary suction time, and solids content were measured to determine the effect of polymer nanofibres on solid-liquid separation. The solid forms of the polymer (either as nanofibre or powder) perform better than the polymer solution in each test, with optimum dosages of 5 wt% mature fine tailings (MFT) loading. Nanofibres could achieve settling rates of 60 m/h, while the other forms were only able to achieve 42 m/h. Additionally, the turbidity of the supernatant obtained after flocculation with nanofibres was 15 nephelometric turbidity units (NTU), while the polymer solution and powder produced turbidites of 162 NTU and 70 NTU, respectively. In addition, polymer nanofibres and powders generated larger flocs compared to the polymer solution, which produced small, homogenized flocs.     

Preparation of bitumen from oil sand by ultracentrifugation

Ultracentrifugation was investigated as a means to obtain solvent-free bitumen from oil sand. The bitumen from three oil sands of varying grades was separated by placing the sands in specially designed tubes and centrifuging for 2 h at 198 000 at 20 °C. For all grades of oil sand, approximately 70% of the bitumen was recovered. The recovered bitumen was compared to the residual remaining on the sand, and to that extracted by the conventional Soxhlet technique. The ultracentrifuged bitumen contained some emulsified water and a small amount of fine solids. The solvent-extracted material was water-free, but contained a small amount of residual solvent and fine solids. The ultracentrifuge caused some fractionation of the bitumen, resulting in a product slightly enriched in asphaltene components compared to the solvent-extracted material. The residual bitumen remaining on the sand was correspondingly slightly depleted in asphaltenes. However, as evidenced by gas Chromatographic simulated distillation data, ultracentrifugation did retain the light (180–220 °C) components of the bitumen which were lost during the solvent removal step following solvent extraction. Other analyses such as density, viscosity and elemental composition verified that ultracentrifugation resulted in some fractionation of bitumen components.     

Scaling inline static mixers for flocculation of oil sand mature fine tailings

Operations to reclaim mature fine tailings (MFT) ponds involve flocculation using high‐molecular‐weight polymers, for which inline static mixers are suited. Three different commercial static mixers were utilized to determine mixing parameters corresponding to optimal dewatering performance of flocculated MFT. MFT was treated with polymer solution under different mixing conditions. The dewatering rates passed through a peak with increasing mean velocity, V and Reynolds number, Re of the fluid. The greater the number of mixer elements, the lower the V and Re at which the peak dewatering rate occurred. Mixing parameters such as G‐value, residence time, and mixing energy dissipation rate of the most rapidly dewatering flocculated MFT were dependent on mixer type and setup. In contrast, peak dewatering rates converged when scaled with respect to specific mixing energy, E, demonstrating that E is a suitable scale‐up parameter for inline static mixing to produce optimally dewatering MFT. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4402–4411, 2015     

Preparation of bitumen from oil sand by centrifugation

Centrifugation was shown to have certain advantages over solvent extraction for the separation of bitumen from oil sand for research purposes. No fractionation of the bitumen during centrifugation was detected by chemical analysis. Some limitations of the method are pointed out.     

Study of fines in bitumen extracted from oil sands by heat-centrifugation

The temperature dependence of, first, the yield of bitumen extracted from oil sands and, second, of the coextracted solid particles in the bitumen was studied. Centrifugal extractions were performed in an argon (inert) atmosphere at temperatures ranging from 30 °C to 150 °C. The co-extracted solid particles were investigated through digital image analysis, instrumental neutron activation analysis and ash yield. The yield of bitumen increases with extracting temperature and is also dependent on the grade and origin of the oil sand. The quantity of fines, e.g. clay minerals or fine sand particles is dependent on the grade and origin of the oil sand. The total amount of co-extracted solid particles is found to be independent of the extracting temperature.     

