Characterization of sol–gel-derived nano-particles separated from oil sands fine tailings

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Abstract

Methodology has been developed to separate nano-particles of amorphous material from Syncrude fine tailings. Both, separated finer solids and residual coarser solids, were characterized by elemental analysis, X-ray powder diffraction, XPS, SEM, infrared spectroscopy, solid-state NMR, density, and surface area measurements. Based on the results of infrared and X-ray diffraction, the amorphous minerals identified in finer solids included allophanes, halloysite, ferrihydrite, and amorphous silica. The finer fraction also contained some crystalline material consisting of muscovite and traces of quartz. The residual coarser solids consisted mostly of quartz, muscovite, and kaolinite.

Introduction

The extraction of bitumen from Athabasca oil sands, using the hot water extraction process, results in the accumulation of large volumes of fluid wastes called fine tailings [1], [2]. A general description of fine tailings would be a complex system of clays, minerals, and organics. According to Camp [3], fine tailings show little tendency to dewater, even when subjected to mechanical dewatering procedures. These clay tailings are acutely toxic to aquatic organisms, and are currently being stored in large tailings ponds. The buildup of these partially settled clay tailings presents not only an environment problem but also a significant repository for non-recyclable water, which eventually must be reclaimed.

The reason for the intractability of the clay tailings has been a subject of several studies [4], [5], [6], [7]. Based on the results of published work, it is generally believed that a combination of residual organics and fine clay particles contribute to the stability of fine tailings. Yong and Sethi [2] have attributed the high water-holding capacity of fine tailings to the presence of amorphous minerals such as iron oxide and clays.

Our group at NRC has been actively involved in research dealing with various aspects of fine tailings [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. As a result, we have developed a number of fractionation schemes to separate fine tailings into various components. The objective of this work was twofold. First to develop fractionation schemes for the separation of amorphous solids (ASs) from oil sands fine tailings, and secondly to characterize the separated solids by both physical and chemical methods. In our previous communications, we have reported preliminary data on the separation and characterization of ASs from oil sands fine tailings using the Tiron extraction method [5], [15], [16]. In this investigation, we have separated ASs of different composition from Syncrude fine tailings using a combination of sol–gel chemistry and a number of separation techniques developed in-house. The solid fractions have been characterized by elemental analysis, X-ray diffraction (XRD), XPS, SEM, infrared spectroscopy, solid-state nuclear magnetic resonance (NMR), and surface area measurement. The characteristics of the ASs obtained by different separation techniques have been compared.

Section snippets

Materials

Aqueous tailings samples, used in this investigation, were obtained from the 17 m level of the Syncrude tailings pond. The physicochemical properties and handling procedures for these samples have been reported previously [7].

Tiron (4,5-dihydroxy-1,3-benzene-disulphonic acid disodium salt) was obtained from Sigma Chemicals, Inc. It was used as 0.1 M aqueous solution containing 5.3 g of anhydrous sodium carbonate. The final pH of the solution was adjusted to 10.5 with sodium hydroxide. The

Physicochemical characterization

Yong and Sethi [2] have attributed the stability of fine tailings to the presence of amorphous materials such as iron oxides and disordered clays. However, their proposed structure of fine tailings did not get much support because of the lack of progress in the detection and separation of amorphous minerals from fine tailings. Many difficulties arise in the characterization of inorganic amorphous materials. By their very nature, amorphous substances are difficult to detect and estimate, and

Conclusions

A very fine fraction has been separated from Syncrude fine tailings. This material was characterized using elemental analysis, X-ray powder diffraction, XPS, SEM, infrared spectroscopy, solid-state NMR, density, and surface area measurements. Several mineral phases identified in the separated colloidal solids included muscovite, kaolinite, halloysite, quartz, gibbsite, ferrihydrite, allophane, and amorphous silica. These mineral phases are associated with organic matter, either transported to

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