Oxidized or degraded oil sands can exhibit poor processability, which is often not correlated with the fines or clay contents in the ore. Chemical markers (such as low pH and high soluble iron and calcium) for oil sands oxidation are sometimes not present even though significant changes in bitumen properties may have occurred. In these cases, changes in bitumen chemistry have been successfully quantified using microscopic techniques developed at CANMET. More recently, an online tool using near infrared (NIR) spectroscopy, which correlates with the CANMET microscopic method, has been developed with Suncor. An on-line technique based on NIR that can quantify the amount of degraded ore coming to the extraction plant from Suncor's Steepbank mine will be useful to Suncor in effectively controlling additions of process aids for treating oxidized or degraded ores.
This paper discusses the processability of oxidized or degraded ores along with a microscopic method for identifying oxidized ore and its correlation with the NIR spectroscopic technique.
Oil sands processing efficiency is dependent upon many factors, including the quality of the ore. The operating companies have developed correlations between extraction recovery and bitumen and fines contents in the ore. These correlations generally fit observed processability, but often ores are encountered with recoveries that fall well outside these simple relationships. These are variously known as bad ores, problem ores, type X ores, or ores with a high misery factor. Detailed characterization can reveal the reasons for such poor processing behaviour and they can sometimes be traced to unusual water chemistries or unusual clay properties. Often, however, changes in bitumen chemistry can be the source of the problem, and this is the focus of the present discussion. Bitumen oxidation and its negative impact on processability has been extensively studied, mostly on stockpiled or stored samples (1–7). Experience at Suncor's Steepbank mine has shown that bitumen changes that may have occurred in geological time frames can also be important in determining processability (8–10).
During the commissioning of the Suncor Steepbank mine, areas of ore were identified that created processing difficulties, in particular high froth densities. The high froth densities resulted in problems in downstream facilities where high solids content in the froth resulted in overloading of the froth treatment centrifuges. These effects were quickly identified with certain areas of the mine and a sampling program was undertaken to identify the causes of the poor processability. The ores linked to the poor processability were generally high-grade ores containing in excess of 12% w/w bitumen (occasionally >14% w/w) with low fines content, that do not fit the normal profile for poorly processing ores. Cryogenic sampling of the froths in the commercial-scale separation cell was carried out in order to help identify the causes of the high froth densities. Macroscopic observation of the froths from the problem ores included very large bubble sizes and sometimes a distinct reddish froth colour (9,12).