Displacement of bitumen from reconstituted oil sands by aqueous solutions

A simple method has been developed for modelling the recovery of bitumen from packed beds of oil sand by water or caustic solution displacement. Batches of reconstituted oil sand were prepared by intimately mixing predetermined amounts of sand, water, and bitumen, thereby permitting the composition of the oil sand to be controlled and varied within a wide range. Dilution of the bitumen with hexadecane facilitated the mixing process and allowed experiments to be performed at low temperatures while maintaining oil-water viscosity ratios comparable to those prevailing at the higher temperatures encountered during hot water or steam displacements in the field. The effects of a wide range of compositional and operational variables were studied using a two-level fractional factorial design technique and the findings are discussed. Of particular interest are the observations that the density and initial connate water saturation of the oil sand exert significantly more effect on bitumen recovery efficiency for the case of water displacement than for caustic solution displacement.     

Flotation kinetics for titanium,zirconium and bitumen recovery from oilsand tailings

The kinetics of heavy mineral and bitumen recovery from oilsand tailings are presented. The results show that the recovery rates for titanium, zirconium and bitumen were affected by addition of surfactants Tretolite F46 and E3453. Recoveries were a function of time and of the minerals and bitumen present.     

Coking of bitumen from Athabasca oil sands. 1. Effect of calcium hydroxide and other reagents

Coke from Athabasca oil sands has limited use as a boiler fuel because of excessive emission of sulphur dioxide during combustion. When the oil sands bitumen is mixed with a small quantity of a suitable reagent such as calcium hydroxide and carbonized in a laboratory unit at ≈ 475 °C, the resultant coke has significantly reduced sulphur dioxide emission during combustion. The organic sulphur of the bitumen is converted to calcium sulphide and sulphate. Further, the addition of this reagent leads to a substantial increase in the yield of liquid products during carbonization. The calcium hydroxide may catalyse the cracking of asphaltenes thereby leading to the increased recovery of liquid distillate.     

Processibility of Athabasca Oil Sand Using a Laboratory Hyd ro t ransport Extraction System (LHES)

A novel laboratory scale apparatus has been developed and used to assess the extraction performance of oil sands under conditions analogous to current industrial processes. The apparatus can be used to investigate independently, the liberation of bitumen from the sand as well as air‐bitumen attachment and bitumen recovery. Experiments show that lower operating temperatures have a detrimental effect on bitumen recovery and controlled air addition is beneficial for recovery. The liberation of bitumen from sand grains has been found to proceed faster than air attachment and bitumen recovery, making the flotation the ratelimiting step in the extraction process. The potential benefit of staged air injection into hydrotransport pipelines as a possible process aid is discussed.     

Calcined oil sands fine tailings as a supplementary cementing material for concrete

In recent years, metakaolin (MK) has received considerable attention, as a high-performance pozzolanic supplementary cementing material for use in concrete. MK is produced by calcining kaolinite at temperatures between 600 and 1000 °C. In the province of Alberta, Canada, the oil sand mining industry produces millions of cubic metres of oil sand tailings that could become a major source of MK. This paper summarizes the behaviour of calcined fine tailings (CFT) as a supplementary cementing material in high-performance concrete and compares its performance to that of MK and silica fume (SF). It was found that CFT has excellent pozzolanic activity in concrete, making it an environmentally friendly and potentially cost effective supplement.     

Viscous characteristics of a Utah tar sand bitumen

The viscous behaviour of an extracted tar sand bitumen has been experimentally examined and the results summarized in this Paper. The material studied was from the Asphalt Ridge, Utah area. The viscosity of the bitumen has been determined as a function of temperature (293–422 K), toluene (solvent) content (0–10%), composition (0–14.6% asphaltenes), oxidation and shear history. In all cases studied, the Arrhenius plots were significantly non-linear at temperatures s> 373 K, with viscous behaviour becoming less sensitive to toluene content with increasing temperature. Low temperature behaviour was strongly dependent on toluene content. The presence of asphaltenes in the bitumen was shown to be a strong viscosity enhancer. Oxidation and shear history were also shown to measurably increase the bitumen viscosity.     

