An Investigation of the Methylene Blue Titration Method for Clay Activity of Oil Sands Samples

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  • The purpose of this report is to use a design of experiment (DOE) approach to examine the main factors affecting the determination of methylene blue index (MBI) values for oil sands samples. The methylene blue titration of clays has become a principle tool to assess extraction efficiency of oil sand ores and as a tool to assess the properties of the various tailings streams. The report uses a Plackett-Burman (PB) DOE approach which is designed to screen a method for the principle factors affecting the test result. It does not reveal interaction between factors that could affect the significance of a main effect in the study. The purpose of the PB DOE screen is to help identify the main effects so that a more complete full factorial DOE can be implemented. A full factorial DOE allows more than two procedures/conditions or levels for each of the main effects identified by a screening DOE. This enables the conditions and procedures for specific factors in a test method to be adjusted simultaneously as other factors are varied. Thus interactions that could affect test results are accounted for which ensures that the final test method exhibits ruggedness and is capable of generating reliable data with good precision. This report is the initial phase in the development of a rugged and robust method for methylene blue (MB) determinations. A principle requirement of the method is the dispersion of the clay samples to ensure methylene blue is capable of complete cation exchange with the clay. A 12 factor PB DOE investigated two mature fine tailings (MFT) samples for the effects of bicarbonate, basic pH adjustment, peroxide treatment, sonication, stirring, soaking, heating and Dean and Stark sample cleaning on dispersion procedures. If the number of procedures needed to disperse the clays can be minimized, without affecting the reliability of the MBI results, the method is easier to perform in a timely manner. Included in the 12-factor PB DOE was an assessment of the effects of acidic pH adjustment, preceding the titration, and variations in filter paper porosity and optional endpoint detection procedures during the titration. A 7-factor PB DOE, using both normal and folded designs, was conducted to confirm features of the 12-factor PB DOE. The main effects studied were peroxide treatment, bicarbonate, basic pH adjustment, stirring at both room temperature and heating at 60˚C, sonication and variation in endpoint detection procedures. The folded design was to help minimize the effects of confounding or aliasing of the data where main effects can be influenced by interactions between main effect components. When this occurs a main effect may be viewed as significant when in fact it is not. The study emphasizes the importance of basic pH and sonication to enhance dispersion. Peroxide treatment was shown in the PB DOE to have beneficial effects when the sample is exposed to lower sonication energies, as in a bath sonicator. However, in a mini-study using a probe sonicator, where the energy generated is greater, peroxide was not found to be essential in aiding dispersion as evident by consistent MBI values even when peroxide was omitted. The importance of acidifying the dispersed sample before titration is also emphasized from the PB DOE studies. The goal of this work is to ultimately develop an automated procedure for MBI determinations. A major challenge is to provide a more objective means of identifying the endpoint of the MB titration. The report proposes a more objective non-visual endpoint based on the current halo procedure. To this end the effect of varying filter paper porosity as well as a comparison of subjective and objective endpoint detection procedures were included in the DOE. Alternative endpoint detection procedures focused on the use of spectroscopy. A spectroscopy procedure which measured changes in the aqueous forms of MB during the titration was included in the 12 factor PB DOE. The report also discusses an innovative use of fibre optic visible spectroscopy to monitor the spectra of clay-MB interactions during the MB titration. The ability to assess whether the MB is interacting on the external or interlamellar surface of clays can enhance the information about the properties of clays in different sample types. This approach is very attractive since much more detail can be mined from the titration data than simply MBI values. This may dramatically improve the characterization of ores and tailings streams and improve process decisions regarding suitable ores for extraction and optional tailings treatments. Finally an attempt to use NMR as a tool to monitor the titration and provide additional insight into the properties of the oil sands samples being titrated with MB is reported. Although NMR is capable of observing methylene blue in an aqueous media, and could be used similar to the spectroscopy method in the 12-factor PB DOE, it is incapable of detecting MB when the clays were also present.

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    Attribution 3.0 International