In-Situ Real-Time Solids Content Measurement of Settling Oil Sands Tailings Based on a Light Scattering Technique

Abstract

Subsurface solids content measurement of oil sands tailings ponds is essential for tailings management and land reclamation activities. Currently, solids content is primarily measured by manual sampling and offline analytical methods. Light scattering can be used to determine particle sizes and concentration in solutions, which can be an alternative technique for solids content measurement. The focus of this thesis is to develop an in-situ subsurface solids content monitoring system based on light scattering technique to monitor the settling process and solids concentration of FFT (Fluid Fine Tailings) in oil sands tailings ponds at different depths. An optical sensor prototype consisting of laser diodes and photodiodes was constructed to conduct experiment using a lab-scale settling tank with both visible (405nm & 658nm) and near-infrared (980nm & 1550nm) wavelengths. The setup was used to determine the settling process. Kaolin was used as a model material as well as FFT samples with different solids concentrations were measured. Both visible and near-infrared wavelength results indicate that the scattered light signal decreased responding to the decrease in solids content. Light scattering technique can provide relative changes in solids content but not the absolute solids content. Several calibration measurements were then conducted to convert the scattered light signal into absolute solids content. A ring setup and a calibration tank were built to conduct measurements for calibration. Because of the differences in power of laser diodes and the differences in sensitivity of photodiodes, correction factors were obtained to correct the calibration tank and settling tank results. Calibration functions were obtained to convert the scattered light signal into absolute sample concentration in weight percent. With a proper calibration procedure, the light scattering technique can be used to determine solids content with good sensitivity of 1 to 2.5 weight percent in different solids content ranges. A gamma-ray sensor was also developed in our research group to measure solids content. The results of solids content measurement using both optical and gamma-ray sensor agree well in the settling tank experiments. The good agreement suggested that the gamma-ray sensor can be used to provide in-situ calibration for the optical sensor.