油砂沥青超声波减粘工艺研究

油砂沥青粘度较大,自然状态下不易流动,严重影响了管道输送及加工,针对目前油砂沥青研究中存在的问题,采用超声波进行了减粘的实验研究。实验综合考察了超声波作用时间、温度、超声波频率、超声波功率等因素对减粘效果的影响。实验结果表明,在适当的超声作用时间(20 min)、适宜的温度(30℃)、适宜的超声波频率(20 kHz)和超声波功率(250 W)的条件下,油砂沥青的减粘率可达80%以上。经超声波处理后的油砂沥青粘度略有恢复,但仍远低于处理前的粘度,超声波减粘效果良好。     

Isolation and characterization of various types of organic matter in oil sands tailings sludge

In bitumen extraction of oil sands by hot water, the problem of sludge accumulation is, at least partially, attributable to the presence of unrecovered bitumen as well as acetone solubles and so called ‘insoluble organic matter’ (IOM) on the surfaces of inorganic particles. A comparative study of the bitumens separated from both sludge and the original oil sands feed suggested that the former was depleted in high molecular weight fractions. Examination of the organic matter extracted from sludge with acetone indicated that asphaltene constituents, as well as long chain fatty acids, could report with the acetone solubles. The structural parameters of the IOM derived from sludge were, in general, similar to those for oil sand IOM.     

Non-isothermal programmed pyrolysis studies of oil sand bitumens and bitumen fractions: 1. Athabasca asphaltene

Characteristic pyrolysis thermograms for 12 gases have been obtained for Athabasca asphaltene, using a combination of non-isothermal, programmed pyrolysis (ambient to 1200 K at 3 K min^?1) and gas chromatography. Such thermograms provide information for the characterization of asphaltenes in the form of gas yields, specific rates and Arrhenius kinetic parameters. All thermograms comprised more than one peak. These peaks lie in distinct temperature zones and are associated with primary and secondary cracking and coking reactions. Useful insights into the structure of Athabasca asphaltene and, indirectly, the composition of its pyrolytic cokes have been obtained. The present results provide a body of useful reference material which may be useful for monitoring processes, which may chemically modify the asphaltene fraction of bitumens and heavy oils, and for comparative studies of asphaltenes from a variety of sources.     

Wettability alteration of solid surface to enhance the bitumen liberation and the water-based processability of weathered oil sands

Weathering often induces bituminous materials adsorbing on the sand grains and leads to poor processability of the oil sands. Chemical and microbial pre-treatment of the prepared weathered ore model and a weathered oil sand ore were carried out to improve the solids surface wettability so as to facilitate the bitumen liberation and recovery. It was found that although all the cetyl trimethylammonium bromide (CTAB), sodium dodecylbenzene sulphonate (SDBS), and microbial culture medium could greatly decrease the surface tension of the solution, the CTAB treatment failed to improve the bitumen liberation, while the SDBS and microbial treatment significantly accelerated the bitumen liberation from the silicon substrates. The wettability analysis showed that the improved bitumen liberation could be attributed to the alteration of the solids surface wettability from hydrophobic to hydrophilic by the SDBS and microbial treatment. Inconsistent with the findings of the bitumen liberation, floatation tests of a weathered ore showed that the CTAB pre-treatment only gave a low bitumen recovery of 33%, while the SDBS and microbial pre-treatment improved the processability of the ore. In particular, the microbial treatment was more effective at removing the adsorbed organics from the solids and improved the surface hydrophilicity, resulting in a much better bitumen recovery of 95%. This work provides a way to improve the processability of the weathered ore by altering the solids surface wettability.     

Wettability of fine solids extracted from bitumen froth

Production of synthetic crude oil from oil sands deposits in northern Alberta involves open pit mining, mixing the mined ore with water, extraction of aerated bitumen from the slurry, removal of water and solids from the froth formed, and upgrading heavy bitumen to liquid hydrocarbons. The success of the froth treatment operation, aimed at removal of fine solids and water from the bituminous froth, depends on the control of wettability of fine solids by the aqueous phase. Fine solids were extracted from bitumen froth by heptane. The partition of the extracted solids in aqueous, organic, and interphases was measured, and the wettability of the solids by water in various diluents was evaluated from contact angle measurements. The effect of diluent composition, sample drying, and surface washing on the wettability and fine particle partition was examined. The partition of fine particles correlated well with their wettabilities, and the results were found to be useful for interpreting the observations from froth treatment practice.