Understanding weathering of oil sands ores by atomic force microscopy

Effect of weathering on colloidal interactions between bitumen and oil sands solids was studied by atomic force microscopy (AFM). The change in bitumen chemistry due to weathering was found to have a negligible effect on the interactions of bitumen with solid particles. However, the increase in solid surface hydrophobicity due to ore weathering reversed the long‐range interaction forces between bitumen and solids from repulsive to attractive with a corresponding increase in adhesion force. The measured force profiles between bitumen and various solids can be well fitted with the extended DLVO theory by considering an additional attractive force. The attractive long‐range force and increased adhesion force make the separation of bitumen from solids more difficult and the attachment of fine solids on liberated bitumen easier, thereby leading to poor bitumen liberation and lower aeration efficiency. Such changes account for the observed poor processability of the weathered ores. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

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.     

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.     

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.     

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.     

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.     

Effect of clays and calcium ions on bitumen extraction from athabasca oil sands using flotation

A novel approach, based on the doping of rich estuarine oil sands with calcium and/or clays, was developed to study bitumen extraction. The batch flotation tests showed that the addition of either calcium ions up to 40 p.p.m., or kaolinite, illite and montmorillonite clays at 1 wt% of oil sands processed had marginal effect on bitumen recovery from the estuarine ores. A sharp reduction in bitumen recovery was observed only when calcium ions greater than 30 p.p.m. and 1 wt% montmorillonite clays were added together. While bitumen recovery correlated well with changes in water/air/bitumen contact angle, no correlation was found between bitumen recovery and measured zeta potential of clays or surface tension of the supernatants from the flotation slurry. The wettability of bitumen was identified as a key element in determining bitumen recovery. The aqueous solution analysis for calcium ions showed that most of the added calcium ions disappeared from the solution when montmorillonite clays were present. The addition of illite or kaolinite clays changed the calcium ion concentration in the slurry only marginally. Stronger adsorption of calcium ions on montmorillonite than on either kaolinite or illite is considered to be responsible for the increased bitumen wettability, and hence reduced bitumen recovery.     

Determination of clay content in Canadian oil sands using x-ray florescence spectroscopy for diagnosis of ore processability

In this study, a simple and robust method based on the use of x-ray fluorescence (XRF) spectroscopy to measure potassium content as an indicator of illite in oil sands was proposed and tested. The XRF results of illite determination were compared with those determined using the conventional methylene blue titration (MBT) method. To test the suitability of the XRF method for determining illite content in various streams of oil sands processing as a diagnosis tool, a toluene-diluted-bitumen solution was used to contaminate solid surfaces prior to their analysis by the XRF and MBT methods. In order to remove the organic matter from the bitumen-contaminated solids for evaluating the XRF and MBT method, toluene washing and low temperature ashing were applied to the bitumen-contaminated solids prior to their analysis. The robustness of the XRF analysis in comparison with the MBT method was further confirmed by analyzing the solids extracted from bitumen froth and tailings stream. The results show that the XRF method was more tolerant to surface contamination and therefore more reliable in determining illite content in oil sands and relevant processing streams. It was also found that the potassium contents measured by the XRF method on solids from 10 ores show a strong correlation with the corresponding fines contents of these ores, indicating that the XRF method can potentially be used to determine the fines content of oil sands and related processing streams.     

油砂沥青质对油砂沥青中甲苯残留的影响

利用热重质谱联用仪（TG-MS）分析了三种油砂沥青（印尼油砂沥青、伊朗油砂沥青、加拿大油砂沥青）中的甲苯残留以及油砂沥青质含量对油砂沥青中甲苯残留的影响,并在此基础上,进一步研究了油砂沥青质中的甲苯残留。结果发现,不同油砂沥青中甲苯残留量存在一定差异,其中印尼油砂沥青中的甲苯残留量最多。进一步对沥青质质量分数分别为10%、19%、30%的油砂沥青样品进行热重质谱实验,发现随着油砂沥青中沥青质含量的增加,甲苯的残留量会成倍增加。以加拿大油砂沥青质为例,研究了油砂沥青质对溶剂残留的影响,发现油砂沥青质具有对甲苯分子的夹带能力,导致甲苯分子在超过自身沸点40℃以上才能从沥青质中分离出来。油砂沥青中其他组分的存在也会加剧沥青质对甲苯的夹带作用。此外,研究还发现,在350~650℃时,油砂沥青质可以热解产生甲苯,而且油砂沥青中的沥青质含量越高,热解生成的甲苯越多。     

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.     

印尼油砂沥青的净化工艺

溶剂萃取法分离油砂制得油砂沥青中含大量机械杂质,影响沥青的品质及后期加工利用。通过XRD和激光粒度仪表征了机械杂质的矿物组成和粒度分布等特性。针对机械杂质的特性,开发了复配试剂,通过稀释剂降黏沥青、复配试剂净化沥青、稀释剂回收再生及循环利用3个操作单元对油砂沥青进行了脱杂净化实验,并分析了净化机理。结果表明：降黏过程,温度70℃、时间10min、稀释剂与沥青比0.3g/g,稀释沥青70℃黏度为3.2Pa·s;净化过程,6%盐酸与稀释沥青比0.2mL/g、CaCl₂与稀释沥青比0.01g/g,温度70℃,混合时间10min,沉降时间20min,机械杂质脱除率可达到93.5%;回收及循环过程,稀释剂回收率为98%,循环使用5次,机械杂质脱除率仍92%以上。该工艺具有沉降时间短、机械杂质脱除彻底的优点。     

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.     

An investigation of the effect of air addition during oil sand conditioning

Bitumen aeration was studied by flooding samples of medium grade oil sand with de‐ionized water under both ambient and high vacuum conditions. The samples were then agitated on a shaker table. Subsequent analysis revealed the presence or absence of an air gap in the sample container was the single most important factor in determining the overall bitumen recovery. Furthermore, samples that were flooded while under high vacuum produced slightly less bitumen compared to samples flooded at atmospheric pressure. This suggests that oil sand that is not under high vacuum when flooded with water contains some amount of indigenous air (see introduction) that would aid in bitumen flotation.     

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.     

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。     

Effect of natural surfactants released from athabasca oil sands on air holdup in a water column

Natural surfactants released from Athabasca oil sands are a crucial component in water‐based bitumen extraction processes. The effect of natural surfactant released from estuarine and marine oil sands on air holdup was investigated using a water column. The air holdup in the resultant supernatant of the conditioned oil sands slurry was found to be much higher than that in de‐ionized water. A further increase in air holdup was observed with the supernatant obtained from the oil sands slurry conditioned with caustic. Aging of the ore prior to bitumen extraction caused an increase in air holdup. The presence of small amount of fine solids in the supernatant resulted in a higher air holdup for all the cases studied. The present study shows that the higher air holdup and poorer processibility of marine ores, compared with estuarine ores, could be accounted for by the release of larger amount of surface active species and the presence of more fine clays in the ores.     

Comparative study of three laboratory methods for the extraction of bitumen from oil sands

Measurements of total organic content and extractable bitumen for a number of different grade oil sands were used to obtain the extraction efficiency of several common bench-scale bitumen recovery techniques. The hot-water process was inefficient for feeds of moderate to high fines content. Soxhlet extraction and spherical agglomeration were found to be of similar efficiency for most grades of feed. For these two processes the efficiency is limited by the mineral fines content, probably because of surface absorption of bitumen components.